Target Insect Pests Research Articles

Does sorption of sulfuryl fluoride by wheat reduce its efficacy against adults and eggs of Rhyzopertha dominica?

Despite its growing importance as a fumigant for grain, there is no information on the impact of sorption on the efficacy of sulfuryl fluoride (SF) against target insect pests. Eggs and adults of a major grain pest, Rhyzopertha dominica, living in wheat (12% m.c.), were fumigated with SF at 0.5, 1, and 2 mg/L for 168 h at 25 °C. Sorption of the fumigant by the grain followed an exponential decay and reduced the mortality rates of both adults and eggs. The partition ratio (K), a measure of physical sorption, had a strong impact on mortality of both adults and eggs. The quadratic model showed the best fit to the data and turning points in the relationship indicated that although mortality increased as concentration increased, physical sorption removed fumigant resulting in a decrease in the mortality rate. There was a linear relationship between mortality and the rate of sorption (k) of SF by the wheat. At each concentration, mortality rate increased as k increased despite sorption continuing, indicating that the chemical sorption rate had little impact on mortality. Sorption of SF into the commodity has the potential to reduce the biological efficacy of the fumigant resulting in potential control failures. Concentration x time protocols may need to be revised to account for this phenomenon.

Acoustic Activity Cycles of Rhynchophorus ferrugineus (Coleoptera: Dryophthoridae) Early Instars After Beauveria bassiana (Hypocreales: Clavicipitaceae) Treatments

Rhynchophorus ferrugineus (Olivier; Coleoptera: Dryophthoridae) is a pest of many crop and ornamental palm tree species in subtropical regions worldwide. Larvae tunnel and feed unseen in the trunks, ultimately causing irreparable harm and killing the palm. Beauveria bassiana (Balsamo-Crivelli; Hypocreales: Clavicipitaceae) Vuillemin is under evaluation as a biological control agent for R. ferrugineus management but its effects are difficult to monitor under field conditions except by acoustic methods. Older (>30 d) larvae treated with B. bassiana display statistically significant reductions in acoustic activity in semi-field studies, but activity of younger larvae has been more difficult to analyze due to their short-duration cycles of increasingly active and then less active feeding and movement, followed by inactive molting. A procedure was developed to characterize effects of B. bassiana treatments by subdividing long-term recording periods into activity cycles. Treatment effects were compared within and across cycles. The procedure demonstrated statistically significant differences among acoustic activity rates over time for 15-d-old larvae exposed to control, 10⁴, or 10⁸ conidia ml–¹B. bassiana treatments. The results suggest that acoustic technology has considerable utility for monitoring of larval development and for evaluating efficacy of pest management treatments in environments where the targeted insect pests are hidden from view.

Automated Remote Insect Surveillance at a Global Scale and the Internet of Things

Τhe concept of remote insect surveillance at large spatial scales for many serious insect pests of agricultural and medical importance has been introduced in a series of our papers. We augment typical, low-cost plastic traps for many insect pests with the necessary optoelectronic sensors to guard the entrance of the trap to detect, time-stamp, GPS tag, and—in relevant cases—identify the species of the incoming insect from their wingbeat. For every important crop pest, there are monitoring protocols to be followed to decide when to initiate a treatment procedure before a serious infestation occurs. Monitoring protocols are mainly based on specifically designed insect traps. Traditional insect monitoring suffers in that the scope of such monitoring: is curtailed by its cost, requires intensive labor, is time consuming, and an expert is often needed for sufficient accuracy which can sometimes raise safety issues for humans. These disadvantages reduce the extent to which manual insect monitoring is applied and therefore its accuracy, which finally results in significant crop loss due to damage caused by pests. With the term ‘surveillance’ we intend to push the monitoring idea to unprecedented levels of information extraction regarding the presence, time-stamping detection events, species identification, and population density of targeted insect pests. Insect counts, as well as environmental parameters that correlate with insects’ population development, are wirelessly transmitted to the central monitoring agency in real time and are visualized and streamed to statistical methods to assist enforcement of security control to insect pests. In this work, we emphasize how the traps can be self-organized in networks that collectively report data at local, regional, country, continental, and global scales using the emerging technology of the Internet of Things (IoT). This research is necessarily interdisciplinary and falls at the intersection of entomology, optoelectronic engineering, data-science, and crop science and encompasses the design and implementation of low-cost, low-power technology to help reduce the extent of quantitative and qualitative crop losses by many of the most significant agricultural pests. We argue that smart traps communicating through IoT to report in real-time the level of the pest population from the field straight to a human controlled agency can, in the very near future, have a profound impact on the decision-making process in crop protection and will be disruptive of existing manual practices. In the present study, three cases are investigated: monitoring Rhynchophorus ferrugineus (Olivier) (Coleoptera: Curculionidae) using (a) Picusan and (b) Lindgren trap; and (c) monitoring various stored grain beetle pests using the stored-grain pitfall trap. Our approach is very accurate, reaching 98–99% accuracy on automatic counts compared with real detected numbers of insects in each type of trap.

Effect of acute pesticide exposure on bee spatial working memory using an analogue of the radial-arm maze.

Pesticides, including neonicotinoids, typically target pest insects by being neurotoxic. Inadvertent exposure to foraging insect pollinators is usually sub-lethal, but may affect cognition. One cognitive trait, spatial working memory, may be important in avoiding previously-visited flowers and other spatial tasks such as navigation. To test this, we investigated the effect of acute thiamethoxam exposure on spatial working memory in the bumblebee Bombus terrestris, using an adaptation of the radial-arm maze (RAM). We first demonstrated that bumblebees use spatial working memory to solve the RAM by showing that untreated bees performed significantly better than would be expected if choices were random or governed by stereotyped visitation rules. We then exposed bees to either a high sub-lethal positive control thiamethoxam dose (2.5 ng−1 bee), or one of two low doses (0.377 or 0.091 ng−1) based on estimated field-realistic exposure. The high dose caused bees to make more and earlier spatial memory errors and take longer to complete the task than unexposed bees. For the low doses, the negative effects were smaller but statistically significant, and dependent on bee size. The spatial working memory impairment shown here has the potential to harm bees exposed to thiamethoxam, through possible impacts on foraging efficiency or homing.

Endophytic Beauveria bassiana in grapevine Vitis vinifera (L.) reduces infestation with piercing-sucking insects

Fungi are important natural pathogens of arthropod pests and are successfully used as biocontrol agents in various crops. In addition to colonizing arthropods, evidence has accumulated that some entomopathogenic fungi like Beauveria bassiana can endophytically colonize a wide array of plant species. However, only limited information is currently available on the endophytic colonization of grapevines with B. bassiana and whether the fungus still maintains its pathogenic habit against insect pests.Greenhouse and field experiments were conducted to optimize endophytic establishment of the entomopathogenic fungus B. bassiana in younger, potted plants and mature grapevine plants in the vineyard. We used two different commercialized B. bassiana strains, applied either as conidial suspensions (ATCC 74040 and GHA) or as a formulated product (Naturalis®, strain ATCC 74040) on grapevine leaves. The potential of endophytic B. bassiana to provide protection against putative target pest insects like the vine mealybug Planococcus ficus was assessed in a bioassay using surface sterilized leaves. Endophytic survival of B. bassiana inside leaf tissues of seven-week-old potted plants was evident for at least 21days after inoculation, irrespective of the inoculum used. Endophytic B. bassiana reduces infestation rate and growth of P. ficus. In the vineyard B. bassiana was detected as an endophyte in mature grapevine plants up to five weeks after last application with significant reduction of infestation with grape leafhopper, Empoasca vitis.

Plant characterization of genetically modified maize hybrids MON-89\xd834-3\xa0\xd7\xa0MON-88\xd817-3, MON-89\xd834-3\xa0\xd7\xa0MON-\xd8\xd86\xd83-6, and MON-\xd8\xd86\xd83-6: alternatives for maize production in Mexico

Environmental risk assessment (ERA) of genetically modified (GM) crops is a process to evaluate whether the biotechnology trait(s) in a GM crop may result in increased pest potential or harm to the environment. In this analysis, two GM insect-resistant (IR) herbicide-tolerant maize hybrids (MON-89Ø34-3 × MON-88Ø17-3 and MON-89Ø34-3 × MON-ØØ6Ø3-6) and one herbicide-tolerant GM hybrid (MON-ØØ6Ø3-6) were compared with conventional maize hybrids of similar genetic backgrounds. Two sets of studies, Experimental Phase and Pilot Phase, were conducted across five ecological regions (ecoregions) in Mexico during 2009–2013, and data were subject to meta-analysis. Results from the Experimental Phase studies, which were used for ERA, indicated that the three GM hybrids were not different from conventional maize for early stand count, days-to-silking, days-to-anthesis, root lodging, stalk lodging, or final stand count. Statistically significant differences were observed for seedling vigor, ear height, plant height, grain moisture, and grain yield, particularly in the IR hybrids; however, none of these phenotypic differences are expected to contribute to a biological or ecological change that would result in an increased pest potential or ecological risk when cultivating these GM hybrids. Overall, results from the Experimental Phase studies are consistent with those from other world regions, confirming that there are no additional risks compared to conventional maize. Results from Pilot Phase studies indicated that, compared to conventional maize hybrids, no differences were detected for the agronomic and phenotypic characteristics measured on the three GM maize hybrids, with the exception of grain moisture and grain yield in the IR hybrids. Since MON-89Ø34-3 × MON-88Ø17-3 and MON-89Ø34-3 × MON-ØØ6Ø3-6 confer resistance to target insect pests, they are an alternative for farmers in Mexico to protect the crop from insect damage. Additionally, the herbicide tolerance conferred by all three GM hybrids enables more cost-effective weed management.

Does Drought Increase the Risk of Insects Developing Behavioral Resistance to Systemic Insecticides?

Increases in severity and frequency of drought periods, average global temperatures, and more erratic fluctuations in rainfall patterns due to climate change are predicted to have a dramatic impact on agricultural production systems. Insect pest populations in agricultural and horticultural systems are also expected to be impacted, both in terms of their spatial and temporal distributions and in their status as pest species. In this opinion-based article, we discuss how indirect effects of drought may adversely affect the performance of systemic insecticides and also lead to increased risk of insect pests developing behavioral insecticide resistance. We hypothesize that more pronounced drought will decrease uptake and increase the magnitude of nonuniform translocation of systemic insecticides within treated crop plants, and that may have two concurrent consequences: 1) reduced pesticide performance, and 2) increased likelihood of insect pests evolving behavioral insecticide resistance. Under this scenario, pests that can sense and avoid acquisition of lethal dosages of systemic insecticides within crop plants will have a selective advantage. This may lead to selection for insect behavioral avoidance, so that insects predominantly feed and oviposit on portions of crop plants with low concentration of systemic insecticide. Limited research has been published on the effect of environmental variables, including drought, on pesticide performance, but we present and discuss studies that support the hypothesis described above. In addition, we wish to highlight the importance of studying the many ways environmental factors can affect, directly and indirectly, both the performance of insecticides and the risk of target insect pests developing resistance.

Knockdown of RNA Interference Pathway Genes in Western Corn Rootworms (Diabrotica virgifera virgifera Le Conte) Demonstrates a Possible Mechanism of Resistance to Lethal dsRNA.

RNA interference (RNAi) is being developed as a potential tool for insect pest management. Increased understanding of the RNAi pathway in target insect pests will provide information to use this technology effectively and to inform decisions related to resistant management strategies for RNAi based traits. Dicer 2 (Dcr2), an endonuclease responsible for formation of small interfering RNA’s and Argonaute 2 (Ago2), an essential catalytic component of the RNA-induced silencing complex (RISC) have both been associated with the RNAi pathway in a number of different insect species including the western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae). We identified both genes from a transcriptome library generated from different tissues and developmental stages of the western corn rootworm, an important target pest for transgenic plants expressing dsRNA targeting essential genes. The expression of these genes was suppressed by more than 90% after injecting gene specific dsRNA into adult rootworms. The injected beetles were then fed vATPase A dsRNA which has previously been demonstrated to cause mortality in western corn rootworm adults. The suppression of both RNAi pathway genes resulted in reduced mortality after subsequent exposure to lethal concentrations of vATPase A dsRNA as well as increased vATPase A expression relative to control treatments. Injections with dsRNA for a non-lethal target sequence (Laccase 2) did not affect mortality or expression caused by vATPase A dsRNA indicating that the results observed with Argo and Dicer dsRNA were not caused by simple competition among different dsRNA’s. These results confirm that both genes play an important role in the RNAi pathway for western corn rootworms and indicate that selection pressures that potentially affect the expression of these genes may provide a basis for future studies to understand potential mechanisms of resistance.

Development of insect-resistant cotton lines with targeted expression of insecticidal gene

In order to address biosafety concerns regarding the constitutive expression of foreign genes in crops, we applied a strategy aimed at confining foreign gene expression in insect wounding sites of cotton. For this purpose, a plant expression construct was designed by cloning the AoPR1 promoter (pathogenesis-related protein gene isolated from Asparagus officinalis) upstream from the insecticidal gene cry1Ac. The Turkish cotton cultivar cv. STN-468 was transformed using the Agrobacterium tumefaciens strain LBA4404 containing the recombinant binary vector pRD400 harboring cry1Ac under a wound-inducible promoter. The neomycin phosphotransferase (nptII) gene was used as a selectable marker at a concentration of 100 mg/L. The primary transformants were analyzed for T-DNA integration and expression using standard molecular approaches. The efficacy of insecticidal gene control of the AoPR1 promoter was investigated using leaf bioassays with 2nd instar larvae of Helicoverpa armigera and Spodoptera littoralis. Positive primary transformants from T0 progeny were further raised under greenhouse conditions to obtain progeny (T1). The introduced gene was properly inherited and expressed in T1 progeny. The mechanical wounding of plants resulted in increased cry1Ac protein levels during 0-48 h of the wounding period. The transgenic lines exhibited appreciable levels of resistance against targeted insect pests in the leaf bioassays. The use of a wound-inducible promoter to drive insecticidal gene expression is a valuable insect resistant management strategy as gene expression will remain limited to the insect biting sites of plant and crop, food and environmental concerns can be minimized.

The entomopathogen Beauveria bassiana has epiphytic and endophytic activity against the tomato leaf miner Tuta absoluta

AbstractThe recent introduction and rapid spread of the tomato leaf miner Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) throughout Europe, Africa and the Middle East poses a severe threat to future cultivation of tomato and other Solanaceae. Among the best practicable means for effective and sustainable control of this invasive insect pest are entomopathogenic fungi, which can either prevent a further spread of this insect to new areas or keep population densities below an economic threshold level. Here, we report on the efficacy of a commercially available mycoinsecticide based on the entomopathogen Beauveria bassiana (Bals.) Vuill. (Ascomycota: Hypocreales) against all four larval stages of T. absoluta. In bioassays, high mortality rates and significantly reduced longevity of larvae were obvious when larvae had fed for a period of around 15 days on leaves with B. bassiana propagules present on the surface as an epiphyte with mortality values corrected for variance in control mortality of 90–100%. In addition, a second mode of action of B. bassiana against T. absoluta larvae was evident in bioassays in the form of an endophytic establishment of this fungus in treated tomato plants. Longevity of T. absoluta L4 larvae was significantly lower in individuals which had fed on surface‐sterilized tomato leaves obtained from plants treated 18 days before the bioassay with a B. bassiana suspension compared to larvae feeding on control plants treated with water. Corrected mortality reached values between 30% and 50% for all larval instars. Growth of tomato plants was not inhibited due to colonization by endophytic B. bassiana and a weak systemic translocation of fungal propagules in non‐treated leaves was evident in the assays. Accordingly, entomopathogenic fungi like B. bassiana express different modes of action again target insect pests, which is of particular relevance for the design of efficient management strategies for invasive pests like T. absoluta.

Survey of arthropod assemblages responding to live yeasts in an organic apple orchard

Associations between yeasts and insect herbivores are widespread, and these inter-kingdom interactions play a crucial role in yeast and insect ecology and evolution. We report a survey of insect attraction to live yeast from a community ecology perspective. In the summer of 2013 we screened live yeast cultures of Metschnikowia pulcherrima, M. andauensis, M. hawaiiensis, M. lopburiensis, and Cryptococcus tephrensis in an organic apple orchard. More than 3,000 arthropods from 3 classes, 15 orders, and 93 species were trapped; ca. 79% of the trapped specimens were dipterans, of which 43% were hoverflies (Syrphidae), followed by Sarcophagidae, Phoridae, Lauxaniidae, Cecidomyidae, Drosophilidae, and Chironomidae. Traps baited with M. pulcherrima, M. andauensis, and C. tephrensis captured typically 2.4 times more specimens than control traps; traps baited with M. pulcherrima, M. hawaiiensis, M. andauensis, M. lopburiensis and C. tephrensis were more species-rich than unbaited control traps. We conclude that traps baited with live yeasts of the genera Metschnikowia and Cryprococcus are effective attractants and therefore of potential value for pest control. Yeast-based monitoring or attract-and-kill techniques could target pest insects or enhance the assemblage of beneficial insects. Manipulation of insect behavior through live yeast cultures should be further explored for the development of novel plant protection techniques.

Metabolomic profiling of permethrin-treated Drosophila melanogaster identifies a role for tryptophan catabolism in insecticide survival

Insecticides and associated synergists are rapidly losing efficacy in target insect pest populations making the discovery of alternatives a priority. To discover novel targets for permethrin synergists, metabolomics was performed on permethrin-treated Drosophila melanogaster. Changes were observed in several metabolic pathways including those for amino acids, glycogen, glycolysis, energy, nitrogen, NAD+, purine, pyrimidine, lipids and carnitine. Markers for acidosis, ammonia stress, oxidative stress and detoxification responses were also observed. Many of these changes had not been previously characterized after permethrin exposure. From the altered pathways, tryptophan catabolism was selected for further investigation. The knockdown of some tryptophan catabolism genes (vermilion, cinnabar and CG6950) in the whole fly and in specific tissues including fat body, midgut and Malpighian tubules using targeted RNAi resulted in altered survival phenotypes against acute topical permethrin exposure. The knockdown of vermilion, cinnabar and CG6950 in the whole fly also altered survival phenotypes against chronic oral permethrin, fenvalerate, DDT, chlorpyriphos and hydramethylnon exposure. Thus tryptophan catabolism has a previously uncharacterized role in defence against insecticides, and shows that metabolomics is a powerful tool for target identification in pesticide research.

Chronic Responses of Daphnia magna Under Dietary Exposure to Leaves of a Transgenic (Event MON810) Bt–Maize Hybrid and its Conventional Near-Isoline

Insect resistance is the second most common trait globally in cultivated genetically modified (GM) plants. Resistance is usually obtained by introducing into the plant’s genome genes from the bacterium Bacillus thuringiensis (Bt) coding for insecticidal proteins (Cry proteins or toxins) that target insect pests. The aim of this study was to examine the hypothesis that a chronic, high-dose dietary exposure to leaves of a Bt–maize hybrid (GM event MON810, expressing a transgenic or recombinant Cry1Ab toxin), exerted no adverse effects on fitness parameters of the aquatic nontarget organism Daphnia magna (water flea) when compared to an identical control diet based on leaves of the non-GM near-isoline. Cry1Ab was immunologically detected and quantified in GM maize leaf material used for Daphnia feed. A 69-kD protein near Bt’s active core-toxin size and a 34-kD protein were identified. The D. magna bioassay showed a resource allocation to production of resting eggs and early fecundity in D. magna fed GM maize, with adverse effects for body size and fecundity later in life. This is the first study to examine GM-plant leaf material in the D. magna model, and provides of negative fitness effects of a MON810 maize hybrid in a nontarget model organism under chronic, high dietary exposure. Based upon these results, it is postulated that the observed transgenic proteins exert a nontarget effect in D. magna and/or unintended changes were produced in the maize genome/metabolome by the transformation process, producing a nutritional difference between GM-maize and non-GM near-isoline.

Effectiveness in the field of Bt rice lines against target pests under various cultural regimes

China has a long history of rice cultivation, incorporating several cultural practices known to influence damage by insect pests. Transgenic Bt rice expresses lepidopteran-specific insecticidal proteins that primarily target lepidopteran insect pests. However, the effectiveness of Bt rice against target insect pests under different cultural regimes has not been evaluated. In this study, the effectiveness of Bt rice lines against rice leaffolder, Cnaphalocrocis medinalis (Guenée) (Lepidoptera: Pyralidae), and striped stem borer, Chilo suppressalis Walker (Lepidoptera: Crambidae), was evaluated under various transplanting densities, crop establishment methods, and planting times. The results showed that Bt rice lines (T2A-1 and T1C-19, containing Cry2A and Cry1C, respectively) could prevent damage by these target pests under a range of cultural practices. Injury by C. medinalis or C. suppressalis on rice did not differ with the rice lines under various transplanting densities. Direct-seeded non-Bt rice MH63 suffered heavier injury by C. medinalis and C. suppressalis than it did with transplanting, whereas injury to the two Bt rice lines did not differ with planting methods. Planting time significantly affected injury by C. medinalis or C. suppressalis on non-Bt rice, whereas injury to Bt rice lines did not differ with planting time. These results suggest that transplanting density, planting method, and planting time did not significantly affect the resistance of two Bt rice lines, due to their high insecticidal activity against target insects.

Cost-Benefit Analysis for Biological Control Programs That Targeted Insect Pests of Eucalypts in Urban Landscapes of California.

As well as being planted for wind breaks, landscape trees, and fuel wood, eucalypts are also widely used as urban street trees in California. They now are besieged by exotic insect herbivores of four different feeding guilds. The objective of the current analysis was to determine the return on investment from biological control programs that have targeted these pests. Independent estimates of the total number of eucalypt street trees in California ranged from a high of 476,527 trees (based on tree inventories from 135 California cities) to a low of 190,666 trees (based on 49 tree inventories). Based on a survey of 3,512 trees, the estimated mean value of an individual eucalypt was US$5,978. Thus, the total value of eucalypt street trees in California ranged from more than US$1.0 billion to more than US$2.8 billion. Biological control programs that targeted pests of eucalypts in California have cost US$2,663,097 in extramural grants and University of California salaries. Consequently, the return derived from protecting the value of this resource through the biological control efforts, per dollar expended, ranged from US$1,070 for the high estimated number of trees to US$428 for the lower estimate. The analyses demonstrate both the tremendous value of urban street trees, and the benefits that stem from successful biological control programs aimed at preserving these trees. Economic analyses such as this, which demonstrate the substantial rates of return from successful biological control of invasive pests, may play a key role in developing both grass-roots and governmental support for future urban biological control efforts.

Biocompatible colloidal dispersions as potential formulations of natural pyrethrins: a structural and efficacy study.

Biocompatible colloidal dispersions of the micro- and nanoemulsion type based on lemon oil terpenes, polysorbates, water, and glycerol were used for the formulation of pyrethrins, botanical insecticides derived from the white pyrethrum daisy, Tanacetum cinerariifolium. The proposed formulation is based on pyrethrin-containing water-in-oil (W/O) microemulsions that could be diluted in one step with an aqueous phase to obtain kinetically stable oil-in-water (O/W) nanoemulsions. Structural characteristics of the micro- and nanoemulsions were evaluated by electron paramagnetic resonance (EPR) spectroscopy, dynamic light scattering (DLS), small angle X-ray scattering (SAXS), and electrical conductivity. Dynamic properties of the surfactant monolayer as evidenced by EPR measurements were affected by the water content, the surfactant, and also the presence of the biocide. DLS and SAXS experiments of the nanoemulsions indicated the existence of two populations of oil droplets dispersed in the aqueous phase, globular droplets of 36-37 nm in diameter, and also larger droplets with diameters >150 nm. All of the applied techniques for structural determination revealed the participation of the biocide in the nanostructure. The insecticidal effect of the encapsulated natural pyrethrin was evaluated in laboratory bioassays upon a target-insect pest, the cotton aphid Aphis gossypii Glover (Hemiptera: Aphididae) in eggplant, and was found to be increased compared to the commercial pyrethrin formulation.

SCREENING OF GERMPLASM AGAINST CASHEW TEA MOSQUITO BUG (HELOPELTIS ANTONII)

Field screening to natural infestation of tea mosquito bug was done for seven consecutive years, in total 18 cashew accessions consisting of released cultivars, promising hybrids and other accessions. The screening trail was conducted at the Regional Fruit Research Station, Vengurle during the years 2004-05 to 2010-11. The damage to the shoot, panicle and nut surface was assessed by scoring in the 0-4 scale system. The result indicated that all the accession are susceptible to tea mosquito bug infestation with not any resistant/tolerant to the target insect pest. The intensity of percent infestation was found to vary among the accessions.

長期累代飼育がイモゾウムシの交尾能力に及ぼす影響

A lot of sterile males need to be released continuously in the target area in the sterile insect technique (SIT). Therefore, mass-rearing of the target pest insects is indispensable for SIT programs. The West Indian sweet potato weevil, Euscepes postfasciatus, has been maintained for over 44 generations (～8 years) for its eradication program in the Okinawa Prefectural Plant Protection Center (Naha, Okinawa, Japan). The selective pressures under mass-rearing conditions are likely to be very different from those of wild ones. The specific selective pressures over many generations under mass-rearing conditions would adversely affect the reproductive capacity of mass-reared insects. Therefore, evaluation of the mating performance of mass-reared males compared with that of wild ones is indispensable in SIT eradication programs. Although we compared mating performance with respect to four reproductive characteristics (duration of mating behavior, mating success, mating competitiveness ability and number of transferred sperm in female spermatheca during copulation) between mass-reared and wild males in E. postfasciatus, there was no evidence that the mass-reared males were inferior to the wild males in terms of mating performance. Thus, we considered that the mass-rearing procedure for at least 44 generations did not adversely influence the male mating activity in E. postfasciatus.

Molecular approaches to improve the insecticidal activity of Bacillus thuringiensis Cry toxins.

Bacillus thuringiensis (Bt) is a gram-positive spore-forming soil bacterium that is distributed worldwide. Originally recognized as a pathogen of the silkworm, several strains were found on epizootic events in insect pests. In the 1960s, Bt began to be successfully used to control insect pests in agriculture, particularly because of its specificity, which reflects directly on their lack of cytotoxicity to human health, non-target organisms and the environment. Since the introduction of transgenic plants expressing Bt genes in the mid-1980s, numerous methodologies have been used to search for and improve toxins derived from native Bt strains. These improvements directly influence the increase in productivity and the decreased use of chemical insecticides on Bt-crops. Recently, DNA shuffling and in silico evaluations are emerging as promising tools for the development and exploration of mutant Bt toxins with enhanced activity against target insect pests. In this report, we describe natural and in vitro evolution of Cry toxins, as well as their relevance in the mechanism of action for insect control. Moreover, the use of DNA shuffling to improve two Bt toxins will be discussed together with in silico analyses of the generated mutations to evaluate their potential effect on protein structure and cytotoxicity.

Bt 양배추가 복숭아혹진딧물의 발육과 기주선택에 미치는 영향

해충저항성 유전자변형 작물은 대상 해충에 대한 방제 효과를 증진시킬 수 있는 효과적인 수단이 될 수 있지만, 생태계 내의 다른 비표적 생물에 부정적인 영향을 줄 가능성 또한 있기 때문에 상업적인 재배에 앞서 이에 대한 충분한 연구가 이루어져야 한다. 본 연구에서는 배추좀나방내성 유전자변형 Bt (Cry1Ac1)양배추가 비표적 곤충인 복숭아혹진딧물에 미치는 영향을 알아보기 위한 기초적인 실험으로서 기주선택실험 및 성장실험을 실시하였다. 기주선택실험에서, 두 개체씩의 Bt 양배추와 모본 양배추에 각각 10마리의 유시 성충(alate virginoparae)을 접종하고, 사흘간 생식(reproduction) 기회를 제공한 후 생산한 약충의 마리수를 측정한 결과, Bt 양배추와 모본 양배추에 낳은 약충의 수가 각각 <TEX>$21.9{\pm}1.8$</TEX>와 <TEX>$22.5{\pm}2.2$</TEX>로 비슷하였다. 성장실험에서, 갓 태어난 무시 약충(apterous virginoparae)을 Bt 양배추 및 모본 양배추를 기주로 하여 키웠을 때, 성충이 될 때까지 걸린 시간은 Bt 양배추와 모본 양배추에서 각각 <TEX>$5.8{\pm}0.2$</TEX>, <TEX>$5.9{\pm}0.1$</TEX> 일(day)로 통계적으로 유의한 차이가 없었고, 개체군 생장률(rm) 또한 <TEX>$0.7{\pm}0.1$</TEX>, <TEX>$0.8{\pm}0.1$</TEX>로 유사하였다. 이상의 결과들로 볼때 Bt 양배추가 복숭아혹진딧물에 미치는 영향이 없거나 미미함을 알 수 있으나, 다양한 관점에서의 보완 연구가 더 필요하다. Transgenic crops that produce insecticidal toxins have a great potential for controlling target pest insects, but there is a growing concern about unintended influences on non-target species. In the present study, the preferences and performance of non-target green peach aphid, Myzus persicae (Sulzer), on transgenic cabbages (Brassica oleracea) that produce Bt toxin (Cry1Ac1) and untransformed control plants were investigated as a part of risk assessment. In a free-choice situation, the number of nymphs larviposited by 10 winged adults over 3 days was <TEX>$21.9{\pm}1.8$</TEX> and <TEX>$22.5{\pm}2.2$</TEX> on transgenic and the control plants, respectively, indicating that the aphids did not discriminate between the two types of plants. In a performance assay, the development time (D) and intrinsic rate of increase (rm) of wingless aphids reared on transgenic and control plants were also similar (D, <TEX>$5.8{\pm}0.2$</TEX> and <TEX>$5.9{\pm}0.1$</TEX> (days) and rm, <TEX>$0.7{\pm}0.1$</TEX> and <TEX>$0.8{\pm}0.1$</TEX>, for transgenic and control plants, respectively). These results suggest that M. persicae is not significantly affected by transgenic Bt cabbage.