The insect fauna of Canada thistle, Cirsium arvense (L.) Scop. in southern Montana by Hilde De Smet-Moens A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in Biological Sciences Montana State University © Copyright by Hilde De Smet-Moens (1982) Abstract: Insects associated with Cirsium arvense (L.) Scop, in southern Montana are reported. Fifty-six phytophagous species and 47 visiting insects were collected, identified and tabulated. Four insect species, Corythucha distincta Osborn and Drake (Hemiptera: Tingidae), Bans sp., poss. cirsii Gilbert (Coleoptera: Curculionidae), Vanessa cardui L. (Lepidoptera: Nymphalidae), and Orellia ruficauda (Fabricius)(Diptera: Tephritidae), were considered conspicuous, because of their damage inflicted to the thistle plant. More insects were found associated with the developing seed heads than with foliage, stems or roots. The information gathered on this local survey can be valuable for future introductions of insect biological control agents. It forms the foundation for follow-up studies with indigenous insect species. Augmentation and redistribution of established monophagous insects, such as Ceuthorynchus litura and Baris sp. should be considered. Transmission experiments are necessary to evaluate the potential of these monophagous insects as thistle pathogen vectors. The combination of two stress-factors will increase the impact on the thistle plant in the field.  STATEMENT OF PERMISSION TO COPY In p re sen t in g t h i s t h e s i s in p a r t i a l f u l f i l l m e n t of th e r e q u i r e ­ ments f o r an advanced degree a t Montana S t a t e U n iv e r s i ty , I agree t h a t t h e Library s h a l l make i t f r e e l y a v a i l a b l e f o r in sp ec t io n . I f u r t h e r agree t h a t permission f o r ex ten s iv e copying of t h i s t h e s i s f o r s ch o la r ly purposes may be gran ted by my major p r o f e s s o r , o r , in h i s absence, by th e D irec to r of L i b r a r i e s . I t is understood t h a t any copying or p u b l i ­ c a t io n o f t h i s t h e s i s f o r f i n a n c i a l ga in s h a l l not be allowed without my w r i t t e n permiss ion . S ig n a tu Ie Date THE INSECT FAUNA OF CANADA THISTLE, CIRSIUM ARVENSE (L.) SCOP IN SOUTHERN MONTANA by . . HILDE DE SMET-MOENS A t h e s i s submit ted in p a r t i a l f u l f i l l m e n t of th e requirements f o r th e degree of ' MASTER OF SCIENCE in B io log ica l Sciences Approved: MONTANA STATE UNIVERSITY Bozeman, Montana August, 1982 / / i i i . ACKNOWLEDGMENTS I wish t o acknowledge and express my a p p rec ia t io n f o r th e c o n t r i ­ bu t ions of t h e fo l lowing people: Dr. W. L. M o r r i l l , my major p r o f e s s o r , f o r h i s p ro f e s s io n a l a s s i s t ­ ance throughout t h i s resea rch p r o j e c t ; The members of my t h e s i s committee. Dr. P. K. Fay , Dr. S. R. Eversman, and Mr. J . M. S to ry , f o r t h e i r t ime and inva luab le advice; Mrs. S. D. Rose, Cura tor of th e M.S.U. Entomological C o l l e c t i o n , f o r her taxonomic advice and help ; All t h e s y s t e m a t i c i s t s who i d e n t i f i e d t h e i n s e c t s mentioned in t h i s r e p o r t : t h e t axonom is t s .o f t h e Systematic Entomology Labora tory , USDA, B e l t s v i l . l e , MD; and th e National Museum of Natural H is to ry , Smithsonian I n s t i t u t i o n , Washington, DC; J . L a t t i n , P. Oman, K. A. P h i l l i p s , and G. M. S to n e d a h l , Oregon S t a t e U n iv e r s i ty , C o r v a l l i s ; L. A. K e l ton , Bio- sys tem a t ic s Research I n s t i t u t e , Ottawa; M. W. Nie lson, Forage In sec ts Research Labora to ry , Tucson, AZ; G. J . Miche ls , J r . , Texas A&M Univer­ s i t y , Amaril lo ; R. J . Beshear , The U n iv e rs i ty of Georgia, Experiment; J . A. Onsager and E. A. Oma, U.S.D.A. Rangeland In se c t Labora tory , Bozeman; R. M. B o h ar t , U n ive rs i ty o f C a l i f o r n i a , Davis; D. K. Young, Michigan S t a t e U n iv e r s i ty , East Lansing; . The Western A g r i c u l tu ra l Research Center and th e Montana weed d i s t r i c t s f o r th e funding of t h i s re sea rch p r o j e c t . TABLE OF CONTENTS VITA .................................................... i.i ACKNOWLEDGMENTS ...................... i i i LIST OF TABLES..................................................................... . v LIST OF FIGURES . . . .............................................................................. vi ABSTRACT ................................................................. v i i INTRODUCTION.................................................... I LITERATURE REVIEW .................... . . . . . . . . 3 The Host P lan t ............................................ ..................... B io log ica l Control of Canada T h i s t l e .................. B io log ica l Control of Canada T h i s t l e in Montana MATERIALS AND METHODS . , ...................... - . ....................... .... 12 Study S i t e s ..................................................................................................... 12 C o l le c t in g M e t h o d s ........................................... 12 Experimental R e a r i n g s ................................................ .... . ' .................. 15 F ie ld S t u d i e s ..................... 16 In s e c t I d e n t i f i c a t i o n .................. 16 RESULTS AND DISCUSSION.................................. . 18 Phytophagous In s e c t s .. ............................................ . 18 V i s i t o r s , P reda to rs and P a r a s i t o i d s . . . . . . . . . . . . 38 Summary...................... .....................................................■ 42 LITERATURE CITED .......................................................................... 46 Page C O (T i V LIST OF TABLES 1. In formation on th e i n s e c t s r e le a se d in Montana f o r t h e b io lo g ic a l con t ro l of Canada t h i s t l e ............................... 10 2. Se lec ted c o l l e c t i o n s i t e s of the 1981 in sec t survey on Canada t h i s t l e ...................... ...................................... .... 14 3. Phytophagous in s e c t s c o l l e c t e d from Canada t h i s t l e , Cirsium aryense (L .) S c o p . , in southern Montana, 1981 . . . . ............................... .............................. 19 4. Average p la n t he ig h ts o f e ig h t Bar is in fe s ted and e i g h t unin fe s t e d t h i s t l e p l a n t s in s i t e s 5 and 6, June 19, 1981 ............................... . . ................................... 30 5. I n f e s t a t i o n of Canada t h i s t l e heads by O r e l l i a ru f icauda ( F a b r i c i u s ) , September 3, 1981 . . . ........................... 37 Table Page 6. V i s i t o r s , p r e d a to r s , and p a r a s i t o i d s c o l l e c te d from Canada t h i s t l e , Cirsium arvense (L .) Scop. in southern Montana, 1981 T ...................... ..................... ..................... 39 7. P a ra s i t i sm of O r e l l i a r u f icauda (F ab r ic iu s ) pupae in Canada t h i s t l e seed heads, S ep tem b er^ , 1981 . . . 43 vi LIST OF FIGURES Figure Page 1. C o l lec t io n s i t e s o f th e i n s e c t survey on Canada t h i s t l e , 1 9 8 1 ............................................................................... 13 2. Emergence t r a p in s i t e 5 . . . ................................. ........................ 17 3. Corythucha d i s t i n c t a a d u l t s feed ing on Canada t h i s t l e leaves . . ............................................ ..................... 23 4. Feeding damage of Corythucha d i s t i n c t a on Canada t h i s t l e . . ............................................... 23 5 . • Aggregation of Corythucha d i s t i n c t a nymphs on th e unde r -s ide of Canada t h i s t l e leaves . . . . . . . . 25 6. Bar is sp. a d u l t feeding on t h i s t l e r o s e t t e ............................... 28 7. Feeding damage of Bar is sp. a d u l t s on potted t h i s t l e p l a n t s in th e in s e c ta ry ...................... .... 31 8. Bar is sp. l a rva in Canada t h i s t l e r o o t ...................... 31 9. Wilted t h i s t l e p l a n t in s i t e 5, i n f e s t e d with Bar is sp . l a r v a e ............................. ............................................. 31 10. Linear r e g re s s io n of p l a n t he ig h t versus la rv a l f r eq u e n cy , August 19 8 1 ........................................................ 33 11. Feeding damage of O r e l l i a r u f i c a u d a . la rvae on Canada t h i s t l e seeds. . -................................... .. ........................... 36 .12. P a r a s i t i z e d O r e l l i a ru f icauda pupa . . . ................................... 44 . ABSTRACT I n s e c t s a s so c ia te d with Cirsium arvense ( I . ) Scop, in southern Montana a re r e p o r t e d . F i f t y - s i x phytophagous species, and 4 7 . v i s i t i n g in s e c t s were c o l l e c t e d , i d e n t i f i e d and t a b u l a t e d . Four i n s e c t s p e c ie s , Corythucha d i s t i n c t a Osborn and Drake (Hemiptera: T ing idae ) , B a n s s p . , poss . c i r s i i G i lb e r t (Coleoptera : C urcu l io n id a e ) , Vanessa^cardui L. ( Lep idopte ra: Nyrnphalidae),. and O r e l l i a ru f icauda ( F a b r i c i u s ) (D ip t e r a : Tephrit i d a e ) , were cons idered , conspicuous , because of t h e i r damage i n f l i c t e d to th e t h i s t l e p l a n t . More i n s e c t s were found a s so c ia te d with the -deve lop ing seed heads than with f o l i a g e , stems or r o o t s . The informat ion ga thered o h . t h i s local survey can be va luable f o r f u t u r e in t r o d u c t io n s of insec t , b io lo g ic a l c on t ro l agen ts . I t forms th e foundation f o r follow-up s tu d ie s with indigenous in s e c t sp e c ie s . Augmentation and r e d i s t r i b u t i o n of e s t a b l i s h e d monophagous in s ec t s such as Ceuthorynchus l i t u r a and Bar is sp. should, be cons ide red . Trans mission experiments a re necessary t o e v a lu a te the p o t e n t i a l of these ' monophagous insects, as t h i s t l e pathogen v e c to r s . The combination of . two s t r e s s - f a c t o r s w i l l inc rease th e impact on th e t h i s t l e p la n t in . t h e f i e l d . - INTRODUCTION C u l tu ra l and chemical con t ro l p r a c t i c e s have h i s t o r i c a l l y been the main approaches t o weed c o n t r o l . Both methods a re aimed a t removing unwanted p l a n t s as qu ick ly as p o s s i b l e , a s h o r t term approach req u i r in g c o n s id e rab le annual expend i tu res of resources and energy (Andres and Gpeden, 1971). B io log ica l con t ro l of weeds has become a popula r a l t e r n a ­ t i v e because i t i s a means of c o n t r o l l i n g weeds w i thout t h e high energy c o s t s of c u l t u r a l p r a c t i c e s and w i thout t h e res idue and p o l lu t i o n prob­ lems of h e r b i c id e s . B io log ica l c o n t ro l o f weeds i s t h e d e l i b e r a t e use of i n s e c t s or o th e r p l a n t p a r a s i t e s t o reduce th e d e n s i ty of a weed t o an accep tab le leve l ( H a r r i s , 1971b). B io co n t ro l , when e f f e c t i v e , i s r e l a t i v e l y inex­ pens ive , l o n g - l a s t i n g and t h e b e n e f i t s a re cumula tive . This approach has s t r e n g th s and weaknesses d i f f e r e n t from o th e r methods and hence i s advantageous under c e r t a i n cond i t ions ( H a r r i s , 1971b; Maw, 1982). Most crops of^arablle land lhave many spec ies of weeds as com pet i to rs . Thus, c o n t r o l l i n g one spec ies through b io lo g ic a l con t ro l would r e q u i r e spray­ ing o r c u l t i v a t i o n f o r c on t ro l o f th e o th e r sp ec ie s . On th e o th e r hand, dominance of one weed spec ie s i s t y p i c a l on range land. Such a domi­ nant weed i s a very s u i t a b l e s u b jec t f o r b io lo g ic a l c o n t r o l . Even a s l i g h t inc rease in p re s su re can have a s i g n i f i c a n t e f f e c t ( H a r r i s , 1971b). One of t h e i n i t i a l s t ep s in developing a b io lo g ic a l weed con tro l program i s t o determine th e n a tu ra l enemies a t t a ck in g th e weed sp ec ie s , 2 in both i t s n a t iv e and i t s p r e s en t geographic ranges (Maw, 1980; H a r r i s , 1971a). I n i t i a l surveys expand in s ig h t and unders tanding of th e weed ecology, hos t ranges , e thology and i n s e c t - h o s t i n t e r r e l a t i o n s h i p s . The informat ion ga thered in th e local s u r v e y s . i n d i c a t e s th e n iches occupied \ ' ■ by indigenous s p e c i e s ̂ so t h a t chances of in t roducing a b iocon t ro l agent t h a t may d u p l i c a t e o r compete with an a l ready p re sen t spec ies a re mini­ mized (Maw, 1976). The o b je c t iv e s of t h i s study were: I) t o determine th e endemic in s e c t fauna a s so c ia t e d with t h e d i f f e r e n t growth s tag es of Canada t h i s t l e , Cirsium arvense ( I . ) S c o p . , in Southern Montana, and 2). to e v a lu a te t h e damage i n f l i c t e d by t h e most conspicuous sp ec ie s . LITERATURE REVIEW The Host P lan t Cirsium arvense ( L , ) Scop, i s a troublesome p e renn ia l weed in Montana. Indigenous t o Europe, Western Asia and Northern A f r i ca , i t was probably in troduced to North America in th e 17th Century (Detmers, 1927; Peschken, 1971). I n f e s t a t i o n s of Canada t h i s t l e now occur throughout t h e a g r i c u l t u r a l a reas of Canada and th e nor thern h a l f of t h e United S t a t e s ( Peschken, 1971; Hitchcock, e t a l . , 1973). A re c en t survey i n d i ­ ca ted t h a t t h i s troublesome weed i n f e s t s 1.5 m i l l io n acres in Montana.1 Canada t h i s t l e damages a wide v a r i e t y of crops by compet i t ive use o f l i g h t , mois ture and n u t r i e n t s (Hodgson, 1977). Heavy i n f e s t a t i o n s in p a s tu r e s and ranges reduce forage y i e l d s c ons ide rab ly . The weed a lso h a r b o r s i in s e c t s t h a t a t t a c k economic crops and is an a l t e r n a t e host f o r some pathogenic organisms (Moore, 1975). Cirsium arvense ( L . ) Scop, i s a polymorphic s p e c ie s . Stem, l e a f and f lower c h a r a c t e r i s t i c s vary c ons ide rab ly . B o tan is t s u su a l ly recog­ n ize t h r e e o r fou r morphological v a r i a n t s , a l l in te rb reed in g f r e e ly (Moore and F rank ton , 1974; Hodgson, 1964; Detmers, 1927). Canada t h i s t l e i s d ioec ious and reproduct ion occurs from seed and rhizome p iece s . Detmers (1927) s t a t e d t h a t honey bees were t h e c h ie f p o l l i n a t i o n agen ts . Jackson,: M. J . , 1982. Personal communication. I 4 In Montana, t h e t h i s t l e p l a n t s emerge in e a r ly May, when the mean weekly a i r tempera ture reaches 5°C (Moore, 1975). Rose t tes a re formed followed by stem e longa t ion approximate ly th r e e weeks a f t e r emergence (Moore, 1975). Flowering begins in mid-June and con t inues in to September. Growth begins decreas ing in J u l y , and ceases by e a r ly August The obnoxious c h a r a c t e r of t h i s weed is due mainly t o t h e rapid v e g e ta t iv e propaga t ion of i t s c reeping ho r izo n ta l rhizomes, giv ing r i s e t o numerous a e r i a l shoots (Moore, 1975). This ex tens ive branched rhizome system makes Canada t h i s t l e d i f f i c u l t to c o n t r o l , C u l tu ra l , mechanical and chemical con t ro l methods can be e f f e c t i v e in c u l t i v a t e d f i e l d s i f used p e r s i s t e n t l y in a long range con t ro l program (Hodgson, 1977). Where Canada t h i s t l e i s a p re v a le n t weed in range land, fa llow f i e l d s , waste lands , roads ides or r a i lw a y s , b io lo g ic a l c o n t ro l by in ­ s e c t s can be a reasonab le ad junc t . These hos t s p e c i f i c i n s e c t s are harmless t o n o n - t a rg e t p l a n t s and may be ab le to m u l t ip ly and d i sp e r se t o ad jacen t i n f e s t a t i o n s . B io log ica l Control of Canada T h i s t l e The p r i n c i p l e s and procedures of b io lo g ic a l weed c o n t ro l have been well de f ined and i l l u s t r a t e d with some s p ec ta cu la r successes (Be Bach, 1964; Van den Bosch, e t a l . , 1982). B io log ica l con t ro l s t r i v e s to reduce th e abundance of a weed spec ies by in troducing o r augmenting th e weed's n a tu ra l enemies. Huffaker (1959) l i s t s examples in which 5 n a t u r a l l y occur r ing in s e c t s have played an important ro l e in a f f e c t in g th e abundance o f a p a r t i c u l a r p l a n t s p e c ie s . . The in t r o d u c t io n of host s p e c i f i c phytophagous organisms has rece ived th e most emphasis to da te (Andres, e t a l . , 1976). . The s teps involved in such a technique are desc r ibed by H a r r i s (1971b). ■ Cirsium arvense ( L.) Scop, i s a prime candida te f o r b io lo g ic a l con t r o l (Hume,.1982; H a r r i s , 1971b, Andres , e t a l . , 1976) because: 1. The p l a n t has l i t t l e o r no value to people o r w i l d l i f e . 2. I t tends to grow in dense p o p u la t io n s , r e p re sen t in g a dominant weed in p a s tu r e and waste a re as . 3. I t i s an in troduced weed, and has very few p a r a s i t e s and p r e d a t o r s . 4. I t i s not c l o s e l y r e l a t e d to major economic crop; p l a n t s ; however a r t i c h o k e (Cynara scolymus I . ) and sa f f low er (Car thamus t i n c t o r i us L.) belong to the same Cyhareae t r i b e . 5. Many of th e t h i s t l e i n f e s t a t i o n s occur in in a c c e s s ib l e . a reas and th us lend themselves t o b iocon t ro l e f f o r t s (S to ry , 1980). 6. The widespread d i s t r i b u t i o n of th e weed w i l l r e s u l t in low c o s t pe r acre of c o n t r o l . T h i s . c o s t per acre w i l l be lower than t h a t of o th e r c on t ro l methods ( H a r r i s , 1979). 6 B io log ica l c o n t ro l w i l l inc rease th e environmental p r e s su re on Canada t h i s t l e . At. b e s t , t h e n a tu ra l enemies may e l im in a te th e need f o r o th e r con t ro l methods over much o f th e p l a n t ' s range and form a sound b a s i s f o r f u t u r e weed management schemes. At l e a s t , they would augment . e x i s t i n g c o n t ro l p r a c t i c e s ('Batra-, e t a l . , 1981) . The Commonwealth I n s t i t u t e of B io log ica l Control began work on th e . c o n t ro l o f Canada t h i s t l e in 1961, with a study of i t s p a r a s i t e s in Europe (Peschken, 1971). Eighty in s e c t :species were found t o feed on th e weed, A l t i c a carduorum-Guer. (C o leo p te ra : Chrysomeli d a e ) , Ceutorhynchus l i t u r a (Fab.) (Coleopte ra : Curculionidae) and Urophora cardui ( I . ) (D ip te ra : T e p h r i t id ae ) were s e l e c te d f o r f u r t h e r study b e ­ cause o f t h e i r apparent hos t s p e c i f i c i t y (Peschken, 1971; Zwolfer , 1964). Al I t h r e e i n s e c t s have been r e leased in Canada and th e United S t a t e s . - .. A l t i c a carduorum Guerin f a i l e d t o . e s t a b l i s h in a l l r e l e a s e s i t e s due t o c l i m a t i c s t r e s s and a t t a c k by in s e c t p reda to rs (Peschken, e t a l . , 1970). Ceutorhynchus l i t u r a (F .) i s e s t a b l i s h e d in a wide range o f c l i ­ mates in Canada (Peschken, e t a l . , 1980), Montana and Idaho; however, t h e range of i n f e s t a t i o n i s inc reas ing very slowly. While t h i s weevil e x e r t s s t r e s s on i t s hos t in th e lab o ra to ry (Peschken and Beecher, 1973) t h e r e i s no evidence t h a t C,. l i t u r a c o n t r o l s Canada t h i s t l e in th e f i e l d (Peschken, et, a l . , 19Q1). 7 Urophora cardui ( L . ) has. become e s t a b l i s h e d and i s spreading in e a s t e r n Canada (Peschken, e t a l . , 1980). A microspor id ian d i sea se of LL cardui (Nosema s p . ) i s one of th e causes leading to f a i l u r e of e s tab l i sh m en t in t h e Western s t a t e s . Other r e a s o n s , such as i n f e r t i l i t y o f t h e f l i e s , o r sp r ing f r o s t k i l l i n g o f th e la rvae may have been add i ­ t i o n a l causes of m o r t a l i t y (Peschken, e t a l . , 1982). Apparently th e tw o .e s t a b l i s h e d in troduced in s e c t s w i l l not con tro l Canada t h i s t l e . Fur the r s t r e s s f a c t o r s from o th e r i n s e c t s , pathogens o r p l a n t compet it ion a re needed to c o n t ro l t h i s weed. Few p o t e n t i a l l y e f f e c t i v e and hos t s p e c i f i c i n s e c t s from Zwolfer 's l i s t (1964) a re s t i l l a v a i l a b l e . T ingis amplia ta H.-S. (H e te r o p te ra: Tingidae) was r e c e n t ly t e s t e d f o r hos t s p e c i f i c i t y in t h e lab o ra to ry . I t was considered unsafe f o r in t ro d u c t io n in Canada, because i t s hosts inc lude s a f f low er and globe a r t i c h o k e . The approval f o r r e l e a s e of Lema c y a n e l l a ' ( I . ) (Coleopte ra: Curcul ionidae) has been withheld be­ cause i t a t t a c k s seve ra l Cirsium spp. indigenous to North America (Peschken, e t a l . , 1980). The p re s en t concern f o r na t ive Cirsium species has become a c r i t i ­ ca l i s su e . Had such s t r i n g e n t host s p e c i f i c i t y requirements been app l ied in th e p a s t , a number of i n s e c t s would never have been r e l e a se d . This f e a r f o r n a t iv e f l o r a could lengthen th e screening process con­ s id e r a b ly and many promising agents could be r e j e c t e d . B io log ica l con­ t r o l could then become im prac t ica l and .very expensive. Peschken (1982) 8 reviewed success fu l b io lo g ic a l weed con t ro l p r o j e c t s and concluded t h a t no t a r g e t weed has ever become r a r e . He s t a t e d t h a t i t i s very un l ike ly t h a t n a t iv e p l a n t s , which a re in equ i l ib r ium with t h e i r own in s e c t fauna, would support a d d i t io n a l i n s e c t sp e c ie s . Popula t ions of Canada t h i s t l e a re a l so a t tacked by numerous indigen­ ous in s e c t s and pathogens. Natura l enemies, a s so c ia ted with Canada t h i s t l e in North America have been repor ted by Moore (1975) , Maw (1976), Watson, e t a l . (1980) , Detmers (1927), and Andres (1980). Among the most impor tant spec ies were: a . The pa in ted lady b u t t e r f l y , Vanessa cardui L. ( =Pyrameis cardui L . , =Cynthia cardui ( I . ) ) ( Lep idop te ra : NymphaTidae). The la rvae o cca s io n a l ly cause s p e c ta c u la r d e f o l i a t i o n of t h i s t l e s in loca l a reas . . I t i s a migratory b u t t e r f l y , and i t s numbers f l u c t u a t e annua l ly , making i t u n r e l i a b l e as a n a tu ra l con t ro l agen t . I t can be a p e s t of sunflower and soybean (Morihara. and. Balsbaugh, 1976) and many o th e r p l a n t s . b. The Canada t h i s t l e midge Dasyneura g ibsoni F e l t (D i p t e r a : Cecidomyii d a e ) , which a t t a c k s t h e developing seed heads. c . O r e l l i a ru f icauda (F . ) ( =Trypeta f l o r e s c e n t i a e L.) (D ip te ra : T e p h r i t id ae ) which a t t a c k s up t o 70% of th e t h i s t l e heads . This seed head f l y was probably a c c id e n ta l l y in troduced from Europe ( H a r r i s , 1971a). 9 d. Cassida rub ig inosa MuelI . (Cdleopte ra : Chrysomeli d a e ) : This b e e t l e was a c c i d e n t a l l y in troduced in to th e United S t a t e s (Ward, 1976), and d e f o l i a t e s Canada t h i s t l e a t high popula­ t i o n s . This f l e a b e e t l e has become widely e s t a b l i s h e d in the Eas te rn United S t a t e s (Ward, 1976). e . The systemic au toec ious r u s t Puccin ia obtegens (Link) T u l . is an endemic pathogen, hos t s p e c i f i c t o Canada t h i s t l e . Natur­ al i n f e c t io n i s not high enough f o r economic c o n t r o l . Since host r e s i s t a n c e i s an impor tant f a c t o r l im i t in g r u s t i n f e c t i o n , an aggress ive s t r a i n may be more e f f e c t i v e as a b io co n t ro l agent of Canada t h i s t l e (Turner , 1981). None of th e l i s t e d spec ie s suppress Canada t h i s t l e popula t ions below th e economic l e v e l . However, i n v e s t ig a t i o n s of th e bio logy o f the most d e s t r u c t i v e organisms could r e s u l t in th e development o f approaches whereby popu la t ions of t h e se n a tu ra l enemies a re augmented to increase t h e i r damage to Canada t h i s t l e (Watson, e t a l . , 1980; Ward, 1976; Turner , 1981). B io log ica l Control of Canada T h i s t l e in Montana The b io lo g ic a l con t ro l program of Canada t h i s t l e in Montana began with t h e l i b e r a t i o n of A l t i c a carduorum Guerin in 1964. Subsequently , th e stem weevil Ceutorhynchus l i t u r a (F . ) was re leased in 1973 and Urophora cardui (L.), in 1978 (S to ry , 1979) (Table I ) . Of t h e t h r e e , Table I . Information on th e i n s e c t s r e l e a se d in Montana f o r the b io lo g ic a l con t ro l of Canada t h i s t l e . a In se c t Date In se c t s Released No. In se c t s Released County where Released Source of In se c t S ta tus . of Insec t A l t i c a carduorum Guerin 1964 200 Ravall i USDA No recovery 1966 200. G a l l a t in USDA No recovery Ceutorhynchus l i t u r a ( F . ) 1973 200 G a l l a t in . USDA Inc. slowly Urophora cardui ( I . ) 1978 92 Ravall i USDA No recovery ^Data from S to ry , J . M., 1979. 11 only Ceutorhynchus l i t u r a ( F . ) has surv ived and become e s t a b l i s h e d . Attempts to r e d i s t r i b u t e th e weevil were made in 1977. a t th e Bozeman s i t e , when 95% of th e shoots were found t o be mined (S to ry , 1980). P lan ts in f e s t e d with C_. l i t u r a la rvae were c o l l e c t e d in June from th e ■ r e l e a s e s i t e and t r a n s p l a n t e d in o th e r a reas of Montana. The reasons f o r f a i l u r e of A I t i c a carduorum Guerin and Urophdra cardui ( L . ) t o e s t a b l i s h in Montana a re not known. Addi t iona l a t tempts t o e s t a b l i s h jJ. cardui w i l l be made as more i n s e c t s become a v a i l a b le (S to ry , 1980). The b io lo g ic a l weed con tro l .p rogram in Montana i s inc reas ing in momentum. I n t e r e s t and awareness by th e pub l ic and academic communities are growing. Endemic p l a n t pathogen's, p a r t i c u l a r l y Puccin ia obtegehs I (Turner, 1981) and S c l e r o t i n i a sc le ro t io rum (Simmonds, 1982) are being in v e s t ig a te d as p o t e n t i a l b iocon t ro l agents a g a in s t Canada t h i s t l e in Montana. The use of p la n t pathogens may extend th e a p p lc i a t i o n of b i o ­ lo g ic a l weed con t ro l t o inc lude c u l t i v a t e d a reas . MATERIALS AND METHODS Study S i t e s A t o t a l of 50 s i t e s were surveyed th roughout the 1981 growing s ea ­ son, s t a r t i n g Apri l 15 and ending September 30 (F igure I).. This period covers r o s e t t e , v e g e t a t i v e , f lowering and f r u i t i n g s tag es o f the t h i s t l e p l a n t . Most o f th e lo c a t io n s r e p re se n t occas ional c o l l e c t i o n s i t e s . Seven were s e l e c te d f o r more i n t e n s iv e weekly o r bi-monthly sampling (Table 2 ) . S e le c t io n of t h e se s i t e s was based on e x t e n t o f t h i s t l e i n f e s t a t i o n , h a b i t a t - t y p e , a c c e s s i b i l i t y and absence o f h e rb ic id e and p e s t i c i d e use. C o l le c t in g Methods The samples were c o l l e c t e d by th e fo llowing methods: 1. . Stands .of Canada t h i s t l e p l a n t s were examined c a r e f u l l y f o r in s e c t i n f e s t a t i o n s and e x te rn a l symptoms of endophagy. Feeding o r o v ip o s i t io n damage was recorded in th e f i e l d and ' whenever p o s s ib l e c o r r e l a t e d with t h e i n s e c t spec ie s p re sen t . 2. Most of t h e in s e c t s were c o l l e c t e d by handpick ing , t h e only method allowing c o r r e c t l o c a l i z a t i o n of the sampled specimens. Sweeping d i s tu rb e d th e in s ec t s and did not always d is lodge in d iv id u a l s on upper and lower p a r t s o f the p l a n t . 3. O ccas iona l ly , a simple polye thylene-bag sampl ing.technique was used (Trumble, e t a l . , 1975). A la rge po lye thy lene bag M ' W O u I* # : occasional c o l le c t io n s i t e s O : se lec ted c o l le c t io n s i t e s Figure I . C o l le c t io n s i t e s of th e i n s e c t survey on Canada t h i s t l e , 1981. 14 Table 2. S e lec ted c o l l e c t i o n s i t e s of t h e 1981 in s e c t survey on Canada t h i s t l e . S i t e Location H ab i ta t . I Agronomy Farm, Bozeman ( G a l l a t i n County) Mowed grass land with n a tu ra l r u s t i n f e s t a t i o n (P. obtegens) o f 52%. (Turner, 198IT. 2 For t E l l i s (G a l l a t i n County) Fallow f i e l d p lan ted with wheat and b a r le y in 1980 3. Southern Research Center Huntley (Yellowstone County) Fallow f i e l d , border ing bar ley f i e l d . 4, Southern. Research Center Huntley (Yellowstone County) Waste a r e a , shaded by high t r e e s 5 B i l l i n g s (Yellowstone County) H i l l s i d e , n a tu ra l h a b i t a t 6 Columbus ( S t i l l w a t e r County) Dis turbed a rea , roads ide 7 Park City ( S t i l l w a t e r County) Roadside, bordering pas tu re land 15 was inver ted over th e t a r g e t p l a n t s and fa s tened a t t h e open end. P lants , were then uprooted, labeled and t ranspor ted , to t h e l a b o ra to ry ' fo r examinat ion. 4. Two to f i v e t h i s t l e p l a n t s were s e l e c te d a t random and uprooted . a t each s i t e . Roots, crowns and stems were d i s s e c te d arid ex­ amined f o r endophagous i n s e c t s . 5. Flower heads and buds were d i s s e c te d in th e f i e l d . By th e end of th e growing season, c o l l e c t i o n s o f seed heads were made at ' d i f f e r e n t s i t e s . Approximately 50% of th e seed heads were ex­ amined in. th e l a b o ra to ry and th e r e s t were s to red in polyethy- Iene bags to recover emerging a d u l t s o f endophagous sp ec ie s . Experimental Rearings . Immature in s e c t s were reared t o th e a d u l t s tage on p o t ted p la n t s o r f r e s h cu t Canada t h i s t l e f o l i a g e in the. i n s e c ta ry . Conspicuous i n s e c t s such as Bar is s p . , poss. c i r s i i G i j b e r t 1 and Corythucha d i s t i n c t a Osborn and Drake were c o l l e c t e d in con ta ine rs and confined t o p o t ted p l a n t s in the. i n s e c t a r y . The ir impact on po t ted Canada t h i s t l e p l a n t s was observed d a i l y . Cages used t o conf ine in s ec t s were c y l i n d r i c a l in shape (22 x 38 cm), and had wooden frames covered by a f i n e mesh c l o t h . ---------------- - r — --------- :------------------------ :----------------------------- Whitehead, D. R. (Systematic Entomological Labora to ry , USDA) . could not supply a p o s i t i v e i d e n t i f i c a t i o n . . We w i l l r e f e r t o i t . as Bar is sp . - 16 Fie ld S tu d i e s S i t e s 5 and .6 (Table 2) were s e l e c te d f o r o b se rva t ions of Baris sp. (Coleopte ra: Curcul ionidae) on Canada t h i s t l e . Both s i t e s were heav i ly in f e s t e d with th e weevil and i t s h o s t . 1. Heights of e ig h t damaged t h i s t l e p l a n t s were recorded in mid-June a t each s i t e and compared with he ig h ts of e ig h t u n in fes ted p la n t s a t t h e same s i t e . D if fe rences were t e s t e d f o r s i g n i f i c a n c e with t h e t - t e s t (P < 0 .0 1 ) . 2. At t h e end of th e growing season, 17 damaged t h i s t l e p l a n t s were uprooted, d i s s e c t e d , and pupal counts were made. A reg ress ion a n a ly s i s was performed of th e p l a n t he tgh t over t h e l a rv a l f r e ­ quency ( P<- 0 .0 1 ) . 3. Emergence t r a p s , each covering approximately two p l a n t s , were p laced in s i t e 5, in e a r l y September, 1981. These c a g e s , made,. , o f f i n e w i r e - n e t t i n g , were con ica l in shape with a diameter of 80 cm. A small t r a p was a t tached on th e top (F igure 2 ) . These t r a p s made i t p o s s ib le to con t ro l seasonal a c t i v i t y of Baris a d u l t s and t o c o l l e c t o th e r i n s e c t spec ies emerging from the same t h i s t l e p l a n t s . In se c t I d e n t i f i c a t i o n In se c t specimens were so r ted and sen t to taxonomic a u t h o r i t i e s f o r i d e n t i f i c a t i o n . 17 Figure 2. Emergence t r a p in s i t e 5. RESULTS AND DISCUSSION The in s e c t s c o l l e c t e d on Canada t h i s t l e were grouped as I) phyto­ phagous in s e c t s (Table 3 ) ; 2) i n s e c t s c o l l e c t i n g po l len o r n e c ta r , i n ­ s e c t s which a re i n c id e n ta l v i s i t o r s , p red a to r s and p a r a s i t o i d s o f o th e r i n s e c t s . In s e c t s c o l l e c t e d a re l i s t e d by o rde r according t o Borror , De Long and T r ip lehorn (1976). Phytophagous In se c t s Table 3 l i s t s 58 s p e c ie s , r e p re se n t in g s ix o r d e r s , 22 f a m i l ie s and 51 genera . All of t h e se spec ies have adopted Canada t h i s t l e as a food p l a n t . Twenty-six spec ies a l so use t h i s a l i e n weed as a reproduc­ t i v e h o s t . However, none of th e se in s e c t s are r e s t r i c t e d s o le ly to Cirsium a r v e n s e , with t h e exception of Ceutorhynchus l i t u r a ( F a b r i c i u s ) , which has been purposely in troduced f o r th e con t ro l of Canada t h i s t l e . On t h e c o n t r a r y , one t h i r d of th e in s e c t s found feeding on Canada t h i s t l e in southern Montana a re e i t h e r minor or major p e s t s of economic c rops . Four s p e c ie s , Corythucha d i s t i n c t a Osborn and Drake (Hemiptera: T ing idae ) , Bar is sp . poss . c i r s i i G i l b e r t (Coleoptera: C urcu l i o n i d a e ) , Vanessa cardui L. (Lepidoptera : Nymphali d a e ) , and O r e l l i a ru f icauda ( F a b r i c i u s ) (D ip te ra : T e p h r i t i d a e ) , were considered conspicuous, because of th e damage they i n f l i c t e d to th e t h i s t l e p l a n t . They can be very 19 Table 3 Phytophagous arvense ( L . ) in s e c t s c o l l e c t e d from Canada t h i s t l e , S c o p . , in southern Montana, 1981. Cirsium Plant Association Insects Frequency in Collection6 Stages6 Feeding0 Part(S)6 Plant Growth Recorded Literature Stage)s r Hosts' Source Orthoptera Acndidae Chortophaga vir ld ifasc ia ta (DeGeer) LC A ECT L R P (15,38) Eri te t t ix simplex (Thomas) O A ECT L R P (15) Melanoplus b iv it ta tus (Say) LC N1A ECT L F P (15.38) M. femur-rubrum (DeGeer) C N1A ECT L F P (15.38) M. packardii Scudder C A ECT L F P (15) M. sanguinipes (Fabricius) C A ECT L F - Gryllidae Allonemobius allardi (Alexander R A ECT L F and Thomas) Hemiptera Miridae Chlamydatus associatus (Uhler) R A ECT - F C (29) Lygus lineolaris (Palisot de Beauvois) R A ECT F F P (29) L. robustus Uhler LC N,A ECT F V1F C (29) L. schulli Knight R A ECT F F P (29) Tingidae Corythucha dist incta Osbom and Drake C E.N.A ECT L R1V1F P (13,15) Pentatomidae Euschistus euschistoides (Vollenmolen) O A ECT L R P (8.15) Euschistus sp . O N ECT L F - Rhytidolomia sp. O A ECT L F - I unidentified sp. O E - L F - Homoptera Membracidae Ceresini sp. O N ECT S F - Publilia modesta (Uhler) C A ECT S R1V P (15) Tortist i lus wlckhami (Van Duzee) R A ECT L F - Cercopidae Aphrophora permutata Uhler O A ECT S V P (15) Philaenus spumarius (L.) C N.A ECT L.S R1V1F P (18) Cicadellidae Aceratagallia sp. R A ECT L F Agallia sp. O A ECT L V Cuerna prob. s t r ia ta (Walker) O N.A ECT L R.V P (43) Empoasca sp. R A ECT L R Euscelidius variegatus (Kirschbaum) R A ECT L F P (6.44) Macrosteles fascifrons (Stall LC A ECT L F P (6,44) Xerophloea v ir id ls (FabricIus) R N ECT L F P (6,15) I unidentified sp. R E S F 20 Table 3. (continued) Insects , Relative Frequency in ColIectiona Stages6 Feeding0 Plant P T a n l “ Part(s)d Association Plant Growth Stage(s)e Recorded Hosts' Literature Source Aphididae Aphis fabae Scopoli O N1A ECT S F P (46) Aphis SP. O N1A ECT S F - Brachycauduscardul (L.) O N1A ECT S F t (45) Capitophorus carduinus (Walker) R N1A ECT S F t (45) DdCtynotus sp. R N1A ECT S F - Pseudococcidae Chnaurococcus t r i f o l l i i (Forbes) R N1A ECT R F P (16) Phenacoccus solani Ferris R N1A ECT S V P (15,16) Coleoptera Mordel Iidae Mordellistena sp. C L END S F P (53) Mordellistena sp. "A" O A ECT L V - Mordellistena sp. "B" O A ECT L V - Chrysomelidae Criocens duodecimpunctatus ( I .) R A ECT L V P (23) Deloyala guttata (Olivier) R A ECT L R P (23) Oiachus auratus (Fabncius) O A ECT L R P (23) Pachybrachys melanostictus Suffnan O A ECT L R1V P (23) Systena blanda Melsheimer R A ECT L F P (15) Tnrhabda prob. convergens LeConte R A ECT L F C (23) Curculionidae Baris s p . , poss. c i r s i i Gilbert C L1A END1ECT R1S R1V1F t (17) Ceutorhynchus l i tura (Fabncius) LC L.A END1ECT S1L R1V t (48) Dysticheus sp. R A ECT L F - Macrorhoptus sp. R A ECT L F - Notaris bimaculatus (Fabricius) R A ECT L R - Otiorhynchus ovatus (L.) O A ECT L V1F P (15,23) Tychlus p ic iro s tr is (FabrIcius) R A ECT L R C (23) Rhinocyllus conicus Froelich C L.A END1ECT F1L R1V1F t (5) Lepidoptera Pterophoridae Pla typti lia carduidactyla (Riley) O L END S V C (15) 21 Table 3. (continued) Insects „ Rela tive. Frequency in Col lection® Stages6 Feedlngc Association Plant Growth Stage(s)e Recorded Hosts' Literature Source Tortrlcldae I unidentified sp. R L ECT L V I unidentified sp. R L ECT L V - Arctlidae Apantesiswilliamsii (Dodge) R L ECT L V C (60) Noctuidae I unidentified sp. O L END R F - Nymphalidae Vanessa (Cynthia) cardul L. O L ECT L V P (15,60) Diptera Sciaridae I unidentified sp. O L END R V1F Cecidomyiidae I unidentified sp. O L END F F _ Tephritidae Orell ia ruficauda (Fabricius) C L1A END,ECT F F C (39) Lauxaniidae Camptoproscopella sp. LC A ECT L.F V.F - aNumber of s ites in which the species appears/50 si tes ; R * Rare (species found in I collection s i te ) , 0 = Occasional (species found in 2-5 collection s i tes ) , LC = Locally coimon (species found in 2-5 collection s i te s , and present in high density), C = Common (species found in more than 5 collection s i tes ) . bE = eggs, L = larvae, N * nymphs. A = adults. cECT = ectophagous, END = endophagous. bR = roots, S = stems, L = leaves, F = flower heads or buds. eR = rosette stage, V = ver tical growth stage, F * flowering and fruiting stages. f t - th is t le s (host plants apparently restricted to closely related genera as Carduus, Clrsiun, and Silybun) c = Composltae (host plants apparently restr ic ted to the Compositae), p * poIyphagous (attacking plants belonging to different families), - * no information. 22 e f f e c t i v e in local a r e a s , al though d e n s i t i e s were too low to a f f e c t the weed po p u la t io n s . Grasshoppers were c o l l e c t e d in most of the samples , with the h e av ie s t i n f e s t a t i o n during f lowering and f r u i t i n g s tag es of the p l a n t . These i n s e c t s a re genera l fe ed e rs and thus have l i t t l e in f luence in the n a tu ra l con t ro l of t h i s t l e s . In a d d i t i o n , they a re cons idered ; economic p e s t s . T h i s t l e r o s e t t e s were examined f o r feeding damage in s i t e I (T ab le .2 ) . The grasshoppers p re fe r r e d r u s t in f e s t ed over hea l thy t h i s t l e p l a n t s . Lewis (1979) sugges ts t h a t such p re fe rences are due to f a v o rab le a l t e r a t i o n s in t h e n u t r i t i o n a l and/or de fens ive chemistry of t h e p l a n t . The most common Hemiptera c o l l e c t e d from Canada t h i s t l e p lan t s were Corythucha d i s t i n c t a Osborn and Drake and severa l Lygus spec ie s . The l a t t e r a re common sapfeeders on g r a s s e s , weeds and a wide v a r i e ty of economic p l a n t s ( K e l to n , 1975). C_. d i s t i n c t a appeared in local popu­ l a t i o n s , p a r t i c u l a r l y in moist h a b i t a t s . This lace bug was found fe e d ­ ing on th e t h i s t l e leaves from e a r ly May th roughout th e growing season of th e p l a n t (F igure 3 ) . Adults and nymphs were h ighly aggregated on th e t h i s t l e leaves and caused brown o r black feeding sca rs (Figure 4),. When la rge numbers occurred per p l a n t , th e leaves became n e c r o t i c . Adults .were c o l l e c t e d in e a r ly May from s i t e s 4, 5 and 7 (Table 2) and conf ined to po t ted t h i s t l e p l a n t s in t h e i n s e c ta ry . A f te r two weeks, most o f th e p l a n t s showed aggregation of nymphs, c lu s t e r e d near the spot 23 Figure 3. Corythucha d i s t i n c t a Figure 4. Feeding damage of a d u l t s feed ing on Corythucha d i s t i n c t a Canada t h i s t l e leaves . on Canada t h i s t l e . 24 where th e eggs were l a i d , on th e under-s ide of the l e a f (F igure 5) . A f te r a per iod of s ix weeks, the lace bugs were p re sen t in such den s i ty t h a t a l l th e leaves were cur led and n e c r o t i c . These p l a n t s f a i l e d to produce flower buds. £ . d i s t i n c t a i s m u l t i v o l t i n e and has two or more g enera t ions per y e a r , depending on th e c l im a t i c cond i t ions (Drake and Ruhoff , 1960). However, n a tu ra l Corythucha popula t ions were too small to cause s u b s t a n t i a l d e f o l i a t i o n o f th e t h i s t l e p l a n t s . Lamp and McCarthy (1982) repor ted t h a t nymphaI popula t ions of (X d i s t i n c t a on Cirsium canescens Nut t , caused n e c ro s i s o f th e leaves , but did not reduce th e seed production of th e p l a n t s . Hosto p l a n t s of C_. d i s t i n c t a a re recorded as being Carduus l a n c e o l a t u s , Cnicus s p . , Cirsium pulcherrimum, £ . c an escen s , Lathyrus n u t t a l l i i , and Althaea s p . , In a d d i t i o n , Essig (1958) repor ted i t s occurrence on balsam r o o t , beans,, corn , l e t t u c e , lup in e , p a r sn ip , squash, and t u r n i p . The s p i t t l e b u g , Philaenus spumarius (L.) was found t o be very abundant in a wide v a r i e t y of h a b i t a t s . The nymphs were observed on th e t h i s t l e r o s e t t e s in e a r l y May, surrounded by a mass of s p i t t l e - l i k e f r o t h . The a d u l t s fed on th e upper p a r t of the t h i s t l e stem throughout th e r e s t of th e summer. FX spumarius i s considered an . im por tan t eco­ nomic p e s t of fo rage crops in e a s t e rn United S ta t e s (Halkka, e t a l . , 1967). However, they appeared to have l i t t l e e f f e c t on th e t h i s t l e p l a n t s . A coincidence of high r u s t (£. ob tegens ) i n f e s t a t i o n (52%) and a high d e n s i ty of s p i t t l e b u g nymphs was observed in s i t e I . In June, 25 Figure 5. Aggregation of Corythucha d i s t i n c t a nymphs on the under-s ide of Canada t h i s t l e , leaves . 26 1981, a t o t a l of 425 t h i s t l e p l a n t s were examined in s i t e I f o r s p i t t l e - bug a t t a c k . An average of 2% p l a n t s were found to be in f e s t e d with s p i t t l e b u g s . ' - P u b l i l i a modesta (Uhler) was c o l l e c t e d only as an a d u l t on Cirsium a rv e n se . Like th e s p i t t l e b u g s , they fed on the upper p a r t of t h e stem from June to September and were a t tended by seve ra l ant spec ies The aphid co lon ie s on Canada t h i s t l e were common in l a t e Ju ly and August Ind iv idua l co lon ies did not reach damaging d e n s i t i e s . The most numerous phytophagous group in the Montana survey was rep resen ted by th e o rd e r of th e C o leo p te ra . As in th e European survey (Zw olfe r , 1964), t h e l a r g e s t b e e t l e family c o l l e c te d in south Montana was th e Curcu l ion idae . Four of th e 15 b e e t l e spec ies feeding on Canada t h i s t l e a re endophagous in t h e i r l a rv a l s ta g e s . Of t h e s e , M orde l l i s tena sp. (M o rd e l l id a e ) , Bar is s p . , poss. c i r s i i G i lb e r t and Rhynocyllus conicus F roe l ich (Curculionidae) occurred in a t l e a s t e i g h t , d i f f e r e n t c o l l e c t i o n s i t e s , with a r e l a t i v e high frequency a t each s i t e . The f i r s t M orde l l i s tena sp. la rvae mining in the t h i s t l e stems were observed by mid-Ju ly . These la rvae overwin te r in old t h i s t l e s t a l k s , and pupate th e fo llowing sp r in g . The a d u l t s , probably emerging in l a t e May, were found feeding on Canada t h i s t l e in June . The la rva l feed ing throughout t h e summer apparen t ly did not a f f e c t t h e normal growth and reproduct ion of t h e t h i s t l e p l a n t . 27 A root-bor ing , w e e v i l , Bar is sp. poss . c i r s i i G i l b e r t , na t ive to . North America, a t tacked Canada t h i s t l e in sou theas te rn Montana. This w eev i l , a l so recorded on o th e r C i r s iu m .spp. ( G i lb e r t , 1964), i s probably th e only indigenous in s e c t approaching th e monophagous h a b i t . G i lb e r t (1964) c l a s s i f i e s j3. f u t i l i s , j3. c i r s i i , B_. brunneipes and Bv monticola as fo u r spec ies of t h e same subgroup, comprising a. complex of c lo se ly r e l a t e d spec ies which a re a l l r e s t r i c t e d t o hos ts in th e genus Cirs ium. Bar is c i r s i i has been recorded on s ix d i f f e r e n t Cirsium hosts in C a l i f o r n i a : Cv querceto rum, Cv o c c i d e n t a l e , Cv c o u l t e r ! , Cv c a l i f o r n i c a , C_. cymosum and £ . fo l io sum . In our survey, Bar is sp. poss. c i r s i i was only observed on Cirsium arvense and was found e s p e c i a l l y in d i s tu rb e d a r e a s , roads ides and g ra s s l a n d s . Both a d u l t and la rva l feeding, were observed in s i t e s 5 and 6 and in th e i n s e c t a r y . ■ Bar is a d u l t s overwin te r as unemerged ad u l t s in th e ro o ts o f t h e i r hos ts and emerged in e a r ly spr ing by making t h e i r way through old l a rv a l g a l l e r i e s t o th e base of th e stem. There was no in d ic a t io n of a c t i v i t y in th e c e l l s of o v e r w in te r in g . a d u l t s . At t h e t ime of emergence, t h e t h i s t l e s were about f i v e to 20 cm t a l l . The weevil s s t a r t e d feed ­ ing between th e newly formed d i s t a l l e a f l e t s of the young t h i s t l e s (F igure 6 ) ; l a t e r in middle and lower l e a f a x i l s of t a l l e r p l a n t s . Genera l ly , two specimens per p la n t were observed, up to fo u r on t a l l e r p l a n t s . The feeding on th e young p l a n t s u sua l ly damaged th e primary v e r t i c a l shoo t . Damaged p la n t s produced new s ide shoo ts , r e s u l t i n g in Figure 6. Bar is sp . a d u l t feeding on t h i s t l e r o s e t t e . 29 a genera l bushy appearance, which were d i s t i n c t i v e in th e f i e l d . Heights of e ig h t damaged t h i s t l e p l a n t s were recorded a t s i t e s 5 and 6 and compared with he igh t of e ig h t un in fe s ted p la n t s a t t h e same s i t e . Adult feeding reduced th e v e r t i c a l growth o f th e t h i s t l e p l a n t s i g n i f i ­ c a n t ly (Table 4 ) . In e a r l y May, Bar is a d u l t s were t r a n s f e r r e d from s i t e 5 t o th e in sec ta ry .a n d confined to p o t t e d t h i s t l e p l a n t s , where t h e i r impact on th e p l a n t s was observed. Most of th e se p l a n t s , a lready under heavy s t r e s s due to low l i g h t i n t e n s i t y , did not su rv ive the a t t a c k o f th e weevil (F igure 7) and th e p l a n t s died w i th in two weeks. F ie ld o b serva t ions in Montana ind ica ted t h a t emerged a d u l t s l ived from two t o four months, were h igh ly lo c a l iz e d in d i s t r i b u t i o n and d ispersed by ambulation or o c ca s io n a l ly by f l i g h t . G i lb e r t (1964) r e p o r t s t h a t t h e r e i s a pe r iod of about t h r e e weeks between emergence and ovipos t ion O vipos i t ion s i t e s , always in th e lower h a l f of th e p l a n t , vary during th e season, becoming p ro g r e s s iv e ly lower on th e main stem. The f i r s t Bar is la rvae were d e tec te d in s i t e 5 by mid J u ly . The la rvae were feed ing a c t i v e l y in th e t h i s t l e r o o t s , about 15 cm below ground l e v e l . The c e n t r a l va scu la r c y l in d e r , as well as t h e c o r t i c a l t i s s u e of t h e r o o t s , were e i t h e r consumed o r used f o r the c o n s t r u c t io n o f th e pupal chamber (F igure 8 ) . By th e end of Ju ly , the small bushy p la n t s w i l t ed and f a i l e d t o produce flower buds (F igure 9 ) . A t o t a l o f 17 w i l ted p la n t s were uprooted by th e end of t h e growing season and unemerged a d u l t s were counted. I found an average of Table 4. Average p l a n t he ig h ts (cm) of e ig h t Bar is i n f e s t e d and e ig h t uninfes ted ' t h i s t l e p l a n t s in s i t e s 5 and 6, June 19, 1981. P lan t Height, * cm S i t e Weevil P resen t Weevil Absent 5 . 29. op 58.10 • 6 32.25 71.00 * P lan t he igh ts were s i g n i f i c a n t l y d i f f e r e n t , t - t e s t (P < 0 . 0 1 ) . 31 Figure 7. Feeding damage of Baris Figure 8 . Bar is sp. la rva in sp. a d u l t s on po t ted Canada t h i s t l e ro o t , t h i s t l e p l a n t s in the i n s e c t a r y . Figure 9. Wilted t h i s t l e p la n t in s i t e 5, i n f e s t e d with Bar is sp. l a rv ae . 32 1.6 unemerged a d u l t s pe r Canada t h i s t l e p l a n t and d iscovered a s i g n i f i ­ can t c o r r e l a t i o n between p la n t h e igh t and la rv a l frequency ( r = 0 . 7 6 6 , P < 0.01) (F igure 10). This could be due to a h igher l a rv a l su rv iva l r a t e in t a l l e r p l a n t s o r to a h ighe r imaginal frequency on th e l a r g e r p l a n t s e a r ly in th e season. The damage i n f l i c t e d by th e weevil i s both d i r e c t and i n d i r e c t , cover ing th e e n t i r e growing season of t h e p l a n t . Adults s t r e s s the p l a n t in e a r l y spr ing by d e s t roy ing th e meris temat ic t i p and a f f e c t in g th e v e r t i c a l growth of t h e p l a n t . Larvae burrow in to th e vascu la r t i s s u e of t h e roo t and block t r a n s p o r t , s tu n t in g th e o v e ra l l growth of. t h e p l a n t and preven t ing seed p roduc t ion . Both a d u l t and l a rv a l fe ed ­ ing render t h e p l a n t s u sc e p t ib l e t o invasion by o th e r organisms. Dis­ eases a s so c ia t e d with weevil damage have not been i d e n t i f i e d . F ie ld , obse rv a t io n s showed t h a t o th e r i n s e c t s invade damaged r o o t s . Two s c a le i n s e c t s , Chnaurococcus t r i f o l i i (Forbes) and Phenococcus so lan i F e r r i s (Homoptera: Pseudococc idae) , and u n id e n t i f i e d S c ia r id a e (D ip te ra) la rvae were c o l l e c t e d from t h i s t l e roo ts damaged by Bar is l a r v a l feed ing . U niden t i f ied f a c t o r s apparen t ly p reven t the buildup of high den­ s i t i e s o f Bar is p opu la t ions . Very l i t t l e i s known about p reda to rs and p a r a s i t e s of th e genus B a r i s . None have been observed in t h e su rvey ,. with th e exception of one Canthar is sp. la rva found a s so c ia t e d with a Bar is la rva in th e t h i s t l e r o o t . The r o l e of in q u i l i n e i n s e c t s i s not y e t known, but i t i s apparent t h a t t h e se i n s e c t s could be compet itors o r 33 1 2 3 4 N o. OF LARVAE .Figure 10. Linear reg re ss ion of p la n t he igh t (cm) versus la rv a l f requency, August 1981. The b value (b = l I .183, S.E.=2.43) is s i g n i f i c a n t l y d i f f e r e n t from zero (P < 0 .0 1 ) . 34 may i n t e r r u p t o r impede o v ip o s i t io n . In a l l c o l l e c t i o n s i t e s in fe s ted . with B a r i s , M orde l l i s tena la rvae were found feeding in th e stem p i th of th e same p l a n t ; In s i t e 6, Rhinocyllus conicus and Bar is were p resen t on th e same p l a n t . G i lb e r t (1964) repor ted t h a t when. larvae of O r e l l i a a re abundant in C irs ium , la rvae of Bar is are sca rce o r wanting. This was supported by my o b se rv a t io n s . Rhinocyllus conicus F roel ich i s a t h i s t l e seed head-feeding w eev i l , in troduced from France f o r t h e con t ro l of Carduus nutans L. (musk t h i s t l e ) . This weevil a l so a t t a c k s Canada t h i s t l e . Larvae of R:, conicus in Canada t h i s t l e seed heads f r eq u e n t ly e a t through, the wall of t h e bud, and thereby become vu lne rab le t o predacious i n s e c t s and sp id e r s (Rees, 1982). A maximum of t h r e e la rvae per f lower bud were observed in our survey. Growth cracks in in fe s ted Canada t h i s t l e seed- heads and stems were very common. Two spec ies o f Lepidoptera were found to d e f o l i a t e t h i s t l e p l a n t s . The most common, Vanessa cardui L . , t h e pa in ted lady, s t a r t e d feeding on th e t h i s t l e leaves in l a t e May, causing cons ide rab le d e f o l i a t i o n in loca l a r e a s . Because i t i s a migratory b u t t e r f l y , i t s numbers f l u c t u a t e widely from year t o y ea r and make i t u n r e l i a b l e as a n a tu ra l control agen t . I t can a l so be a p e s t of sunflower and soybean (Morihara and Balsbaugh, 1976). The a r t i ch o k e plume moth, P l a t y p t i l i a ca rd u id ac ty la R i ley , was reared on f i e l d c o l l e c t e d t h i s t l e stems. I t i s considered a troublesome p e s t o f globe a r t i c o k e in C a l i f o r n i a (E ss ig , 1958). 35 Most, a d u l t Dip te ra c o l l e c t e d in t h e Montana survey were considered occas iona l v i s i t o r s , with the. exception of th e seed-head f l y , O re I l i a ru f icauda ( F a b r i c i u s ) , r e p re se n t in g one of th e most common in s e c t s in our survey. Adul ts appeared on th e flower buds from e a r ly summer throughout Ju ly . The la rvae feed on th e t h i s t l e seeds (F igure 11) and weave a coccoon of pappus h a i r s , in which they overwin te r . By the end of th e summer a t o t a l of 350 seed-heads were c o l l e c te d a t fo u r d i f f e r e n t s i t e s . Of t h e s e , 170 were d i s s e c t e d in th e labo ra to ry and 0. r u f icauda pupae were counted. The remaining seed-heads were s to red to recover emerging £ . r u f icauda a d u l t s and p o s s ib l e p a r a s i t e s . Our study showed an upper l i m i t o f 38% heads a t tacked by £ . r u f icauda with an average of 1.5 la rvae per. head (Table 5 ) . This i s 32% le s s than V ir ly and Watson (1977) r epo r ted from s tu d ie s a t Macdonald Col lege (Quebec). A high . occurrence of jR. conicus in s i t e s A an d .B, and Bar is sp . in s i t e s . C and .D, a re probably reducing o r i n h i b i t i n g th e 0. r u f icauda i n f e s t a t i o n . An u n id e n t i f i e d Cecidomyiidae la rva f r e q u e n t ly occurred in my c o l l e c t i o n s throughout t h e summer. The la rvae were.found feeding in the young f lower buds. All a t tempts t o . r e a r t h i s in sec t f a i l e d . This could p o s s ib ly be Dasyneura g ibsoni F e l t , as repor ted by Detmers (1927) in ­ f e s t i n g both s tam inate and carpel l a t e t h i s t l e heads. 36 Figure 11. Feeding damage of O r e l l i a ru f icauda , la rv ae on Canada t h i s t l e seeds . 37 Table 5. I n f e s t a t i o n of Canada t h i s t l e heads by O r e I l i a ru f icauda ( F a b r i c i u s ) , September 3, 1981. % . Heads Attacked Mean Number of Pupae/Head . . S i t e A 38.30 2.04 (n=60) S i t e B . (n=37) 33.30 2.16 S i t e C . 7.70 1.00 . ( n=52) S i t e D. 9.50 1.00 (n=21) n = t o t a l number of seed heads examined f o r each c o l l e c t i o n s i t e . 38 V i s i t o r s , P reda to rs and P a r a s i t o i ds The v i s i t o r s included in Table 6- a re po l len c o l l e c t o r s , nec ta r f e e d e r s , o r i n s e c t s tend ing on aphids and membracids. Most of th e predaceous i n s e c t s c o l l e c t e d in th e Montana survey a re common p red a to r s preying on immature o r small i n s e c t s , such as aphids o r t h r i p s . Larvae of Phyllobaenus sp . were observed feeding on 0. ru f icauda la rvae in Canada t h i s t l e seed-heads . Formica podzolica Francoeur was found tend ing aphids on Canada t h i s t l e . This spec ies i s known t o h a rv e s t R. conicus la rvae on Canada t h i s t l e (Rees, 1982). Of t h e p a r a s i t i c Hymenoptera, l i s t e d in Table 6, two sp ec ie s , Pteromalus sp . and Eurytoma sp. were c o l l e c t e d from pupal chambers of Rv conicus in t h i s t l e seed heads . In e a r l y August, a t o t a l of 615 seed heads were c o l l e c t e d in s i t e 2 and examined in the l a b o ra to ry . Rv conicus i n f e s t a t i o n was based on pupal chamber counts . One hundred twenty-two (20%) seed-heads were found to be in fe s ted with Rv c o n icu s . Of t h e s e , 20% conta ined a d u l t P te ro m a l id s , i d e n t i f i e d as Pteromalus sp. None of t h e se were rea red from Rv conicus larvae and have not been r e ­ corded as p a r a s i t o i d s of Rv conicus in th e United S t a t e s (Dowd and Kok, 1982; Rees, 1982). Sur les (1974) repor ted Eurytoma sp. (Eurytomidae) as a l a rv a l p a r a s i t o i d o f Rv conicus in Europe. The p a r a s i t o i d s rea red from O r e l l i a r u f icauda pupae and larvae in t h e i r i sec tary were i d e n t i f i e d as Eulophidae (Hymenoptera). At the end of t h e summer, Canada t h i s t l e , seed-heads , c o l l e c te d a t fo u r d i f f e r e n t 39 Table 6 V i s i t o r s , p r e d a t o r s , and p a r a s i t o i d s c o l l e c t e d from Canada t h i s t l e , Cirsium arvense (L.) Scop, in southern Montana, 1981. Relative Frequency in Collection^ Stages Plant Plant Growth Insects Collectedb P art(s)c Stage(s )d Habits Source Hemiptera Anthocoridae Orius t r is t ic o lo r (White) Nabidae O N1A F F predaceous on mites (1,30) aphids, th rip s , other small insects and eggs Nabis alternates Parshley Reduviidae LC N1A L R.V.F predaceous on aphids,(30) thrips and other small insects Sinea diadema (Fabncius) Lygaeidae R A L F predaceous on soft (8,30) bodied insects Geocoris sp. Neuroptera Hemerobiidae R N1A L V1F Micromus vanolosus Hagen Chrysopidae O A L F Chrysopa carnea Stephens O A L F pollen and nectar (7) feeder Coleoptera Elateridae Ctenicera gIauca (Germar) R A L R flower v is ito r (15) Cantharidae Cantharis sp. O A L R predaceous on Aphis (15,23) Drob. Canthans sp. R L R F - Anobiidae Tricorvnus productus White R A L R - Dermestidae Attagenus canadensis Casey R A L R flower v is ito r (23) Cleridae Phyllobaenus or lsohydnocera sp. O L F F Feeding on 0. ru fIcauda leaves Pers. observ predaceous on wood- boring insects (23) Phyllobaenus sp. R A L V Trichodes ornatus Say R A F F flower v is ito rs larvae predaceous on (15.23) bees and wasps 40 Table 6. (continued) Insects Keiative Frequency in Collection* Stages Collectedb Plant P art(s)c Plant Growth Stage(s)d Habits Source Melyndae Collops bipunctatus Say O A L V.F flower v is ito rs (15.23) Collops tr ic o lo r (Say) R A L V.f - Malachius aeneus L. . R A L V - Coccinel Iidae Brachyacantha ursina (Fabricius) R A L V . Coccinella transversoguttata transversoguttata Falderman O A L F Hippodamia convergens Guerin LC E.L.A L F predaceous on Aphis s p . , eggs and larvae predaceous on Aphis (15) H. parenthesis (Say) R A L F (15) H. quinquesignata qumqueslgnata (Kirby) LC E.L.A L R.V.F sp. predaceous on Aphis (15) Hyperaspis undulata (Say) R A L F sp predaceous on var- (15) Scymnus (Pullus) postpinctus Casey R A L R ious unarmored scales Lepidoptera PyralIdae I unidentified sp. LC A L V Blastobasidae I unidentified sp. R A L V . Diptera Chironomidae Cricotopus sp. R A L R Sciaridae Bradysia sp. R A F F Bombyllidae Systoechus vulgaris Loew LC A F F predaceous on grass- (9) Syrphidae Sphaerophoria philanthus (Meigen) LC A F F hopper egg pods S yrltta piplens (L .) O A F F - Anthomyiidae Delia platura (Meigen) O A F F larva is a pest of (9) vegetables 41 Table 6. (continued) Insects Keiative Frequency in Collectiona Stages Collectedb Plant P a r tts lc Plant Growth Stage(s)d Habits Source Scathophagidae Scathophagastercorarla (L.) O A L V predaceous on blow­ fly and house fly (15) Tachinidae Hyalomya a ld rich it Townsend R A F F parasite of Hemiptera (9) P eleteria sp. R A F F - Hymenoptera Xyelidae Xyela obscura (Strobl) R A F F - Braconidae Bracon sp. R* A F F - Ichneumonidae Thyrateles sp .. poss. Iugubrator (Gravenhorst) R A L V parasite of several Nymphalldae (31) I unidentified sp. R A L V - I unidentified sp. R A F F - Eulophidae I unidentified sp. O L F F parasite of 0. ruficauda larvae (pers. observ) I unidentified sp. C L F F parasite of 0. ruficauda larvae (pers. observ) Pteromalidae Pteromalus sp. LC L.A F F - EuryLomidae Eurytoma sp. O A F F - Chrysidldae Hedychrum sp iloventer French R A F F parasite of Cecerine wasp (Bohart, R.M. pers. comm.) Formicidae Formica neoclara Emery O A S.L R.V.F Tending aphids (66) F. obscunventris c l Ivia Creighton LC A S1L R.V Tending aphids ( 6 6 ) F. podzolica Francoeur R A S.L V.F Tending aphids (pers. observ) Formica sp. R A S.L F Tending Membracids (pers. observ) Hyrmica Incompleta Provancher O A S.L V - Pompilidae PomplIus sp. R A F F predaceous on spiders (31) Apidae Apis m ellifera L. LC A F F feeding on nectar and (31) pollen Bombus sp. O A F F feeding on nectar and (31) pollen aNumber of s ite s in which the species appears/50 s ite s ; R « Rare (species found in I co llection s i te ) , O = Occasional (species found in ?-5 collection s ite s ) . LC = Locally common (species found in 2-5 collection s i te s , and present in high density). C = Common (species found in more than 5 collection s ite s ) . bE = eggs, L = larvae. N = nymphs. A = adults. cR = roots, S = stems. L = leaves, F = flower heads or flower buds. dR = rosette stage. V = vertical growth stage, F * flowering and fru iting stages. 42 s i t e s were examined f o r 0. ru f icauda i n f e s t a t i o n (Table 5 ) . At th e same time p a r a s i t i z e d 0. r u f icauda pupae were counted (Table 7, Figure 12). An average inc idence of 49% p a ra s i t i sm was observed. Summary Whenever Canada t h i s t l e i s found , i t has a la rge number of i n s e c t s a s so c ia t e d with i t . Although,many of those i n s e c t s a re s t r a y s from o th e r p l a n t s , many of them can be considered as i n c id e n ta l v i s i t o r s and about one t h i r d of th e l i s t e d phytophagous spec ies a lso a t t a c k economic p l a n t s . Only a few in s e c t s were considered conspicuous because of t h e i r damage i n f l i c t e d to th e t h i s t l e p l a n t and because of t h e i r commonness t o th e c o l l e c t i o n s . The in s e c t survey in southern Montana in d ic a te s t h a t Cirsium arvense has been ex p lo i te d by th r e e seed head-feeding i n s e c t s , th r e e s tem-boring i n s e c t s , one roo t -bo r ing i n s e c t , and two d e f o l i a t i n g agen ts . Consider ing t h e i r inc idence of a t t a c k , more in s ec t s were a ssoc ia ted with the .deve lop ing seed heads than with f o l i a g e , stems o r fo o ts . Although some in s e c t s caused co n s ide rab le p l a n t s t r e s s , f u r t h e r s t r e s s f a c t o r s from o th e r i n s e c t s and pathogens are needed to c o n t r o l ■ t h i s weed. Few p o t e n t i a l l y e f f e c t i v e and hos t s p e c i f i c in s e c t s from Zw olfe r ' s l i s t . a r e s t i l l a v a i l a b l e f o r f u t u r e in t r o d u c t io n s . Thus, the informat ion ga thered in t h i s survey could form the foundat ion f o r fol low-up s tu d i e s on endemic sp ec ie s . Stenophagous i n s e c t s , as 43 Table 7. P a ra s i t i sm of O r e l I l a ru f icauda (F ab r ic iu s ) pupae in Canada t h i s t l e seed heads, September 3, 1981. Total # Tota l # Total # Heads Attacked Pupae P a r a s i t i z e d Pupae S i t e A ■ 23 ■ 47 21 (n=60). . S i t e B (n=37) . 12 - 26 7 S i t e C- (n=52) 4 4 3 S i t e D. (n=21) 2 2 I h = Tota l number of seed heads examined f o r each c o l l e c t i o n s i t e . 44 45 Ceuthorynchus I i t u r a and Bar is s p . , which a re e s t a b l i s h e d , but are spreading s lowly , could be augmented and r e d i s t r i b u t e d over th e s t a t e . The p o t e n t i a l o f th e combination of two s t r e s s - f a c t o r s , to in ­ c rease th e impact on th e t h i s t l e p l a n t s in th e f i e l d , should be in v es t ! g a ted . In s e c t damage and a pathogen form a p e r f e c t combination. 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