Efficient Sex Pheromone Trapping: Catching 
The Sweetpotato Weevil, Cylas formicarius
Authors: G. V. P. Reddy, Nirupa Gadi, & Anthony J. 
Taianao
This is a postprint of an article that originally appeared in Journal of Chemical Ecology in July 
2012.  The final publication is available at Springer via 
http://dx.doi.org/10.1007/s10886-012-0160-4 
Reddy, G.V.P., N. Gadi, and A.J. Taianao. 2012. Efficient sex pheromone trapping: catching the 
sweetpotato weevil Cylas formicarius.  Journal of Chemical Ecology 38: 846–853. 
doi: 10.1007/s10886-012-0160-4 
Made available through Montana State University’s ScholarWorks 
scholarworks.montana.edu 
Efficient Sex Pheromone Trapping: Catching The 
Sweetpotato Weevil, Cylas formicarius
G. V. P. Reddy & Nirupa Gadi & Anthony J. Taianao
Received: 14 December 2011 /Revised: 17 March 2012 /Accepted: 24 May 2012 /Published online: 11 July 2012
# Springer Science+Business Media, LLC 2012
Abstract The sweetpotato weevil, Cylas formicarius
(Fabricius) (Coleoptera: Brentidae), is the most serious pest
of sweetpotato around the world, damaging sweetpotatoes
in the field and in storage, as well as being a quarantine pest.
Because the larval period is spent within vines or tubers, and
the adults are nocturnal, chemical control frequently is not
effective. In addition, there are few natural enemies, and
pheromone-based trapping does not appear to reduce the
damage level. In the present study, we evaluated a number
of parameters that affect pheromone-based trap catch, in-
cluding trap design, trap size, trap color, and height at which
the traps are placed. Pherocon unitraps caught higher numbers
than ground, funnel water, or delta traps. Medium-sized traps
(13×17.5 cm) were more effective than larger or smaller traps.
In a color-choice test, C. formicarius preferred red over gray,
brown, blue, white, yellow, black, or red traps; light red was
more attractive than other shades of red. Maximum catches
were obtained when the traps were set 50 cm above the crop
canopy. Light-red unitraps with pheromone lures caught more
adults than identical traps without lures, suggesting that
C. formicarius is influenced by both visual and olfactory cues.
Pheromone-baited light-red unitraps, 13×17.5 cm, installed
50 cm above the crop canopy, were the most effective at
catching C. formicarius adults, and they appear to have the
greatest potential for use in trap-and-kill strategies and eradi-
cation programs.
Keywords Sex pheromone .Cylas formicarius . Traps
characteristics . Trap design . Size . Color . Height .
Coleoptera . Curculionidae . Brentidae
Introduction
The sweetpotato, Ipomoea batatas (L.) Lam. (Convolvulaceae),
is one of the most important food crops in the world, particularly
in emerging countries, where it is a food staple (Woolfe, 1992).
Its production is severely affected by several insect pests
(Chalfant et al., 1990), of which the sweetpotato weevil,Cylas
formicarius (Fabricius) (Coleoptera: Brentidae), is the most
serious worldwide (Austin et al., 1991). Feeding by this
weevil elicits terpenoid production in sweet-potato storage
tubers that results in damaged, unpalatable tubers (Uritani et
al., 1975). Sutherland (1986) reported that yield losses due to
C. formicarius damage range from 5 to 80 %. The weevil
completes its life cycle within either the tubers or vines of the
sweetpotato plant, but prefers tubers (Strong, 1983).
Because of the high incidence of C. formicarius on
sweetpotatoes, some growers in the Mariana Islands of the
South Pacific have become frustrated and given up cultiva-
tion entirely. Even small weevil populations can cause se-
vere damage to tubers, especially because the pest is present
throughout the year in warm conditions (Sutherland, 1986),
with weevil incidence extremely high during the hot and
humid season (Chalfant et al., 1990). In Micronesia, C.
formicarius infestations are particularly severe. Our prelim-
inary trapping studies conducted over a year indicate that
populations are high throughout Guam. Guam and other
Micronesian Islands are in the midst of a decline in sweet-
potato production because of the impact of this weevil
(Hwang, 2001). Anecdotally, according to local growers
and authorities, thousands of sweetpotato plants in this
G. V. P. Reddy (*)
Western Triangle Ag Research Center, Montana State University,
9546 Old Shelby Rd,
Conrad, MT 59425, USA
e-mail: reddy@montana.edu
N. Gadi :A. J. Taianao
Western Pacific Tropical Research Center,
College of Natural and Applied Sciences, University of Guam,
Mangilao, Guam 96923, USA
region have been damaged by C. formicarius. Although
some control methods exist, chemical application is both
undesirable and expensive. Without effective control, wee-
vil populations are likely to cause very high or complete loss
of sweetpotato production in Guam and other Micronesian
Islands.
Chemical control in the field reduces C. formicarius
numbers, but with varying degrees of success (Talekar,
1983). The protected position of the larvae, developing
within the vines and tubers, limits the effectiveness of
chemical treatments (Sutherland, 1986). Chalfant et al.
(1990) reported a range of hormones and insect growth
regulators that have varying effects on C. formicarius, but
further research on these techniques is required. Cultural
controls, such as the use of C. formicarius–resistant cultivars
of I. batatas, non-infested planting material, and crop rotation,
along with various management regimes, also reduce pest
infestations (Jansson et al., 1987).
The cryptic feeding habits of the larvae, and the nocturnal
activity of the adults make detection and control of infesta-
tions difficult. Resistant varieties of sweetpotato have not
yet been used by growers (Downham et al., 2001). Sex-
pheromone lures are effective in detecting infestations at
low population levels, and for use as a component of control
and management (Reddy and Guerrero, 2004, 2010). Coffelt
et al. (1978) isolated and bioassayed the female-produced
sex pheromone of C. formicarius. Heath et al. (1986) puri-
fied, identified, and synthesized the active component as
(Z)-3-dodecen-1-ol (E)-2-butenoate, and field studies on
the development of traps and lures for this species were
carried out (Jansson et al., 1992, 1993). The electrophysio-
logical and behavioral responses of C. formicarius showed
the synthetic compound to be highly attractive in the field,
highlighting its potential for use in pest control (Sureda et
al., 2006). Mass trapping has suppressed populations of C.
formicarius males in several countries (e.g., Yasuda, 1995),
although there has not always been concomitant reductions
in the infestation rates or increases in sweetpotato yields
(see, e.g., Braun and Van De Fliert, 1999). However, use of
the pheromone in a pest-management strategy in India has
resulted in a considerable reduction of damage, leading to a
53 % increase in production of marketable tubers (Pillai
et al., 1993). Trapping also has reduced the number of roots
damaged by C. formicarius in the Caribbean (Alcázar et
al., 1997, Jackson and Bohac, 2006). It has been esti-
mated that the use of pheromone-baited traps as part of
an integrated pest-management program for C. formicarius
could reduce one to three insecticide applications per season
(Hwang, 2000).
Characteristics such as trap design, size, color, and height
are known to influence the efficacy of pheromone-baited
traps for other species of tropical weevils (Reddy et al.,
2011). Therefore, we undertook field studies to evaluate
the effects of trap characteristics that may increase the
effectiveness of trapping programs for C. formicarius.
Methods and Materials
Experimental Field Sites Experiments were carried out on
the island of Guam (USA) at 4 locations: Latte Heights
(13°26′ N, 144°48′ E, 79.9 m above sea level), Dededo
(13°30′N, 144°51′ E, 96.9 m), Mangilao (13.43°N, 144.80°E,
54.3 m), and the University of Guam’s Agricultural Experi-
ment Station (AES) in Yigo (13.31°N, 144.52°E′, 138 m). The
prevailing temperature, relative humidity, and wind velocity
were recorded during the experimental period. Nearby sweet-
potato fields were covered densely with various invasive plant
species such as Chromolaena odorata (L.) R.M. King & H.
Rob. (Asteraceae), Panicum maximum Jacq (Poaceae), Lan-
tana camara (L.) (Verbenaceae), and Bidens alba (L.)
(Asteraceae). In addition, the morning glory, Ipomoea triloba
(L.), known to be a major alternative host for C. formicarius
(Austin et al., 1991), was present at most of the study
locations.
Trap Design In the first experiment, four different types of
traps, ground, funnel water, Pherocon unitrap, and Pherocon
delta were evaluated. The ground trap (Fig. 1a) was con-
structed in our laboratory from a 120×60×0.5 cm piece of
white corrugated plastic board, with a 50×8 cm slit baffle
fitted at the top to prevent weevils from escaping (Reddy et
al., 2005). Traps were sealed at all corners and along edges
Fig. 1 The four trap designs used
J Chem Ecol (2012) 38:846–853 847
with marine adhesive sealant, and water mixed with a liquid
dishwashing detergent (1–3 %) was placed in the bottom
container to retain adults. The lower outer edges of the
ground traps were covered with earth to prevent weevils
from crawling under them.
Funnel water traps (Fig. 1b) were commercially available
from Trécé Incorporated (Adair, OK, USA). Each trap con-
sisted of a transparent, covered plastic cup (1 L capacity)
with two 3 cm circular holes in the sides, near the top;
250 ml of water mixed with detergent (1–3 %) were placed
in the bottom of the cup. The trap was fitted with a wire
linkage allowing it to be hung from a wooden post in the
field.
The Pherocon unitraps (also called bucket traps), 20.5 cm
high×13 cm diam. also were obtained from Trécé Incorpo-
rated (Fig. 1c). Each unitrap consisted of a funnel-shaped
white plastic receptacle, with a yellow plastic lid and holder
for lures, mounted over a bucket for retaining captured
insects. Because the unitrap incorporated a funnel ending
in a pot from which insects could not escape, no detergent
solution was used.
The Pherocon VI delta traps (Fig. 1d) also were from
Trécé Incorporated. Each trap consisted of a sheet of white
cardboard folded into a triangular tube with partially open
ends. The sticky trapping surface was provided by an ex-
changeable card (18.5 cm2) that slid in and out swiftly and
easily. The partial end closures could be opened flat for
counting of the catch and for exchange of trapping cards.
The trap was fitted with a wire linkage allowing it to be
hung from a wooden post in the field.
Pheromone Lures Pheromone lures of rubber septa loaded
with Z3-dodecenyl-E2-butenoate, sealed in an impermeable
bag for shipping and storage, were obtained from Chem
Tica Internacional S.A. (San José, Costa Rica). The lure
packs, each containing 10 mg of pheromone and emitting
the active ingredient at <0.01 mg/day (Material Safety Data
Sheet, ChemTica Internacional, S.A.), were stored at 4 °C
until use. Lures were suspended on wires inside the ground
traps, Pherocon unitraps, and funnel water traps. In the
Pherocon delta traps, the lures were placed at the centers
of the exchangeable sticky cards. Although C. formicarius
pheromone can remain active in the field for 30–64 d (Jansson
et al., 1992), our lures were changed at 30-d intervals, as
recommended by Hwang (2000).
Effect of Trap Design The four trap types, with their pher-
omone lures, were placed at randomly chosen locations
about 10 m apart in sweetpotato fields at the 4 test locations.
Tests were replicated three times at each site to yield 12
replications. Traps without pheromone lures were used as
controls. Overall, 96 traps were used: 8 treatments (4 trap
designs, each with and without lures)×3 replications×4
sites. Each week, the trapped adult weevils were removed
and counted and their numbers recorded. Traps were washed
and rinsed, and new detergent solution added. We rotated
trap positions weekly at each location to diminish positional
effects on trap catch. The study was conducted from
Feb–June 2010.
Effect of Trap Size In the second experiment, the effective-
ness of four sizes of Pherocon unitraps (20.5 cm height×
18 cm diam., 20.5×13 cm, 17.5×7.5 cm, 11×9 cm) was
compared. At each site, three traps of each size were set up
and their positions rotated weekly. Tests were replicated
three times at each site to yield 12 replications. The study
used 48 traps (4 trap sizes×3 replications×4 sites). The
experiment was conducted from July–Oct. 2010.
Effect of Trap Color In the third experiment, 13-cm diam.
Pherocon unitraps were covered entirely with brown, black,
gray, yellow, red, white, green, or blue vinyl tape and tested
independently (8 traps colors×3 replications×4 sites) at the
same sites. The experiment was carried out from Nov.
2010–Feb. 2011. Color characteristics of the tape were
determined using a Konica Minolta CR-410 Chromometer
(Minolta Instrument Systems, Ramsey, NJ, USA) and are
given in Table 1.
Effect of Shade of Color In the fourth experiment, different
shades of red (light red, tomato red, dark red, and candy-
apple red) were evaluated. The trap used was again the 13-
cm diam. Pherocon unitrap, and the shades were tested
independently (4 shades of red×3 replications×4 sites) at
the same sites. The experiment was conducted fromMar–June
2011. Different red trap-color measurement values are given
in Table 2.
Effect of Trap Height In the fifth experiment, 60 (traps with
5 different heights×3 replications×4 sites) light red, 13-cm-
diam. Pherocon unitraps were placed at ground level and at
50, 100, 150, and 200 cm above the crop canopy, 10 m
apart. Trap height was adjusted according to crop growth in
the field. Observations on trap catches were made at weekly
intervals. The experiment was carried out from July–Sept.
2011.
Relative Effects of Visual and Olfactory Cues In the sixth
experiment, light red, 13-cm-diam. Pherocon unitraps,
placed 50 cm above the crop canopy, were baited with
pheromone lures or left unbaited (1 trap with, and 1 without,
lure×3 replications×4 sites024 traps). The experiment was
carried out at the same sites from Oct.–Dec. 2011.
Statistical Analysis Trap catch data were transformed by log
(x+1) to fit the assumption of homogeneity of variance for
848 J Chem Ecol (2012) 38:846–853
ANOVA. Because all responses used were count variables, a
one-way Poisson ANOVA model was fitted, by means of
the GLIMMIX Procedure SAS Version 9.3 (SAS Institute,
2009). The least square means test was used to make mul-
tiple comparisons for differences among treatments.
Results
Effect of Trap Design Traps of all the designs baited with
pheromone lures captured C. formicarius but differed in
numbers of adults caught: mean catches were in the order
Pherocon unitrap > funnel water trap > ground trap >
Pherocon delta trap. Pherocon unitraps captured more adults
than funnel water traps (F022.4; df07, 21; P<0.05; Fig. 2),
and ground traps more than Pherocon delta traps. Traps
without lures (control) caught no adults. During the exper-
imental period, the average temperature was 28.5 °C, the
average relative humidity 65–80 %, and the average wind
velocity 5.8 m.sec−1. The Pherocon unitrap, which caught
more adults than all the other traps, was selected for all
further experiments.
Effect of Trap Size The smaller and larger traps were less
effective than medium-sized traps. Pherocon unitraps of
13 cm diam. caught more (F08.6; df03,23; P<0.05;
Fig. 3) C. formicarius adults (59.7±1.2 adults/trap) than
did the next larger size (16.9±0.8 adults/trap) and the two
smallest size traps (29.1±1.3 and 32.0±1.6 adults/trap, re-
spectively); catches in the two smallest traps did not differ
Table 1 Specifications of the colors of traps used
Trap color L* a* b* Chroma (C) Hue angle (h°)
Black 30.44±0.06 0.42±0.03 −1.08±0.04 1.16±0.05 –
Brown 35.26±0.18 3.98±0.03 3.94±0.02 5.60±0.03 44.66±0.11
Gray 39.83±0.11 −0.17±0.02 −2.23±0.01 2.24±0.01 85.64±0.47
Yellow 82.57±0.02 −2.92±0.03 84.02±0.27 84.07±0.27 91.99±0.02
Red 42.84±0.11 49.88±0.28 19.44±0.20 53.54±0.34 21.29±0.09
White 92.29±0.03 1.34±0.01 −2.59±0.04 2.91±0.03 –
Green 43.50±0.08 −27.32±0.03 1.72±0.09 27.37±0.03 176.39±0.19
Blue 36.02±0.10 15.19±0.10 −35.82±0.12 38.91±0.14 292.98±0.08
Means (± SD) were generated from three observations
L* indicates a measure of “lightness” that runs through the center of the color chart; 100 at the top represents white, and zero at the bottom
represents black
The a* axis, which runs left to right on the color chart, indicates a red shade when greater than zero (positive) and a green shade when lower than
zero (negative). Similarly, the b* axis, which runs vertically through the color chart, indicates a yellow shade when positive and a blue shade when
negative (Wrolstad et al., 2005)
Chroma is related to the saturation of a color, with lower chroma values being less saturated
The hue angle is expressed on a 360° grid on which 0°0red, 90°0yellow, 180°0green, and 270°0blue
Table 2 Specifications of the shades of red used on traps
Trap color L* a* b* Chroma (C) Hue angle (h°)
Candy-apple red 43.13±0.06 49.34±0.23 19.53±0.28 53.06±0.21 21.59±0.31
Tomato red 47.92±0.02 43.82±0.06 26.86±0.01 51.40±0.06 31.51±0.03
Light red 50.03±0.06 47.62±0.06 28.79±0.08 55.65±0.09 31.16±0.04
Dark red 42.76±0.06 43.06±1.20 19.67±0.02 47.34±1.09 24.56±0.61
Means (± SD) were generated from three observations
L* indicates a measure of “lightness” that runs through the center of the color chart; 100 at the top represents white, and zero at the bottom
represents black
The a* axis, which runs left to right on the color chart, indicates a red shade when greater than zero (positive) and a green shade when lower than
zero (negative). Similarly, the b* axis, which runs vertically through the color chart, indicates a yellow shade when positive and a blue shade when
negative (Wrolstad et al., 2005)
Chroma is related to the saturation of a color, with lower chroma values being less saturated.
The hue angle is expressed on a 360° grid on which 0°0red, 90°0yellow, 180°0green, and 270°0blue
J Chem Ecol (2012) 38:846–853 849
from each other. Therefore, the 13 cm traps were used for all
further experiments. During the experimental period, the av-
erage temperature was 30.2 °C, the average relative humidity
65–80 %, and the average wind velocity 5.2 m.sec−1.
Effect of Trap Color Red unitraps caught more adult C.
formicarius than those of any other color tested (F011.31,
df07, P<0.05; Fig. 4), followed, in descending order, by
grey, brown, blue, white, yellow, black and green traps;
green traps caught fewer adults than any other. Therefore,
red traps were used for all subsequent experiments. During
the experimental periods, the average temperature was
27.8 °C, the average relative humidity 65–80 %, and average
wind velocity was 4.4 m.sec−1.
Effect of Shade of Red Light-red unitraps caught more
adults (F010.22, df03, P<0.05; Fig. 5) than traps of other
shades. Candy-apple red caught the fewest, whereas tomato
red and dark red traps did not differ. Therefore, light-red
traps were used for all subsequent experiments. During the
experimental period, the average temperature was 29.4 °C,
the average relative humidity 65–80 %, and the average
wind velocity 6.2 m.s−1.
Effect of Trap Height Traps installed 50 cm above the crop
canopy caught more adults (F08.14, df04, P<0.01; Fig. 6)
than traps positioned on the ground or at other heights. There-
fore, traps were positioned at 50 cm above the ground height
for the remaining experiment. During the experimental peri-
ods, the average temperature was 27.3 °C, the average relative
humidity 65–80%, and the average wind velocity 4.4 m.sec−1.
Relative Effects of Visual and Olfactory Cues Light-red
Pherocon Unitraps baited with pheromone lures caught
more adults (mean of 1028.8±18.5) than those without lures
(mean of 22.0±8.8; F013.22, df01, P<0.001). During the
experimental period, the average temperature was 30.5 °C,
the average relative humidity 65–80 %, and the average
wind velocity 7.8 m.sec−1.
0
10
20
30
40
50
60
70
PUL FWL GTL PDL PUN FWN GTN PDN
M
ea
n
  
SE
 
a
du
lts
/tr
a
p/
w
ee
k
A
B
B
C
0 0 0 0
Fig. 2 Mean (± SE) numbers of adult Cylas formicarius caught by
Pherocon unitrap with pheromone lure (PUL), funnel water trap with
lure (FWL), ground trap with lure (GTL), Pherocon delta trap with lure
(PDL), Pherocon unitrap without lure (PUN), funnel water trap without
lure (FWN), ground trap without lure (GTN), and Pherocon delta trap
without lure (PDN). Different capital letters indicate differences among
treatments (two-way ANOVAwith Poisson model, least square means,
P<0.005). Means were generated from 12 replicates (3 replicates per
location×4 sites)
0 20 40 60 80
7.5×17.5
9 17.5
13×17.5
18×17.5
Mean  SE adults/trap/week
Tr
a
p 
siz
e 
(cm
)
A
B
B
B
±
Fig. 3 Mean (± SE) numbers of adult Cylas formicarius caught in
pheromone-baited Pherocon unitraps of different size. Different capital
letters indicate differences among treatments (one-way ANOVA with
Poisson model, least square means, P<0.05). Bars represent means of
12 replicates (3 replicates per location×4 sites)
0
20
40
60
80
100
120
140
160
180
Red Gray Brown Blue White Yellow Black Green
M
ea
n
  
SE
 
a
du
lts
/tr
a
p/
w
ee
k
A
B B
C C
C C
D
±
Fig. 4 Mean (± SE) numbers of adult Cylas formicarius caught in
pheromone-baited Pherocon unitraps of different color. Different cap-
ital letters indicate differences among treatments (one-way ANOVA
with Poisson model, least square means, P<0.01). Bars represent
means of 12 replicates (3 replicates per location×4 sites)
0
100
200
300
400
500
600
700
800
900
1000
1100
Light red Tomato red Dark red Candy-apple 
Red
M
ea
n
 
SE
 a
du
lts
/tr
a
p/
w
ee
k A
BC
B
C
±
Fig. 5 Mean (± SE) numbers of adult Cylas formicarius caught in
pheromone-baited Pherocon unitraps of different shades of red. Different
capital letters indicate differences among treatments (one-way ANOVA
with Poisson model, least square means, P<0.01). Bars represent means
of 12 replicates (3 replicates per location×4 sites)
850 J Chem Ecol (2012) 38:846–853
Discussion
Nearly 10 years ago, Japanese scientists eradicated West
Indian sweetpotato weevil, Euscepes postfasciatus
(Fairmore) (Coleoptera: Curculionidae), from the Kume
islands of Okinawa (Kuba et al., 2000) by means of the
search and kill method. For C. formicarius, a similar ap-
proach should be considered. Because C. formicarius is
more widespread in most sweetpotato growing areas than
was E. postfasciatus, it will not be easy to eradicate.
Pheromone-baited traps are useful for detecting the spread
of C. formicarius and in alerting both growers and scientists
to its presence, both in sweet-potato plants and in wild
Ipomoea plants that harbor the weevil. Widespread indis-
criminate destruction of Ipomoea spp. is not advisable,
because these plants could be important to the local ecosys-
tem, but infested plants around current or past sweetpotato
plantings could be identified by means of pheromone-baited
traps, and then uprooted, and burned.
Another approach, that of release of sterile males, is in
use in the Okinawa islands for the control of C. formicarius
and E. postfasciatus (Moriya, 1997), but this technique may
have limited value because, unlike melon fly, Bactrocera
cucurbitae (Coquillett) (Diptera: Tephritidae) (Koyama et
al., 2004), C. formicarius adults are not especially active
fliers. Like other members of the family Brentidae, C. for-
micarius adults crawl from place to place (Chalfant et al.,
1990), limiting the extent to which sterile males might mate
with normal females. While C. formicarius is not a strong
flier, it readily mates when on foliage, and this is what is
targeted with the male sterilization approach. In addition to
C. formicarius, other Coleoptera also have been treated in
sterile insect technique (SIT) programs, such as the cock-
chafer, Melolontha vulgaris L. (Scarabaeidae), and the boll
weevil, Anthonomus grandis Boheman (Curculionidae),
with remarkable results (Dyck et al., 2005). Nevertheless,
an efficient pheromone-trapping technique is required for C.
formicarius, either to use in conjunction with SIT programs,
or for management or eradication.
According to Jackson and Bohac (2006), although cur-
rent trap designs are effective for monitoring C. formicarius,
they are cumbersome, difficult to sustain, or costly. Those
authors suggested that more work is needed to develop
simple, inexpensive, and effective traps for monitoring C.
formicarius. Our results showing that Pherocon unitraps
were more effective than other types for C. formicarius
apparently contrast with the study of Smit et al. (1997),
who reported that Unitraps performed relatively poorly for
the congeneric C. puncticollis (Boheman) and C. brunneus
F. (Coleoptera: Curculionidae). They also reported that Uni-
traps were commercially available, but were too expensive
for routine use in Uganda. Although, the trap design we
used was identical to that in their study, the different relative
trap efficiencies may be due to differences in behavior
between the African sweetpotato weevils they studied
and C. formicarius.
Of the 10 trap designs evaluated by Jackson and Bohac
(2006), a funnel trap (a modification of a water-pan trap)
and the Pherocon sticky trap were the most effective for
capturing adults. The better performance of the unitraps,
compared to the generic water funnel trap in our study,
may have been due to the continuous rainfall received by
our study areas. Simple water-pan traps often are used in
developing countries (Pillai et al., 1993), but we found them
to be the least effective.
In our study, the medium-sized (13-cm diam.) trap out-
performed both larger and smaller traps. The importance of
trap size for other weevil species has been highlighted in a
previous study (Reddy et al., 2011). Trap-catch differences
for Arhopalus rusticus nubilus (Le-Conte) (Coleoptera:
Cerambycidae) and Xyleborus spp. between 8- and 16-unit
traps may be related to differences in trap surface area for
interception of beetles, or to preference for taller vertical
silhouettes (Hoover et al., 2000). In contrast, catches of the
reproduction weevil, Hylobius pales Herbst (Curculionidae),
in 16-unit traps were 54 % lower than those in 8-unit traps
(Miller and Crowe, 2009).
The study reported here is the first to demonstrate a color
preference by C. formicarius, although the importance of
color preference by nocturnal insects and other curculionid
weevils has been demonstrated previously (Reddy et al.,
2011). Abdallah and Al-Khatri (2005) reported that more
adult Rhynchophorus ferrugineus Olivier (Coleoptera:
Curculionidae) were attracted to red and orange, than to
blue, traps. Our findings differ from those of Smit et al.
(1997), who observed that trap color was not critical for C.
puncticollis and C. brunneus, although red traps had lower
catches than yellow and white traps, which were the predom-
inant colors available in Uganda.
0
200
400
600
800
1000
1200
1400
ground 50 cm 100 cm 150 cm 200 cm
M
ea
n
  
N
um
be
r S
E 
±
 a
du
lts
/tr
a
p 
Height above crop canopy
A
B
B
C
D
Fig. 6 Mean (± SE) numbers of adult Cylas formicarius caught in
light red unitraps mounted at different heights in a sweet-potato
field. Different capital letters indicate differences among treat-
ments (one-way ANOVA with Poisson model, least square means,
P<0.05). Bars represent means of 12 replicates (3 replicates per
location×4 sites)
J Chem Ecol (2012) 38:846–853 851
In our study, traps installed 50 cm above the crop canopy
had higher catches than those at other heights. These results
differ from those of Yasuda et al. (1992), who reported that
sticky traps, at the same height as the crop canopy, caught
more C. formicarius than traps at heights up to 300 cm.
Because nocturnal weevils habitually crawl to the topmost
leaves of sweetpotato plants (Proshold et al., 1986),
pheromone traps surrounded by sweetpotato foliage should
capture more insects than traps that are not surrounded (Jans-
son et al., 1992). Trap height is known to influence capture of
other weevil pests. For example, Faleiro (2006) reported the
greatest R. ferrugineus catches at 1.0 m above the ground.
Smit et al. (1997) noted that raising the trap until the
entrance holes were 15 or 30 cm above the canopy
improved catches of C. puncticollis, whereas catches
of C. brunneus were unaffected by trap height. Our
results on trap height effectiveness contrast with those
on C. formicarius by Proshold et al. (1986), who reported
that raising the trap above crop height critically reduced adult
catches.
Visual cues alone influence the behavior or catches of
weevil populations (Reddy and Raman, 2011). In the pres-
ent study, we found that light red traps caught more C.
formicarius than other traps. We suggest that trap color
could be important because the flight activity of C. formi-
carius may occur during crepuscular times. Björklund et al.
(2005) reported that traps baited solely with odor or solely
with visual stimuli catch more pine weevils, Hylobius abie-
tis (L.) (Coleoptera: Curculionidae), than stimulus-free
traps. Odor and visual stimuli also have been shown to have
additive effects on trap catch (Reddy, 2012), and traps with a
combination of odor and visual stimuli catch more weevils
than traps with odor or visual stimuli alone (Björklund et al.,
2005). In the current study, traps baited with pheromone
captured more C. formicarius than did identical traps with-
out pheromone. This result is in agreement with previous
observations on several other weevils that use olfactory
(pheromones), rather than visual, cues (see Reddy et al.,
2011, and references therein), although Tansey et al.
(2010) reported that the cabbage seedpod weevil, Ceuto-
rhynchus obstrictus (Marsham) (Coleoptera: Curculionidae)
also is influenced by visual cues. Reeves (2011) described
the importance and use of vision for locating host plants,
with some recent examples showing that vision can be even
more important than olfaction.
We conclude that trap design, size, color, and height
affect the response of C. formicarius to pheromone-baited
traps. In particular, the 17.5×13-cm, light-red Pherocon
unitraps baited with pheromone lures and installed 50 cm
above the crop canopy gave the highest catches of C.
formicarius. These results are useful and should be
taken into consideration when trap-and-kill strategies are
developed.
Acknowledgements This project was supported by FY 2011 Pacific
Islands Area Conservation Innovation Grants (PIA-CIG) Program,
Grant Agreement No. 69-9251-11-902, The Natural Resources Con-
servation Service (NRCS)-USDA; Western Integrated Pest Manage-
ment Center (WIPMC) Award # 2007-51120-03885/ University of
California, Davis sub-award # 07 -001492-GUAM3, and USDA Hatch
funds (Project# GUA0561). In accordance with federal law and USDA
policy, this institution is prohibited from discrimination on the basis of
race, color, national origin, sex, age, or disability. We also thank R.
Gumataotao, G. McNassar, and J. Remolona for help during field
work. Part of the work was made possible from two Summer Appren-
ticeship Programs for Nirupa Gadi and A.J. Taianao at the University
of Guam.
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