Pesticide-Induced Hormesis in Arthropods: Towards Biological Systems

The lifelong effects of anoxia hormesis in solitary bees

The stimulatory and protective response known as hormesis elicits an often over compensatory response resulting in life-history trait improvements. There are an array of abiotic and biotic agents that have been shown to trigger hormesis; most commonly studied are chemicals, temperature, and low oxygen. Investigations into low-oxygen exposures that activate the hormetic response reveal that insect performance can be dramatically improved by single short low-oxygen events, but the focus of this work has been primarily on short-term, transitory protection afforded by hormesis. Few reports examine whether the effect is longer lasting or lifelong. We previously reported that one hour of anoxia was enough to induce a hormetic response in the alfalfa leafcutting bee, Megachile rotundata (Hymenoptera: Megachilidae). Here, we investigated the long-term effects of this response by looking at starvation resistance, flight, and locomotory activity throughout the life of the adult bees. In addition, we studied the effects of anoxia hormesis on multiple reproductive metrics. Anoxia hormesis had lifelong positive effects for flight in both sexes. We also recorded higher starvation survival in bees that experienced hormesis. This improvement in performance came at a steep reproductive cost (ie reduction in fecundity). However, no costs or benefits were passed to the next generation. We hypothesize that using anoxia hormesis in the context of pollination services by this species should result in bees that are more active in the field, thereby increasing the numbers of visits to flowers throughout their entire life.

Hidden target, hidden effects: chlorantraniliprole on the coffee leaf miner (Leucoptera coffeella)

Agricultural insecticide usage presents a complex challenge, particularly when addressing hidden targets such as concealed pest species. Typically, insecticide spraying targets either the host plant or the soil substrate, reaching the target when the pests move or feed, yet their vulnerability when concealed remains low. This study delves into the often-obscure effects of insecticides on hidden herbivore species, focusing specifically on the diamide insecticide chlorantraniliprole and its impact on the concealed insect herbivore, the coffee leaf miner Leucoptera coffeella (Guérin-Mèneville & Perrottet) (Lepidoptera: Lyonetidae). We document the progressive effects of chlorantraniliprole from egg-laying through the insect's development and reproductive output. By examining egg-laying preferences, development, survival, respiration rate, leaf consumption, and polysaccharide and protein accumulation, alongside fecundity, in two field-collected leaf miner populations, we elucidate chlorantraniliprole's broader effects. While the insecticide did not alter the leaf miner's egg-laying preferences, one population exhibited higher larval survival, indicating chlorantraniliprole resistance. This chlorantraniliprole-resistant population displayed a lower respiration rate-indicative of reduced stress-and higher leaf consumption, accompanied by increased sugar and protein accumulation. Although this population showed lower adult longevity, it exhibited higher fecundity. These findings highlight the multifaceted impacts of insecticides, extending beyond survival to affect development, fecundity, and potential fitness. Variations in response among insect populations suggest that resistant insects may outperform susceptible ones even under sublethal exposure, with significant implications for management strategies and future outbreaks.

Thermal modulation of insecticide-induced hormetic and oxidative responses in insect pests

Environmental global changes are dramatically affecting agroecosystems. Insects have been shown to present various responses to multi-stress conditions (i.e., increase in temperature and exposure to contaminants). However, there is a knowledge gap on how temperature can modulate the hormetic effects in individuals sublethally exposed to chemical stressors. Here, we investigated how temperature (15, 20, 25, and 28 °C) modulates the effects of lethal and sublethal exposure to insecticides (imidacloprid) on the longevity, fecundity, and oxidative stress of a pest insect, the aphid Mysus persicae. Our results showed additive and interactive effects of temperature and insecticide on the stimulatory and oxidative responses of the insect pest. Overall, imidacloprid was 2.4-fold less toxic at 15 °C (3.547 μg/ml) than at 20 °C (1.482 μg/ml) and 24.6 to 19.8-fold less toxic than at 25 °C (0.144 μg/ml) and 28 °C (0.179 μg/ml) respectively. Furthermore, although the exposure of female aphids to most sublethal concentrations resulted in a decrease in their longevity and fecundity compared to the control, some of the sublethal concentrations produced positive effects in these parameters for the exposed individuals. The magnitude of induced sublethal effects varied between temperatures and occurred in similar ranges of low concentrations at temperatures 15 °C and 20 °C, and at temperatures 25 °C and 28 °C. Additionally, imidacloprid low concentrations induced a temperature-dependent production of reactive oxygen species in exposed insects at 12 and 24 h after exposure indicating oxidative stress. Our study supplies valuable data on how temperature modulates pesticide-mediated hormesis that can alter ecological interactions and functions within agroecosystems with potential implications in pest management.

Transcriptome and Neuroendocrinome Responses to Environmental Stress in the Model and Pest Insect Spodoptera frugiperda

The fall armyworm, Spodoptera frugiperda, is one of the most notorious pest insects, causing damage to more than 350 plant species, and is feared worldwide as an invasive pest species since it exhibits high adaptivity against environmental stress. Here, we therefore investigated its transcriptome responses to four different types of stresses, namely cold, heat, no water and no food. We used brain samples as our interest was in the neuroendocrine responses, while previous studies used whole bodies of larvae or moths. In general, the responses were complex and encompassed a vast array of neuropeptides (NPs) and biogenic amines (BAs). The NPs were mainly involved in ion homeostasis regulation (ITP and ITPL) and metabolic pathways (AKH, ILP), and this was accompanied by changes in BA (DA, OA) biosynthesis. Cold and no-water stress changed the NP gene expression with the same patterns of expression but clearly separated from each other, and the most divergent pattern of expression was shown after no-food stress. In conclusion, our data provide a foundation in an important model and pest insect with candidate NPs and BAs and other marker candidate genes in response to environmental stress, and also potential new targets to manage pest insects.

Pesticide immunotoxicity on insects - Are agroecosystems at risk?

Recent years have witnessed heightened scrutiny of the non-target sublethal effects of pesticides on behavioural and physiological traits of insects. Traditionally, attention has focused on investigating pesticides' primary modes of action, often overlooking the potential secondary mechanisms. This review brings forth the nuanced impacts of sublethal pesticide exposure on the immune system of target and non-target insect species. Pesticides, such as for example neonicotinoids, suppress immune response, while others, like certain organophosphates and some insect growth regulators (IGRs), appear to bolster immunocompetence under certain circumstances. Beyond their individual impacts, the synergic effects of pesticide mixtures on insect immunity are garnering increasing interest. This review thus summarizes recent advances in the immunomodulatory effects of pesticides, detailing both mechanisms and consequences of such interactions. The implications of these effects for ecosystem preservation and viability of beneficial organisms, such as pollinators and natural enemies of pests, are discussed. The review also considers further research directions on pesticide secondary modes of action and explores potential implications for integrated pest management (IPM) programs, as several model organisms studied are crop pest species. While current data provide an expansive overview of how insect innate immunity is modulated, concrete endpoints remain elusive requiring further research into pesticide secondary modes of actions.

Reimagining agrochemical pollution mitigation: Leveraging hormesis for sustainable environmental solutions

Emerging evidence reveals that low doses of stress stimulate, and high doses suppress, organism responses - a phenomenon known as hormesis. Here, we propose a framework for harnessing hormesis principles to optimize agrochemical use and mitigate pollution. We discuss how hormesis can be applied in agrochemical context and highlight challenges and needs beyond scientific research, offering a perspective for sustainable environmental solutions.

The interplay between temperature and an insecticide mixture modulates the stimulatory response of sublethally exposed Myzus persicae

Temperature can interact with chemical pesticides and modulate their toxicity. Sublethal exposure to pesticides is known to trigger hormetic responses in pests. However, the simultaneous effects of temperature and sublethal exposure to single or mixture-based insecticides on the insects' stimulatory responses are not frequently considered in toxicological studies. Here we investigated the combined effects of temperature on the lethal and sublethal responses of the green peach aphid Myzus persicae after exposure to commercial formulations of a neonicotinoid (thiamethoxam) and a pyrethroid (lambda-cyhalothrin) and their mixture. Firstly, the concentration-response curves of the insecticides were determined under four temperatures (15 °C, 20 °C, 25 °C, and 28 °C) by the leaf dipping method. Subsequently, the sublethal concentrations C0, CL1, CL5, CL10, CL15, CL20, and CL30 were selected to assess sublethal effects on aphids' longevity and reproduction under the same temperatures. The results showed that the mixture of thiamethoxam + lambda-cyhalothrin caused greater toxicity to aphids compared to the formulations with each active ingredient alone and that the toxicity was higher at elevated temperatures. Furthermore, the exposure to low concentrations of the mixture (thiamethoxam + lambda-cyhalothrin) and the separated insecticides induced stimulatory responses in the longevity and fecundity of exposed aphid females, but the occurrence of such hormetic responses depended on the insecticide type, its sublethal concentration, and the temperature as well as their interactions.

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.

A Sex-Specific Trade-Off Between Pesticide Resistance and Tolerance to Heat-Induced Sterility in Tetranychus urticae

Current pest management relies extensively on pesticide application worldwide, despite the frequent rise of pesticide resistance in crop pests. This is particularly worrisome because resistance is often not costly enough to be lost in populations after pesticide application, resulting in increased dependency on pesticide application. As climate warming increases, effort should be put into understanding how heat tolerance will affect the persistence of pesticide resistance in populations. To address this, we measured heat tolerance in two populations of the spider mite crop pest Tetranychus urticae that differ in the presence or absence of a target-site mutation conferring resistance to etoxazole pesticide. We found that developmental time and fertility, but not survival, were negatively affected by increasing temperatures in the susceptible population. Furthermore, we found no difference between resistant and susceptible populations in all life-history traits when both sexes developed at control temperature, nor when females developed at high temperature. Resistant heat-stressed males, in contrast, showed lower fertility than susceptible ones, indicating a sex-specific trade-off between heat tolerance and pesticide resistance. This suggests that global warming could lead to reduced pesticide resistance in natural populations. However, resistant females, being as affected by high temperature as susceptible individuals, may buffer the toll in resistant male fertility, and the shorter developmental time at high temperatures may accelerate adaptation to temperature, the pesticide or the cost thereof. Ultimately, the complex dynamic between these two factors will determine whether resistant populations can persist under climate warming.

Less is more: The hormetic effect of titanium dioxide nanoparticles on plants

Titanium dioxide nanoparticles have attracted considerable attention due to their extensive applications; however, their multifaceted influence on plant physiology and the broader environment remains a complex subject. This review systematically synthesizes recent studies on the hormetic effects of TiO2 nanoparticles on plants - a phenomenon characterized by dual dose-response behavior that impacts various plant functions. It provides crucial insights into the molecular mechanisms underlying these hormetic effects, encompassing their effects on photosynthesis, oxidative stress response and gene regulation. The significance of this article consists in its emphasis on the necessity to establish clear regulatory frameworks and promote international collaboration to standardize the responsible adoption of nano-TiO2 technology within the agricultural sector. The findings are presented with the intention of stimulating interdisciplinary research and serving as an inspiration for further exploration and investigation within this vital and continually evolving field.

One hundred important questions facing plant science derived using a large language model

Artificial intelligence (AI) is advancing rapidly and continually evolving in various fields. Recently, the release of ChatGPT has sparked significant public interest. In this study, we revisit the '100 Important Questions Facing Plant Science' by leveraging ChatGPT as a valuable tool for generating thought-provoking questions relevant to plant science. These questions primarily revolve around the utilization of plants in product development, understanding plant mechanisms, plant-environment interactions, and enhancing plant traits, with an emphasis on sustainable product development. While ChatGPT may not capture certain crucial aspects highlighted by scientists, it offers valuable insights into the questions generated by experts. Our analysis demonstrates that ChatGPT can be cautiously employed as a supportive tool to facilitate, streamline, and expedite specific tasks in plant science.

Lethal and Sublethal Effects of Cyromazine on the Biology of Musca domestica Based on the Age-Stage, Two-Sex Life Table Theory

Cyromazine is a triazine insect growth regulator insecticide that is recommended for control of Musca domestica worldwide. Cyromazine is highly effective in causing mortality of M. domestica; however, some aspects of its lethal and sublethal effects on the biology of M. domestica are still unknown. The present study explored lethal and sublethal effects on several biological traits and population parameters of M. domestica. Concentration-response bioassays of cyromazine against third-instar larvae of M. domestica exhibited sublethal and lethal effects from concentrations of 0.03 (LC10), 0.06 (LC25), and 0.14 (LC50) μg/g of a larval medium. Exposure of M. domestica larvae to these concentrations resulted in reduced fecundity, survival, longevity and oviposition period, and delayed development of immature stages (i.e., egg hatch time and larval and pupal durations) in the upcoming generation of M. domestica. The values of population parameters such as intrinsic rate of increase, finite rate of increase, net reproductive rate, age-specific survival rate and fecundity, and age-stage life expectancy and reproductive value, analyzed using the age-stage and two-sex life table theory, were significantly reduced in a concentration-dependent manner in comparison with the control group. In conclusion, the study highlights the significant effects of cyromazine on the biology of M. domestica that could help suppress its population in cases of severe infestations.

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.

Conserved grasslands support similar pollinator diversity as pollinator-specific practice regardless of proximal cropland and pesticide exposure

Pollinator diversity and abundance are declining globally. Cropland agriculture and the corresponding use of agricultural pesticides may contribute to these declines, while increased pollinator habitat (flowering plants) can help mitigate them. Here we tested whether the relative effect of wildflower plantings on pollinator diversity and counts were modified by proportion of nearby agricultural land cover and pesticide exposure in 24 conserved grasslands in Iowa, USA. Compared with general grassland conservation practices, wildflower plantings led to only a 5% increase in pollinator diversity and no change in counts regardless of the proportion of cropland agriculture within a 1 km radius. Pollinator diversity increased earlier in the growing season and with per cent flower cover. Unexpectedly, neither insecticide nor total pesticide concentrations on above-ground passive samplers were related to pollinator diversity. However, pollinator community composition was most strongly related to date of sampling, total pesticide concentration, and forb or flower cover. Our results indicate very little difference in pollinator diversity between grassland conservation practices with and without wildflower plantings. Given the relatively high economic costs of wildflower plantings, our research provides initial evidence that investment in general grassland conservation may efficiently conserve pollinator diversity in temperate regions of intensive cropland agriculture.

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.

Effects of acephate and glyphosate-based agrochemicals on the survival and flight of Plebeia lucii Moure, 2004 (Apidae: Meliponini)

The conservation of terrestrial ecosystems depends largely on the preservation of pollinators, mainly bees. Stingless bees are among the main pollinators of native plants and crops in tropical regions, where they can be exposed to agrochemicals while foraging on contaminated flowers. In the present study, we investigated the effects on stingless bees of both a commonly used insecticide and herbicide in Brazil. Plebeia lucii Moure, 2004 (Apidae: Meliponini) foragers were orally chronically exposed to food contaminated with different concentrations of commercial formulations of the insecticide acephate or the herbicide glyphosate. Bee mortality increased with increasing agrochemical concentrations. Depending on its concentration, the acephate-based formulation reduced the lifespan and impaired the flight ability of bees. The glyphosate-based formulation was toxic only under unrealistic concentrations. Our results demonstrate that realistic concentrations of acephate-based insecticides harm the survival and alter the mobility of stingless bees. The ingestion of glyphosate-based herbicides was safe for forager bees under realistic concentrations.

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.

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.

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.

Butenolide Insecticide Flupyradifurone Affects Honey Bee Worker Antiviral Immunity and Survival

Honey bees face many environmental stressors, including exposure to pesticides and pathogens. A novel butenolide pesticide, flupyradifurone, was recently introduced to the US and shown to have a bee-friendly toxicity profile. Like the much-scrutinized neonicotinoids that preceded it, flupyradifurone targets the insect nervous system. Some neonicotinoids have been shown to interfere with antiviral immunity, which raised the concern that similar effects may be observed with flupyradifurone. In this study, we investigated how flupyradifurone and a neonicotinoid, clothianidin, affect the ability of honey bee workers to combat an infection of Israeli acute paralysis virus (IAPV). We exposed workers to field-realistic doses of the pesticides either with or without co-exposure with the virus, and then tracked survival and changes in viral titers. We repeated the experiment in the spring and fall to look for any seasonal effects. We found that flupyradifurone caused elevated mortality in the fall, but it did not lead to increased virus-induced mortality. Flupyradifurone also appeared to affect virus clearance, as bees co-exposed to the pesticide and virus tended to have higher viral titers after 48 hours than those exposed to the virus alone. Clothianidin had no effect on viral titers, and it actually appeared to increase resistance to viral infection in spring bees.

Hormesis: A General Biological Principle

Hormesis drives biological modifications from cells to higher levels of biological organization and emerges as a general basic principle of biology, integrating evolution, ecology, medicine, physiology, toxicology, and public health.