Control Of Lepidopteran Pests Research Articles

Lynamicin B is a Potential Pesticide by Acting as a Lepidoptera-Exclusive Chitinase Inhibitor.

Insect group h chitinase is a promising target for designing non-target safe pesticides in that it is exclusively distributed in lepidopteran insects, over 80% of which are agricultural pests. In this work, lynamicin B was discovered to be an inhibitor of OfChi-h, the group h chitinase from the lepidopteran pest Ostrinia furnacalis. Lynamicin B was revealed to competitively inhibit OfChi-h with a Ki value of 8.76 μM and does not significantly inhibit other chitinases. The co-crystal structure of lynamicin B and OfChi-h revealed that the dichloroindolyl group of lynamicin B occupies an unexplored pocket below subsites +1 and +2 of the substrate-binding cleft, which is vital for its selectivity. Feeding experiments demonstrated that lynamicin B exhibited high insecticidal activities against other lepidopteran pests Mythimna separata and Spodoptera frugiperda besides O. furnacalis. Moreover, lynamicin B did not affect Trichogramma ostriniae, a natural enemy of O. furnacalis. This study provides a natural-derived potent pesticide for the control of lepidopteran pests, leaving its natural enemy unaffected.

Proteomic Analysis and Promoter Modification of Bacillus thuringiensis to Improve Insecticidal Vip3A Protein Production.

Insecticidal protein Vip3A secreted from B. thuringiensis is a potential biocontrol agent for control of lepidopteran pests. Under laboratory conditions, high albeit variable Vip3A production from the local isolate Bt294 was only obtained from a much enriched TB culture medium. Proteomic analysis and strain improvement were therefore performed to improve Vip3A production. Studies indicated that the buffer capacity, carbon source, and nitrogen source are critical to efficiently produce Vip3A. Medium with lower amounts of peptone and yeast extract (compared to TB), with an additional carbon source and phosphate buffer (LB*G medium) was found to give reasonable yields of Vip3A. Proteomic analysis revealed higher expression of proteins involved in glutamate and histidine biosynthesis in cells cultured in TB compared to LB about 58 and 33 times, respectively. Experiments confirmed that glutamate supplementation could increase Vip3A production. In addition, promoter substitution with that of cry3A increased Vip3A yields by about 20-30%. Overall, very high yields of Vip3A could be obtained by culturing Bt294 (Pcry3A-vip3Aa64) in LB*G medium with glutamate supplementation.

Managing Fall Armyworm in Africa: Can Bt Maize Sustainably Improve Control?

The recent invasion of Africa by fall armyworm, Spodoptera frugiperda, a lepidopteran pest of maize and other crops, has heightened concerns about food security for millions of smallholder farmers. Maize genetically engineered to produce insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) is a potentially useful tool for controlling fall armyworm and other lepidopteran pests of maize in Africa. In the Americas, however, fall armyworm rapidly evolved practical resistance to maize producing one Bt toxin (Cry1Ab or Cry1Fa). Also, aside from South Africa, Bt maize has not been approved for cultivation in Africa, where stakeholders in each nation will make decisions about its deployment. In the context of Africa, we address maize production and use; fall armyworm distribution, host range, and impact; fall armyworm control tactics other than Bt maize; and strategies to make Bt maize more sustainable and accessible to smallholders. We recommend mandated refuges of non-Bt maize or other non-Bt host plants of at least 50% of total maize hectares for single-toxin Bt maize and 20% for Bt maize producing two or more distinct toxins that are each highly effective against fall armyworm. The smallholder practices of planting more than one maize cultivar and intercropping maize with other fall armyworm host plants could facilitate compliance. We also propose creating and providing smallholder farmers access to Bt maize that produces four distinct Bt toxins encoded by linked genes in a single transgene cassette. Using this novel Bt maize as one component of integrated pest management could sustainably improve control of lepidopteran pests including fall armyworm.

Influence of the Color, Shape, and Size of the Clay Model on Arthropod Interactions in Turfgrass.

Many predatory arthropods occur naturally in turfgrass, and they provide adequate control of lepidopteran pests, such as fall armyworm, Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), and black cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae). Recording predation is challenging under field conditions because predators rarely leave any evidence. Clay models were successfully employed for studying predation, and this technique is underutilized in turfgrass. Little is known about whether the characteristics of clay models, such as color, shape, and size, influence arthropod interactions in turfgrass. To improve the utility of clay models in turfgrass, the influence of the color, shape, and size of clay models on arthropod interactions was studied by exposing clay models during daytime and nighttime in a turfgrass field. The results showed that arthropods interacted with clay models, and various types of impressions were recorded, including paired marks, scratches, cuts, and pricks. Although the color of the clay model had no significant effects on arthropod interactions during the night, significantly greater numbers of impressions were noticed on the blue and green models than on the yellow models during the daytime. The caterpillar-shaped models captured significantly greater densities of impressions than the beetle-shaped models. Additionally, the number of impressions significantly increased with an increase in the size of the model regardless of shape.

Tetrastichus howardi (Hymenoptera: Eulophidae): first report of parasitism in Oxydia vesulia (Lepidoptera: Geometridae).

The adaptation of native lepidopteran species to eucalyptus plantations reduces the productivity of this crop in Brazil. Oxydia vesulia Cramer (Lepidoptera: Geometridae) is a secondary pest, frequently reported in eucalyptus plantations with population outbreaks and economic damages. Methods of biological control of this pest may include the use of the exotic pupae endoparasitoid Tetrastichus howardi Olliff (Hymenoptera: Eulophidae), reported as efficient to controlling lepidopteran pests. The parasitism of O. vesulia caterpillars and pupae by T. howardi was evaluated under controlled conditions (25 ± 1 ºC, 60 ± 20% humidity and 12:12 h L:D). Each O. vesulia caterpillar or pupae was individually placed in a flat-bottom tube with 10 and 15 females of T. howardi for 48h, respectively. The parasitoids were removed after that period, the caterpillars were fed and the pupae were maintained until emergence of the parasitoid or formation of pupae and emergence of adults of this pest. The fourth-instar caterpillars of O. vesulia, after the parasitism period, were kept in pots with Eucalyptus urophylla leaves, changed daily until the end of the experiment. A total of 40% of the caterpillars died before the pre-pupae stage, 40% reached the pupae stage and died due to inadequate adult formation and 20% generated moths, but none adult parasitoid emerged from the caterpillars. All pupae of O. vesulia were parasitized and showed emergence of parasitoids. The parasitism of O. vesulia caterpillars and pupae by T. howardi shows the potential of this natural enemy for the integrated management of this defoliator pest in eucalyptus plantations.

Use of Light Trap for Controlling Cabbage Pests

Cabbage leaf caterpillars (Plutella xylostella L.) and cabbage head caterpillars (Crocidolomia binotalis Zell.) are key pests of cabbage in Indonesia. Crop loss due to both pests can reach as high as 50-100%. In general, the pests control done by the farmers is still based on the use of insecticides. Therefore, it is necessary to identify another method that is environmentally friendly. This study aimed at determining the effectiveness of the light trap in controlling P. xylostella and C. binotalis. The experiment was conducted at the Margahayu Experimental Garden, the Indonesian Vegetable Research Institute in Lembang (1,250 m asl.), from March to July 2018. The experiment was designed using the paired comparison with two treatments. The treatments tested were: (A) using light traps + control threshold and (B) without light traps + sprayed with insecticide twice a week. Each treatment consisted of six replications. The results showed that the use of light traps was able to suppress the population of P. xylostella and S. litura larvae and egg masses of C. binotalis. It also reduced the frequency of insecticide spray by 81.82% and insecticide costs by 77.61 %. Cabbage cultivation using a light trap could maintain cabbage yield equivalent to yield on the treatment used insecticides twice a week and gave more profitable than insecticide spray twice a week. Therefore, the use of a light trap for controlling lepidopteran pests in cabbage cultivation was properly adopted.

The implications of homozygous vip3Aa20- and cry1Ab-maize on Spodoptera frugiperda control

Historically, Bt maize hybrids have been produced with the Bt alleles in a hemizygous state. Homozygous Bt transgenes increase the expression of Bt proteins in plants; however, recent studies have only briefly explored the zygosity of Bt transgenes in maize hybrids and its effects on the control of lepidopteran pests. In this study, we investigated whether an additional allelic dose of the single Bt events Bt11 and MIR162, and a pyramided version (Bt11 + MIR162 + GA21) would impact Bt protein expression in leaves and increase the control of fall armyworm, Spodoptera frugiperda, in leaves and grains of near-isogenic maize hybrids. Our results revealed that homozygous Bt hybrids had higher Cry1Ab and Vip3Aa20 protein concentrations in leaves than their hemizygous versions. However, higher concentrations of Bt proteins in homozygous versions did not increase the control of S. frugiperda. Hybrids expressing Cry1Ab, hemizygous and homozygous for the transgene, had similar mortality of S. frugiperda fed on leaves and grains as the non-Bt near-isogenic version, likely due to resistance of the pest to Cry1Ab. High susceptibility to Vip3Aa20 caused all larvae to die on hemizygous and homozygous MIR162 leaves. Also, larvae that survived on Vip3Aa20 grains did not gain weight after four days of feeding, regardless of the Bt zygosity of Vip3Aa20-expressing grains. Additional implications of Bt zygosity in maize hybrids on insect resistance management strategies are discussed.

Plasticity in life features, parasitism and super-parasitism behavior of Bracon hebetor, an important natural enemy of Galleria mellonella and other lepidopteran host species.

The wasp, Bracon hebetor Say, is an important potential biocontrol agent of a wide range of lepidopteran insect species. The current study was subjected to compare these ectoparasitoid fitness traits on different host species belonging to the order Lepidoptera. Moreover, we determine the population dynamic with different host densities, sex ratio patterns, super-parasitism, longevity, paralysis success, and reproductive potential under laboratory conditions. Our results revealed that oviposition increased with an increase in host density, while the adult emergence and egg hatching were decreased due to the super-parasitism on host larvae. A higher male and female-biased population were observed when virgin and mated females offered fresh hosts. Adults' longevity was recorded more in females than males when kept only with bee honey + royal jelly + host larvae. The mean duration of egg-adult development was recorded higher on Galleria mellonella and lowest on Busseola fusca. The parasitization rate, super-parasitism, and cumulative fecundity of mated and virgin female wasps with different host species were observed higher on specific host Galleria mellonella while it was lower on Phthorimaea operculella. Furthermore, the parasitoids having mating experience preferred fresh, while the parasitoids' lack of mating experiences preferred paralyzed host under olfactometer test. Besides, this research has produced novel facts on the biology of parasitic wasp, B. hebetor that may guide the advancement of sustainable biological control programs to control lepidopteran pests.

Knockout of SldsRNase1 and SldsRNase2 revealed their function in dsRNA degradation and contribution to RNAi efficiency in the tobacco cutworm, Spodoptera litura

The application of RNA interference (RNAi) methods to control lepidopteran pests is difficult because of lower RNAi efficiency in these insects. Numerous studies concluded that dsRNA degrading nucleases (dsRNases) could be one of the factors involved in reducing RNAi efficiency in insects. The knockdown of genes coding for dsRNases is not successful due to inefficient RNAi in these insects. CRISPR/Cas9 system could help to knockout genes coding for dsRNases. Here, we knocked out two gut-specific dsRNase genes identified in the previous studies by using CRISPR/Cas9 system. The homozygous mutant strains containing knockout of one of the two dsRNases (SL1KO or SL2KO) and the double genes homozygous strain with knockout of both dsRNases (SL1SL2KO) showed 79.3%, 40.4% and 96.3% decrease in dsRNA-degrading activity, respectively. The nuclease activity in the gut fluid and the hemolymph was decreased by 83.2% and 23.3%, respectively, in SL1SL2KO strain as compared to the WT. Also, the level of fed dsRNA was almost 20 times higher in the SL1SL2KO strain than that in WT strain, but a similar dsRNA persistence time as detected in the hemolymph collected from SL1SL2KO and WT. Comparative analysis of RNAi response between SL1SL2KO and the WT strain showed that knockout of both dsRNases increased RNAi efficiency as the target gene mRNA levels were suppressed by feeding dsRNA to SL1SL2KO.

Improvement of host-induced gene silencing efficiency via polycistronic-tRNA-amiR expression for multiple target genes and characterization of RNAi mechanism in Mythimna separata.

SummaryHost‐induced gene silencing (HIGS) emerged as a new strategy for pest control. However, RNAi efficiency is reported to be low in Lepidoptera, which are composed of many important crop pests. To address this, we generated transgenic plants to develop HIGS effects in a maize pest, Mythimna separata (Lepidoptera, Noctuidae), by targeting chitinase encoding genes. More importantly, we developed an artificial microRNA (amiR) based PTA (polycistronic‐tRNA‐amiR) system for silencing multiple target genes. Compared with hpRNA (hairpin RNA), transgenic expression of a PTA cassette including an amiR for the gut‐specific dsRNA nuclease gene MsREase, resulted in improved knockdown efficiency and caused more pronounced developmental abnormalities in recipient insects. When target gene siRNAs were analysed after HIGS and direct dsRNA/siRNA feeding, common features such as sense polarity and siRNA hotspot regions were observed, however, they differed in siRNA transitivity and major 20‐24nt siRNA species. Core RNAi genes were identified in M. separata, and biochemical activities of MsAGO2, MsSID1 and MsDcr2 were confirmed by EMSA (electrophoretic mobility shift assay) and dsRNA cleavage assays, respectively. Taken together, we provide compelling evidence for the existence of the RNAi mechanism in M. separata by analysis of both siRNA signatures and RNAi machinery components, and the PTA system could potentially be useful for future RNAi control of lepidopteran pests.

Enhanced hydrolysis of β-cypermethrin caused by deletions in the glycin-rich region of carboxylesterase 001G from Helicoverpa armigera.

Carboxylesterase (CarE) is a major class of enzyme involved in the detoxification of toxic xenobiotics in various insect species. Previous work has shown that the carboxylesterase gene CarE001G found in Helicoverpa armigera is more active and can metabolize synthesized pyrethroids, such as β-cypermethrin, one of the commonly used commercial insecticides for lepidopteran pest control. In addition, CarE001G is very special as it has a very specific glycine-rich region located adjacent to its C-terminal. But whether mutations in this unique sequence can change the biochemistry and function of CarE001G are unknown. In this study, four variants of CarE001G with different deletions in the glycine-rich region were obtained and functionally expressed in Escherichia coli. The recombinant proteins were purified and confirmed by Western blot and mass spectrometry analyses. These mutant enzymes showed high catalytic efficiency toward the model substrate α-naphthyl acetate. Inhibition study showed that β-cypermethrin had relatively strong inhibition on CarE activities. In vitro metabolism assay showed that the mutant enzymes significantly enhanced their metabolic activities toward β-cypermethrin with specific activities between 4.0 and 5.6 nmol L-1 min-1 mg-1 protein. Molecular docking analyses consistently demonstrated that deletion mutations in the glycine-rich region may facilitate the anchoring of the β-cypermethrin molecule in the active binding pocket of the mutant enzymes. The data show that deletion mutations can cause qualitative change in the capacity of CarEs in the detoxification of β-cypermethrin. This indicates that deletion mutations in the glycine-rich region may have the potential to cause synthesized pyrethroid (SP) resistance in H. armigera in the future. © 2020 Society of Chemical Industry.

Toxicity and sublethal effects of chlorantraniliprole and indoxacarb on Spodoptera littoralis (Lepidoptera: Noctuidae)

Chlorantraniliprole and indoxacarb insecticides exhibit good efficiency for control lepidopteran pests. The current study is a comprehensive analysis of the effect of lethal and sublethal concentrations of these insecticides on Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) by using the leaf dipping technique. The LC50 values ranged from 0.06 to 1.07 mg/L, and 0.005 to 0.81 mg/L for chlorantraniliprole and indoxacarb, respectively. Our results showed that the treatment of the 2nd instar larvae with LC50 concentrations of these insecticides significantly increased the length of larval and pupal duration as well as pupal weight in most cases. While, no significant differences have been found in the percentage of hatchability except for LC50 equivalent of indoxacarb. Female behavior regarding calling activity decreased by 50–60% following exposure to the LC50 concentration of both insecticides. Gas chromatography analysis results showed that both insecticides lowered pheromone titer except at chlorantraniliprole LC50 equivalent for (Z,E)-9,12-tetradecadien-l-ol acetate, and indoxacarb LC10 equivalent for (Z)-9-tetradecenyl acetate. Additionally, the activity of mixed-function oxidases and glutathione S-transferase were elevated relative to control. The carboxylesterase activity significantly increased when assayed with both chlorantraniliprole concentrations and indoxacarb LC10 equivalent. These results indicate that chlorantraniliprole and indoxacarb could be effective for S. littoralis control.

Evaluation of an Experimental Foliar Product for Control of Lepidopteran Pests on Cabbage in Wisconsin, 2020

Evaluation of an Experimental Foliar Product for Control of Lepidopteran Pests on Cabbage in Wisconsin, 2020

DNA Damage in Liver Cells of the Tilapia Fish Oreochromis mossambicus Larva Induced by the Insecticide Cyantraniliprole at Sublethal Doses During Chronic Exposure.

Cyantraniliprole can effectively control lepidopteran pests and has been used all over the world. In general, the risk of cyantraniliprole seems low for fish, but the toxicity selectivity among different fish species was not clear. Here, we present the methods for the acute toxicity and chronic effects of cyantraniliprole by using juvenile tilapia (Oreochromis mossambicus). Based on this test, 96h LC50 of cyantraniliprole to tilapia was 38.0mg/L. After exposed for 28days, specific growth rates of the blank control, solution control, and the treatments of 0.037, 0.37 and 3.7mg/L of cyantraniliprole were 1.14, 0.95, 0.93, 0.82, and 0.70% per day, respectively. The results of micronucleus experiment and single cell gel electrophoresis showed that cyantraniliprole damaged DNA in liver cells of tilapia larvae. Quantitative PCR results showed that cyantraniliprole could induce the upregulation of Rpa 3 that is responsible for the DNA repair. The significant downregulation of Chk 2 gene was related to p53 pathway. It is therefore proposed that cyantraniliprole causes DNA damage in liver cells of tilapia and activates DNA damage and repair pathways.

Detection of ryanodine receptor target-site mutations in diamide insecticide-resistant Spodoptera frugiperda in China.

Spodoptera frugiperda (Lepidoptera: Noctuidae) is a widely distributed pest of corn. Since it invaded China in 2018, it has caused serious damage to local corn production. Chlorantraniliprole, an anthranilic diamide insecticide, has been widely used to control lepidopteran pests. Tetrachloropyramid is a new allosteric modulator insecticide developed based on chlorantraniliprole, so it has a similar mechanism and insecticidal effect. In this study, we investigated resistance levels to chlorantraniliprole and tetrachloropyramid in S. frugiperda from 13 populations in China. Among the populations tested, the relative highest resistance to chlorantraniliprole occurred in the Guangzhou population, and the most susceptible to chlorantraniliprole was found in the Wuhan population. The lethal dosage LD50 value of the Guangzhou population against chlorantraniliprole was 27.8-fold higher than that of the Wuhan population. Minimal differences were observed among S. frugiperda populations in terms of sensitivity to tetrachloropyramid. Heterozygous mutations at the I4734 site of the ryanodine receptor (RyR) were found, while no mutations were found in the G4891 site. The mutations were detected in only two of the 786 individuals analyzed, one from the Qinzhou population and other from the Anshun population (frequency below 2% in both cases). There were no significant differences in the expression levels of RyR between Guangzhou and Wuhan populations. In summary, our results indicate that: (i) S. frugiperda has low resistance levels to diamide insecticides in China; and (ii) the differences in relative resistance among the 13 populations analyzed are not caused by the mutations in RyR or the expression of RyR.

Characterization, expression patterns, and transcriptional responses of three core RNA interference pathway genes from Ostrinia nubilalis

RNA interference (RNAi) is commonly used in the laboratory to analyze gene function, and RNAi-based pest management strategies are now being employed. Unfortunately, RNAi is hindered by inefficient and highly-variable results when different insects are targeted, especially lepidopterans, such as the European corn borer (ECB), Ostrinia nubilalis (Lepidoptera: Crambidae). Previous efforts to achieve RNAi-mediated gene suppression in ECB revealed low RNAi efficiency with both double-stranded RNA (dsRNA) injection and ingestion. One mechanism that can affect RNAi efficiency in insects is the expression and function of core RNAi pathway genes, such as those encoding Argonaut 2 (Ago2), Dicer 2 (Dcr2), and a dsRNA binding protein (R2D2). To determine if deficiencies in these core RNAi pathway genes contribute to low RNAi efficiency in ECB, full-length complementary DNAs encoding OnAgo2, OnDcr2, and OnR2D2 were cloned, sequenced, and characterized. A comparison of domain architecture suggested that all three predicted proteins contained the necessary domains to function. However, a comparison of evolutionary distances revealed potentially important variations in the first RNase III domain of OnDcr2, the double-stranded RNA binding domains of OnR2D2, and both the PAZ and PIWI domains of OnAgo2, which may indicate functional differences in enzymatic activity between species. Expression analysis indicated that transcripts for all three genes were expressed in all developmental stages and tissues investigated. Interestingly, the introduction of non-target dsRNA into ECB second-instar larvae via microinjection did not affect OnAgo2, OnDcr2, or OnR2D2 expression. In contrast, ingestion of the same dsRNAs resulted in upregulation of OnDcr2 but downregulation of OnR2D2. The unexpected transcriptional responses of the core machinery and the divergence in amino-acid sequence between specific domains in each core RNAi protein may possibly contribute to low RNAi efficiency in ECB. Understanding the contributions of different RNAi pathway components is critical to adapting this technology for use in controlling lepidopteran pests that exhibit low RNAi efficiency.

Effectiveness of Trichogramma pretiosum in controlling lepidopterous pests of soybean crops

Controlling lepidopteran pests in soybean in Uruguay usually involves the application of chemical insecticides with risks to health and the environment. As part of an inundative biological control program using Trichogramma pretiosum, a plot trial at three sites located in the department of Soriano (Uruguay), in the 2019-2020 growing season, compared this conventional practice with different doses of the egg parasitoid, number of release capsules per hectare, different number of releases in the culture cycle and ground and aerial releases (with or without release capsules). Using the cloth method, the number of larvae per linear meter and the defoliation percentage were evaluated over 6 weekly samplings. Although the best results were obtained with the application of chemical insecticides, two releases of T. pretiosum by terrestrial methods, 20 days apart, or 4 weekly applications by means of a drone, reached the best results below the thresholds of sanitary intervention, both options with 200,000 parasitoids per hectare. This biological tool can differentiate and value Uruguayan agricultural production.

Bacillus thuringiensis Effect on the Vegetative Development of Cotton Plants and the Biocontrol of Spodoptera frugiperda

Bacillus thuringiensis (Bt) is used worldwide as a tool for controlling lepidopteran pests. Recent studies have demonstrated the possibility of its use as an endophytic organism, controlling insects and promoting plant growth. In this aspect, strains of Bt toxic to lepidopteran pests were inoculated both onto seeds and into cotton plants and were assessed for effectiveness in controlling Spodoptera frugiperda and its effect on promoting plant growth. It was observed that the results obtained from the interaction between the Bt strains (S1450 HD-1, S1905, S2122, S2124) and the cotton genotypes (BRS 8H, BRS Aroeira and BRS 286) showed different growth responses. The results also showed that all the strains may not be suitable to explore the biological control mechanism without undermining plant health. Therefore, the strain S2122, the BRS 8H genotype and seed inoculation were selected to continue the tests by using two concentrations of the bacterium. The results of Bt strain inoculation in seeds and into cotton plants showed that, although plant height, number of leaves, and development stage were influenced by Bt inoculation, overall, there was no significant improvement in the plant growth. The plants that were inoculated with Bt also interfered in the weight of Spodoptera frugiperda, however, did not cause the pest mortality. The collected results suggest that there is a close relationship between the Bt strain and the cotton crop and that colonizing mechanism of the bacterium can be useful in situations that there is an inefficiency of the control measures, since the endophytic Bt makes the pest more susceptible to be controlled by other practices, improving management effectiveness.

Contact toxicity and antifeedant activity of binary mixtures of piperine and β-asarone against the crop pests, Spodoptera litura and Mythimna separata (Lepidoptera: Noctuidae)

Plants produce arrays of secondary metabolites that act synergistically to deter and/or intoxicate herbivores. In this study, we evaluated the toxicity of piperine and β-asarone, individually and in binary mixtures, to examine their synergistic effects against larvae of two generalist herbivores, Spodoptera litura and Mythimna separata. Acute toxicity of piperine after topical application was lower than that of β-asarone for second instar larvae of both S. litura and M. separata (LD50 53.65 and 7.52 µg/larva, respectively, after 24 h). However, all mixtures produced synergistic, antifeedant effects. Mixtures of either 56.65 or 7.52 µg/larva of piperine + 18 µg/larva of β-asarone were highly synergistic in term of their acute toxicity (synergistic factor 11 and 44 for S. litura and M. separata, respectively). The more concentrated mixture also had the strongest antifeedant effects when presented on artificial diet to both species, S. litura and M. separata (56.64% and 62.30% at 24 h, respectively). Our results suggest that the combination of piperine and β-asarone is a greater deterrent than either pure compound alone. Use of this mixture may provide better crop protection rather than that offered by single compounds for controlling lepidopteran pests.

Transcriptomic analyses of chemosensory genes in Trichogramma japonicum (Hymenoptera: Trichogrammatidae)

Insects perceive dangerous or attractive chemicals in the environment (such as the presence of predators, food or mates) through their olfaction and gustation. This leads to host searching, mate finding and other behaviors that are critical for insect survival. These vital activities are mediated by many chemosensory receptor proteins, including odorant receptors (ORs), gustatory receptors (GRs) and ionotropic receptors (IRs). Trichogramma japonicum Ashmead (Hymenoptera: Trichogrammatidae) is a commonly used egg parasitoid for controlling lepidopteran pests in rice fields. To reveal the roles of its olfactory and gustatory systems in biological control, we systematically analyzed major chemosensory receptor genes from T. japonicum. Through transcriptomic analyses of male and female heads, we found that the differentially expressed genes (DEGs) were mainly related to chemosensory functions, and there were more chemosensory-related genes expressed in female heads than male heads, which may be related to the need for females to search for their hosts or sense male pheromone. Furthermore, we identified 66 chemosensory receptor genes, including 51 ORs, seven IRs and eight GRs, that were most closely relate to those of other hymenopteran species according to the results of both Blast best-hit and phylogenetic analyses. The tissue expression profile showed that 65 of the 66 chemosensory receptors were highly expressed in the heads, suggesting their putative roles in olfaction and gustation. In addition, the sex-specific expression patterns suggested their potential functions in host-seeking or mate sensing behaviors. This study may provide base for further understanding the olfactory and gustatory systems of T. japonicum and increasing its efficiency in pest control in the future.