Browsing by Author "Reddy, Gadi V. P."

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Action Threshold Treatment Regimens for Red Spider Mite (Acari: Tetranychidae) and Tomato Fruitworm (Lepidoptera: Noctuidae) on Tomato
(2013-09) Reddy, Gadi V. P.; Tangtrakulwanich, Khanobporn
The tomato fruitworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), is the foremost pest of tomato in the Mariana Islands. Similarly, the red spider mite, Tetranychus marianae McGregor (Acari: Tetranychidae), is a chief pest of vegetables particularly on tomato, Solanum lycopersicum L. (Solanaceae). However, the infestations by T. marianae are heavy during the early stages of crop growth, while infestations of H. armigera become prominent at later stages. Because no threshold levels are available for these pests, many growers apply up to 15 chemical applications per tomato cropping period. To reduce the regular spray schedules chemical applications and to prevent damage to foliage and fruit quality, the present study was undertaken for the development of action threshold levels for the timing of chemical applications for T. marianae and H. armigera on tomato in the Mariana Islands. Therefore, different threshold levels were evaluated for timing applications of Sun-spray 6E® horticultural oil against T. marianae and Aza-Direct®, neem against H. armigera on tomato in the wet and dry seasons at 2 locations, Dededo and Inaranjan, in Guam, USA during 2011 and 2012. Based on T. marianae infested leaves, incidence of T. marianae and yield levels, the plots sprayed at 8–12 mites/leaf in the dry season and 8–14 mites/leaf during the wet season had significantly lower leaf damage and T. marianae densities compared to a greater number of mites/leaf, regular based sprays and control plots. Likewise, an initial spray scheduled when 2 eggs of H. armigera were detected on 10 of the samples, followed by an added spray only if 2 damaged fruit or H. armigera larvae were detected per 50 immature fruit resulted in lower percent fruit damage and higher marketable yield compared to other threshold levels or a regular spray schedule.
Age-related sperm production, transfer, and storage in the sweet potato weevil, cylas formicarius (fabricius) (coleoptera: Curculionidae)
(2016-11) Hiroyoshi, Satoshi; Kohama, Tsuguo; Reddy, Gadi V. P.
The relationship between sperm production, insemination rate, and sperm transfer were studied in the sweet potato weevil, Cylas formicarius. Older adult males retained more sperm in the testes-seminal vesicle complex (TSC) and thus more was ejaculated into females at first mating. Number of matings per day for males was relatively constant across different ages, and frequent mating resulted in a reduced amount of sperm transferred to females, especially in young males. Young virgin males had a relatively small ejaculate, and almost all sperm transferred to females was stored in the spermatheca, whereas older virgin males transferred a larger amount of sperm to females, in whom sperm was found in both the spermatheca and post-spermathecal organs (PSO) after mating. The number of sperm in the PSO decreased markedly within 24 h after mating, but amounts in the spermatheca remained the same. Just where the sperm in the PSO went is a point that remained undetermined. The amount of sperm in the spermatheca was reduced more rapidly in females that laid eggs than in females that did not, although sperm reduction occurred even in the latter. Insemination of this weevil corresponded with the volume of the spermatheca, and the amount of sperm stored in the TSC was determined by the age and mating history of the males.
Antixenosis, Antibiosis, and Potential Yield Compensatory Response in Barley Cultivars Exposed to Wheat Stem Sawfly (Hymenoptera: Cephidae) under Field Conditions
(2020-08) Achhami, Buddhi B.; Reddy, Gadi V. P.; Sherman, Jamie D.; Peterson, Robert K. D.; Weaver, David K.
Wheat stem sawfly, Cephus cinctus Norton, is an economically serious pest of cereals grown in North America. Barley cultivars were previously planted as resistant crops in rotations to manage C. cinctus, but due to increasing levels of injury to this crop, this is no longer a valid management tactic in Montana. Therefore, we aimed to understand antixenosis (behavioral preference), antibiosis (mortality), and potential yield compensation (increased productivity in response to stem injuries) in barley exposed to C. cinctus. We examined these traits in eight barley cultivars. Antixenosis was assessed by counting number of eggs per stem and antibiosis was assessed by counting infested stems, dead larvae, and stems cut by mature larvae. Potential yield compensation was evaluated by comparing grain yield from three categories of stem infestation: 1) uninfested, 2) infested with dead larva, and 3) infested cut by mature larva at crop maturity. We found the greatest number of eggs per infested stem (1.80 ± 0.04), the highest proportion of infested stems (0.63 ± 0.01), and the highest proportion of cut stems (0.33 ± 0.01) in ‘Hockett’. Seven out of eight cultivars had greater grain weight for infested stems than for uninfested stems. These cultivars may have compensatory responses to larval feeding injury. Overall, these barley cultivars contain varying levels of antixenosis, antibiosis, and differing levels of yield compensation. Our results provide foundational knowledge on barley traits that will provide a framework to further develop C. cinctus resistant or tolerant barley cultivars.
Approaches and mechanisms for ecologically based pest management across multiple scales
(2016-08) Zhao, Zi-Hua; Reddy, Gadi V. P.; Hui, Cang; Li, Bai-Lian
The past 50 years have seen substantial change of agroecosystems in the world, including an intensified use of agrochemicals and expansion of cropland, resulting in a rapid loss of biodiversity and a reduction of ecosystem services. The effects of these changes, at both the field and landscape scale, on ecologically based pest management (EBPM) in agroecosystems have become increasingly important. Here, we review the theories, important approaches and mechanisms of habitat management practices (at multiple spatial scales) that can be applied to facilitate EBPM in crop fields and even over larger landscapes. In particular, we discuss links between pest outbreaks and rapid changes of habitat composition at local and regional scales. We also summarize recent progress of habitat management and their application to pest management, which is an activity that we believe must be implemented at multiple spatial scales to successfully conserve ecosystem services and address environmental issues related to crop pest control.
Are Sweetpotato Weevils (Coleoptera: Brentidae) Differentially Attracted to Certain Colors?
(2014-01) Gadi, Nirupa; Reddy, Gadi V. P.
The sweetpotato weevil Cylas formicarius (F.) (Coleoptera: Brentidae) is one of the most serious insects causing damage to sweetpotatoes in the world. Small populations of these insects can cause severe damage to tubers of the crop. Without proper and effective control, weevil populations are likely to cause a huge or complete loss of sweetpotato production in sweetpotato growing areas. Consequently, there is an urgent need for development of an eco-friendly control method for this weevil. Although some control methods are effective, toxic pesticides applications are detrimental and damaging to our environment. Although pheromone traps are currently being used, no effective control of this weevil was achieved. Therefore, studies were carried out as part of the development of a trapping system for C. formicarius. Previous color-choice field tests have confirmed that C. formicarius preferred red traps over gray, green, brown, blue, white, yellow, or black; light red was more attractive than other shades of red. The current study aimed to know whether C. formicarius behavior changes in indoor conditions. Among the eight colored traps tested in the laboratory, green-colored traps were more effective in attracting C. formicarius than all other colors. It attracted nearly double the number of weevils than standard traps presently being used by growers. Based on these results, it is recommended to use green-colored traps to mass trap weevils (by attracting and killing) from sweetpotatoes grown under indoor (storage) conditions.
Arthropod Development's Response to Temperature: a Review and New Software for Modeling
(2018-11) Mirhosseini, Mohammad A.; Fathipour, Yaghoub; Reddy, Gadi V. P.
Among environmental factors, temperature has a direct and crucial influence on the key life processes of survival, development, reproduction, and movement of poikilothermic animals and hence their population dynamics. The lower and upper temperature thresholds and optimal temperature have ramifications for all major life processes, where within a specific range, a temperature change results in a proportional rise or fall of the rate of any given process. There are some basic approaches for modeling development response to temperature in arthropods. The oldest and most widely used model is a simple linear description of arthropod development in relation to temperature. The linear model forms the basis of the well-known thermal summation or degree-day (DD) approach to timing prediction. The second approach for predicting arthropod development rate is nonlinear mathematical models. However, given the fundamental role of thermal models in forecasting and integrated pest management programs, the main purpose of this paper was to facilitate the use of thermal models to estimate the developmental response of arthropods to temperature and select the appropriate model with a view to goodness-of-fit and generalizability by designing a user-friendly software. In this paper, the linear and most common nonlinear thermal models and the main criteria for selecting appropriate models are also reviewed.
Bioactivity of Selected Eco-Friendly Pesticides Against Cylas formicarius (Coleoptera:Brentidae)
(2012-12) Leng, P. H.; Reddy, Gadi V. P.
Seven low risk pesticides including 1.2% azadirachtin (Azadirachta indica), extracts from Morinda citrifolia, petroleum oil 97%, Beauveria bassiana strain GHA, mixed essential oils (rosemary oil: 0.25%, peppermint oil: 0.25%, thyme oil: 0.25%, clove oil: 0.25% and other ingredients: 99.00%), spinosad and malathion, were evaluated against adults of the sweetpotato weevil, Cylas formicarius (Fabricius) (Coleoptera: Brentidae) to determine potential insecticidal, repellent and feeding deterrence effects. Among the pesticides tested, A. indica and spinosad showed high insecticidal, repellent and feeding deterrence activity against C. formicarius. Spinosad, A. indica and malathion showed significantly higher insecticidal activity against C. formicarius. Similarly, these pesticides showed high repellency activity against adults, particularly 3–4 h after the treatment. The lowest food consumption was observed with the A. indica (0.8 g/adult/192 h), and the highest (9.9 g/adult/192 h) was with the petroleum oil spray. The other tested pesticides showed comparable activities. The chemicals we tested—particularly neem and spinosad—are therefore promising candidates as ecofriendly chemicals that could potentially replace broad-spectrum synthetic neurotoxins for control of C. formicarius.
Biorational versus conventional insecticides – Comparative field study for managing red spider mite and fruit borer on tomato
(2014-10) Reddy, Gadi V. P.; Miller, R. H.
Tomato, Lycopersicum esculentum L. (Solanaceae), is an important crop worldwide that is grown both outdoors and under protected structures, for fresh market consumption and for processing. In the Mariana Islands, tomato is grown as an outdoor crop throughout the year. Tomatoes are attacked by a variety of pests, including the tomato fruitworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), and, in Pacific islands, the red spider mite Tetranychus marianae McGregor. These pests cause scarring, tissue damage, and aberrations in fruit shape or color, making the tomatoes undesirable for fresh market. Also, insect bodies, excretia or parts in fruits reduce their market suitability. Field trials aimed at improving management of these pests were undertaken at two locations in Guam (Yigo and Inarajan), USA in 2012 and 2013, assessing the efficacy of different biorational and conventional insecticides against T. marianae and H. armigera on tomato. At both locations, the mean percentage of mite-infested leaves and the population density of T. marianae were higher in control than in treated plots. An integrated pest management (IPM) program comprising sprays of selective insecticides (Petroleum spray oil, Beauveria bassiana, azadirachtin, and Bacillus thuringiensis), evaluated at 15, 30, 45 and 60 days after transplantation of tomato seedlings, significantly reduced the number of T. marianae-infested leaves and the density of T. marianae over plots treated with carbaryl, malathion, six applications of B. bassiana or B. thuringiensis and over both controls at both locations. Similarly, significantly lower fruit damage by H. armigera was recorded in the plots treated with the IPM program than in plots treated with carbaryl, malathion, or the control treatments at both locations. Marketable tomato yields from the plots which received with the IPM program were significantly greater at both locations than were those in the other treatments.
Can a Semiochemical-Based Trapping Method Diminish Damage Levels Caused by Rhabdoscelus obscurus (Coleoptera: Curculionidae)?
(2012-09) Reddy, Gadi V. P.; Shi, Pei-Jian; Mann, C. R.; Mantanona, D. M. H.; Dong, Z.
The New Guinea sugarcane weevil, Rhabdoscelus obscurus (Boisduval) (Coleoptera: Curculionidae), is an important pest of palms, ornamental nurseries, and sugarcane in the Pacific Islands. Without effective control methods, R. obscurus populations can cause major or complete loss of palm production in Guam and other Micronesian Islands. Moreover, R. obscurus has inflicted severe attacks on coconut trees on Guam. The role of monitoring is important in judging the dynamics of R. obscurus and recording area wide population trends. There is no precise research information available on the trap catch threshold levels relative to the damage caused by R. obscurus. Here we investigated the assessment of trap catch threshold levels and the potential for predicting R. obscurus larval damage by using adult pheromone trap captures. Spatial patterns of capture were studied in relation to subsequent larval damaged betel nut plants at various locations in Guam, United States, during 2010-2012. The generalized additive model was used to describe the effects of the treatment level (traps/ha), ranging from 0 to 12, and time on reducing the damage of R. obscurus to palms. We find that these two predictors are statistically significant, and the treatment level is demonstrated to be the crucial predictor for reducing the damage. There is no significant difference in effectively controlling the damage between the treatment levels of 9 and 12 traps/ha. At least 9 traps/ha is suggested for effectively controlling the damage based on results from the current study.
Characterization of resistance to Cephus cinctus Norton (Hymenoptera: Cephidae) in barley germplasm
(2018-04) Varella, Andrea C.; Talbert, Luther E.; Achhami, Buddhi B.; Blake, Nancy K.; Hofland, Megan L.; Sherman, Jamie D.; Lamb, Peggy F.; Reddy, Gadi V. P.; Weaver, David K.
Most barley cultivars have some degree of resistance to the wheat stem sawfly (WSS), Cephus cinctus Norton (Hymenoptera: Cephidae). Damage caused by WSS is currently observed in fields of barley grown in the Northern Great Plains, but the impact of WSS damage among cultivars due to genetic differences within the barley germplasm is not known. Specifically, little is known about the mechanisms underlying WSS resistance in barley. We characterized WSS resistance in a subset of the spring barley CAP (Coordinated Agricultural Project) germplasm panel containing 193 current and historically important breeding lines from six North American breeding programs. Panel lines were grown in WSS infested fields for two consecutive years. Lines were characterized for stem solidness, stem cutting, WSS infestation (antixenosis), larval mortality (antibiosis), and parasitism (indirect plant defense). Variation in resistance to WSS in barley was compared to observations made for solid-stemmed resistant and hollow-stemmed susceptible wheat lines. Results indicate that both antibiosis and antixenosis are involved in the resistance of barley to the WSS, but antibiosis seems to be more prevalent. Almost all of the barley lines had greater larval mortality than the hollow-stemmed wheat lines, and only a few barley lines had mortality as low as that observed in the solid-stemmed wheat line. Since barley lines lack solid stems, it is apparent that barley has a different form of antibiosis. Our results provide information for use of barley in rotation to control the WSS and may provide a basis for identification of new approaches for improving WSS resistance in wheat.
Comparative effect of integrated pest management and farmers' standard pest control practice for managing insect pests on cabbage (Brassica spp.)
(2011-03) Reddy, Gadi V. P.
BACKGROUND: Studies were conducted on experimental cabbage plantings in 2009 and on experimental and commercial plantings in 2010, comparing farmers' current chemical standard pesticide practices with an integrated pest management (IPM) program based on the use of neem (Aza-Direct) and DiPel (Bacillus thuringiensis). In experimental plantings, the IPM program used six or eight applications of neem and DiPel on a rotational basis. The standard-practice treatments consisted of six or eight applications of carbaryl and malathion or control treatment. RESULTS: The IPM treatments reduced pest populations and damage, resulting in a better yield than with the standard chemical or control treatment. When IPM treatment included three applications of neem plus three applications of DiPel (on a rotational basis in experimental fields), it again reduced the pest population and damage and produced a better yield than the standard practice. The lower input costs of the IPM program resulted in better economic returns in both trials. CONCLUSIONS: The IPM components neem and DiPel are suitable for use in an IPM program for managing insect pests on cabbage (Brassica spp.).
Comparison of Thermal Performance Equations in Describing Temperature-Dependent Developmental Rates of Insects: (I) Empirical Models
(2015-12) Shi, Pei-Jian; Reddy, Gadi V. P.; Chen, Lei; Ge, Feng
Temperature greatly affects the developmental duration of insects at their different stages, and many mathematical models exist for describing their temperature-dependent developmental rates. It is important to choose a suitable model to predict outbreaks of pest insects under climate change. However, previous comparisons among these models were usually based on a single species. In the present study, we compared the six nonlinear models (the BriÃ©re-1, BriÃ©re-2, Lactin, Performance-2, beta, and Ratkowsky models) based on the goodness of fit and the trade-off between the modelâ€™s goodness of fit and structural complexity, using 10 temperature-dependent developmental rate datasets on insects to make the conclusions general. We found that the square root model (i.e., the Ratkowsky model) fitted all datasets well, and the curve shape produced by this model also approximates the curve shape of thermodynamically based mathematical models. The square root model was originally derived to be applicable to the growth rates of bacteria, and until now it has been generally ignored in entomology. We were mainly concerned with the predicted results obtained by using this model on observations of temperature-dependent developmental rates. We found that the square root model described well the pooled developmental rates in the low-, mid-, and high-temperature ranges, and we believe that it merits wider use in entomology.
Comparison of Thermal Performance Equations in Describing Temperature-Dependent Developmental Rates of Insects: (III) Phenological Applications
(2018-11) Shi, Pei-Jian; Fan, Mei-Ling; Reddy, Gadi V. P.
The developmental times of poikilotherms at different stages are significantly affected by temperature. Most mathematical models describing the temperature-dependent developmental rates of poikilotherms are built according to the experimental data at various constant temperatures. However, these models can also be applied to the developmental rates at variable temperatures. It is more meaningful to use models to predict the occurrence times of pest insects that actually represent the completion for a particular developmental stage (e.g., hatching, pupation, eclosion) under a natural thermal environment. For some developmental stages, insects might experience a period of high temperatures. In this case, skewed bell-shaped nonlinear models are more reasonable than the linear and exponential models because in the high-temperature region the developmental rate decreases with temperature increasing. We used the accumulated developmental progress method that combines three representative nonlinear models to compare the model validity in predicting the egg\'s earliest hatching date of bamboo locust in different years. We found that for the springtime phenological event the simple Arrhenius\' equation obtains the best goodness of fit. This study also provides a general R function that permits users to employ nonlinear parametric models to predict the occurrence times of insect phenology. In fact, if the investigation data cannot reflect the temperature-based phenological models proposed here, we have to consider whether the data set is reliable or whether the temperature is the crucial factor that determines the occurrence time of interest. The present study is valuable for the integrated management of pest insects because the biological or chemical control timing relies on the prediction on the occurrence time of phenological events.
Damage Patterns, Monitoring, and Management of Procontarinia mangiferae (Diptera: Cecidomyiidae) in Pakistan
(2016-09) Rehman, Hafiz M.; Mahmood, Riaz; Razaq, Muhammad; Reddy, Gadi V. P.
Since 2005, mango has been damaged by a group of new pests, the gall midges, in all mango-growing areas of Pakistan. Little is known about these pests in Pakistan. In this report, we present information on the occurrence, damage patterns, methods for monitoring, and management of Procontarinia mangiferae (Felt), a mango gall midge found in the country. At the study site (Rahim Yar Khan, a district of the province Punjab, Pakistan), the pest was active from January/February to April as eggs, larvae, and adults on mango inflorescence buds, branches (axillaries), and immature fruits. Females of P. mangiferae oviposited in inflorescence tissues, and larvae, after feeding on plant tissues, dropped to the soil under the mango trees for pupation from February to April. Mango trees in commercial orchards were more heavily damaged by P. mangiferae than were isolated trees in farmer fields (66.7%). The adults of P. mangiferae were captured on sticky traps of all tested colors, and were in flight from January to May. Captures per trap were highest on yellow traps, followed by green, blue, and clear traps. Control of mango gall midge was effectively provided by the synthetic insecticide bifenthrin (Talstar 10 EC) and also by application of neem seed kernel extract on the tree canopy if integrated with raking the soil under the mango tree canopy.
Developing nominal threshold levels for Phyllotreta cruciferae (Coleoptera: Chrysomelidae) damage on canola in Montana, USA
(2014-12) Tangtrakulwanich, Khanobporn; Reddy, Gadi V. P.; Wu, Shaohui; Miller, John H.; Ophus, Victoria L.; Prewett, Julie
The flea beetles Phyllotreta cruciferae (Goeze) and Phyllotreta striolata (F.) (Coleoptera: Chrysomelidae) are serious pests infesting canola (Brassica napus L.; Brassicales: Brassicaceae) in the Northern Great Plains of the United States. In Montana, P. cruciferae is the only flea beetle species that attacks canola during the crop growing stage. Management of P. cruciferae is usually focused on treating adults feeding on canola seedlings, which is the stage most vulnerable to flea beetle damage. In the Golden Triangle area in Montana, canola growers traditionally use seed treatments or calendar based spraying to control P. cruciferae. Here, we compared calendar-based spraying with seed treatment and threshold-based treatment. The experiment treatments included threshold levels (15–20, 25, 45% of leaf area damaged), calendar based sprays (15, 30 and 45 day intervals after plant emergence), seed treatments (imidacloprid), and untreated controls. The trials were done at two locations (Conrad and Western Triangle Agricultural Research Center). We found that calendar-based spraying at a 15-day interval did not differ significantly in yields from threshold-based treatment at 15–20% leaf damage. Also, the seed treatment did not give significantly higher yields compared to calendar-based sprays. A negative correlation was detected between leaf damage and yield in each treatment. Overall, calendar-based and threshold-based treatments were most effective in improving yields. However, treatment made at the threshold of 15–20% leaf area damage is recommended in order to reduce the number of chemical applications and also to reduce the possibility of selecting for resistance in flea beetles.
Development of semiochemical-based strategies for old-house borer, Hylotrupesbajulus (Coleoptera: Cerambycidae)
(2011-08) Reddy, Gadi V. P.
Earlier studies have demonstrated that among the eight differently colored ground traps tested in the greenhouse, black colored traps were the most effective compared with the performances of brown, yellow, red, grey, blue, white, and green traps. In the present study, efficiency of ground traps with different shades of black (black thick, pure black, mix black and black medium) were evaluated in the greenhouse for the capture of Hylotrupes bajulus. Black thick colored traps caught significantly higher H. bajulus than traps with other shades of black. Therefore, black thick colored ground traps are recommended to use for monitoring and mass trapping H. bajulus in museums and human dwellings.
Dispersal distance determines the exponent of the spatial Taylor's power law
(2016-09) Shi, Pei-Jian; Sandhu, Hardev S.; Reddy, Gadi V. P.
The equation describing a power-law relationship between the mean and variance of population abundance in space or time is known as Taylor's power law (TPL), initially observed in samples of insects. Factors determining the TPL exponent are of particular concern to ecologists because the observations of the exponent usually range 1-2. Recent studies have suggested that TPL is caused solely by statistical artifacts rather than biological processes, with the corresponding statistical models lacking linkages to explicit population demography. In this study, we used two special forms of the Neyman-Scott cluster point process to study the effect of offspring dispersal distance from the parents on the TPL exponent. Results showed that dispersal distance could largely affect the TPL exponent. The response curve of TPL exponent to dispersal distance is similar to the shape of the left-skewed gamma distribution function multiplied by a constant which can permit its maximum value to exceed 1. That means, short-distance dispersals could produce large TPL exponents relative to the whole response curve. However, the TPL exponent will decline in the case that the dispersal is extremely short or long. To better understand the function of the exponent of TPL on fitness, we attempted to link plant seed dispersal ability to the TPL exponent, and we discussed the trade-off between investing in propagation energy and in performance energy of plants. Dispersal overlap of offspring each other to an extent can cause a large TPL exponent, providing maximum fitness in a population. A novel theoretical frame was proposed to explain the role of spatial TPL relationships in affecting the fitness of plants.
Effects of Irradiation Dose on Sperm Production, Insemination, and Male Mating Possible Period in the Sweetpotato Weevil (Coleoptera: Brentidae)
(2018-05) Hiroyoshi, Satoshi; Mistunaga, Takayuki; Kohama, Tsuguo; Reddy, Gadi V. P.
The sterile insect technique (SIT) has been used for the control or eradication of target insect pests. To successfully apply SIT, it is very important to clarify the effect of irradiation on male reproduction in the target pest, because their mating and spermiogenesis abilities affect the success of eradication program. The sweetpotato weevil, Cylas formicarius (Fabricius) (Coleoptera: Brentidae) is a notorious and worldwide pest of sweet potato. We investigated the effect of irradiation at five doses ranging from 0 (control) to 150 Gy on 9-d-old males. Survival rate of the control (no treatment) remained high from day 10 to 20 of adult life, whereas higher doses of irradiation reduced it, maximally by approximately 70%. Mating rates showed a similar tendency. Radiation dose neither affected sperm production nor sperm transfer at any dose, although spermiogenesis is active during the adult stage. However, radiation dose affected the lifetime total of ejaculated sperm number, likely because of fewer matings by irradiated males. These results suggest that use of a dose of 150 Gy or higher is appropriate for the final step of eradication of this weevil. At least, lower dose of irradiation may arise the inadequate sterilization, resulting in a failure of eradication program. We conclude that weekly release of sweetpotato weevil sterilized with high dose, achieving complete sterilization, could be useful for eradication program after reducing the population by male annihilation method.
Effects of juvenile hormone analogue (methoprene) and 20-hydroxyecdysone on reproduction in Polygonia c-aureum (Lepidoptera: Nymphalidae) in relation to adult diapause
(2017-05) Hiroyoshi, Satoshi; Reddy, Gadi V. P.; Mitsuhashi, Jun
We investigated the effects of juvenile hormone analogue (methoprene) and 20-hydroxyecdysone on female and male reproduction in a nymphalid butterfly, Polygonia c-aureum. This butterfly has a facultative adult diapause controlled by the corpora allata and brain. Methoprene seems to terminate reproductive diapause, although transplantation experiments indicate that the activity of the corpora allata does not affect male mating behavior Endo (Dev Growth Differ 15:1-10, 1973a), suggesting that the brain may be involved in diapause. We found that exposure to methoprene promoted the development of ovaries and of the male accessory glands and simplex. On the other hand, exposure to 20-hydroxyecdysone did not promote the development of female and male reproductive organs and eupyrene sperm movement from the testis to the duplex in the adult stage. Ecdysteroid titer in both sexes was consistently low in adults. These results suggest that imaginal diapause is largely regulated by juvenile hormone in this butterfly.
Effects of pre-overwintering conditions on eupyrene and apyrene spermatogenesis after overwintering in Polygonia c-aureum (Lepidoptera: Nymphalidae)
(2017-07) Hiroyoshi, Satoshi; Yoshimura, Jin; Iwabuchi, Kikuo; Reddy, Gadi V. P.; Mitsuhashi, Jun
Sperm polymorphism is widely known in invertebrates. In insects, Lepidoptera has two types of sperm: nucleated eupyrene (fertile) sperm and anucleated apyrene (unfertile) sperm. These sperm types are produced during post-embryogenesis, and eupyrene spermatogenesis precedes apyrene spermatogenesis. During overwintering, spermatogenesis stops and a portion of undifferentiated-stage spermatocytes degenerate. After overwintering, spermatogenesis restarts with unaffected spermatogonia. However, how new spermatozoa arise in the adult testes after overwintering is not known in Lepidoptera. In this study, we investigated the spermatogenesis events in the nymphalid butterfly Polygonia c-aureum after overwintering under various environmental conditions. Our results indicate that both eupyrene and apyrene spermatogenesis restart at any stopping stage and sperm of these types are regenerated in no particular order after adult insect overwintering. This suggests that the spermatogenesis occurring after overwintering proceeds without embryogenetic restrictions related to the developmental sequence.