Insect Life Histories Research Articles

In search of ecological determinants of fungal infections: Asemi-field experiment with folivorous moths.

Natural enemies shape the fate of species at both ecological and evolutionary time scales. While the effects of predators, parasitoids, and viruses on insects are well documented, much less is known about the ecological and evolutionary role of entomopathogenic fungi. In particular, it is unclear to which extent may the spatiotemporal distribution patterns of these pathogens create selective pressures on ecological traits of herbivorous insects. In the present study, we reared three lepidopteran species in semi‐natural conditions in a European hemiboreal forest habitat. We studied the probability of the insects to die from fungal infection as a function of insect species, food plant, study site, (manipulated) condition of the larvae, and the phenological phase. The prevalence of entomopathogenic fungi remained low to moderate with the value consistently below 10% across the subsets of the data while as many as 23 fungal species, primarily belonging to the families Cordycipitaceae, Aspergillaceae, and Nectriaceae, were recorded. There were no major differences among the insect species in prevalence of the infections or in the structure of associated fungal assemblages. The family Cordycipitaceae, comprising mainly obligatory entomopathogens, dominated among the pathogens of pupae but not among the pathogens of larvae. Overall, there was evidence for a relatively weak impact of the studied ecological factors on the probability to be infected by a fungal pathogen; there were no effects of food plant, study site, or phenology which would be consistent over the study species and developmental stages of the insects. Nevertheless, when the prevalence of particular fungal taxa was studied, Akanthomyces muscarius was found infecting insects fed with leaves of only one of the food plant, Betula spp. Feeding on a particular plant taxon can thus have specific fitness costs. This demonstrates that fungus‐mediated effects on insect life history traits are possible and deserve attention.

Kr-h1, a Cornerstone Gene in Insect Life History.

Insect life cycle is coordinated by hormones and their downstream effectors. Krüppel homolog1 (Kr-h1) is one of the crucial effectors which mediates the actions of the two critical hormones of insects, the juvenile hormone (JH) and 20-hydroxyecdysone (20E). It is a transcription factor with a DNA-binding motif of eight C2H2 zinc fingers which is found to be conserved among insect orders. The expression of Kr-h1 is fluctuant during insect development with high abundance in juvenile instars and lower levels in the final instar and pupal stage, and reappearance in adults, which is governed by the coordination of JH, 20E, and miRNAs. The dynamic expression pattern of Kr-h1 is closely linked to its function in the entire life of insects. Over the past several years, accumulating studies have advanced our understanding of the role of Kr-h1 during insect development. It acts as a universal antimetamorphic factor in both hemimetabolous and holometabolous species by directly inhibiting the transcription of 20E signaling genes Broad-Complex (Br-C) and Ecdysone induced protein 93F (E93), and steroidogenic enzyme genes involved in ecdysone biosynthesis. Meanwhile, it promotes vitellogenesis and ovarian development in the majority of studied insects. In addition, Kr-h1 regulates insect behavioral plasticity and caste identity, neuronal morphogenesis, maturation of sexual behavior, as well as embryogenesis and metabolic homeostasis. Hence, Kr-h1 acts as a cornerstone regulator in insect life.

Repeated exposure of fluazinam fungicides affects gene expression profiles yet carries no costs on a nontarget pest.

Fungicides are used to control pathogenic fungi of crop species, but they have also been shown to alter behavioral, life history and fitness related traits of nontarget insects. Here, we tested the fungicide effects on feeding behavior, survival and physiology of the nontarget pest insect, the Colorado potato beetle (CPB) (Leptinotarsa decemlineata). Feeding behavior was studied by a choice test of adult beetles, which were allowed to choose between a control and a fungicide (fluazinam) treated potato leaf. Larval survival was recorded after 24 and 72h exposure to control and fungicide-treated leaves with 2 different concentrations. The adults did not show fungicide avoidance behavior. Similarly, survival of the larvae was not affected by the exposure to fungicides. Finally, to understand the effects of fungicides at the physiological level (gene expression), we tested whether the larval exposure to fungicide alter the expression of 5 metabolic pathway and stress associated genes. Highest concentration and 72-h exposure caused upregulation of 1 cytochrome P450 (CYP9Z14v2) and 1 insecticide resistance gene (Ldace1), whereas metabolic detoxification gene (Ugt1) was downregulated. At 24-h exposure, highest concentration caused downregulation of another common detoxification gene (Gs), while both exposure times to lowest concentration caused upregulation of the Hsp70 stress tolerance gene. Despite these overall effects, there was a considerable amount of variation among different families in the gene expression levels. Even though the behavioral effects of the fungicide treatments were minor, the expression level differences of the studied genes indicate changes on the metabolic detoxifications and stress-related pathways.

Temperature-modified density effects in the black soldier fly: low larval density leads to large size, short development time and high fat content

The effects of biotic and abiotic factors on insect life histories have been extensively studied. However, the impact of some crucial aspects, such as larval density (crowding) and the effects of environmental interactions, have often been overlooked. This study aims to determine the effects of larval density and temperature on life-history traits in the black soldier fly (BSF). Our results showed an increase in prepupal mass, pupal mass, prepupal-to-pupal mass loss, survival, prepupal fat content, adult mass, adult longevity and a reduction in larval and pupal development time at low densities. Larval density was maintained throughout the entire larval period and larval survival was determined at the 4th instar and at prepupation. Larvae were reared at three different larval densities (1, 5 and 10 larvae/cm2), at three temperature treatments (23, 27 and 30 °C) and food was provided ad libitum. High densities, on the contrary, resulted in an increase in development time, mortality and a decrease in prepupal mass loss. Temperature significantly affected all studied traits except survival, prepupal fat content and adult longevity, and notably modified the larval density effects on prepupal mass, pupal mass, adult mass, prepupal-to-pupal mass loss, prepupal fat content, duration of larval period, and adult longevity. Males and females differed in all studied life-history traits except adult mass. We conclude that density and temperature and their interaction-related effects during larval development considerably affect BSF larval life-history traits. Therefore, these effects should be carefully considered when planning for insect mass rearing.

Elevational patterns of life history and ecological trait diversity of aquatic insects in the middle of the Lancang River: The effects of climate and land use variables

Elevational patterns of life history and ecological trait diversity of aquatic insects in the middle of the Lancang River: The effects of climate and land use variables

Identification of Chemosensory Genes Based on the Antennal Transcriptomic Analysis of Plagiodera versicolora.

Simple SummaryIn this study, we conducted a transcriptome analysis of adult antennae in Plagiodera versicolora (Coleoptera: Chrysomelidae) and identified a total of 98 candidate chemosensory genes, encoding 40 odorant receptors (ORs), 7 ionotropic receptors (IRs), 13 gustatory receptors (GRs), 10 chemosensory proteins (CSPs), 24 odorant binding proteins (OBPs), and 4 sensory neuron membrane proteins (SNMPs). The tissue expression profiles showed that almost all PverOBPs and PverORs were highly expressed in the antennae. In addition, the results revealed that PverOBP10, PverOBP12, PverOBP18, PverOR24, and PverOR35 showed female-biased expression profiles, indicating that these receptors may be involved in some female-specific behaviors such as oviposition site seeking. This work greatly promotes the understanding of the olfactory system and will help provide insight for functional studies of the chemoreception mechanism in P. versicolora.Insects can sense surrounding chemical signals by their accurate chemosensory systems. This system plays a vital role in the life history of insects. Several gene families participate in chemosensory processes, including odorant receptors (ORs), ionotropic receptors (IRs), gustatory receptors (GRs), chemosensory proteins (CSPs), odorant binding proteins (OBPs), and sensory neuron membrane proteins (SNMPs). Plagiodera versicolora (Coleoptera: Chrysomelidae), is a leaf-eating forest pest found in salicaceous trees worldwide. In this study, a transcriptome analysis of male and female adult antennae in P. versicolora individuals was conducted, which identified a total of 98 candidate chemosensory genes including 40 ORs, 7 IRs, 13 GRs, 10 CSPs, 24 OBPs, and 4 SNMPs. Subsequently, the tissue expression profiles of 15 P. versicolora OBPs (PverOBPs) and 39 ORs (PverORs) were conducted by quantitative real-time PCR. The data showed that almost all PverOBPs and PverORs were highly expressed in the male and female antennae. In addition, several OBPs and ORs (PverOBP10, PverOBP12, PverOBP18, PverOR24, and PverOR35) had higher expression levels in female antennae than those in the male antennae, indicating that these genes may be taking part in some female-specific behaviors, such as find mates, oviposition site, etc. This study deeply promotes further understanding of the chemosensory system and functional studies of the chemoreception genes in P. versicolora.

Elevated CO2 aggravates invasive thrip damage by altering its host plant nutrient and secondary metabolism

As atmospheric CO2 concentration continues to increase, plants using CO2 as raw materials for photosynthesis will inevitably be affected, which in turn affects the life history and behavior of herbivorous insects. Our previous research has shown increased food intake and aggravated damage of western flower thrips, Frankliniella occidentalis to kidney bean (Phaseolus vulgaris) caused by elevated CO2 (eCO2), however the molecular mechanism of this phenomenon is unclear. In this study, the comparative transcriptome analysis combined with corresponding phenotypic changes were studied to reveal the molecular mechanism of interaction between F. occidentalis and P. vulgaris under eCO2. Inferred from the results, eCO2 had different degrees of inhibition to the defense responses caused by thrips infestation in P. vulgaris leaf sap based on nutrients, plant hormones and secondary metabolites, making P. vulgaris leaves less resistant to thrips under eCO2 compared to ambient CO2 (aCO2). Besides, the contents of glucose, trehalose, triglycerides and free fatty acids in F. occidentalis adults increased significantly after feeding on the P. vulgaris leaf sap with significantly increased soluble sugars content under eCO2, which might lead to glucolipid metabolic disorders and increased food intake of F. occidentalis adults. The results indicated that decreased plant defense of P. vulgaris and increased food intake of F. occidentalis adults were combined to aggravate the thrips damage under eCO2, providing a theoretical basis for future occurrence trend of thrips under eCO2.

Seed treatment for managing fall armyworm as a defoliator and cutworm on maize: plant protection, residuality, and the insect life history.

The highly polyphagous and invasive fall armyworm (FAW, Spodoptera frugiperda) can feed on different plant parts of host crops, damaging whorls and stalks in early maize growth stages. Systemic insecticide seed treatment (IST) could minimize this damage, although the residual efficacy may vary with the plant tissue damaged. Using damage rating scales and artificial infestation in controlled conditions, we determined the potential of IST against FAW attacking maize whorl leaves or the stalk base. Chlorantraniliprole, cyantraniliprole, or thiodicarb + imidacloprid IST similarly killed > 80% FAWs for 1 or 2 weeks after plant emergence depending on the plant tissue attacked. The residual efficacy (i.e. time after plant emergence sustaining > 80% larval mortality) lasted from the first to the eleventh day (VE-V3 maize growth stages), while for cutworm on the maize stalk base, it lasted 3-7 days after plant emergence (V1-V2 stages). In terms of damage, the ISTs lasted 15 days after emergence (V4 stage) for FAW on whorl leaves and 10 days (V3 stage) for FAW feeding on the stalk base. The larvae surviving on the seed-treated plants underwent sublethal effects in growth and development, reducing insect fitness. Diamide or carbamate + neonicotinoid seed treatments kill FAW larvae on maize whorls or stalks in favorable edaphoclimatic and insecticide-susceptibility conditions. The cumulative impacts of systemic IST on aboveground insect pests go beyond mortality. The ISTs studied can be valuable against FAW in maize, for instance, to help protect varieties that may not express sufficient insect resistance in maize early growth stages.

IN1336] Argentine ant, Linepithema humile (Mayr) (Insecta: Hymenoptera: Formicidae)

The Argentine ant, Linepithema humile (Mayr), is an insect native to South America, but an invasive species in many parts of the world. It is globally distributed. Linepithema humile is considered a pest species, primarily due to its feeding habits of tending and protecting honeydew producing insects, such as scale insects, which are often damaging to crops and ornamental plants. This aggressive, populous ant species also has a negative effect on native ant species. Linepithema humile colonies have multiple queens, allowing colonies to grow and spread rapidly. Under certain conditions, the argentine ant may also become a household pest if it finds a way into homes. Linepithema humile has been designated as a tramp ant species, meaning that it has an incredible ability to spread and establish in new areas and is difficult to control. Linepithema humile, like other tramp species, can establish in new locations quickly due to the multi-queen nature of the colonies, their abitlity to forage and find resources, and the extensive network of interrelated colonies they are able to form. This document provides an in-depth synopsis of the insect's life history, biology, and management.

Microorganisms Associated with Mosquito Oviposition Sites: Implications for Habitat Selection and Insect Life Histories.

Mosquitoes are considered one of the most important threats worldwide due to their ability to vector pathogens. They are responsible for the transmission of major pathogens such as malaria, dengue, zika, or chikungunya. Due to the lack of treatments or prophylaxis against many of the transmitted pathogens and an increasing prevalence of mosquito resistance to insecticides and drugs available, alternative strategies are now being explored. Some of these involve the use of microorganisms as promising agent to limit the fitness of mosquitoes, attract or repel them, and decrease the replication and transmission of pathogenic agents. In recent years, the importance of microorganisms colonizing the habitat of mosquitoes has particularly been investigated since they appeared to play major roles in their development and diseases transmission. In this issue, we will synthesize researches investigating how microorganisms present within water habitats may influence breeding site selection and oviposition strategies of gravid mosquito females. We will also highlight the impact of such microbes on the fate of females’ progeny during their immature stages with a specific focus on egg hatching, development rate, and larvae or pupae survival.

Potential of Quercetin to Reduce Herbivory without Disrupting Natural Enemies and Pollinators

Quercetin is one of the most abundant flavonoids in terrestrial plants and pollen. In living plants, quercetin can function as a secondary metabolite to discourage insect herbivory. Literature on insect-quercetin interactions was searched and data synthesized to test the hypothesis that quercetin can become an effective biocide to reduce herbivory without disrupting natural enemies and pollinators. The USDA, National Agricultural Library, DigiTop Navigator platform was used to search the literature for harmful versus nonharmful effects of quercetin on insect behavior, physiology, and life history parameters. Quercetin effects were evaluated on herbivores in five insect orders, natural enemies in two orders, and pollinators in one order. Quercetin was significantly more harmful to Hemiptera, Diptera, and Lepidoptera but significantly more nonharmful to Coleoptera. Harmful and nonharmful effects to Orthoptera were indistinguishable. Quercetin had significantly more harmful (than nonharmful) effects on herbivores when data from the five insect orders were combined. Quercetin concentration (mg/mL) did not significantly affect these results. Quercetin was significantly more nonharmful to natural enemies (Coleoptera and Hymenoptera, combined) and pollinators (Hymenoptera). This study suggests that quercetin could prevent herbivory without disrupting natural enemies and pollinators, but field experiments are necessary to substantiate these results.

Neuropeptides as potential modulators of behavioral transitions in the ant Cataglyphis nodus.

Age-related behavioral plasticity is a major prerequisite for the ecological success of insect societies. Although ecological aspects of behavioral flexibility have been targeted in many studies, the underlying intrinsic mechanisms controlling the diverse changes in behavior along the individual life history of social insects are not completely understood. Recently, the neuropeptides allatostatin-A, corazonin, and tachykinin have been associated with the regulation of behavioral transitions in social insects. Here, we investigated changes in brain localization and expression of these neuropeptides following major behavioral transitions in Cataglyphis nodus ants. Our immunohistochemical analyses in the brain revealed that the overall branching pattern of neurons immunoreactive (ir) for the three neuropeptides is largely independent of the behavioral stages. Numerous allatostatin-A- and tachykinin-ir neurons innervate primary sensory neuropils and high-order integration centers of the brain. In contrast, the number of corazonergic neurons is restricted to only four neurons per brain hemisphere with cell bodies located in the pars lateralis and axons extending to the medial protocerebrum and the retrocerebral complex. Most interestingly, the cell-body volumes of these neurons are significantly increased in foragers compared to freshly eclosed ants and interior workers. Quantification of mRNA expression levels revealed a stage-related change in the expression of allatostatin-A and corazonin mRNA in the brain. Given the presence of the neuropeptides in major control centers of the brain and the neurohemal organs, these mRNA-changes strongly suggest an important modulatory role of both neuropeptides in the behavioral maturation of Cataglyphis ants.

Size matters: larger galls produced by Eutreta xanthochaeta (Diptera: Tephritidae) on Lippia myriocephala (Verbenaceae) predict lower rates of parasitic wasps

Gall induction is one of the main life strategies of endophagous insects, which serves to provide food and protection against natural enemies. It is proposed that gall size is one of the most important traits in the life history of the inducer insect, since a balance exists between the protection afforded by the gall and exposure to natural enemies. The aims of this study were first to describe the trophic interactions between E. xanthochaeta and its native parasitoids on a new host plant Lippia myriocephala, and then to assess the relationships between gall size, location on the plant architecture and parasitism rates. A community of seven native parasitoid morphospecies was found, representing 22.2% of the overall parasitism, highlighting two wasp species, Torymus sp. (Torymidae) and Pteromalinae (Pteromalidae) as the most abundant. Gall size exhibited significant variations related to their distribution within the plant architecture, with a gradual reduction in size found from the main stem toward the peripheral branches. Such differences were associated with an increase in parasitized pupae and smaller galls were found to be more susceptible to parasitoid attack. Parasitism rates revealed that Torymus sp. uses a broader gall size range than Pteromalinae, and we hypothesized that such variations may be related to certain morphological traits of the parasitoids such as ovipositor length, since the former presents an ovipositor nearly four times longer than the latter. Thus, we infer that growth of bigger galls reduced the likelihood of parasitism of the flies.

Neurodevelopmental and transcriptomic effects of CRISPR/Cas9-induced somatic orco mutation in honey bees

In insects, odorant receptors facilitate olfactory communication and require the functionality of the highly conserved co-receptor gene orco. Genome editing studies in a few species of ants and moths have revealed that orco can also have a neurodevelopmental function, in addition to its canonical role in adult olfaction, discovered first in Drosophila melanogaster. To extend this analysis, we determined whether orco mutations also affect the development of the adult brain of the honey bee Apis mellifera, an important model system for social behavior and chemical communication. We used CRISPR/Cas9 to knock out orco and examined anatomical and molecular consequences. To increase efficiency, we coupled embryo microinjection with a laboratory egg collection and in vitro rearing system. This new workflow advances genomic engineering technologies in honey bees by overcoming restrictions associated with field studies. We used Sanger sequencing to quickly select individuals with complete orco knockout for neuroanatomical analyses and later validated and described the mutations with amplicon sequencing. Mutant bees had significantly fewer glomeruli, smaller total volume of all the glomeruli, and higher mean individual glomerulus volume in the antennal lobe compared to wild-type controls. RNA-Sequencing revealed that orco knockout also caused differential expression of hundreds of genes in the antenna, including genes related to neural development and genes encoding odorant receptors. The expression of other types of chemoreceptor genes was generally unaffected, reflecting specificity of CRISPR activity in this study. These results suggest that neurodevelopmental effects of orco are related to specific insect life histories.

The impact of temperature on the life cycle of Gasterophilus pecorum in northwest China

BackgroundThe departure of the mature larvae of the horse stomach bot fly from the host indicates the beginning of a new infection period. Gasterophilus pecorum is the dominant bot fly species in the desert steppe of the Kalamaili Nature Reserve (KNR) of northwest China as a result of its particular biological characteristics. The population dynamics of G. pecorum were studied to elucidate the population development of this species in the arid desert steppe.MethodsLarvae in the freshly excreted feces of tracked Przewalski’s horses (Equus przewalskii) were collected and recorded. The larval pupation experiments were carried out under natural conditions.ResultsThere was a positive correlation between the survival rate and the number of larvae expelled (r = 0.630, p < 0.01); the correlation indicated that the species had characteristic peaks of occurrence. The main periods during which mature larvae were expelled in the feces were from early April to early May (peak I) and from mid-August to early September (peak II); the larval population curve showed a sudden increase and gradual decrease at both peaks. Under the higher temperatures of peak II, the adults developing from the larvae had a higher survival rate, higher pupation rate, higher emergence rate and shorter eclosion period than those developing from peak I larvae. Although G. pecorum has only one generation per year, its occurrence peaked twice annually, i.e. the studied population has a bimodal distribution, which doubles parasitic pressure on the local host. This phenomenon is very rarely recorded in studies on insect life history, and especially in those on parasite epidemiology.ConclusionThe period during which G. pecorum larvae are naturally expelled from the host exceeds 7 months in KNR, which indicates that there is potentially a long period during which hosts can become infected with this parasite. The phenomenon of two annual peaks of larvae expelled in feces is important as it provides one explanation for the high rate of equine myiasis in KNR.Graphical

Wide Diurnal Temperature Amplitude and High Population Density Can Positively Affect the Life History of Sitobion avenae (Hemiptera: Aphididae).

Diurnal temperature amplitude is known to have a large influence on insect life history. Population density affects intraspecific competition and many other aspects of insect life history. However, there is limited information on the interactive effects of these factors on insects. Here, we tested the interactive effects of three diurnal temperature amplitudes (22 ± 0°C, 22 ± 6°C, and 22 ± 12°C) and three population densities on the development, survival, longevity, and fecundity of the English grain aphid Sitobion avenae (Fabricius) (Homoptera: Aphididae). At a constant temperature, increasing population density reduced the growth and survival of early-instar nymphs, increased longevity, and reduced fecundity. At a low population density, increasing temperature amplitude inhibited nymph development. However, even at a high temperature amplitude, nymph survival rate was higher than expected, and reproduction was possible because the recovery of the lower night-temperatures eliminated thermal stress. Increasing the population density reduced, and even reversed, the negative effects of the wide temperature amplitude. This may reflect synergistic interactions between population density and wide temperature amplitude as these stressors each incur energetic costs. These findings emphasize the importance of temperature amplitude and population density for improving prediction accuracy and damage assessment during pest control modeling.

Relative importance of ecological versus biological traits in driving range sizes of African dragonflies

AbstractAimEcological traits (e.g. biotope specialisation and habitat preference) and biological traits (e.g. mobility and life history) are highly variable among species. In insect conservation, considerable focus has been on ecological generalisation, with species occupying many biotope types (generalists) often assumed to be widely distributed, whereas species occupying few biotope types (specialists) are assumed as rare and localised. Although this may be valid in most cases, there is an increasing recognition that functional traits, such as insect mobility and life history, have similar importance as drivers of range size among species. Here, we investigate ecological and biological traits simultaneously to determine their relative importance as drivers of range size variation. We hypothesise that ecological traits are primary drivers, whereas biological traits related to mobility and life history are less important drivers of range size.LocationSub‐Saharan Africa.Taxon115 sub‐Saharan dragonfly species.MethodsFive measures of species range size were obtained from the Odonata Database of Africa. Number of biotope types occupied by adults and larvae, larval habitat preference and adult biological trait information were collated from published sources. We explore the relationships between ecological and biological traits. Using linear mixed models and model averaging, we determine the relative importance of number of biotope types occupied, overall habitat preference and traits related to mobility and life history that drive dragonfly range size while accounting for phylogenetic relationships among focal species.ResultsDragonflies occupying more biotope types had wider ranges, although these relationships were overall weak. Dragonflies with longer and later breeding seasons had wider ranges. Overall habitat preference and mobility traits had low importance in our models.Main conclusionsEcological versus biological traits are interactive in shaping the geographical ranges of dragonfly species across Africa. Single traits are weak predictors of species range sizes and we recommend investigating multiple traits simultaneously to improve the accuracy of predictions. In doing so, more informed decisions can be made to ensure effective large‐scale conservation of dragonflies.

Chemical Ecology, Biochemistry, and Molecular Biology of Insect Hydrocarbons.

Insect cuticular hydrocarbons (CHCs) consist of complex mixtures of straight-chain alkanes and alkenes, and methyl-branched hydrocarbons. In addition to restricting water loss through the cuticle and preventing desiccation, they have secondarily evolved to serve a variety of functions in chemical communication and play critical roles as signals mediating the life histories of insects. In this review, we describe the physical properties of CHCs that allow for both waterproofing and signaling functions, summarize their roles as inter- and intraspecific chemical signals, and discuss the influences of diet and environment on CHC profiles. We also present advances in our understanding of hydrocarbon biosynthesis. Hydrocarbons are biosynthesized in oenocytes and transported to the cuticle by lipophorin proteins. Recent work on the synthesis of fatty acids and their ultimate reductive decarbonylation to hydrocarbons has taken advantage of powerful new tools of molecular biology, including genomics and RNA interference knockdown of specific genes, to provide new insights into the biosynthesis of hydrocarbons.

Indirect effect of elevated CO2 concentration on Bemisia tabaci MEAM1 feeding on Bt soybean plants

AbstractThe development of herbivore insects is influenced by the quality of their host plants. Elevated CO2 alters plant metabolism, which may change the nutritional quality of the plant, modifying the life history and feeding behaviour of herbivore insects. Understanding how insect pests respond to increasing CO2 concentration is essential for predicting the impact of the pest on food security. In this study, we investigated the effects of elevated CO2 (eCO2) on the life history and feeding behaviour of the MEAM1 species of Bemisia tabaci on a Bt soybean cultivar. We found that eCO2 increased the egg to adult development time and reduced the reproductive responses (fecundity and fertility) of B. tabaci. The whitefly B. tabaci that fed on the soybean plants grown under eCO2 conditions was negatively influenced by several traits related to the host plant resistance, such as the time spent on phloem sap ingestion. Furthermore, we evaluated the changes in the C:N concentration and plant morphology of the Bt plants. The biomass (weight of leaves and stems) of the Bt soybean plants grown under eCO2 conditions was significantly increased, and the elevated C:N ratio in the phenological stage V6 (i.e. when the plants had six trifoliate leaves developed) was the most pronounced difference in the Bt soybean plants subjected to eCO2 treatment. Taken together, our results indicate that Bt plants cultivated under eCO2 inhibit B. tabaci feeding, which can reduce whitefly infestations of the soybean fields.

Determinants of optimal insecticide resistance management strategies

The use of insecticides to control agricultural pests has resulted in resistance developing to most known insecticidal modes of action. Strategies by which resistance can be slowed are necessary to prolong the effectiveness of the remaining modes of action. Here we use a flexible mathematical model of resistance evolution to compare four insecticide application strategies: (i) applying one insecticide until failure, then switching to a second insecticide (sequential application), (ii) mixing two insecticides at their full label doses, (iii) rotating (alternating) two insecticides at full label dose, or (iv) mixing two insecticides at a reduced dose (with each mixture component at half the full label dose). The model represents target-site resistance.Multiple simulations were run representing different insect life-histories and insecticide characteristics. The analysis shows that none of the strategies examined were optimal for all the simulations. The four strategies: reduced dose mixture, label dose mixture, sequential application and label dose rotation, were optimal in 52%, 22%, 20% and 6% of simulations respectively.The most important trait determining the optimal strategy in a single simulation was whether or not the insect pest underwent sexual reproduction. For asexual insects, sequential application was most frequently the optimal strategy, while a label-dose mixture was rarely optimal. Conversely, for sexual insects a mixture was nearly always the optimal strategy, with reduced dose mixture being optimal twice as frequently as label dose mixture. When sequential application of insecticides is not an option, reduced dose mixture is most frequently the optimal strategy whatever an insect’s reproduction.