Insecticide-induced hormesis and arthropod pest management

Nutrition, pesticide exposure, and virus infection interact to produce context-dependent effects in honey bees (Apis mellifera)

Declines in pollinator health are frequently hypothesized to be the combined result of multiple interacting biotic and abiotic stressors; namely, nutritional limitations, pesticide exposure, and infection with pathogens and parasites. Despite this hypothesis, most studies examining stressor interactions have been constrained to two concurrent factors, limiting our understanding of multi-stressor dynamics. Using honey bees as a model, we addressed this gap by studying how variable diet, field-realistic levels of multiple pesticides, and virus infection interact to affect survival, infection intensity, and immune and detoxification gene expression. Although we found evidence that agrochemical exposure (a field-derived mixture of chlorpyrifos and two fungicides) can exacerbate infection and increase virus-induced mortality, this result was nutritionally-dependent, only occurring when bees were provided artificial pollen. Provisioning with naturally-collected polyfloral pollen inverted the effect, reducing virus-induced mortality and suggesting a hormetic response. To test if the response was pesticide specific, we repeated our experiment with a pyrethroid (lambda-cyhalothrin) and a neonicotinoid (thiamethoxam), finding variable results. Finally, to understand the underpinnings of these effects, we measured viral load and expression of important immune and detoxification genes. Together, our results show that multi-stressor interactions are complex and highly context-dependent, but have great potential to affect bee health and physiology.

Agricultural insect pests as models for studying stress-induced evolutionary processes

Agricultural insect pests (AIPs) are widely successful in adapting to natural and anthropogenic stressors, repeatedly overcoming population bottlenecks and acquiring resistance to intensive management practices. Although they have been largely overlooked in evolutionary studies, AIPs are ideal systems for understanding rapid adaptation under novel environmental conditions. Researchers have identified several genomic mechanisms that likely contribute to adaptive stress responses, including positive selection on de novo mutations, polygenic selection on standing allelic variation and phenotypic plasticity (e.g., hormesis). However, new theory suggests that stress itself may induce epigenetic modifications, which may confer heritable physiological changes (i.e., stress-resistant phenotypes). In this perspective, we discuss how environmental stress from agricultural management generates the epigenetic and genetic modifications that are associated with rapid adaptation in AIPs. We summarise existing evidence for stress-induced evolutionary processes in the context of insecticide resistance. Ultimately, we propose that studying AIPs offers new opportunities and resources for advancing our knowledge of stress-induced evolution.

Tetraniliprole risk assessment: Unveiling a hidden threat for managing a generalist herbivore

Insecticide resistance poses a significant challenge in managing generalist herbivores such as the tobacco cutworm (TCW), Spodoptera litura. This study investigates the potential risks associated with using the novel diamide insecticide tetraniliprole to control TCW. A tetraniliprole-resistant strain was developed through twelve generations of laboratory selection, indicating an intermediate risk of resistance development. Field monitoring in China revealed a significant incidence of resistance, particularly in the Nanchang (NC) population (>100-fold). Tetraniliprole showed moderate to high cross-resistance to multiple insecticides and was autosomally inherited with incomplete dominance, controlled by multiple genes, some of which belong to the cytochrome P450 family associated with enhanced detoxification. Life table studies indicated transgenerational hormesis, stimulating TCW female fecundity and increasing population net reproduction rates (R0). These findings suggest a potential for pest resurgence under tetraniliprole use. The integrated risk assessment provides a basis for the sustainable management of TCW using tetraniliprole.

Differential susceptibility of Spodoptera frugiperda (Lepidoptera: Noctuidae) to single versus pyramided Bt traits in Brazilian soybean: what doesn't kill you makes you stronger?

BACKGROUND

Lepidopteran pest control in agriculture has become heavily dependent on cultivars that express Bacillus thuringiensis (Bt) toxins as 'plant-incorporated protectants'. However, populations of Spodoptera frugiperda (Smith) in Brazil appear resistant to the Bt traits currently available in commercial soybean cultivars.

RESULTS

This study evaluated S. frugiperda life history when feeding on three different Bt soybean cultivars. Cultivars expressing Cry1Ac + Cry1F and Cry1A.105 + Cry2Ab2 + Cry1Ac Bt toxins caused 100% larval mortality in S. frugiperda. Both non-Bt and Cry1Ac-expressing soybean induced transgenerational effects that increased the survival of subsequent generations. A Cry1Ac soybean diet reduced the generation time (T) of S. frugiperda relative to non-Bt soybean, resulting in shorter generation time and more rapid population growth.

CONCLUSION

The implications of these results revealed how diet can alter aspects of insect life history and biology, and have important implications for sustainable management of S. frugiperda on soybean. © 2024 Society of Chemical Industry.

Pesticide exposure triggers sex-specific inter- and transgenerational effects conditioned by past sexual selection

Environmental variation often induces plastic responses in organisms that can trigger changes in subsequent generations through non-genetic inheritance mechanisms. Such transgenerational plasticity thus consists of environmentally induced non-random phenotypic modifications that are transmitted through generations. Transgenerational effects may vary according to the sex of the organism experiencing the environmental perturbation, the sex of their descendants or both, but whether they are affected by past sexual selection is unknown. Here, we use experimental evolution on an insect model system to conduct a first test of the involvement of sexual selection history in shaping transgenerational plasticity in the face of rapid environmental change (exposure to pesticide). We manipulated evolutionary history in terms of the intensity of sexual selection for over 80 generations before exposing individuals to the toxicant. We found that sexual selection history constrained adaptation under rapid environmental change. We also detected inter- and transgenerational effects of pesticide exposure in the form of increased fitness and longevity. These cross-generational influences of toxicants were sex dependent (they affected only male descendants), and intergenerational, but not transgenerational, plasticity was modulated by sexual selection history. Our results highlight the complexity of intra-, inter- and transgenerational influences of past selection and environmental stress on phenotypic expression.

Hormetic effect induced by Beauveria bassiana in Myzus persicae

BACKGROUND

Myzus persicae, a serious sap-sucking pest of a large variety of host plants in agriculture, is traditionally controlled using chemical insecticides but there is interest in using biopesticides as restrictions are increasingly placed on the use of broad-spectrum pesticides.

RESULTS

Here, we show that in Petri dish experiments, high concentrations of the fungal entomopathogen Beauveria bassiana led to rapid mortality of M. persicae, although at a low concentration (1 × 104 conidia mL-1) there is a hormetic effect in which survival and fecundity are enhanced. Hormetic effects persisted across a generation with reduced development time and increased fecundity in the offspring of M. persicae exposed to B. bassiana. The whole-plant experiment points to a hormetic effect being detected in two out of three tested lines. The impact of these effects might also depend on whether M. persicae was transinfected with the endosymbiont Rickettsiella viridis, which decreases fecundity and survival compared with aphids lacking this endosymbiont. This fecundity cost was ameliorated in the generation following exposure to the entomopathogen.

CONCLUSION

Although B. bassiana is effective in controlling M. persicae especially at higher spore concentrations, utilization of this entomopathogen requires careful consideration of hormetic effects at lower spore concentrations, and further research to optimize its application for sustainable agriculture is recommended. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Imidazolium salt's toxic effects in larvae and cells of Aedes aegypti and Aedes albopictus (Diptera: Culicidae)

Aedes aegypti and Aedes albopictus are the main vectors of arboviruses such as Dengue, Chikungunya and Zika, causing a major impact on global economic and public health. The main way to prevent these diseases is vector control, which is carried out through physical and biological methods, in addition to environmental management. Although chemical insecticides are the most effective strategy, they present some problems such as vector resistance and ecotoxicity. Recent research highlights the potential of the imidazolium salt "1-methyl-3-octadecylimidazolium chloride" (C18MImCl) as an innovative and environmentally friendly solution against Ae. aegypti. Despite its promising larvicidal activity, the mode of action of C18MImCl in mosquito cells and tissues remains unknown. This study aimed to investigate its impacts on Ae. aegypti larvae and three cell lines of Ae. aegypti and Ae. albopictus, comparing the cellular effects with those on human cells. Cell viability assays and histopathological analyses of treated larvae were conducted. Results revealed the imidazolium salt's high selectivity (> 254) for mosquito cells over human cells. After salt ingestion, the mechanism of larval death involves toxic effects on midgut cells. This research marks the first description of an imidazolium salt's action on mosquito cells and midgut tissues, showcasing its potential for the development of a selective and sustainable strategy for vector control.

The sublethal concentration of acetamiprid suppresses the population growth of 2 species of wheat aphids, Sitobion miscanthi and Schizaphis graminum (Hemiptera: Aphididae)

Sitobion miscanthi and Schizaphis graminum (Rondani) are the 2 main aphid species that occur simultaneously, causing significant loss to wheat production. Acetamiprid has been used to control a variety of pests, including aphids. In this study, the sublethal effect of acetamiprid on S. miscanthi and S. graminum was evaluated using life-table analyses. The results showed that acetamiprid has a high toxicity to S. miscanthi and S. graminum with a LC50 of 1.90 and 3.58 mg/L at 24 h, respectively. The adult longevity and fecundity of S. miscanthi and S. graminum F0 generation were significantly reduced after being exposed to a sublethal concentration of acetamiprid. Additionally, the sublethal concentration of acetamiprid had negative transgenerational effects on S. miscanthi and S. graminum, which showed a significant decrease in fecundity and population life-table parameters involving age-stage-specific survival rate (sxj), age-specific survival rate (lx), and intrinsic rate of increase (r). Furthermore, the population projections showed that the total population size of S. miscanthi and S. graminum was significantly lower in the aphid group exposed to sublethal concentration of acetamiprid compared to the control group. These results suggest that sublethal concentration of acetamiprid suppresses the population growth of S. miscanthi and S. graminum. This finding is beneficial to the control of wheat aphids, and is important to fully understand the role of acetamiprid in integrated pest management.

Insects to the rescue? Insights into applications, mechanisms, and prospects of insect-driven remediation of organic contaminants

Traditional and emerging contaminants pose significant human and environmental health risks. Conventional physical, chemical, and bioremediation techniques have been extensively studied for contaminant remediation. However, entomo- or insect-driven remediation has received limited research and public attention. Entomo-remediation refers to the use of insects, their associated gut microbiota, and enzymes to remove or mitigate organic contaminants. This novel approach shows potential as an eco-friendly method for mitigating contaminated media. However, a comprehensive review of the status, applications, and challenges of entomo-remediation is lacking. This paper addresses this research gap by examining and discussing the evidence on entomo-remediation of various legacy and emerging organic contaminants. The results demonstrate the successful application of entomo-remediation to remove legacy organic contaminants such as persistent organic pollutants. Moreover, entomo-remediation shows promise in removing various groups of emerging contaminants, including microplastics, persistent and emerging organic micropollutants (e.g., antibiotics, pesticides), and nanomaterials. Entomo-remediation involves several insect-mediated processes, including bio-uptake, biotransfer, bioaccumulation, and biotransformation of contaminants. The mechanisms underlying the biotransformation of contaminants are complex and rely on the insect gut microbiota and associated enzymes. Notably, while insects facilitate the remediation of contaminants, they may also be exposed to the ecotoxicological effects of these substances, which is often overlooked in research. As an emerging field of research, entomo-remediation has several knowledge gaps. Therefore, this review proposes ten key research questions to guide future perspectives and advance the field. These questions address areas such as process optimization, assessment of ecotoxicological effects on insects, and evaluation of potential human exposure and health risks.

Sublethal acetamiprid affects reproduction, development and disrupts gene expression in Binodoxys communis

At present, understanding of neonicotinoid toxicity in arthropods remains limited. We here evaluated the lethal and sublethal effects of acetamiprid in F0 and F1 generations of Binodoxys communis using a range of sublethal concentrations. The 10% lethal concentration (LC10) and half lethal concentration (LC25) of ACE had negative effects on the B. communis survival rate, adult longevity, parasitism rate, and emergence rate, and significantly prolonged the duration of the developmental cycle. ACE also had intergenerational effects, with some biological indices affected in the F1 generation after pesticide exposure. Transcriptomic analysis demonstrated that differentially expressed genes were enriched in specific pathways including the amino acid metabolism, carbohydrate metabolism, energy metabolism, exogenous metabolism, signal transduction, and glutathione metabolism pathways. These results indicated strong contact toxicity of ACE to B. communis, which may inhibit their biological control capacity. These results improve our understanding of the toxicological mechanisms of parasitic natural enemies in response to insecticide exposure.

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.

Sublethal and Transgenerational Effects of Reduced-Risk Insecticides on Macrolophus basicornis (Hemiptera: Miridae)

Reduced-risk insecticides and mirid predators have been used to control Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) in tomato crops. However, even when causing low mortality to the beneficial insects, these products might cause side effects. This study investigated the sublethal and transgenerational effects of buprofezin, cyantraniliprole, and spiromesifen on Macrolophus basicornis (Stal) (Hemiptera: Miridae). After 72 h of exposure of third-instar nymphs and adults to residues on tomato leaves, adult couples were formed and kept in cages with residue-free tomato leaves. The leaves were changed every 48 h and the offspring were assessed in 6 different periods. Body size was assessed by measuring the hind-tibia length of adults (F0) from exposed nymphs and in three different offspring groups. None of the insecticide residues caused a reduction on offspring populations or affected the body size of adults in generation F0. Regardless, buprofezin and spiromesifen reduced the tibia length of adults (F1) from exposed nymphs assayed in the third mating period. Cyantraniliprole did not affect any parameter and could be recommended for control of B. tabaci in association with M. basicornis releases. This study may contribute to future field assays of the compatibility of these insecticides with M. basicornis.

Low concentrations of selenium nanoparticles enhance the performance of a generalist parasitoid and its host, with no net effect on host suppression

BACKGROUND

The environmental and economic costs of conventional insecticides have stirred an interest in alternative management tactics, including the use of nanotechnologies. Selenium nanoparticles (SeNPs) have many applications in agriculture but may not be compatible with biological control; however, low concentrations of SeNPs may benefit natural enemies via hormesis. This study investigates the concentration-dependent effects of SeNPs (0-1000 mg L-1 ) on Anisopteromalus calandrae (Howard) (Hymenoptera: Pteromalidae), a generalist parasitoid of stored product pests.

RESULTS

The LC50 of SeNPs was 1540 mg L-1 for female parasitoids and 1164 mg L-1 for males. SeNPs had a significant hormetic effect; average lifespan increased by 10% at a concentration of 4.03 mg L-1 for females and by 35% at 13.83 mg L-1 for males. In a bioassay including hosts [the azuki bean beetle, Callosobruchus chinensis (L.) (Coleoptera: Chrysomelidae: Bruchinae)], a low concentration of SeNPs (25 mg L-1 ) enhanced the performance of female parasitoids; lifespan increased by 23% and the number of offspring increased by 88%. However, the number of emerging hosts did not significantly decrease; in the absence of parasitism, SeNPs actually improved host emergence by 17%.

CONCLUSION

Because higher concentrations of SeNPs reduced parasitoid lifespan, whereas low concentrations enhanced not only parasitoid performance but also host emergence, practitioners should exercise caution when considering SeNPs for use in integrated pest management. © 2023 Society of Chemical Industry.

Hormesis, the Individual and Combined Phytotoxicity of the Components of Glyphosate-Based Formulations on Algal Growth and Photosynthetic Activity

The occurrence of the market-leading glyphosate active ingredient in surface waters is a globally observed phenomenon. Although co-formulants in pesticide formulations were considered inactive components from the aspects of the required main biological effect of the pesticide, several studies have proven the high individual toxicity of formulating agents, as well as the enhanced combined toxicity of the active ingredients and other components. Since the majority of active ingredients are present in the form of chemical mixtures in our environment, the possible combined toxicity between active ingredients and co-formulants is particularly important. To assess the individual and combined phytotoxicity of the components, glyphosate was tested in the form of pure active ingredient (glyphosate isopropylammonium salt) and herbicide formulations (Roundup Classic and Medallon Premium) formulated with a mixture of polyethoxylated tallow amines (POEA) or alkyl polyglucosides (APG), respectively. The order of acute toxicity was as follows for Roundup Classic: glyphosate < herbicide formulation < POEA. However, the following order was demonstrated for Medallon Premium: herbicide formulation < glyphosate < APG. Increased photosynthetic activity was detected after the exposure to the formulation (1.5-5.8 mg glyphosate/L and 0.5-2.2 mg POEA/L) and its components individually (glyphosate: 13-27.2 mg/L, POEA: 0.6-4.8 mg/L), which indicates hormetic effects. However, decreased photosynthetic activity was detected at higher concentrations of POEA (19.2 mg/L) and Roundup Classic (11.6-50.6 mg glyphosate/L). Differences were demonstrated in the sensitivity of the selected algae species and, in addition to the individual and combined toxicity of the components presented in the glyphosate-based herbicides. Both of the observed inhibitory and stimulating effects can adversely affect the aquatic ecosystems and water quality of surface waters.

Chemical Exposure of Synthetic Pyrethroid on Deltamethrin Under the Selection Pressure over the Generations: A Reproductive Potential Study of Anopheles stephensi

Biochemical synthetic pyrethroids, deltamethrin are presently used insecticides for the control of mosquito vector-borne diseases in worldwide. Mosquito re-emergence with diseases becoming a serious problem due to development of insecticide resistance. The comprehensive knowledge on the underlying mechanisms of resistance against deltamethrin is required for implementation of an efficient vector control programme. The assessment of the biological fitness of a mosquito strain exposed to insecticide pressure is extremely vital because it provides information on the development of resistance. In the present study, the adult stage of malaria vector, Anopheles stephensi, was designated for the study of deltamethrin resistance (F40 generations). The non-blood-fed, laboratory-reared females to sub-lethal doses of deltamethrin (0.004%, 0.005%, 0.007%, or 0.01%) exposed to every generation for up to F40. The adult mosquito susceptibility was performed by WHO standard method for evaluation. After 24 h, mortality was recorded in both treated and control groups. Therefore, the biological fitness characteristics such as feeding, fecundity, hatchability, egg retention, immature duration, adult emergence, and adult life span were studied to assess the exposed deltamethrin under selection pressure as compared to the unexposed (control) population. The laboratory selection of An. stephensi exposed deltamethrin over the generations were diminished its biological fitness. Information on biological fitness including reproductive potential of mosquito strain under selection pressure against deltamethrin is incredibly necessary because it would facilitate in resistance management. Baseline information gives in this experiment will guide for future studies on the susceptibilities of wild malaria mosquito populations in India.

Combined effects of spinetoram and Microcystis aeruginosa on Daphnia pulex offspring: Maternal effects and multigenerational implications

The increasing occurrence of harmful algal blooms (HABs) in freshwater ecosystems detrimentally affect global water environments. Zooplankton's role in controlling HABs is hindered by contaminant exposure, necessitating research into combined stressors' ecological impacts. The response of Daphnia, a freshwater keystone species, to environmental stressors can be influenced by its maternal effects. Here, we investigated the combined effects of the world-widely used insecticide spinetoram and non-toxic HABs species Microcystis aeruginosa on the life-history traits of D. pulex offspring produced from different maternal food conditions. Four maternal groups were established, with each group receiving a specific blend of C. vulgaris (Ch) and M. aeruginosa (Ma) in varying proportions: A (100% Ch), B (90% Ch + 10% Ma), C (80% Ch + 20% Ma), and D (70% Ch + 30% Ma). The offspring from the third brood were gathered, and a 21-day experiment was carried out, involving various feeding groups (AA, AD, BA, BB, CA, CC, DA, and DD). Results demonstrated that grazing on M. aeruginosa by D. pulex induced maternal effects on their offspring, with the continuous exposure group showing an enhanced tolerance to M. aeruginosa. This study also unveiled that spinetoram could interfere with the molting of D. pulex, leading to developmental retardation. The Recovery Group exhibited an intriguing phenomenon: under the influence of both concentrations of the pesticide spinetoram (0.18, 0.35 μg L-1), D. pulex produced more offspring. This might be due to a combined strategy of allocating more energy towards reproduction in response to low-quality food and a potential hormetic effect from low concentrations of spinetoram. Assessing the interplay of combined stressors across multiple generations, encompassing harmful algal blooms (HABs) and environmental pollutants, is essential for predicting population responses to evolving environmental conditions. This understanding is vital for the protection and management of aquatic environments and ecosystems.

Low concentrations of cyantraniliprole negatively affects the development of Spodoptera frugiperda by disruption of ecdysteroid biosynthesis and carbohydrate and lipid metabolism

In addition to the acute lethal toxicity, insecticides might affect population dynamics of insect pests by inducing life history trait changes under low concentrations, however, the underlying mechanisms remain not well understood. Here we examined systemic impacts on development and reproduction caused by low concentration exposures to cyantraniliprole in the fall armyworm (FAW), Spodoptera frugiperda, and the putative underlying mechanisms were investigated. The results showed that exposure of third-instar larvae to LC10 and LC30 of cyantraniliprole significantly extended larvae duration by 1.46 and 5.41 days, respectively. Treatment with LC30 of cyantraniliprole significantly decreased the pupae weight and pupation rate as well as the longevity, fecundity and egg hatchability of female adults. Consistently, we found that exposure of FAW to LC30 cyantraniliprole downregulated the mRNA expression of four ecdysteroid biosynthesis genes including SfNobo, SfShd, SfSpo and SfDib and one ecdysone response gene SfE75 in the larvae as well as the gene encoding vitellogenin (SfVg) in the female adults. We also found that treatment with LC30 of cyantraniliprole significantly decreased the whole body levels of glucose, trehalose, glycogen and triglyceride in the larvae. Our results indicate that low concentration of cyantraniliprole inhibited FAW development by disruption of ecdysteroid biosynthesis as well as carbohydrate and lipid metabolism, which have applied implications for the control of FAW.

Impact of a glyphosate-based herbicide on the longevity, fertility, and transgenerational effects on Chrysopa pallens (Rambur) (Neuroptera: Chrysopidae)

Glyphosate-based herbicides (GBHs) are common herbicide formulations used in the field and are increasingly used worldwide with the widespread cultivation of herbicide-tolerant genetically modified crops. As a result, the risk of arthropod exposure to GBH is increasing rapidly. Chrysopa pallens (Rambur) (Neuroptera: Chrysopidae) is a common predatory natural enemy in agroecosystems, which is exposed to GBH (Roundup®) while preying on pests. To identify and characterize the potential effects of GBH on C. pallens, the life tables of C. pallens larvae and adults fed with GBH were constructed. Moreover, the effects of GBH treatment on the expression of genes involved in insulin signalling in adults were analyzed using qRT-PCR. The results showed that GBH treatment altered the pupal period and preadult stage of C. pallens larvae. However, it did no effect on longevity, fecundity, and population parameters and two insulin receptor genes (InR1, InR2), a serine/threonine kinase (Akt), an extracellular-signal-regulated kinase (erk), and vitellogenin (Vg1) expression of C. pallens. Adults feeding on GBH significantly altered development, longevity, and differences in the mean generation time of the F0 generation. However, GBH feeding only minimally influenced the growth and population parameters of the F1 generation. In addition, InR1, InR2, erk, and Vg1 expression in the F0 generation were downregulated on the fifth day of feeding on GBH. Furthermore, the expression levels of InR1, InR2, Akt, erk, and Vg1 in C. pallens decreased with the increase of GBH concentration, although the expression levels returned to control levels on the tenth day. Overall, the consumption of the GBH by larvae and adults of C. pallens had minimal effect on the growth and population parameters of C. pallens. The findings of this study can provide a reference for elucidating the environmental risks of GBH, guiding the optimal use of glyphosate in agricultural practices in the future.

Sublethal Effects of Emamectin Benzoate on Development and Reproduction and RNAi of the Vitellogenin Gene in Spodoptera frugiperda

Spodoptera frugiperda, one of the most destructive corn pests in the world, invaded China in December 2018. In this study, sublethal concentrations (LC10 and LC30) of emamectin benzoate (EB) were used to treat pesticide-free treatment (PFT) and EB treatment (ET) of S. frugiperda. In PFT, compared with the control (CK), the pupal weight, hatching rate, and pupation rate of LC10 and LC30 groups were significantly reduced. The fecundity and the expression of vitellogenin gene (SfVg) were decreased after LC30 treatment, while the LC10 treatment groups showed no significant difference from the control group. In ET, compared to CK, the fecundity was increased by 11.14 and 18.8%. The expression of SfVg was upregulated by 2.6 times after LC30 treatment. Moreover, RNAi-mediated SfVg knockdown resulted in a nearly 70% reduction in oviposition. The result provided a theoretical basis for optimizing the application of EB and Vg-dsRNA in the control of S. frugiperda.

Curcumin-PVP improves the in vitro efficacy of ivermectin against resistant and susceptible Haemonchus contortus

Ivermectin (IVM) resistance in parasitic nematodes such as Haemonchus contortus has spurred a search for substances that help to recover its efficacy. One potential agent is the natural product curcumin (CUR). In this study, CUR was combined with polyvinylpyrrolidone (PVP) (CUR/PVP) to improve its solubility and biological applicability. This study determined the effect of CUR preincubation on the effective concentration 50% (EC50) of IVM in three H. contortus isolates with different susceptibilities to IVM. The IVM EC50 was determined for three H. contortus isolates with different IVM susceptibilities using the larval migration inhibition (LMI) test. The three isolates were (i) PARAISO (IVM resistant), (ii) FMVZ-UADY (IVM susceptible), and (iii) CENID-SAI INIFAP (reference IVM susceptible). The L3 of each isolate were preincubated for 3 h with one of three concentrations of CUR (μg curcumin/mL): CONC-1 (3.67), CONC-2 (5.67), or CONC-3 (8.48). Corresponding controls were performed without CUR. The EC50 of IVM was determined for each isolate after they were exposed to the different CUR concentrations. The EC50 of IVM differed between the isolates PARAISO > FMVZ-UADY > CENID-SAI INIFAP (P < 0.05). The CUR preincubation at CONC-1 did not decrease the EC50 of IVM for any of the three isolates, suggesting a hormetic effect. By contrast, CUR preincubation at CONC-2 or CONC-3 decreased the IVM EC50 for the PARAISO isolate (P < 0.05) compared with the reference isolate and reduced the EC50 of IVM for the FMVZ-UADY and CENID-SAI INIFAP isolates below the EC50 for the CENID-SAI INIFAP isolate without CUR preincubation. In conclusion, preincubation of H. contortus L3 with CUR reduced the EC50 of IVM for field isolates classified as resistant and susceptible to IVM. The CUR preincubation reduced the IVM resistance factor in the different isolates tested.

Callosobruchus maculatus males and females respond differently to grandparental effects

In this study, we used the cowpea weevil Callosobruchus maculatus (Coleoptera: Chrysomelidae) and two essential oils (mint and rosemary) to investigate the effect of the parents (F0) exposure to a sublethal dose of essential oil on grand offspring (F2) encountering the same essential oil. Then we evaluated biological parameters, including immature development time, sex ratio, adult emergence, egg number, egg hatch, longevity, and mating behaviors in three generations (F0, F1, and F2). Results showed when F0 experienced essential oil in the embryonic stage, parental and grandparental effects were more severe than adulthood experiences. Also, grandparental effects increased or decreased reactions of F2 generation when faced with a similar essential oil, depending on grand offspring sex. For example, when grandparents experienced rosemary essential oil in the embryonic stage, they produced more tolerant female grand offspring with a better ability to cope with the same essential oil (increased adult longevity and egg number). However, male grandoffspring were more sensitive (had a higher mortality percentage and less copulation success). Grandparental effects of exposure to mint essential oil diminished female grand offspring longevity and improved male copulation behavior parameters such as increased copulation duration and decreased rejection by females. In all, grandparental effects were different in male and female grand offspring based on the essential oil type experienced by F0.

Sublethal chemical stimulation of arthropod parasitoids and parasites of agricultural and environmental importance

An increasing number of studies have reported stimulation of various organisms in the presence of environmental contaminants. This has created a need to critically evaluate sublethal stimulation and hormetic responses of arthropod parasitoids and parasites following exposure to pesticides and other contaminants. Examining this phenomenon with a focus on arthropods of agricultural and environmental importance serves as the framework for this literature review. This review shows that several pesticides, with diverse chemical structures and different modes of action, applied individually or in combination at sublethal doses, commonly stimulate an array of arthropod parasitoids and parasites. Exposure at sublethal doses can enhance responses related to physiology (e.g., respiration, total lipid content, and total protein content), behavior (e.g., locomotor activity, antennal drumming frequency, host location, and parasitization), and fitness (longevity, growth, fecundity, population net and gross reproduction). Concordantly, the parasitic potential (e.g., infestation efficacy, parasitization rate, and parasitoid/parasite emergence) can be increased, and as a result host activities inhibited. There is some evidence illustrating hormetic dose-responses, but the relevant literature commonly included a limited number and range of doses, precluding a robust differentiation between sub- and superNOAEL (no-observed-adverse-effect level) stimulation. These results reveal a potentially significant threat to ecological health, through stimulation of harmful parasitic organisms by environmental contaminants, and highlight the need to include sublethal stimulation and hormetic responses in relevant ecological pesticide risk assessments. Curiously, considering a more utilitarian view, hormesis may also assist in optimizing mass rearing of biological control agents for field use, a possibility that also remains neglected.

Mosquito larvae exposed to a sublethal dose of photosensitive insecticides have altered juvenile development but unaffected adult life history traits

BACKGROUND

Larvicides are critical for the control of mosquito-borne diseases. However, even sublethal exposure to a larvicide can alter development and life history traits, which can then affect population density and disease transmission dynamics. Photosensitive insecticides (PSIs) are a promising class of larvicide that are toxic when ingested and activated by light. We investigated whether the time of day when exposure occurs, or the process of pupation, affects larval susceptibility to PSI phototoxicity in the mosquito Anopheles gambiae, and whether sublethal exposure to PSIs alters life history traits.

METHODS

Larvae were treated with lethal concentrations of the PSIs methylene blue (MB) and rose bengal (RB), and larval survival was measured at various times of day. Additionally, larvae were exposed to two concentrations of each PSI that resulted in low and medium mortality, and the life history traits of the surviving larvae were measured.

RESULTS

Pupation, which predominantly occurs in the evening, protected larvae from PSI toxicity, but the toxicity of PSIs against larvae that had yet to pupate was unaffected by time of day. Larval exposure to a sublethal concentration of MB, but not RB, shortened the time to pupation. However, larval exposure to a sublethal concentration of RB, but not MB, increased pupal mortality. Neither PSI had a meaningful effect on the time to eclosion, adult longevity, or adult melanization potential.

CONCLUSIONS

PSIs are lethal larvicides. Sublethal PSI exposure alters mosquito development, but does not affect adult life history traits.

Stimulation of insect vectors of pathogens by sublethal environmental contaminants: A hidden threat to human and environmental health?

Sublethal stimulation and hormetic responses are increasingly identified and acknowledged in scientific research. However, the occurrence and characteristics of such responses in insect vectors of pathogens are little explored and poorly understood. Here, we collate significant evidence from the scientific literature showing that sublethal doses of environmental contaminants, such as pesticides, microplastics, and plasticizers, induce stimulation and hormetic responses in insect vectors of pathogens of agricultural and public health importance, including mosquitoes, other dipterans, psyllids, aphids, and planthoppers. Physiological, behavioral, and demographic traits can be enhanced by exposure to lower subtoxic contaminant doses while being inhibited by higher toxic doses. Energetic trade-offs can also occur, especially at sublethal doses higher than the no-observed-adverse-effect level (NOAEL). The relevant literature is limited and so are the number of doses commonly included in the studies, precluding firm conclusions and enhanced understanding. Nevertheless, these effects are significant and could undermine human and environmental health, and thus sustainability agendas, if ultimately the transmission of pathogens and disease spread and severity are increased. Further research is urgently needed to tackle these phenomena, especially under field conditions. The findings discussed here are relevant to chemical risk assessment and chemical safety evaluations, in which all possible effects from the lowest to higher doses should be considered.

Sublethal phosphine fumigation induces transgenerational hormesis in a factitious host, Corcyra cephalonica

BACKGROUND

The rice moth, Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae) is a pest of stored grains and widely used as a factitious host during the mass rearing of several natural enemies of crop pests. Hormesis is well-documented in pest insects, to some extent in natural enemies of pests.

RESULTS

We report transgenerational stimulatory effects of the widely used fumigant, phosphine. The study reports the consequences of sublethal, low lethal and median lethal concentrations (LC5 , LC25 and LC50 ) and untreated control for two sequential generations of the species (G1 to G2 ). In this study, we investigated the life-history traits, nutrient reserves (protein, lipid and carbohydrate) and larval gut microbiome (using 16 s rRNA V3-V4 metagenomics sequencing) of C. cephalonica. Stimulatory effects were observed for various biological traits of C. cephalonica, notably adult longevity, emergence and increased egg hatchability when exposed to LC5 of phosphine. The total protein, lipid and carbohydrate contents of C. cephalonica also were found to be significantly increased by LC5 in both generations. The microbial diversity of LC5 treated larval gut was higher and found to be different from the rest of the treatments. This is the first report showing hormesis to a fumigant insecticide.

CONCLUSION

Our findings increase knowledge on the interaction between hormesis, nutrient reserves and gut bacteria in C. cephalonica exposed to insecticides. Overall, the present study establishes phosphine-induced hormesis at LC5 in the host C. cephalonica, which might help improve the quality of mass rearing of various natural enemies. © 2023 Society of Chemical Industry.

Functional response of an egg parasitoid, Trichogramma chilonis Ishii to sublethal imidacloprid exposure

BACKGROUND

The effectiveness of a biological control agent depends on how well it can control pests and how compatible it is with pesticides. Therefore, we reported the multigenerational effect of a commonly used insecticide, imidacloprid, on the functional response of a widely acclaimed egg parasitoid, Trichogramma chilonis Ishii, to different densities of the host Corcyra cephalonica Stainton eggs. The study investigated the outcomes of the median lethal concentration (LC50 ) and sublethal concentrations (LC5 , LC30 ), along with control treatments for five continuous generations (F1 to F5 ).

RESULTS

The results showed that the F5 generation of LC30 , both of the F1 and F5 generations of LC50 , and the control all had a Type II functional response. A Type I functional response was exhibited for the F1 generation of LC30 and both generations of LC5 . The attack rate on host eggs treated with LC5 and LC30 did not change (decrease) with the shift in the type of functional response as compared to the control. A significant increase in the searching efficiency (a) was observed in the later generation (F5 ) under the exposure of LC5 and LC30 imidacloprid concentrations. A lower handling time (Th ) in both generations of the LC5 followed by LC30 treated individuals was observed when compared with the control and LC50 treatments. The per capita parasitization efficiency (1/Th ) and the rate of parasitization per handling time (a/Th ) were also considerably higher in both the generations of LC5 and LC30 than in the control and LC50 , thereby implying positive effects of imidacloprid on the parasitization potential of T. chilonis.

CONCLUSION

Altogether, these multigenerational outcomes on the functional response of T. chilonis could be leveraged to control the intractable lepidopteran pests under the mild exposure of imidacloprid in integrated pest management (IPM) programs as well as in the mass rearing of the parasitoid, T. chilonis. © 2023 Society of Chemical Industry.

Low-dose chemical stimulation and pest resistance threaten global crop production

Pesticide resistance increases and threatens crop production sustainability. Chemical contamination contributes to the development of pest resistance to pesticides, in part by causing stimulatory effects on pests at low sub-toxic doses and facilitating the spread of resistance genes. This article discusses hormesis and low-dose biological stimulation and their relevance to crop pest resistance. It highlights that a holistic approach is needed to tackle pest resistance to pesticides and reduce imbalance in accessing food and improving food security in accordance with the UN's Sustainable Development Goals. Among others, the effects of sub-toxic doses of pesticides should be considered when assessing the impact of synthetic and natural pesticides, while the promotion of alternative agronomical practices is needed to decrease the use of agrochemicals. Potential alternative solutions include camo-cropping, exogenous application of phytochemicals that are pest-suppressing or -repelling and/or attractive to carnivorous arthropods and other pest natural enemies, and nano-technological innovations. Moreover, to facilitate tackling of pesticide resistance in poorer countries, less technology-demanding and low-cost practices are needed. These include mixed cropping systems, diversification of cultures, use of 'push-pull cropping', incorporation of flower strips into cultivations, modification of microenvironment, and application of beneficial microorganisms and insects. However, there are still numerous open questions, and more research is needed to address the ecological and environmental effects of many of these potential solutions, with special reference to trophic webs.

Risk assessment of predatory lady beetle Propylea japonica's multi-generational exposure to three non-insecticidal agrochemicals

The effects of non-insecticidal agrochemicals on pest natural predators remain largely unexplored except bees and silkworm. The herbicide quizalofop-p-ethyl (QpE), fungicide thiophanate-methyl (TM), and plant growth regulator mepiquat chloride (MC) have been extensively applied as non-insecticidal agrochemicals. Here, we systematically evaluated multiple effects of these 3 non-insecticidal agrochemicals on three generations of Propylea japonica, an important agroforestry predatory beetle, including the effects on its development, reproduction, enterobacteria, and transcriptomic response. The results showed that QpE exhibited a hormetic effect on P. japonica, thus significantly increasing the survival rate of generation 2 (F2) females, generation 3 (F3) females, and F3 males and body weight of F3 males. However, three successive generations exposed to TM and MC had no significant effect on longevity, body weight, survival rate, pre-oviposition period, and fecundity of P. japonica. Additionally, we investigated the effects of MC, TM, and QpE exposure on gene expression and gut bacterial community of F3 P. japonica. Under MC, TM, and QpE exposure, the overwhelming genes of P. japonica (99.90 %, 99.45 %, and 99.7 %) remained unaffected, respectively. Under TM and MC exposure, differentially expressed genes (DEGs) were not significantly enriched in any KEGG pathway, indicating TM and MC did not significantly affect functions of P. japonica, but under QpE exposure, the expression levels of drug metabolism-related genes were down-regulated. Although QpE treatment did not affect gut dominant bacterial community composition, it significantly increased relative abundances of detoxification metabolism-related bacteria such as Wolbachia, Pseudomonas and Burkholderia in P. japonica. However, TM and MC had no significant effect on the gut bacterial community composition and relative abundance in P. japonica. This study revealed for the first time the mechanism by which P. japonica might compensate for gene downregulation-induced detoxification metabolism decline through altering symbiotic bacteria under QpE exposure. Our findings provide reference for the rational application of non-insecticidal agrochemicals.

Hormetic effects of neonicotinoid insecticides on Rhizoglyphus robini (Acari: Acaridae)

The stimulation of biological processes by sublethal doses of insecticides or other stressors is known as hormesis. Here, we have evaluated whether exposure to field-relevant or low concentrations of neonicotinoids induce changes in the reproductive capacity of the bulb mite Rhizoglyphus robini (Acari: Acaridae). Among the tested neonicotinoids imidacloprid, thiamethoxam, and dinotefuran, the highest hormetic effect on the reproduction of R. robini occurred 24 h after the 48 h exposure period to imidacloprid at concentrations of 70 and 140 mg a.i./L. Despite the stimulating effects of imidacloprid on mite reproduction, no significant differences were observed in the offspring (F₁) for biological aspects including egg hatch rate, embryonic period and sex ratio, while an increase was found in the duration of development time from egg to adult. Evaluation of the detoxification enzyme activities of treated adults showed that the highest activity of carboxyl/cholinesterases, cytochrome P450s, and glutathione S-transferases was obtained when exposed to 70, 140 and 70 mg a.i./L imidacloprid, immediately after the exposure period, respectively. Also, an increase in the activity of the antioxidant enzyme catalase was observed compared to that of the control. After imidacloprid pretreatment (140 mg a.i./L), the tolerance of adult mites to diazinon was increased about two-fold. This study shows that exposure to imidacloprid can induce hormetic effects on R. robini and could severely complicate its control due to a higher reproduction, enhanced detoxification enzyme activities, and increased tolerance against other pesticides.

Evaluation of Transgenerational Effects of Sublethal Imidacloprid and Diversity of Symbiotic Bacteria on Acyrthosiphon gossypii

Symbiotic bacteria and hormesis in aphids are the driving forces for pesticide resistance. However, the mechanism remains unclear. In this study, the effects of imidacloprid on the population growth parameters and symbiotic bacterial communities of three successive generations of Acyrthosiphon gossypii were investigated. The bioassay results showed that imidacloprid had high toxicity to A. gossypii with an LC₅₀ of 1.46 mg·L^-1. The fecundity and longevity of the G0 generation of A. gossypii decreased when exposed to the LC₁₅ of imidacloprid. The net reproductive rate (R₀), intrinsic rate of increase (r_m), finite rate of increase (λ), and total reproductive rate (GRR) of G1 and G2 offspring were significantly increased, but those of the control and G3 offspring were not. In addition, sequencing data showed that the symbiotic bacteria of A. gossypii mainly belonged to Proteobacteria, with a relative abundance of 98.68%. The dominant genera of the symbiotic bacterial community were Buchnera and Arsenophonus. After treatment with the LC₁₅ of imidacloprid, the diversity and species number of bacterial communities of A. gossypii decreased for G1-G3 and the abundance of Candidatus-Hamiltonella decreased, but Buchnera increased. These results provide insight into the resistance mechanism of insecticides and the stress adaptation between symbiotic bacteria and aphids.

Isolation, purification and biochemical characterization of Conopomorpha cramerella farnesol dehydrogenase

In Southeast Asia, Conopomorpha cramerella (Snellen) which is commonly known as the cocoa pod borer (CPB) moth has been identified as the most detrimental pest of Theobroma cacao L. Apart from the various side effects on human health and non-target organisms, heavily relying on synthetic pyrethroid insecticides to control CPB infestations also increases the environmental contamination risks. Thus, developing biorational insecticides that minimally affect the non-target organism and environment by targeting the insect growth regulation process is needed to manage the pest population. In insects, juvenile hormones (JH) regulate critical biological events, especially metamorphosis, development and reproduction. Since the physiological roles of JH III vary among different organisms, the biochemical properties, especially substrate specificity and analogue inhibition, may also be different. Therefore, studies on the JH III biosynthetic pathway enzymes in both plants and insects are beneficial to discover more effective analogues. Bioinformatic analysis and biochemical characterization of a NADP⁺ -dependent farnesol dehydrogenase, an intermediate enzyme of the JH III pathway, from C. cramerella (CcFolDH), were described in this study. In addition, the farnesol analogues that may act as a potent analogue inhibitor for CcFolDH ware determined using in vitro enzymatic study. The phylogenetic analysis indicated that CcFolDH shared a close phylogenetic relationship to the honeybee's short-chain dehydrogenase/reductase. The 27 kDa CcFolDH has an NADP(H) binding domain with a typical Rossmann fold and is likely a homotetrameric protein in the solution. The enzyme had a greater preference for substrate trans, trans-farnesol and coenzyme NADP⁺ . In terms of analogue inhibitor inhibition, hexahydroxyfarnesyl acetone showed the highest inhibition (the lowest K_i ) compared to other farnesol analogues. Thus, hexahydroxyfarnesyl acetone would serve as the most potent active ingredient for future biorational pesticide management for C. cramerella infestation. Based on the bioinformatic analyses and biochemical characterizations conducted in this research, we proposed that rCcFolDH differs slightly from other reported farnesol dehydrogenases in terms of molecular weight, substrate preference, coenzymes utilization and analogue inhibitors selection.

Mechanisms underlying the effects of low concentrations of chlorantraniliprole on development and reproduction of the fall armyworm, Spodoptera frugiperda

It is well known that sublethal dose of insecticides induces life history trait changes of both target and non-target insect species, however, the underlying mechanisms remain not well understood. In this study, the effects of low concentrations of the anthranilic diamide insecticide chlorantraniliprole on the development and reproduction of the fall armyworm (FAW), Spodoptera frugiperda, were evaluated, and the underlying mechanisms were explored. The results showed that exposure of FAW to LC₁₀ and LC₃₀ chlorantraniliprole prolonged the larvae duration, decreased the mean weight of the larvae and pupae, and lowered the pupation rate as well as emergence rate. The fecundity of female adults was also negatively affected by treatment with low concentrations of chlorantraniliprole. Consistently, we found that exposure of FAW to LC₃₀ chlorantraniliprole downregulated the mRNA expression of juvenile hormone (JH) esterase (SfJHE), leading to the increase of JH titer in larvae. We also found that treatment with low concentrations of chlorantraniliprole suppressed the expression of ribosomal protein S6 kinase1 (SfS6K1) in female adults, resulting in the downregulation of the gene encoding vitellogenin (SfVg). These results provided insights into the mechanisms underlying the effects of low concentrations of insecticides on insect pests, and had applied implications for the control of FAW.

Sub-lethal effects of spinetoram application interacts with temperature in complex ways to influence respiratory metabolism, life history and macronutrient composition in false codling moth (Thaumatotibia leucotreta)

In many pests, insecticide efficacy is dependent on environmental conditions, including ambient temperature. However, it remains unknown if thermal history alters sub-lethal effects to potentially enhance or reduce pesticide resistance in the false codling moth (FCM), Thaumatotibia leucotreta. Here, using FCM, a pest of economic importance in South Africa infesting several commercial food crops, we report results of sub-lethal exposure to spinetoram, an insecticide that disrupts the nervous system. We investigate whether insecticide efficacy is temperature dependent or perhaps interacts with thermal history by testing the effect of a combination of a sub-lethal dose of spinetoram (4 mg/100 ml) and developmental temperature acclimation (22˚C and 28˚C, i.e., a few degrees above or below optimal development temperatures) on the metabolic rate, life history traits and body composition of FCM in the laboratory. A sub-lethal dose of spinetoram reduced metabolic rate of FCM pupae significantly, led to smaller pupal mass and decreased emergence rates. Additionally, males acclimated at 28 °C had a significantly higher emergence rate compared to males acclimated at 22 °C. Body water, body lipids and body protein reserves of adult FCM tended to be higher in the insecticide treatment compared to the control in the 22 °C acclimation group. In the 28 °C acclimation group, body water, lipids and proteins were lower in the insecticide treatment versus the control. Furthermore, sex influenced both emergence rate and body composition with the direction of change depending on insecticide and temperature treatments. Overall, a sub-lethal dose of spinetoram negatively affects body composition and life history traits but interacts with temperature in complex ways. Therefore, both lethal and sub-lethal effects of spinetoram on FCM, in combination with information on the thermal environment experienced by the pest, should be taken into consideration when pest control decisions are made.

Effects of imidacloprid-induced hormesis on the development and reproduction of the rose-grain aphid Metopolophium dirhodum (Hemiptera: Aphididae)

Field populations of insect pests are affected by sub-lethal doses of insecticides, leading to hormesis. Imidacloprid is a neonicotinoid insecticide widely used to control various sucking insect pests, including aphids. In this study, the effects of sub-lethal concentrations of imidacloprid on the life table traits of the rose-grain aphid Metopolophium dirhodum (Walker) were evaluated on parental and first filial generations. The results showed that sub-lethal concentrations of imidacloprid significantly reduced the fecundity, adult longevity, and reproductive period of M. dirhodum in parental generation (F₀). However, the imidacloprid-induced hormetic effects on development and reproduction were detected in the F₁ generation. These hormetic effects were indicated by significantly higher adult longevity, fecundity, survival rate, intrinsic and finite rates of increase, and net reproductive rate of first filial generation (F₁) of M. dirhodum. Our finding indicated that the application of sub-lethal concentrations of imidacloprid inhibited parental generation (F₀), but it significantly stimulated the population growth of filial generation (F₁) in the M. dirhodum. The results support the inclusion of insecticides in integrated pest management programs for managing wheat aphids.

Potential demographic impact of the insecticide mixture between thiacloprid and deltamethrin on the cotton aphid and two of its natural enemies

The use of pesticides impairs biological control in the agroecosystems and thus compromises the effectiveness of natural enemies against populations of pest species. The concerns over pesticides should expand beyond mortality and encompass their sublethal effects and their consequences to the target insect species and natural enemies to aid in our understanding of the potential and consequential use of these compounds. The present study aimed to determine the effects of an insecticide mixture on life-history and demographic parameters of the cotton aphid Aphis gossypii Glover (Hemiptera: Aphididae) and two of its main parasitoids - Aphidius flaviventris Kurdjumov (Hymenoptera: Aphelinidae) and Aphidius colemani Viereck (Hymenoptera: Braconidae). Based on the obtained results, thiacloprid + deltamethrin in its lethal concentration dose 20% of the pest population (LC₂₀) significantly affected the cotton aphid for two generations, increasing developmental time and demographic parameters. The LC₂₀ manifested changes in many demographic parameters of the parasitoid A. flaviventris. This concentration also increased preadult and female longevity, total pre-ovipositional period, and mean generation time (T) of A. colemani, but no other demographic parameters were affected. Nonetheless, the insecticide mixture did not affect the parasitism rate of A. colemani. Thus, the thiacloprid + deltamethrin mixture significantly impaired the cotton aphid population and its parasitoid A. flaviventris. Therefore, the use of thiacloprid + deltamethrin is not encouraged for controlling the parasitoid A. flaviventris, but it is a relatively safe compound for A. colemani.

Sub-lethal doses of imidacloprid alter food selection in the invasive garden ant Lasius neglectus

Despite several restrictions to their use, neonicotinoid insecticides are still widely employed worldwide. Residual sub-lethal amounts of these chemicals can have detrimental effects on the behavior of non-target insects. Toxic effects on economically important species such as bees have been widely documented, but less is known about their toxic action on other social insects, such as ants. In this study, we assessed the effect of different sub-lethal doses of the neonicotinoid imidacloprid on the ability of colonies of the invasive ant Lasius neglectus to select the most profitable resource. We used Y-shaped mazes having an imidacloprid-polluted or an unpolluted sucrose solution on the two branches. Two sucrose (0.1 M, 0.5 M) and two imidacloprid (1 μg/ml, 10 μg/ml) concentrations were used. In parallel, we evaluated the marking activity of foragers who fed on the same solutions. We found that the 0.1 M sugar solution polluted with 1 μg/ml imidacloprid was significantly more frequently selected in binary choices experiments than the unpolluted resource. Moreover, the ingestion of the same combination of sugar and imidacloprid significantly increased the marking rate of foragers. The higher concentration of the pollutant had lower effects, probably because of the hormesis phenomenon. Results suggest that the lower sub-lethal dose of imidacloprid can lead ants to select again the polluted resource. This "active" selection of the pollutant may magnify the negative effects on the colonies. Due to their ecological role, any impairment of ant survival or behavior may have detrimental cascade effects on the whole ecosystem.

Thiamethoxam in soybean seed treatment: Plant bioactivation and hormesis, besides whitefly control?

Amid concerns on the myriad of existing chemical stressors in agroecosystems, pesticides and particularly neonicotinoid insecticides are in the forefront. Despite that, these neurotoxic compounds remain the dominant group of insecticides in worldwide use with the added versatility of use in seed coatings. Such use sparks environmental concerns counterbalanced by their reported insecticidal efficacy and potential plant bioactivation. Nonetheless, this alleged double benefit and interconnection expected with neonicotinoids has been little explored particularly when the whole plant phenology is considered. Regardless of the expected efficacy against targeted insect pest species, like whiteflies, neonicotinoids may spark dual effect on plants - negative at higher concentrations, positive at low concentrations, which is consistent with the hormesis phenomenon that may be expressed as a plant bioactivation. This effect may also cascade to the targeted insect species, what deserves attention. Therefore, soybean seeds treated with increasing concentrations of the neonicotinoid thiamethoxam were followed throughout their development in greenhouse, recording the plant response and yield, besides their effect in whiteflies (Bemisia tabaci MEAM1). Thiamethoxam application was correlated to leaf contents of thiamethoxam and its metabolite clothianidin. Plant hormesis was found for leaf area and root growth, but not for other plant morphological or physiological parameters, nor plant yield. The insecticide concentration-dependency compromised whitefly population growth without evidence of cascading any plant-mediated hormesis to the insects. Thus, although plant hormesis was recognized with thiamethoxam in treated soybean seeds in relevant parameters, no evidence of plant bioactivation was observed to justify its use with such a secondary objective, nor did this hormesis impair whitefly control.

Research Trends, Biases, and Gaps in Phytochemicals as Insecticides: Literature Survey and Meta-Analysis

A 76-year literature survey and meta-analyses were carried out to recognize the trends, biases, and knowledge gaps of studies focusing on major groups of compounds of botanical origin, or phytochemicals, as insecticides. The survey found that the main phytochemicals prospected as insecticides belong to the following major chemical groups: terpenoids, terpenes, and carbonyl, all of which were tested, mainly against beetles (Coleoptera), caterpillars (i.e., larvae of Lepidoptera), and mosquitoes and other flies (i.e., Diptera). These studies are burgeoning at an exponential rate, with an evident focus on mortality endpoint estimates, but they are also neglecting sublethal assessments. China and India in Asia, as well as Brazil in the Americas, were responsible for most studies. The majority of the papers used stored grain insects as experimental models, which limits the applicability and representativeness of the findings. As a result, the main modes of exposure tested were fumigation and contact, which leads to the prevalence of estimates of lethal concentration in these studies. Therefore, a broader range of insect species deserves testing, with suitable modes of exposure identifying and characterizing the main molecules responsible for the insecticidal activity, which is seldom performed. Attention to these needs will circumvent current biases and allow the recognition of the main patterns of association between the origin and structure of phytochemicals and their insecticidal effects.

Sublethal effects of chlorfenapyr on Plutella xylostella (Lepidoptera: Plutellidae)

BACKGROUND

The diamondback moth (DBM), Plutella xylostella (L.), is the most destructive pest of cruciferous vegetables worldwide. Chlorfenapyr is an important insecticide for controlling DBM. The impacts of three sublethal doses (LC₁ , LC₁₀ and LC₃₀ ) of chlorfenapyr on the chlorfenapyr-exposed DBM individuals and their unexposed F₁ and F₂ offspring were investigated in order to reveal the non-lethal deleterious effects of chlorfenapyr and its potential hormetic effects.

RESULTS

LC₁ significantly increased female pupa weight of F₀ and F₁ generations, and F₀ fecundity as well as F₁ gross reproduction rate (GRR). The LC₁ -elicited rise in emergency rate and fecundity was significantly greater in F₀ than in F₁ . By contrast, LC₃₀ significantly decreased age-specific survival rates, pupation rate, male pupal weight, emergence rate and fecundity of F₀ and F₁ generations as well as female adult proportion and GRR, net reproduction rate (R₀ ), intrinsic rate of increase (r_m ) and finite rate of increase (λ) of F₁ generation. The LC₃₀ -induced reductions in pupation rate, adult emergence rate, male and female pupa weight, and fecundity were greater in F₁ than in F₀ . While LC₁₀ elicited only a mild inhibition (extension of pupal duration) in F₀ , it yielded both deleterious (drops in female proportion and age-specific survivals) and hormetic effects (ups in male longevity and female fecundity) in F₁ .

CONCLUSION

The results demonstrate that the sublethal effects of chlorfenapyr on DBM vary from inhibition to stimulatory hormesis, depending on the dose and generation. © 2022 Society of Chemical Industry.

Combined effects of global warming and chlorpyrifos exposure on the annual fish Nothobranchius furzeri

Global warming and environmental pollution threaten aquatic ecosystems. While interactive effects between both stressors can have more than additive consequences, these remain poorly studied for most taxa. Especially chronic exposure trials with vertebrates are scarce due to the high time- and monetary costs of such studies. We use the recently-established fish model Nothobranchius furzeri to assess the separate and combined effects of exposure to the pesticide chlorpyrifos (at 2 µg/L and 4 µg/L) and a 2 °C temperature increase. We performed a full life-cycle assessment to evaluate fitness-related endpoints including survival, total body length, maturation time, fecundity, critical thermal maximum (CTmax) and locomotor activity. Exposure to 4 µg/L chlorpyrifos slowed down male maturation, reduced fecundity and impaired growth of the fish. While the temperature increase did not affect any of the measured endpoints on its own, the combination of exposure to 2 µg/L CPF with an increase of 2 °C reduced growth and severely reduced fecundity, with almost no offspring production. Together, these findings suggest that climate change may exacerbate the impact of environmental pollution, and that interactive effects of chronic exposure to multiple stressors should be considered to predict how populations will be affected by ongoing global change.

Sublethal Effects of Thiamethoxam on Biological Traits and Detoxification Enzyme Activities in the Small Brown Planthopper, Laodelphax striatellus (Fallén)

The small brown planthopper (Laodelphax striatellus (Fallén), Hemiptera: Delphacidae), is an important agricultural pest of rice, and neonicotinoid insecticides are commonly used for controlling L. striatellus. However, the sublethal effects of thiamethoxam on L. striatellus remain relatively unknown. In this study, an age-stage life table procedure was used to evaluate the sublethal effects of thiamethoxam on the biological parameters of L. striatellus. Additionally, activities of carboxylesterase, glutathione S-transferase, and cytochrome P450 monooxygenase in the third instar nymphs were analyzed. The results indicated that the survival time of F0 adults and the fecundity of female adults decreased significantly after the third instar nymphs were treated with sublethal concentrations of thiamethoxam (LC15 0.428 mg/liter and LC30 0.820 mg/liter). The developmental duration, adult preoviposition period, total preoviposition period, and mean generation time of the F1 generation increased significantly, whereas the fecundity of the female adults, intrinsic rate of increase (ri), and finite rate of increase (λ) decreased significantly. The oviposition period was significantly shorter for the insects treated with LC30 than for the control insects. Neither sublethal concentrations had significant effects on the adult longevity, net reproduction rate (R0), or gross reproduction rate (GRR) of the F1 generation. The activities of carboxylesterase, glutathione-S-transferase, and cytochrome P450 monooxygenase increased significantly after the thiamethoxam treatments. These results indicate that sublethal concentrations of thiamethoxam can inhibit L. striatellus population growth and enhance detoxification enzyme activities.

Assessment of sublethal and transgenerational effects of spirotetramat, on population growth of cabbage aphid, Brevicoryne brassicae L. (Hemiptera: Aphididae)

The cabbage aphid (Brevicoryne brassicae L.) is a devastating pest of cruciferous crops causing economic damage worldwide and notably owing to its increasing resistance to commonly used pesticides. Such resistance prompts the development of integrated pest management (IPM) programs that include novel pesticides being effective against the aphids. Spirotetramat is a novel insecticide used against sap-sucking insect pests, particularly aphids. This study evaluated the toxicity of spirotetramat to adult apterous B. brassicae after 72 h using the leaf dipping method. According to the toxicity bioassay results, the LC₅₀ value of spirotetramat to B. brassicae was 1.304 mgL^-1. However, the sublethal concentrations (LC₅ and LC₁₅) and transgenerational effects of this novel insecticide on population growth parameters were estimated using the age-stage, two-sex life table theory method. The sublethal concentrations (LC₅; 0.125 mgL^-1 and LC₁₅; 0.298 mgL^-1) of spirotetramat reduced the adult longevity and fecundity of the parent generation (F₀). These concentrations prolonged the preadult developmental duration while decreasing preadult survival, adult longevity and reproduction of the F₁ generation. The adult pre-reproductive period was also extended by spirotetramat treatment groups. Subsequently, the population growth parameters such as the intrinsic rate of increase r, finite rate of increase λ and net reproductive rate R ₀ of the F₁ generation were decreased in spirotetramat treatment groups whereas, the mean generation time T of the F₁ generation was not affected when compared to the control. These results indicated the negative effect of sublethal concentrations of spirotetramat on the performance of B. brassicae by reducing its nymphal survival, extending the duration of some immature stages and suppressing the population growth of B. brassicae. Overall, we demonstrated that spirotetramat is a pesticide showing both sublethal activities, and transgenerational effects on cabbage aphid; it may be useful for implementation in IPM programs against this aphid pest.

Toxicity of Essential Oil of Mentha piperita (Lamiaceae) and its Monoterpenoid Menthol Against Tetranychus urticae Kogan 1836 (Acari: Tetranychidae)

Essential oils from plants have remarkable biological properties, for example as insecticides and acaricides. Here we provide chemical analysis and evaluate the toxicity of the essential oil of Mentha piperita (Lamiaceae) and its main constituent menthol against Tetranychus urticae Kogan 1836 (Acari: Tetranychidae), a polyphagous pest present in agricultural landscapes. The essential oil was obtained from M. piperita leaves via hydrodistillation. Subsequently, concentration-response bioassays in adult females (fumigation and contact) were conducted to evaluate the lethal effect on the mite with three exposure intervals. We also evaluated the reproductive performance of females after exposure. Both substances were lethal in the fumigation bioassay, in addition, the essential oil was about 6-fold more toxic than menthol after 24 and 48 h of exposure. The fecundity of T. urticae females decreased inversely proportional to the increase of the used concentrations. Essential oil contact tests showed sublethal effects, with low mortality and reproductive stimulation of T. urticae females. Therefore, menthol and M. piperita essential oil can be considered potential acaricides for T. urticae by fumigant exposure due to the deleterious effect in adults and reduction in the number of individuals in subsequent generations, that represents a promising management tool.

Chemical Control of Mosquitoes and the Pesticide Treadmill: A Case for Photosensitive Insecticides as Larvicides

Insecticides reduce the spread of mosquito-borne disease. Over the past century, mosquito control has mostly relied on neurotoxic chemicals-such as pyrethroids, neonicotinoids, chlorinated hydrocarbons, carbamates and organophosphates-that target adults. However, their persistent use has selected for insecticide resistance. This has led to the application of progressively higher amounts of insecticides-known as the pesticide treadmill-and negative consequences for ecosystems. Comparatively less attention has been paid to larvae, even though larval death eliminates a mosquito's potential to transmit disease and reproduce. Larvae have been targeted by source reduction, biological control, growth regulators and neurotoxins, but hurdles remain. Here, we review methods of mosquito control and argue that photoactive molecules that target larvae-called photosensitive insecticides or PSIs-are an environmentally friendly addition to our mosquitocidal arsenal. PSIs are ingested by larvae and produce reactive oxygen species (ROS) when activated by light. ROS then damage macromolecules resulting in larval death. PSIs are degraded by light, eliminating environmental accumulation. Moreover, PSIs only harm small translucent organisms, and their broad mechanism of action that relies on oxidative damage means that resistance is less likely to evolve. Therefore, PSIs are a promising alternative for controlling mosquitoes in an environmentally sustainable manner.

The dynamic changes of genes revealed that persistently overexpressed genes drive the evolution of cyflumetofen resistance in Tetranychus cinnabarinus

Changes in gene expression are associated with the evolution of pesticide resistance in arthropods. In this study, transcriptome sequencing was performed in 3 different resistance levels (low, L; medium, M; and high, H) of cyflumetofen-resistant strain (YN-CyR). A total of 1 685 genes, including 97 detoxification enzyme genes, were upregulated in all 3 stages, of which 192 genes, including 11 detoxification enzyme genes, showed a continuous increase in expression level with resistance development (L to H). RNA interference experiments showed that overexpression of 7 genes (CYP392A1, TcGSTd05, CCE06, CYP389A1, TcGSTz01, CCE59, and CYP389C2) is involved in the development of cyflumetofen resistance in Tetranychus cinnabarinus. The recombinant CYP392A1 can effectively metabolize cyflumetofen, while CCE06 can bind and sequester cyflumetofen in vitro. We compared 2 methods for rapid screening of resistance molecular markers, including short-term induction and 1-time high-dose selection. Two detoxification enzyme genes were upregulated in the field susceptible strain (YN-S) by induction with 20% lethal concentration (LC₂₀ ) of cyflumetofen. However, 16 detoxification enzyme genes were upregulated by 1-time selection with LC₈₀ of cyflumetofen. Interestingly, the 16 genes were overexpressed in all 3 resistance stages. These results indicated that 1 685 genes that were upregulated at the L stage constituted the basis of cyflumetofen resistance, of which 192 genes in which upregulation continued to increase were the main driving force for the development of resistance. Moreover, the 1-time high-dose selection is an efficient way to rapidly obtain the resistance-related genes that can aid in the development of resistance markers and resistance management in mites.

Toxicological and transcriptomic effects in Mythimna separata (Lepidoptera: Noctuidae) exposed to chlorantraniliprole and functional characterization of glutathione S-transferases

BACKGROUND

Chlorantraniliprole (CAP) is an efficient anthranilic diamide insecticide against economically important pests such as the oriental armyworm, Mythimna separata (Lepidoptera: Noctuidae). Resistance to CAP may develop due to enhanced enzymatic detoxification. The glutathione S-transferase (GST) superfamily in M. separata has not been systematically characterized. The aim of this study was therefore to explore the effects of lethal and sublethal doses of CAP on M. separata larvae, screen differentially expressed genes (DEGs) responding to CAP exposure, identify and characterize the GST superfamily, and analyze the metabolism of CAP by recombinant GSTs.

RESULTS

The toxicity bioassay showed that CAP was active against M. separata third-instar larvae. LC50 was 17.615, 3.127, and 1.336 mg/L after 24, 48, and 72 h, respectively. Poisoned larvae showed contracted somites and disrupted midgut. Total GST activity in larvae was significantly elevated 24 h after CAP exposure. RNA-sequencing generated 43 055 unigenes with an average length of 1010 bp, and 567 up-regulated and 692 down-regulated DEGs responding to CAP treatment were screened. Thirty-five GST genes were identified from unigenes, including 31 cytosolic, three microsomal, and one unclassified. The expression profile of GST genes was analyzed using samples from different developmental stages, adult tissues, and CAP treatments. Metabolic assays indicated that CAP was depleted by recombinant MseGSTe2 and MseGSTs6.

CONCLUSIONS

This study provides insight into the toxicological and transcriptomic effects in M. separata larvae exposed to CAP. The identification and functional characterization of the GST superfamily will improve our understanding of CAP detoxification by GSTs. © 2022 Society of Chemical Industry.

Fungicides have transgenerational effects on Rhopalosiphum padi but not their endosymbionts

BACKGROUND

While several agricultural fungicides are known to directly affect invertebrate pests, including aphids, the mechanisms involved are often unknown. One hypothesis is that fungicides with antibacterial activity suppress bacterial endosymbionts present in aphids which are important for aphid survival. Endosymbiont-related effects are expected to be transgenerational, given that these bacteria are maternally inherited. Here, we test for these associations using three fungicides (chlorothalonil, pyraclostrobin and trifloxystrobin) against the bird cherry-oat aphid, Rhopalosiphum padi, using a microinjected strain that carried both the primary endosymbiont Buchnera and the secondary endosymbiont Rickettsiella.

RESULTS

We show that the fungicide chlorothalonil did not cause an immediate effect on aphid survival, whereas both strobilurin fungicides (pyraclostrobin and trifloxystrobin) decreased survival after 48 h exposure. However, chlorothalonil substantially reduced the lifespan and fecundity of the F1 generation. Trifloxystrobin also reduced the lifespan and fecundity of F1 offspring, however, pyraclostrobin did not affect these traits. None of the fungicides consistently altered the density of Buchnera or Rickettsiella in whole aphids.

CONCLUSIONS

Our results suggest fungicides have sublethal impacts on R. padi that are not fully realized until the generation after exposure, and these sublethal impacts are not associated with the density of endosymbionts harbored by R. padi. However, we cannot rule out other effects of fungicides on endosymbionts that might influence fitness, like changes in their tissue distribution. We discuss these results within the context of fungicidal effects on aphid suppression across generations and point to potential field applications. © 2022 Society of Chemical Industry.

Evolutionary consequences of pesticide exposure include transgenerational plasticity and potential terminal investment transgenerational effects

Transgenerational plasticity, the influence of the environment experienced by parents on the phenotype and fitness of subsequent generations, is being increasingly recognized. Human-altered environments, such as those resulting from the increasing use of pesticides, may be major drivers of such cross-generational influences, which in turn may have profound evolutionary and ecological repercussions. Most of these consequences are, however, unknown. Whether transgenerational plasticity elicited by pesticide exposure is common, and the consequences of its potential carryover effects on fitness and population dynamics, remains to be determined. Here, we investigate whether exposure of parents to a common pesticide elicits intra-, inter-, and transgenerational responses (in F0, F1, and F2 generations) in life history (fecundity, longevity, and lifetime reproductive success), in an insect model system, the seed beetle Callosobruchus maculatus. We also assessed sex specificity of the effects. We found sex-specific and hormetic intergenerational and transgenerational effects on longevity and lifetime reproductive success, manifested both in the form of maternal and paternal effects. In addition, the transgenerational effects via mothers detected in this study are consistent with a new concept: terminal investment transgenerational effects. Such effects could underlie cross-generational responses to environmental perturbation. Our results indicate that pesticide exposure leads to unanticipated effects on population dynamics and have far-reaching ecological and evolutionary implications.

Radiation Hormesis to Improve the Quality of Adult Spodoptera litura (Fabr.)

Mass rearing of insects of high biological quality is a crucial attribute for the successful implementation of sterile insect release programs. Various ontogenetic stages of Spodoptera litura (Fabr.) were treated with a range of low doses of ionizing radiation (0.25-1.25 Gy) to assess whether these gamma doses could elicit a stimulating effect on the growth and viability of developing moths. Doses in the range of 0.75 Gy to 1.0 Gy administered to eggs positively influenced pupal weight, adult emergence, and growth index, with a faster developmental period. The enhanced longevity of adults derived from eggs treated with 0.75 Gy and 1.0 Gy, and for larvae and pupae treated with 1.0 Gy, indicated a hormetic effect on these life stages. Furthermore, the use of these hormetic doses upregulated the relative mRNA expression of genes associated with longevity (foxo, sirtuin 2 like/sirt1, atg8) and viability/antioxidative function (cat and sod), suggesting a positive hormetic effect at the transcriptional level. These results indicated the potential use of low dose irradiation (0.75-1 Gy) on preimaginal stages as hormetic doses to improve the quality of the reared moths. This might increase the efficiency of the inherited sterility technique for the management of these lepidopteran pests.