Ontogenetic morphological changes of the venom apparatus in 4 eupelmid egg parasitoids.

Parasitoid wasps, notably egg parasitoids of the family Eupelmidae (Hymenoptera: Chalcidoidea), a key natural enemy of insect pests, offer a sustainable approach to pest management in agriculture. This study investigated the venom apparatus's developmental dynamics across 4 species of eupelmid egg parasitoids: Anastatus. japonicus, Anastatus fulloi, Mesocomys trabalae and Mesocomys albitarsis. A comprehensive anatomical investigation revealed differences in the dimensions of the venom apparatus across different developmental stages in adult females. We found that the venom apparatus of these 4 studied species consists of a venom gland and a reservoir with an associated Dufour's gland. As the length of post-emergence increases, a significant enlargement in the venom apparatus is evident across all the studied parasitoid species. Notably, M. albitarsis consistently exhibites the shortest venom gland length, whereas that of A. fulloi is the longest among the observed species. At the high day age, the width of venom glands of the 2 Mesocomys species surpasses those of the Anastatus species; for the volume of the venom reservoir, there is a steady increase in all 4 species before the age of 6­7 days, with a decline on 8th day, especially for A. japonicus. This research provided new insights into the developmental trajectories of venom apparatus in eupelmid egg parasitoids and the potential impact of venom potency on their success.

Comparative genomics reveals evolutionary drivers of the dietary shift in Hemiptera.

Hemiptera insects exhibit a close relationship to plants and demonstrate a diverse range of dietary preferences, encompassing phytophagy as the predominant feeding habit while a minority engages in carnivorous or haematophagous behaviour. To counteract the challenges posed by phytophagous insects, plants have developed an array of toxic compounds, causing significant evolutionary selection pressure on these insects. In this study, we employed a comparative genomics approach to analyse the expansion and contraction of gene families specific to phytophagous insect lineages, along with their adaptive evolutionary traits, utilising representative species from the Hemiptera order. Our investigation revealed substantial expansions of gene families within the phytophagous lineages, especially in the Pentatomomorpha branch represented by Oncopeltus fasciatus and Riptortus pedestris. Notably, these expansions of gene families encoding enzymes are potentially involved in hemipteran-plant interactions. Moreover, the adaptive evolutionary analysis of these lineages revealed a higher prevalence of adaptively evolved genes in the Pentatomomorpha branch. The observed branch-specific gene expansions and adaptive evolution likely contribute significantly to the diversification of species within Hemiptera. These results help enhance our understanding of the genomic characteristics of the evolution of different feeding habits in hemipteran insects.

Parasitic behaviour and developmental morphology of Anastatus japonicus reared on the factitious host Antheraea pernyi.

The egg parasitoid Anastatus japonicus is a key natural enemy in the biological control of various agricultural and forestry pests. It is particularly used against the brown marmorated stink bug Halyomorpha halys and the emerging defoliator pest Caligula japonica in East Asia. It has been proved that the eggs of Antheraea pernyi can be used as a factitious host for the mass production of A. japonicus. This study systematically documented the parasitic behaviour and developmental morphology exhibited by A. japonicus on the eggs of A. pernyi. The parasitic behaviour of A. japonicus encompassed ten steps including searching, antennation, locating, digging, probing, detecting, oviposition, host-feeding, grooming, and resting. Oviposition, in particular, was observed to occur in three stages, with the parasitoids releasing eggs during the second stage when the body remained relatively static. Among all the steps of parasitic behaviour, probing accounted for the longest time, constituting 33.1% of the whole time. It was followed by digging (19.3%), oviposition (18.5%), antennation (9.6%), detecting (7.4%), and the remaining steps, each occupying less than 5.0% of the total event time. The pre-emergence of adult A. japonicus involves four stages: egg (0 to 2nd day), larva (3rd to 9th day), pre-pupa (10th to 13th day), pupa (14th to 22nd day), and subsequent development into an adult. Typically, it takes 25.60 ± 0.30 days to develop from an egg to an adult at 25℃. This information increases the understanding of the biology of A. japonicus and may provide a reference for optimising reproductive devices.

Heavy metal exposure reduces larval gut microbiota diversity of the rice striped stem borer, Chilo suppressalis.

Cadmium (Cd), a widely distributed environmental pollutant in agroecosystems, causes negative effects on crops and herbivores through bottom-up processes. The gut microbial community of an insect can play a critical role in response to metal stress. To understand how microbiota affect the stress responses of organisms to heavy metals in agroecosystems, we initially used 16S rRNA sequencing to characterize the larval gut microbiota of Chilo suppressalis, an important agricultural pest, exposed to a diet containing Cd. The species richness, diversity, and composition of the gut microbial community was then analyzed. Results revealed that while the richness (Chao1 and ACE) of gut microbiota in larvae exposed to Cd was not significantly affected, diversity (Shannon and Simpson) was reduced due to changes in species distribution and relative abundance. Overall, the most abundant genus was Enterococcus, while the abundance of the genera Micrococcaceae and Faecalibaculum in the control significantly superior to that in Cd-exposed pests. Phylogenetic investigation of microbial communities by the reconstruction of unobserved states (PICRUSt) showed that the intestinal microorganisms appear to participate in 34 pathways, especially those used in environmental information processing and the metabolism of the organism. This study suggests that the gut microbiota of C. suppressalis are significantly impacted by Cd exposure and highlights the importance of the gut microbiome in host stress responses and negative effects of Cd pollution in agroecosystems.

Comparison of the biology of Frankliniella intonsa and Megalurothrips usitatus on cowpea pods under natural regimes through an age-stage, two-sex life table approach.

Two thrips, Megalurothrips usitatus (Bagnall) and Frankliniella intonsa (Trybom) are major pests of cowpea in South China. To realistically compare the growth, development and reproductive characteristics of these two thrips species, we compared their age-stage, two-sex life tables on cowpea pods under summer and winter natural environmental regimes. The results showed that the total preadult period of M. usitatus was 8.09 days, which was significantly longer than that of F. intonsa (7.06 days), while the adult female longevity of M. usitatus (21.14 days) was significantly shorter than that of F. intonsa (25.77 days). Significant differences were showed in male adult longevity (10.68 days for F. intonsa and 16.95 days for M. usitatus) and the female ratio of offspring (0.67 for F. intonsa and 0.51 for M. usitatus), and the total preadult period of M. usitatus (16.20 days) was significantly longer than that of F. intonsa (13.66 days) in the winter regime. The net reproductive rate (summer: R0 = 85.62, winter: R0 = 105.22), intrinsic rate of increase (summer: r = 0.3020 day-1, winter: r = 0.2115 day-1), finite rate of increase (summer: λ = 1.3526 day-1, winter: λ = 1.2356 day-1) and gross reproduction rate (summer: GRR = 139.34, winter: GRR = 159.88) of F. intonsa were higher than those of M. usitatus (summer: R0 = 82.91, r = 0.2741, λ = 1.3155, GRR = 135.71; winter: R0 = 80.62, r = 0.1672, λ = 1.1820, GRR = 131.26), and the mean generation times (summer: T = 14.73 days, winter: T = 22.01 days) of F. intonsa were significantly shorter than those of M. usitatus (summer: T = 16.11 days, winter: T = 26.25 days). These results may contribute to a better understanding of the bioecology of different thrips species, especially the interspecific competition between two economically important cowpea thrips with the same ecological niche in a changing environment.

Odorant-Binding Proteins and Chemosensory Proteins in Spodoptera frugiperda: From Genome-Wide Identification and Developmental Stage-Related Expression Analysis to the Perception of Host Plant Odors, Sex Pheromones, and Insecticides.

Spodoptera frugiperda is a worldwide generalist pest with remarkable adaptations to environments and stresses, including developmental stage-related behavioral and physiological adaptations, such as diverse feeding preferences, mate seeking, and pesticide resistance. Insects' odorant-binding proteins (OBPs) and chemosensory proteins (CSPs) are essential for the chemical recognition during behavioral responses or other physiological processes. The genome-wide identification and the gene expression patterns of all these identified OBPs and CSPs across developmental stage-related S. frugiperda have not been reported. Here, we screened for genome-wide SfruOBPs and SfruCSPs, and analyzed the gene expression patterns of SfruOBPs and SfruCSPs repertoires across all developmental stages and sexes. We found 33 OBPs and 22 CSPs in the S. frugiperda genome. The majority of the SfruOBP genes were most highly expressed in the adult male or female stages, while more SfruCSP genes were highly expressed in the larval or egg stages, indicating their function complementation. The gene expression patterns of SfruOBPs and SfruCSPs revealed strong correlations with their respective phylogenic trees, indicating a correlation between function and evolution. In addition, we analyzed the chemical-competitive binding of a widely expressed protein, SfruOBP31, to host plant odorants, sex pheromones, and insecticides. Further ligands binding assay revealed a broad functional related binding spectrum of SfruOBP31 to host plant odorants, sex pheromones, and insecticides, suggesting its potential function in food, mate seeking, and pesticide resistance. These results provide guidance for future research on the development of behavioral regulators of S. frugiperda or other environmentally friendly pest-control strategies.

Melanin Synthesis Pathway Interruption: CRISPR/Cas9-mediated Knockout of dopa decarboxylase (DDC) in Harmonia axyridis (Coleoptera: Coccinellidae).

CRISPR/Cas9 technology is a very powerful genome editing tool and has been used in many insect species for functional genomics studies through targeted gene mutagenesis. Here, we successfully established CRISPR/Cas9 research platform in Asian multi-colored ladybird beetle, Harmonia axyridis, an important natural enemy in biological control. In this study, one pivotal gene dopa decarboxylase (DDC) in melanin synthesis was targeted by CRISPR/Cas9 to generate mutants in H. axyridis by CRISPR/Cas9 technology. Our results showed that injection of single guide RNA of the DDC and Cas9 protein into preblastoderm eggs induced one insertion and four deletion (indels) mutant H. axyridis. Mutations of HaDDC gene generated 25% mutant rate with melanin missing phenotype in larva, pupa,l and adult stage. The predation ability of the fourth instar larvae has no significant difference between wild (control) and mutant H. axyridis (G0), while these mutant fourth instar larvae had longer developmental period than that of the wild type. Consequently, the total predation of the fourth instar larvae was significantly increased in H. axyridis mutants comparing with the wild type. These results indicated that the success of CRISPR/Cas9 gene editing in H. axyridis. The gene editing platform in H. axyridis would facilitate the gene function research and promote special strain of predatory ladybird beetle generation.

Biological Control with Trichogramma in China: History, Present Status, and Perspectives.

Trichogramma species make up one of the most commonly used groups of natural enemies for biological control programs worldwide. Given the major successes in using Trichogramma to control economically important lepidopterous pests on agricultural crops in China, the biology and ecology of these wasps have been intensively studied to identify traits that contribute to successful biological control. Since the 1960s, improved mass production of Trichogramma and better augmentative release methods to suppress agricultural pests have been achieved. We review the history of research and development; current knowledge on biodiversity and bio-ecology of the species used; and achievements in mass-rearing methods, release strategies, and current large-scale applications in China. In addition, we discuss potential issues and challenges for Trichogramma research and applications in the future.

Trophic transfer and toxicity of heavy metals from dengue mosquito Aedes aegypti to predator dragonfly Tramea cophysa.

Heavy metal pollution in aquatic habitats can be detrimental to both prey and predators in a food web. To investigate the potential for bio-transfer and bioaccumulation of heavy metals between specific trophic levels, 3rd instar larvae of Aedes aegypti were exposed to mercury (Hg), lead (Pb), cadmium (Cd), copper (Cu), and zinc (Zn) for three consecutive generations and fed to dragonfly (Tramea cophysa) nymphs. Exposure to Hg caused the highest mortality in A. aegypti larvae and T. cophysa nymphs. Bioaccumulation and life-history parameters of A. aegypti, including egg hatching time, larval and pupal duration, male and female life span, and fecundity, were also evaluated after metals exposure. All life-history parameters except larval duration were significantly affected by heavy metal treatments. Bioaccumulation of metals in A. aegypti larvae and adults gradually and significantly increased from 1st to 3rd generation. To the best of our knowledge, this is the first study describing the acute toxicity of heavy metals to mosquitoes. Our study shows that heavy metals cause dietary toxicity to an aquatic predator, dragonfly, via trophic transfer, which could have considerable consequences on aquatic ecosystems.

Toxicological risk assessment of some commonly used insecticides on Cotesia flavipes, a larval parasitoid of the spotted stem borer Chilo partellus.

Cotesia flavipes Cameron is an important larval parasitoid exploited for the control of the spotted stem borer, Chilo partellus (Swinhoe). Several studies have evaluated the toxic effects of insecticides on C. partellus, however, little is known about non-target effects of insecticides on this parasitoid, when used to control C. partellus. This laboratory study evaluated the lethal and sublethal effects of twelve insecticides on C. flavipes. Residual toxicity tests showed that organophosphates (chlorpyrifos, triazophos and profenofos) exhibited highest contact toxicity to C. flavipes adults with a LC50 range from 0.63 to 1.05 mg a.i/l, while neonicotinoids (nitenpyram, acetamiprid and imidacloprid) were less toxic to C. flavipes with a LC50 range from 1.27 to 139.48 mg a.i/l. Sugar-insecticide feeding bioassays showed that organophosphates, pyrethroids (cypermethrin, bifenthrin and lambda-cyhalothrin) and carbamates (thiodicarb, carbaryl and methomyl) were highly toxic to C. flavipes adults and caused 100% mortality at 48 h of exposure, while imidacloprid caused 66% mortality at 48 h of exposure. Risk quotient analysis showed that among all tested insecticides, imidacloprid and acetamiprid were less toxic to C. flavipes adults with a risk quotient value of 0.88 and 1.6, respectively. Furthermore, exposure of immature C. flavipes through their host bodies significantly decreased the parasitism rate at their F1 and F2 generations. Risk quotient analysis of insecticides indicated that imidacloprid and acetamiprid were the least toxic to C. flavipes. This study provides important information that will be used in incorporating the most suitable insecticides in integrated pest management programs with reduced negative impacts on non-target beneficial arthropods.

Identification of Serratia marcescens isolated from Antheraea pernyi eggs and determination of bacterial pathogenicity and transmission pathway.

The Chinese oak silkworm, Antheraea pernyi, is an important alternate host for mass production of Trichogramma parasitoids, which play a vital role in the biological control of lepidopterous pests in China. The quality of A. pernyi eggs is particularly important for mass production of these parasitoids. In this study, a pathogenic bacterium, isolated and purified from A. pernyi eggs that had turned gray in color, was identified as Serratia marcescens. We used morphology, biochemistry and 16S rDNA analysis to characterize the strain, which was named "APE strain". Serratia marcescens APE strain was determined to be the causal bacterium associated with the disease in the eggs, verified by a test based on Koch's Postulates. We tested the pathogenicity of S. marcescens APE strain on A. pernyi eggs; the percentage of diseased (gray) eggs reached 57.78% when uninfected eggs were exposed to a concentration of 1 × 109 cfu/mL bacterial suspension for 7 h. S. marcescens was transmitted mechanically by Trichogramma parasitoids. The transmission rate was 25.56%. In a horizontal transmission test, the highest percentage of uninfected eggs that developed infections was 51.43% after being treated with contents of diseased eggs for 12 h. In a vertical transmission test, the number of infected eggs per treated adult female was 63.8-92.3 after treatment with different S. marcescens concentrations, significantly lower than the 304.3 eggs per female in the control group. Furthermore, the percentage of infected (gray) eggs produced by adult moths exposed to bacteria in the larval stage was 80.5-85.3%.

Molecular and Potential Regulatory Mechanisms of Melanin Synthesis in Harmonia axyridis.

Melanization is a common phenomenon in insects, and melanin synthesis is a conserved physiological process that occurs in epidermal cells. Moreover, a comprehensive understanding of the mechanisms of melanin synthesis influencing insect pigmentation are well-suited for investigating phenotype variation. The Asian multi-colored (Harlequin) ladybird beetle, Harmonia axyridis, exhibits intraspecific polymorphism based on relative levels of melanization. However, the specific characteristics of melanin synthesis in H. axyridis remains elusive. In this study, we performed gene-silencing analysis of the pivotal inverting enzyme, tyrosine hydroxylase (TH), and DOPA decarboxylase (DDC) in the tyrosine metabolism pathway to investigate the molecular and regulatory mechanism of melanin synthesis in H. axyridis. Using RNAi of TH and DDC genes in fourth instar larvae, we demonstrated that dopamine melanin was the primary contributor to the overall body melanization of H. axyridis. Furthermore, our study provides the first conclusive evidence that dopamine serves as a melanin precursor for synthesis in the early pupal stage. According to transcription factor Pannier, which is essential for the formation of melanic color on the elytra in H. axyridis, we further demonstrated that suppression of HaPnr can significantly decrease expression levels of HaTH and HaDDC. These results in their entirety lead to the conclusion that transcription factor Pannier can regulate dopamine melanin synthesis in the dorsal elytral epidermis of H. axyridis.

Parasitism and Suitability of Different Egg Ages of the Leguminivora glycinivorella (Lepidoptera: Tortricidae) for Three Indigenous Trichogramma Species.

Pod borers are economically important soybean pests in temperate and tropical regions. However, the biological control of these pests using their natural insect enemies has been poorly studied to date. Indigenous natural populations of three Trichogramma (Hymenoptera: Trichogrammatidae) species, Trichogramma chilonis Ishii, Trichogramma ostriniae Pang & Chen, and Trichogramma leucaniae Pang & Chen, were collected from Leguminivora glycinivorella (Matsumura) (Lepidoptera: Tortricidae) eggs in soybean fields in China. In this study, we compare the parasitic capacities and suitabilities of three indigenous Trichogramma species on L. glycinivorella eggs at various ages. Host eggs of all ages were accepted by T. chilonis, T. ostriniae, and T. leucaniae. T. chilonis tended to parasitize 0-2-d-old eggs more than 3-4-d-old eggs. There were no significant differences in parasitism between the 0-2-d-old eggs and the 1-4-d-old eggs for T. ostriniae and T. leucaniae. For eggs at various ages, T. chilonis parasitized the smallest number of eggs, while T. leucaniae and T. ostriniae exhibited similar parasitic capacities. With 0-d-old host eggs, T. ostriniae developed over the longest time period (8.7 d), and T. leucaniae produced the most female progeny (87.9%). Both T. leucaniae and T. ostriniae had similar developmental times, survival rates and percentages of female progeny with 1-3-d-old eggs. These results show that T. leucaniae can parasitize host eggs at varying ages with the best development and suggest that it may be a valuable biological control agent for soybean pod borers.

Development, Survival, and Reproduction of Megacopta cribraria (Heteroptera: Plataspidae) at Different Constant Temperatures.

The plataspid Megacopta cribraria (F.), an economic pest of soybeans, Glycine max (L.) Merrill, in Asia recently invaded North America and has become not only an important pest of soybean but also a nuisance pest. Although much is reported about M. cribraria in its native and invasive range, little information has been documented on the effect of temperatures on its development, longevity, and reproduction. We evaluated the influence of five constant temperatures (17-33°C) on the development, survival, fecundity, and population growth of M. cribraria in the laboratory. The developmental time for egg and nymph stages was shortened significantly with increasing temperature. The developmental time from egg to adult emergence was 114.81, 76.26, 44.54, and 38.54 d at 17, 21, 25, and 29°C, respectively. The nymphs of M. cribraria could not complete full development at a constant 33°C. The developmental threshold temperature estimated for egg to adult was 14.25°C, with a thermal constant of 849.56 degree-days. Females had the longest preoviposition period at 21°C (54.33 d), and the preoviposition period was shortened significantly as the temperature increased. Females had the longest oviposition period (35.33 d) and the highest fecundity (159.67 eggs per female) at 25°C and did not lay any eggs at 17°C. Female longevity was found to be shortest (44.0 d) at 29°C, and similar (75.67-81.50 d) at 17-25°C. The population trend index of M. cribraria was the highest (46.47) at 25°C, followed by 29°C (10.84) and 21°C (6.70). The results will be useful for predicting the phenology and population dynamics of M. cribraria and will provide some biological information on the invasive species in its nonnative range.

Effects of rearing host species on the host-feeding capacity and parasitism of the whitefly parasitoid Encarsia formosa.

Parasitoids of the Encarsia genus (Hymenoptera: Aphelinidae) are important biological control agents against whiteflies. Some of the species in this genus not only parasitize their hosts, but also kill them through host feeding. The whitefly parasitoid, Encarsia formosa Gahan, was examined to determine whether the rearing host species affects its subsequent host-feeding capacity and parasitism. E. formosa wasps were reared on Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae) and Bemisia tabaci (Gennadius) 'Q', and their subsequent host-feeding capacity and parasitism of T. vaporariorum and B. tabaci were examined. E. formosa reared on T. vaporariorum were significantly larger in body size than those reared on B. tabaci, but these wasps killed a similar number of whitefly nymphs by host feeding when they attacked the same host species on which they were reared. Regardless of the species on which it was reared, E. formosa fed significantly more on the B. tabaci nymphs than on the T. vaporariorum nymphs. The number of whitefly nymphs parasitized by E. formosa differed between the wasps reared on T. vaporariorum and those reared on B. tabaci depending on which whitefly species was offered as a host. In addition, the wasps reared on T. vaporariorum parasitized significantly more on T. vaporariorum than those reared on B. tabaci. The wasps reared on B. tabaci, however, parasitized similar numbers of whiteflies of both host species. The results indicated that the host-feeding capacity of E. formosa was affected more by the host species attacked than by the rearing host species, but the parasitism was affected by the host species attacked and the rearing host species. Generally, E. formosa reared on T. vaporariorum killed more T. vaporariorum nymphs by parasitism and host feeding than those reared on B. tabaci. Additionally, a similar number of B. tabaci nymphs were killed by parasitism and host feeding regardless of the rearing host species. Currently coexistence of B. tabaci and T. vaporariorum on vegetable crops usually occurs in some areas; our results may provide helpful information on using mass-reared parasitoids against mixed whitefly infestations in biological control programs.

Dual Effects of Cold Storage and Stored Host Eggs of Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) on the Reproductive Capacity of Telenomus remus Nixon (Hymenoptera: Scelionidae).

Spodoptera frugiperda is the preferred host of the parasitoid Telenomus remus. Cold storage can preserve a sufficient quantity of parasitoids and their hosts in a laboratory colony for mass release. First, the effects of cold storage on the reproductive capacity of T. remus reared on non-stored S. frugiperda eggs and the hatching rate of unparasitized S. frugiperda eggs were investigated. Further, the dual effects of cold storage and stored S. frugiperda eggs on the reproductive capacity of T. remus were studied to determine the optimal storage conditions and the maximal shelf life for both the host and the parasitoid. The emergence rate, the number of adults produced, and the female proportion of T. remus were affected by cold storage factors. Pupae stored at 13 °C for 15 days is optimum for T. remus reared on non-stored S. frugiperda eggs. Spodoptera frugiperda eggs could only be stored at 10 °C for five days to be suitable for rearing T. remus. The optimum cold storage conditions for T. remus parasitizing stored eggs were 7 °C for 5 days in the larval stage. The maximal shelf lives of T. remus parasitizing cold-stored S. frugiperda eggs were 10 days. Cold storage affected the hatching rate of S. frugiperda eggs, thereby further affecting the reproductive capacity of T. remus. The findings suggest that different storage conditions should be used when mass-rearing T. remus on stored and non-stored eggs. Telenomus remus should be reproduced using fresh laid S. frugiperda eggs for maximum shelf life.

Egg coverings in insects: ecological adaptation to abiotic and biotic selective pressures.

Insects have evolved a spectrum of strategies that facilitate survival in the face of adverse environmental conditions and bottom-up or top-down pressures. The egg is the first stage in the life cycle of most insects. It is not only immobile but in many insects is the stage that survives unfavourable seasons when food resources are unavailable. Eggs are targeted by oophagous natural enemies and also are subject to abiotic stresses. In response to these diverse stresses, insects have developed various egg protection strategies. Females of many insects lay eggs in clusters and then use their own body resources to cover them to provide protection from harsh environments and biotic attack. Such egg protection strategies have allowed some herbivorous insects to thrive in new environments and become serious invasive pests. Females of many insects protect their eggs in other ways (e.g. laying eggs in concealed places, direct parental care) while others do not provide protection at all. Here, we review various egg protective strategies in insects. Our focus is on adaptive ecological mechanisms and temporal variation as well as the benefits and costs of egg coverings. We highlight several case studies on how these egg protective traits might impede biological control of globally important agricultural and forest pests and propose a framework for incorporating egg protective traits into biological control programs especially for invasive insect pests.

Transgenerational hormesis and sublethal effects of five key insecticides for controlling Spodoptera frugiperda on its endoparasitoid Cotesia marginiventris.

BACKGROUND: The endoparasitoid Cotesia marginiventris (Cresson) is a promising biological control agent of the fall armyworm (FAW) Spodoptera frugiperda (Smith). Because the application of insecticides is one of the prime choices in pest management, we evaluated the sublethal and transgenerational effects of the five key insecticides-chlorantraniliprole, emamectin benzoate, spinetoram, Bacillus thuringiensis (Bt), and Mamestra brassicae nucleopolyhedrovirus (MbNPV)-on the parasitoid. RESULTS: Exposure to five insecticides at a concentration causing 10% mortality (LC10 ) caused hormetic effects in the parent generation (F0 ) by increasing the parasitism and reducing the immature duration. Interestingly, the hormetic response was also observed in the offspring generation indirectly exposed to the insecticides. Furthermore, insecticides increased the parasitism rate by 6.32-14.73% in the F1 generation, which was similar to that of the F0 generation (3.96-11.81%) compared with the control. No significant adverse effect was observed on the number of emerged parasitoids of the F1 and F2 generations. However, insecticides had a detrimental impact on body size and fecundity in the F1 and F2 generations, which showed a small body size with shorter hind tibiae and a significant reduction in the female ratio compared with the control; the exception was that chlorantraniliprole significantly improved the female ratio in the F2 generation. CONCLUSIONS: Five insecticides at LC10 induced transgenerational hormetic and sublethal effects on C. marginiventris. Our results provide a scientific basis for a better understanding of the long-term impacts of insecticides at sublethal doses on parasitoids, facilitating the development of improved integrated pest management programs for FAW control. © 2023 Society of Chemical Industry.

Parasitic behavior and developmental morphology of Mesocomys trabalae (Hymenoptera: Eupelmidae), a promising parasitoid of the Japanese giant silkworm Caligula japonica (Lepidoptera: Saturniidae).

The egg parasitoid Mesocomys trabalae Yao, Yang, and Zhao is used as a biocontrol agent against the emerging defoliator pest Caligula japonica Moore in East Asia. It has been proven that the eggs of Antheraea pernyi Guérin-Méneville can be used as a factitious host for the mass production of M. trabalae. We examined the parasitic behavior and morphological characteristics of the developmental stages of M. trabalae reared on A. pernyi eggs. The parasitic behavior of M. trabalae encompasses 10 steps, involving searching, antennation, locating the oviposition site, drilling, probing, detecting, oviposition, host feeding, grooming, and resting, with the oviposition step further divided into 3 stages. We determined that the parasitoid released an egg during the second stage of the oviposition step, while her body remained in a relatively static state. Among all the steps in parasitic behavior, probing occupied the longest time, accounting for 26.33% of the entire parasitism process. It was followed by oviposition (15.88%), drilling (15.10%), antennation (13.09%), detecting (10.79%), host feeding (10.02%), and the remaining steps, each occupying less than 5.00% of the total time in steps. The pre-emergence of adult M. trabalae comprised of 4 stages: egg (0-1 day), larva (2-6 days), prepupa (7-11 days), pupa (12-20 days), followed by the development into an adult, and it usually took 20-22 days to develop from an egg into an adult at 25°C. This study advances our understanding of the biology of Mesocomys parasitoids and their mass-rearing for use in augmentation programs.

Light intensity differentially mediates the life cycle of lepidopteran leaf feeders and stem borers.

BACKGROUND: Leaf feeders, such as Spodoptera frugiperda and Spodoptera litura, and stem borers Ostrinia furnacalis and Chilo suppressalis, occupy two different niches and are well adapted to their particular environments. Borer larvae burrow and inhabit the interior of stems, which are relatively dark. By contrast, the larvae of leaf feeders are exposed to sunlight during feeding. We therefore designed series of experiments to evaluate the effect of light intensity (0, 2000, and 10 000 lx) on these pests with different feeding modes. RESULTS: The development of all four pests was significantly delayed at 0 lx. Importantly, light intensity affected the development of both male and female larvae of borers, but only significantly affected male larvae of leaf feeders. Furthermore, the proportion of female offspring of leaf feeders increased with increasing light intensity (S. frugiperda: 33.89%, 42.26%, 57.41%; S. litura: 38.90%, 51.75%, 65.08%), but no significant differences were found in stem borers. This research also revealed that the survival rate of female leaf feeders did not vary across light intensities, but that of males decreased with increasing light intensity (S. frugiperda: 97.78%, 85.86%, 61.21%; S. litura: 95.83%, 73.54%, 58.99%). CONCLUSION: These results improve our understanding of how light intensity affects sex differences in important lepidopteran pests occupying different feeding niches and their ecological interactions with abiotic factors in agroecosystems. © 2024 Society of Chemical Industry.