Stimulatory sublethal response of a generalist predator to permethrin: hormesis, hormoligosis, or homeostatic regulation?

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.

Non-target pesticide impacts on pest natural enemies: Progress and gaps in current knowledge

Avoiding pesticide non-target effects on natural enemies is a cornerstone of conservation biological control. Recent advances in this field have included increased examination of nuanced sublethal effects, including microbiome changes. There is an interest in lifetable-based approaches, while also simplifying results to reduce the amount of information a grower needs to interpret to make a judicious application decision. Newer pesticides are showing promise for selectivity to both natural enemies and humans. Major research gaps still remain, with few published studies on ground-dwelling natural enemies, herbicides, adjuvants, or pesticide mixes. Translating the results of laboratory assays to field-level effects remains a major challenge. Field studies examining entire management programs and meta-analyses of laboratory studies may begin to address this issue.

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.

Responses of signal crayfish Pacifastacus leniusculus to single short-term pulse exposure of pesticides at environmentally relevant concentrations

Although pesticides are often discharged into surface waters in pulses as opposed to a sustained release, the effect of episodic pollution events on freshwater crayfish is largely unknown. We monitored change in heart rate and distance moved to assess the response of signal crayfish Pacifastacus leniusculus to short-term exposure to environmentally relevant concentrations of metazachlor (MTZ), terbuthylazine (TER), and thiacloprid (TCL). Crayfish exposed to 20 µg/L of MTZ exhibited a significant increase in mean heart rate and distance moved. Increased heart rate was detected at 118 ± 74 s post-exposure to MTZ. There were no significant differences in mean heart rate and distance moved in crayfish exposed to 6 µg/L of TCL and 4 µg/L of TER. A significant correlation between heart rate and distance moved was found in all exposed groups. These results suggest that pulse exposure to MTZ impact crayfish physiology and behavior during short-term period. With pulse exposure to TCL and TER, crayfish not exhibiting a locomotor response may continue to be exposed to lower, but potentially harmful, levels of pollutants. Evidence of the impacts of pesticide pulse at environmentally relevant concentrations on crayfish is scarce. Further study is required to determine the ecological effects of such events on freshwater crayfish.

Biological and physiological responses of two Bradysia pests, Bradysia odoriphaga and Bradysia difformis, to Dinotefuran and Lufenuron

Bradysia odoriphaga and Bradysia difformis are destructive root maggots that cause severe losses to vegetables, flowers and edible fungi. Due to the long-term dependence on single pesticides, Bradysia resistance to insecticides has increased, and field control efficacy has decreased obviously. To screen alternative insecticides, and compare the insecticide susceptibility of these two species, we tested the toxicity of eight insecticides to B. odoriphaga and B. difformis, and measured the sublethal effects of Dinotefuran and Lufenuron on life-history parameters and detoxification enzyme activities. Bioassay results indicated that Dinotefuran and Lufenuron had relatively higher toxicity to B. odoriphaga and B. difformis compared to other neonicotinoid and insect growth regulator insecticides, respectively. Significant adverse impacts caused by sublethal concentrations (LC₂₀) of Dinotefuran and Lufenuron on the life-history parameters of F0 and F1 generations of B. odoriphaga and B. difformis were observed. These included reduced survival, prolonged larval development and reduced adult longevity and fecundity. B. odoriphaga had greater resistance and adaptation to insecticides than B. difformis, and an LC₂₀ concentration of Dinotefuran stimulated the reproduction of B. odoriphaga F1 generation and increased the life table parameters. Detoxifying enzymes (CarE and GSTs) and P450 activities fluctuated after a sublethal concentration (Dinotefuran and Lufenuron) treatment, and at the peak value of enzyme activities, the enhancement of detoxifying enzymes of B. odoriphaga was significantly higher than that of B. difformis. These results indicated that Dinotefuran and Lufenuron should be considered as alternatives to other insecticides for control of root maggots. B. odoriphaga exhibited stronger adaptation to insecticides than B. difformis. These data provide guidance for control of root maggots, and the basic information presented here can help reveal the differences in adaptive mechanisms between B. odoriphaga and B. difformis.

Hormesis and insects: Effects and interactions in agroecosystems

Insects in agroecosystems contend with many stressors - e.g., chemicals, heat, nutrient deprivation - that are often encountered at low levels. Exposure to mild stress is now well known to induce hormetic (stimulatory) effects in insects, with implications for insect management, and ecological structure and function in agroecosystems. In this review, we examine the major ecological niches insects occupy or guilds to which they belong in agroecosystems and how hormesis can manifest within and across these groups. The mechanistic underpinnings of hormesis in insects are starting to become established, explaining the many phenotypic hormetic responses observed in insect reproduction, development, and behavior. Whereas potential effects on insect populations are well supported in laboratory experiments, field-based hypothesis-driven research on hormesis is greatly lacking. Furthermore, because most ecological paradigms are founded within the context of communities, entomological agroecologists interested in hormesis need to 'level up' and test hypotheses that explore effects on species interactions, and community structure and functioning. Embedded in this charge is to continue experimentation on herbivorous pest species while shifting more focus towards insect natural enemies, pollinators, and detritivores - guilds that play crucial roles in highly functioning agroecosystems that have been understudied in hormesis research. Important areas for future insect agroecology research on hormesis are discussed.

Balancing nutrients in a toxic environment: the challenge of eating

Insect herbivores can regulate their food intake by mixing food sources with different nutrient content, but face the resulting challenge of ingesting various plant secondary metabolites. How insects deal with toxins in a complex nutrient environment is unclear. Here we investigated the influence of a classic plant secondary metabolite, allyl glucosinolate (sinigrin), and its hydrolyzed product allyl isothiocyanate (AITC), on the development of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) when fed on diets with different protein-to-carbohydrate (p : c) ratios. We also examined the effects of these toxins on larval biochemistry, by chemically analyzing the frass produced by insects feeding on the different diets. As expected, AITC had a greater negative effect than sinigrin on H. armigera life-history traits. However, AITC at low concentration appeared to have a positive effect on some traits. Both sinigrin and AITC-induced detoxification activity in the gut, and the reaction was related to diet protein concentration. High-protein diets can provide the required free amino acid, especially cysteine, needed for the detoxification process. The nutrient content of the diet influences how plant secondary metabolites are handled, and the use of artificial diets in experiments investigating the metabolic fate of plant secondary compounds needs to be carefully evaluated.

Sub-lethal effects of a Bt-based bioinsecticide on the biological conditioning of Anticarsia gemmatalis

Bioinsecticides based on Bacillus thuringiensis (Bt) Berliner, 1915 are widely used to control lepidopteran in several crops. However, surviving insects exposed to the sub-lethal concentration of Bt-based bioinsecticides can suffer a multitude of effects on the biological conditioning known as hormesis. Here, we aimed to provide a clearer understanding of the biological conditioning of Anticarsia gemmatalis (Hübner, 1818), exposed to different concentrations of a Bt-based bioinsecticide, by assessing life table parameters over three generations. We defined five sub-lethal concentrations (LC₅, LC₁₀, LC₁₅, LC₂₀, and LC₂₅) from the response curve estimate of A. gemmatalis. Deionized water was used as a control. We assessed the parameters of eggs-viability and the duration of the stages, incubation, larval, pre-pupal, pupal, adult, pre-oviposition and total biological cycle. Data were used to construct the fertility life table using the two-sex program. The survival curves showed greater variation in the proportion of individuals at each development stage using the LC₂₅. The sub-lethal concentrations did not influence the incubation-eggs period, pre-pupal and pupal. However, the larval and adult stages using LC₂₅ and LC₁₀ were the most affected. Changes in sex ratio were observed using LC₂₀ and LC₅. The toxic effect of Bt-based bioinsecticide interfered mainly in the parameters of fertility, sex ratio, net reproduction rate (R0), and gross reproduction rate (GRR).

Do nanoparticles cause hormesis? Early physiological compensatory response in house crickets to a dietary admixture of GO, Ag, and GOAg composite

This study aimed to identify the physiological responses of house cricket females following short-term exposure to relatively low dietary doses of graphene oxide (GO, 20 μg · g^-1 food), silver (Ag, 400 μg · g^-1 food) nanoparticles (NPs), or graphene oxide‑silver nanoparticle composite (GO-AgNPs, 20: 400 μg · g^-1 food). Energy intake and distribution were measured on the third, sixth, and tenth day. A semi-quantitative API®ZYM assay of digestive enzyme fingerprints was performed on the third and tenth day of continuous treatment. Physicochemical properties of the NPs were obtained by combining SEM, EDX spectrometry, AFM, and DLS techniques. The obtained results showed decreased energy consumption, particularly assimilation as an early response to dietary NPs followed by compensatory changes in feeding activity leading to the same consumption and assimilation throughout the experimental period (10 days). The increased activities of digestive enzymes in NP-treated females compared to the control on the third day of the experiment suggest the onset of compensatory reactions of the day. Moreover, the insects treated with GO-AgNP composite retained more body water, suggesting increased uptake. The observed changes in the measured physiological parameters after exposure to NPs are discussed in light of hormesis.

Spatial distribution and colonization pattern of Bemisia tabaci in tropical tomato crops

BACKGROUND

In precision integrated pest management, management tactics are implemented only where and when needed, by identifying the sites where the pest population has reached economic thresholds. Tomato, Solanum lycopersicum (Linn.), is a vegetable cultivated worldwide, but its production is reduced by insect pests such as the whitefly, Bemisia tabaci (Genn.). To improve management, there is a need to understand B. tabaci spatial dynamics in tomato fields, which will elucidate colonization patterns and may improve management of this pest. Thus, this study was conducted to assess the spatial autocorrelation, distribution, and colonization patterns of B. tabaci in 19 commercial tomato fields through the growing season.

RESULTS

A total of 69 isotropic variograms were fit for B. tabaci. The insect distribution was aggregated with a strong level of spatial dependence. Ranges of spatial dependence varied from 0.53 to 19.05 m and 0.5 to 20 m for adults and nymphs, respectively. Overall, densities of adults and nymphs were higher and reached the economic threshold mainly at the field edges.

CONCLUSION

Our results suggest a colonization pattern for B. tabaci starting at the edges and spreading inwards in to the tomato fields. This study can improve B. tabaci management in tomato fields, especially scouting and decision-making to treat fields. Scouting for this pest should be directed to the field edges, with sample points at least 20 m apart from each other for independent insect counts. © 2020 Society of Chemical Industry.

Low Doses of a Neonicotinoid Stimulate Reproduction in a Beneficial Predatory Insect

Biological stimulation induced by low doses of toxicants or other stressors is known as hormesis. Hormetic stimulation of life history traits in insect pests can negatively impact agriculture, but stimulation of beneficial insects could be leveraged to enhance biological control agents. We examined whether low doses of imidacloprid could enhance oviposition, fecundity, fertility, and survival in the beneficial stink bug predator, Podisus maculiventris (Say) (Hemiptera: Pentatomidae), exposed at different life stages and across two generations. When treated as young adults, P. maculiventris fecundity was stimulated at 0.5 and 1.0 mg/liter imidacloprid (<2% of the field rate) without changes in time to oviposition, fertility, and survival. Nymphs exposed to 0.015 mg/liter imidacloprid (<1% of the field rate) also had stimulated reproduction without effects on oviposition, fertility, and survival, but treatment of nymphs at 0.15 and 1.5 mg/liter imidacloprid stimulated fecundity at the expense of fertility and survival. In another experiment we found reproductive stimulation can occur trans-generationally without major reduction in fertility or survival. Our results suggest biocontrol producers may be able to strategically apply low doses of stress to natural enemies during culturing without compromising fitness in subsequent generations.

Hormesis-induced gap between the guidelines and reality in ecological risk assessment

Guidelines of ecological risk assessment (ERA) used worldwide, based on S-shaped threshold dose-response curve, fail to consider hormesis, a biphasic dose-response model represented as a J-shaped or an inverted U-shaped curve, that occurs in real-life environment. Now that humans are routinely exposed to chemicals below the threshold where hormetic stimulation prevails, it is noteworthy that over-strictness about chemical control also means a waste of limited resources. So hormesis leads to the gap between guidelines with S-shaped model and reality with hormesis model concerning ERA. In this study, hormetic effects of sulfachloropyridazine (SCP) on the bioluminescence of Aliivibrio fischeri (A. f) under 41 conditions to simulate the real environment were investigated and compared with ERA practice by some parameters, such as no observed effect concentration (NOEC), hormetic-stimulatory range (HSR) and goal concentration (GC). Not only is the reproducibility of hormesis in real-life contexts confirmed, binomial distribution (p = 0.644 > 0.05) of the relative position of GC and HSR is also found, revealing a 50% probability for GC to falls in HSR, which proves the over-strictness of ERA both qualitatively and quantitatively. This study provides a novel view for ERA that hormetic principles should dominate, and conditions where S-shaped dose-response model works should be singled out on a specific basis to bridge the hormesis-induced gap.

Bt-induced hormesis in Bt-resistant insects: Theoretical possibility or factual concern?

The biphasic dose-response of a stressor where low amounts of a toxicant may stimulate some biological processes is a recent focus of attention in insecticide ecotoxicology. Nonetheless, the importance and management consequences of this phenomenon of pesticide-induced hormesis remain largely unrecognized. Curiously, the potential induction of hormesis by insecticidal proteins such as Bacillus thuringiensis toxins (i.e., Bt toxins), a major agriculture pest management tool of widespread use, has been wholly neglected. Thus, we aimed to circumvent this shortcoming while assessing the potential occurrence of hormesis induced by the Bt toxin Cry1Fa in its main target pest species - the fall armyworm Spodoptera frugiperda. Concentration-response bioassays were carried out in a Bt-susceptible and a Bt-resistant population providing the purified Cry1Fa toxin in artificial diet and recording the insect demographic parameters. As significant hormetic effect was detected in both populations with a significant increase in the net reproductive rate and the intrinsic rate of population growth, the potential occurrence of Bt-induced hormesis was subsequently tested providing the insects with leaves from transgenic Bt maize expressing the toxic protein. The performance of the Bt-resistant insects was not different in both maize genotypes, indicating that the leaf expression of the Bt protein did not promote hormesis in the resistant insects. Thus, despite the Bt-induced hormesis detected in the purified protein bioassays, the phenomenon was not detected with current levels of Bt expression in maize minimizing the risk of this additional efficacy constraint besides that of field occurrence of Bt resistance.

Selectivity of novel and traditional insecticides used for management of whiteflies on the parasitoid Encarsia formosa

BACKGROUND

Encarsia formosa Gahan is the most important parasitoid exploited for the control of whitefly pests of vegetable crops. However, the non-target effects of recently developed insecticides for controlling whiteflies toward this biocontrol agent is little documented. Here we evaluated the susceptibility of E. formosa adults and juveniles to eight commonly used insecticides against whiteflies.

RESULTS

Residual toxicity tests on glass showed that E. formosa adults were susceptible (over 98% mortality after 6 h treated) to field concentrations of the tested neonicotinoids (imidacloprid, acetamiprid, nitenpyram and thiamethoxam), abamectin, cyantraniliprole, and sulfoxaflor at their field concentrations. Pyriproxyfen was harmless to both adult and pupae of E. formosa. A risk quotient analysis showed that toxicity of pyriproxyfen to E. formosa adults was the lowest, followed by acetamiprid and cyantraniliprole. In the leaf residues test, mortality of E. formosa adults under all insecticides decreased when the residue age increased. Interestingly, E. formosa experiencing contact with the residues of most insecticides, except pyriproxyfen and abamectin, parasitized significantly more hosts 5-days after treatment, suggesting a hormetic effect on parasitism.

CONCLUSION

The risk assessment of insecticides indicated that pyriproxyfen and cyantraniliprole were the least toxic to E. formosa. Our results suggest that the inclusion of the insecticides in sustainable integrated pest management programs of whiteflies should be carefully evaluated on a case-by-case basis. © 2019 Society of Chemical Industry.

Toxicity and cytopathology mediated by Bacillus thuringiensis in the midgut of Anticarsia gemmatalis (Lepidoptera: Noctuidae)

Bioinsecticides and transgenic plants, based on Bacillus thuringiensis (Bt) toxins are important when managing Anticarsia gemmatalis Hübner (Lepidoptera: Noctuidae), a soybean defoliator pest. The interaction of these toxins with the caterpillar’s midgut cells determines their efficacy as an insecticide. The objective was to evaluate the toxicity of B. thuringiensis, subsp. kurstaki strain HD-1 and cytopathological changes mediated by these bacterial toxins in the midgut of A. gemmatalis caterpillars. Insecticidal efficacy was determined by calculating lethal concentration values (LC₂₅, LC₅₀, LC₇₅, LC₉₀ and LC₉₉) in the laboratory. Midgut fragments from A. gemmatalis were extracted after bacterial ingestion and evaluated by light, transmission electron and confocal microscopy. The Bt median lethal concentrations showed toxicity [LC₅₀ = 0.46 (0.43–0.49) mg mL⁻¹] to fourth instar A. gemmatalis caterpillars after 108 hours. Bt induces severe cytotoxicity to A. gemmatalis midgut epithelial cells with increasing exposure over time, causing cellular disorganization, microvillus degeneration, cell fragmentation and protrusion, peritrophic membrane rupture, and cell vacuolization. The cell nuclei presented condensed chromatin and an increase in lysosome numbers. Apoptosis occurred in the midgut cells of caterpillars exposed to Bt. A regenerative response in A. gemmatalis caterpillars was observed 8 hours after exposure to Bt, however this response was not continuous. Toxins produced by Bt are harmful to A. gemmatalis at median concentration with structural damage and death of the midgut epithelial cells of this insect.

Permethrin induces histological and cytological changes in the midgut of the predatory bug, Podisus nigrispinus

Insecticides used in the agriculture and forestry have side effects on non-target organisms used as natural enemies. This study evaluated the histopathology and cytotoxicity of permethrin on the midgut of the non-target predatory bug, Podisus nigrispinus (Heteroptera: Pentatomidae) used in the biological control of pest insects. The toxicity and survival of this insect were determined using six concentrations of permethrin via ingestion. Histological and ultraestutural changes of the midgut of P. nigrispinus were analyzed after exposure to permethrin. The insecticide caused toxicity in P. nigrispinus with LC₅₀ = 0.46 μg L^-1 and survival of 47% after 72 h of exposure. The histological changes in the midgut were irregularly bordered epithelium, cytoplasmic vacuolization and apocrine secretions in the lumen after 6 h following exposure to the insecticide. Cytotoxic effects such as granules and vacuoles secreted into the lumen, presence of autophagosomes, and dilatation of infolds of the basal plasma membrane were observed in the three regions of the midgut. Cells of the midgut in apoptosis occurred after 12 h of exposure. Permethrin causes toxic effects, inhibits survival, and produces changes in the histology and cytology of the midgut in P. nigrispinus, suggesting that the cell stress induced by this insecticide can disrupt physiological processes such as digestion, compromising the potential of the predator as a biological control agent of pests. The low selectivity of permethrin to a non-target organism such as the predatory bug, P. nigrispinus indicates that the associated use of this insecticide in biological control should be better evaluated.

Evaluation of Insecticides induced hormesis on the demographic parameters of Myzus persicae and expression changes of metabolic resistance detoxification genes

Insecticide induced-hormesis is a bi-phasic phenomenon generally characterized by low-dose induction and high-dose inhibition. It has been linked to insect pest outbreaks and insecticide resistance, which have importance in the integrated pest management (IPM). In this paper, hormesis effects of four insecticides on demographic parameters and expression of genes associated with metabolic resistance were evaluated in a field collected population of the green peach aphid, Myzus persicae Sulzer. The bioassay results showed that imidacloprid was more toxic than acetamiprid, deltamethrin and lambda-cyhalothrin. After exposure to sublethal doses of acetamiprid and imidacloprid for four generations, significant prolonged nymphal duration and increased fecundity were observed. Subsequently, mean generation time (T) and gross reproductive rate (GRR) was significantly increased. Moreover, expression of CYP6CY3 gene associated with resistance to neonicotinoids was increased significantly compared to the control. For pyrethriods, across generation exposure to sublethal doses of lambda cyhalothrin and deltamethrin prolonged the immature development duration. However, the expression of E4 gene in M. persicase was decreased by deltamethrin exposure but increased by lambda cyhalothrin. Based on results, demographic fitness parameters were effected by hormetic dose and accompanied with detoxifying genes alteration, hence, which would be evaluated in developing optimized insect pest management strategies.

Spraying pyrethroid and neonicotinoid insecticides can induce outbreaks of Panonychus citri (Trombidiformes: Tetranychidae) in citrus groves

Panonychus citri (McGregor) (Trombidiformes: Tetranychidae) is one of the main defoliator mites in citrus groves. In Brazil, P. citri was formerly considered a secondary pest, but in recent years, the population levels of this mite have increased in many groves, requiring additional acaricide applications for its control. The population growth of P. citri is associated with the increase in the number of applications of pyrethroid and neonicotinoid insecticides to control insect citrus pests. This study assessed the effects of pyrethroid (deltamethrin, esfenvalerate, λ-cyhalothrin) and neonicotinoid (imidacloprid and thiamethoxam) insecticides on biological, behavioral and demographic parameters of P. citri. None of the insecticides tested affected larval hatching, but deltamethrin, esfenvalerate, and λ-cyhalothrin reduced the survival of larvae and protonymphs. Deltamethrin, esfenvalerate, and λ-cyhalothrin induced a significant increase in the fecundity of surviving females. Pyrethroids also caused repellency and changed feeding and oviposition preferences. In contrast, imidacloprid and thiamethoxam did not affect the survival of immature stages, but imidacloprid significantly increased fecundity. Imidacloprid and thiamethoxam did not cause any repellent effect or changes in the feeding and oviposition preferences. Based on the demographic parameters, deltamethrin, λ-cyhalothrin, and imidacloprid increased R_o, r, and λ, whereas esfenvalerate and thiamethoxam were similar to the control. Therefore, the use of these insecticides (especially deltamethrin, λ-cyhalothrin, and imidacloprid) requires caution, such as avoiding repeated use of these compounds during the periods of P. citri incidence in citrus groves.

Spinosad-mediated effects on the walking ability, midgut, and Malpighian tubules of Africanized honey bee workers

BACKGROUND

The global decline in Apis mellifera colonies is attributed to multiple factors, including pesticides. The bioinsecticide spinosad was initially recognized as safe for non-target organisms; however, its toxicity has been changing this view. Here, we investigated the survival, behavioral changes, and structural changes in the midgut and Malpighian tubules of A. mellifera treated orally with a spinosad formulation.

RESULTS

The field-recommended concentration of spinosad killed 100% of the bees. The 5% and 50% lethal concentrations (LC₅ and LC₅₀ , respectively) of spinosad altered the behavioral activity, reducing the walking distance and velocity, and increased the resting time in comparison to the control. The LC₅₀ caused disorganization of the epithelia of tested organs and induced oxidative stress and cell death.

CONCLUSIONS

The present work provides new insights into the debate about the role of bioinsecticides in the mortality of Africanized honey bees. Even at very low concentrations, the spinosad formulation was toxic to the vital organs midgut and Malpighian tubules and adversely affected walking behavior. This detailed evaluation of the impact of the bioinsecticide on A. mellifera will contribute to the clarification of disturbances probably caused by spinosad formulations, which can be used to develop more sustainable protocols in agriculture. © 2017 Society of Chemical Industry.

Sublethal effects of chlorfenapyr on the life table parameters, nutritional physiology and enzymatic properties of Bradysia odoriphaga (Diptera: Sciaridae)

Bradysia odoriphaga (Diptera: Sciaridae) is the major pest affecting Chinese chive production. Chlorfenapyr is a halogenated pyrrole-based pro-insecticide that is currently used to control insects and mites on a variety of crops. In the present study, fourth-instar larvae of B. odoriphaga were exposed to chlorfenapyr at LC₁, LC₂₀ and LC₅₀ concentrations. The developmental duration of the treated larvae was not significantly different, but fecundity was significantly increased in the LC₁ and LC₂₀ treatment groups compared with the control group. The population parameters of the LC₁ treatment group were increased significantly, whereas those of the LC₅₀ treatment group were reduced significantly compared with the control. The food consumption by larvae and pupal weight were significantly increased under the LC₁ treatment and decreased under the LC₅₀ treatment compared with the control. Moreover, chlorfenapyr decreased the lipid, carbohydrate and trehalose contents significantly, whereas the total protein content was increased compared with the control. Additionally, the activities of protease, lipase and trehalase were significantly decreased. Chlorfenapyr treatment for 24 h also induced the activities of glutathione S-transferase (GST), carboxylesterase (CarE) and O-demethylation. The results of this study suggest that low lethal concentrations of chlorfenapyr can affect oviposition, population development, the activities of digestion and detoxification enzymes, and nutrient accumulation in B. odoriphaga. This study provides valuable information for the assessment and rational application of chlorfenapyr for effective control of this pest.

Can Plant Defence Mechanisms Provide New Approaches for the Sustainable Control of the Two-Spotted Spider Mite Tetranychus urticae?

Tetranychus urticae (T. urticae) Koch is a cosmopolitan, polyphagous mite which causes economic losses in both agricultural and ornamental plants. Some traits of T. urticae hamper its management, including a short life cycle, arrhenotokous parthenogenesis, its haplodiploid sex determination system, and its extraordinary ability to adapt to different hosts and environmental conditions. Currently, the use of chemical and biological control are the major control methods used against this mite. In recent years, some studies have focused on plant defence mechanisms against herbivores. Various families of plant compounds (such as flavonoids, glucosinolates, or acyl sugars) have been shown to behave as acaricides. Plants can be induced upon appropriate stimuli to increase their resistance against spider mites. This knowledge, together with the understanding of mechanisms by which T. urticae detoxifies and adapts to pesticides, may complement the control of this pest. Herein, we describe plant volatile compounds (VOCs) with repellent activity, and new findings about defence priming against spider mites, which interfere with the T. urticae performance. The use of VOCs and defence priming can be integrated into current management practices and reduce the damage caused by T. urticae in the field by implementing new, more sustainable crop management tools.

Non-target impacts of soybean insecticidal seed treatments on the life history and behavior of Podisus nigrispinus, a predator of fall armyworm

The treatment of seeds with systemic insecticides has become a common practice worldwide. However, this prophylactic use of insecticides has been questioned recently because of the potential risks to non-target organisms. This study assessed the non-target effects of chlorantraniliprole and thiamethoxam seed treatments on the life history and walking behavior of Podisus nigrispinus (Dallas), as well as the efficacy of these insecticides for controlling Spodoptera frugiperda (Smith). Thiamethoxam caused mortality of P. nigrispinus, increased the pre-oviposition period, and reduced the oviposition period and the fecundity and survival of females compared to chlorantraniliprole. In contrast, the life expectancy of P. nigrispinus females was prolonged by chlorantraniliprole, which also increased the intrinsic rate of growth (rm) and the finite growth rate (λ), and reduced the population doubling time (DT) compared to thiamethoxam. The net reproductive rate (R0) and mean generation time (T) were not affected by either insecticide treatment, and neither were the walking velocity of P. nigrispinus females, nor the distance they covered. Both chlorantraniliprole and thiamethoxam reduced soybean leaf consumption by S. frugiperda larvae. Given the observed lethal and sublethal effects, soybean seed treatments with chlorantraniliprole and thiamethoxam were judged to present low and moderate risks for P. nigrispinus, respectively.

Inductions of reproduction and population growth in the generalist predator Cyrtorhinus lividipennis (Hemiptera: Miridae) exposed to sub-lethal concentrations of insecticides

BACKGROUND

The miridbug, Cyrtorhinus lividipennis, is a significant predacious enemy of rice planthoppers. The effects of sub-lethal concentrations of triazophos, deltamethrin and imidacloprid on fecundity, egg hatchability, expression levels of genes associated with reproduction, and population growth in C. lividipennis were investigated.

RESULTS

The fecundities for three pair combinations (♀_c × ♂_t , ♀_t × ♂_c and ♀_t × ♂_t ) treated with sub-lethal concentrations of the insecticides triazophos, deltamethrin and imidacloprid (LC₁₀ and LC₂₀ ) showed a significant increase compared to the untreated pairs (♀_c × ♂_c ). However, sub-lethal concentration treatments did not affect the egg hatchability. The ClVg expression levels of female adults exposed to triazophos, deltamethrin and imidacloprid (LC₂₀ ) increased by 52.6, 48.9 and 91.2%, respectively. The ClSPATA13 expression level of adult males exposed to triazophos, deltamethrim and imidacloprid (LC₂₀ ) increased by 80.7, 41.3 and 48.3%, respectively. Furthermore, sub-lethal concentrations of insecticides (LC₂₀ ) caused increased population numbers in C. lividipennis.

CONCLUSION

Sub-lethal concentrations of triazophos, deltamethrin and imidacloprid stimulated reproduction and enhanced population growth of C. lividipennis. The reproductive stimulation might result from the up-regulation of ClVg or ClSPATA13. These findings may be useful in mediating populations of planthoppers. © 2017 Society of Chemical Industry.

Lethal and sublethal effects of cyantraniliprole on Helicoverpa assulta (Lepidoptera: Noctuidae)

Cyantraniliprole is a novel anthranilic diamide insecticide registered for the control of many sucking and chewing insect pests including the oriental tobacco budworm, Helicoverpa assulta (Guenée), which is an important lepidopteran pest of tobacco in China. This study determined the lethal and sublethal effects of cyantraniliprole on a treated parental generation and on an untreated offspring generation of H. assulta. Cyantraniliprole was incorporated in the diet of 3rd-instar larvae of the parental generation. Cyantraniliprole was highly toxic to the parental generation: after a 72-h feeding period, the LC₅₀ was 0.176mg/L. Cyantraniliprole tended to increase the developmental time of parental larvae, and the LC₃₀ significantly reduced the pupation rate and the pupal weight. Cyantraniliprole also significantly decreased the intrinsic rate of increase (r_m) and finite rate of increase (λ), and increased the doubling time (Dt). Treatment of the parental generation with the LC₃₀ decreased the pupal weight and adult fecundity, and increased adult deformity in the parental and offspring generations. Cyantraniliprole did not significantly affect the pupal period, the percentage of females, or adult longevity in either generation. These results suggest that both the lethal and sublethal effects of cyantraniliprole might suppress H. assulta population growth by reducing the insect's survival, development, and reproduction.

Sexual Success after Stress? Imidacloprid-Induced Hormesis in Males of the Neotropical Stink Bug Euschistus heros

Environmental stress in newly-emerged adult insects can have dramatic consequences on their life traits (e.g., dispersion, survival and reproduction) as adults. For instance, insects sublethally exposed to environmental stressors (e.g., insecticides) can gain fitness benefits as a result of hormesis (i.e., benefits of low doses of compounds that would be toxic at higher doses). Here, we experimentally tested whether sublethal exposure to the insecticide imidacloprid would hormetically affect the sexual fitness of newly-emerged adults of the Neotropical brown stink bug Euschistus heros (Hemiptera: Heteroptera: Pentatomidae), which is the most abundant and prevalent insect pest in Neotropical soybean fields. We evaluated the sexual fitness of four couple combinations: unexposed couples, exposed females, exposed males, and exposed couples. Sublethal exposure to dry residues (i.e., contact) of imidacloprid (at 1% of recommended field rate) did not affect insect survival, but led to higher mating frequencies when at least one member of the couple was exposed. However, the average mating duration was shortened when only females were exposed to imidacloprid. Moreover, exposed males showed higher locomotory (walking) activity, lower respiration rates and induced higher fecundity rates when mated to unexposed females. Although the reproductive tracts of exposed males did not differ morphometrically from unexposed males, their accessory glands exhibited positive reactions for acidic and basic contents. Our findings suggest that males of the Neotropical brown stink bug hormetically increase their sexual fitness when cued by impending insecticidal stress in early adulthood.

Pesticide-Induced Stress in Arthropod Pests for Optimized Integrated Pest Management Programs

More than six decades after the onset of wide-scale commercial use of synthetic pesticides and more than fifty years after Rachel Carson's Silent Spring, pesticides, particularly insecticides, arguably remain the most influential pest management tool around the globe. Nevertheless, pesticide use is still a controversial issue and is at the regulatory forefront in most countries. The older generation of insecticide groups has been largely replaced by a plethora of novel molecules that exhibit improved human and environmental safety profiles. However, the use of such compounds is guided by their short-term efficacy; the indirect and subtler effects on their target species, namely arthropod pest species, have been neglected. Curiously, comprehensive risk assessments have increasingly explored effects on nontarget species, contrasting with the majority of efforts focused on the target arthropod pest species. The present review mitigates this shortcoming by hierarchically exploring within an ecotoxicology framework applied to integrated pest management the myriad effects of insecticide use on arthropod pest species.

Demonstration of an adaptive response to preconditioning Frankliniella occidentalis (Pergande) to sublethal doses of spinosad: a hormetic-dose response

Sublethal doses of some insecticides have been reported to either stimulate or reduce the survival and fecundity of insects. Many sublethal-effect studies have been conducted after exposure of only one generation to sublethal insecticides, and there is little information about the sublethal effects on insects after long-term exposure to sublethal insecticides. In this study, changes in biological characteristics were investigated in spinosad-susceptible (Spin-S) and sublethal-spinosad-treated (Spin-Sub) strains of Frankliniella occidentalis (Pergande) after exposure to their corresponding sublethal concentrations of spinosad. The results showed that for the Spin-S strain, the LC10 concentration of spinosad slightly affected the biotic fitness both in parents and offspring of F. occidentalis. The LC25 concentration of spinosad prolonged the development time, reduced the fecundity, and significantly reduced the intrinsic rate of increase, the net reproductive rate and the finite rate of increase in the Spin-S strain. However, the negative effects were not as pronounced in the offspring (F1 generation) as in the parent generation. For the Spin-Sub strain, the LC10 and LC25 concentrations of spinosad had little negative effect on the development and fecundity, and no significant difference was found between the effects of the LC10 and LC25 treatments on the Spin-Sub strain. The Spin-Sub strain exhibited a shorter developmental time, and larger intrinsic rates of increase and net reproductive rates, compared with the corresponding treatments of the Spin-S strain. These findings combined with our previous studies suggest that the biotic fitness increased in the Spin-Sub strain and the strain became more adaptable to sublethal doses of spinosad, compared with the Spin-S strain. Physiological and biochemical adaptation may contribute to these changes after long treatment times at sublethal doses.

A single hot event stimulates adult performance but reduces egg survival in the oriental fruit moth, Grapholitha molesta

Climate warming is expected to increase the exposure of insects to hot events (involving a few hours at extreme high temperatures). These events are unlikely to cause widespread mortality but may modify population dynamics via impacting life history traits such as adult fecundity and egg hatching. These effects and their potential impact on population predictions are still largely unknown. In this study, we simulated a single hot event (maximum of 38°C lasting for 4 h) of a magnitude increasingly found under field conditions and examined its effect in the oriental fruit moth, Grapholitha molesta. This hot event had no impact on the survival of G. molesta adults, copulation periods or male longevity. However, the event increased female lifespan and the length of the oviposition period, leading to a potential increase in lifetime fecundity and suggesting hormesis. In contrast, exposure of males to this event markedly reduced the net reproductive value. Male heat treatment delayed the onset of oviposition in the females they mated with, as well as causing a decrease in the duration of oviposition period and lifetime fecundity. Both male and female stress also reduced egg hatch. Our findings of hormetic effects on female performance but concurrent detrimental effects on egg hatch suggest that hot events have unpredictable consequences on the population dynamics of this pest species with implications for likely effects associated with climate warming.

Insecticide-mediated shift in ecological dominance between two competing species of grain beetles

Competition is a driving force regulating communities often considered an intermittent phenomenon, difficult to verify and potentially driven by environmental disturbances. Insecticides are agents of environmental disturbance that can potentially change ecological relationships and competitive outcomes, but this subject has seldom been examined. As the co-existing cereal grain beetle species Sitophilus zeamais Motschulsky and Rhyzopertha dominica F. share a common realized niche, directly competing for the same resources, they were used as models in our study. Intraspecific competition experiments were performed with increasing insect densities and insecticide doses in additive and replacement series using various density combinations of both beetle species maintained on insecticide-free or -sprayed grains. Insecticide-mediated release from competitive stress was not observed in our study of intraspecific competition in grain beetles. The insecticide enhanced the effect of insect density, particularly for the maize weevil S. zeamais, further impairing population growth at high densities. Therefore, insecticide susceptibility increased with intraspecific competition favoring insecticide efficacy. However, the effect of insecticide exposure on competitive interaction extends beyond intraspecific competition, affecting interspecific competition as well. Sitophilus zeamais was the dominant species when in interspecific competition prevailing in natural conditions (without insecticide exposure), but the dominance and species prevalence shifted from S. zeamais to R. dominica under insecticide exposure. Therefore, high conspecific densities favored insecticide efficacy, but the strength of the relationship differs with the species. In addition, the insecticide mediated a shift in species dominance and competition outcome indicating that insecticides are relevant mediators of species interaction, potentially influencing community composition and raising management concerns as potential cause of secondary pest outbreaks.

Insecticide-induced hormesis and arthropod pest management

Ecological backlashes such as insecticide resistance, resurgence and secondary pest outbreaks are frequent problems associated with insecticide use against arthropod pest species. The last two have been particularly important in sparking interest in the phenomenon of insecticide-induced hormesis within entomology and acarology. Hormesis describes a biphasic dose-response relationship that is characterized by a reversal of response between low and high doses of a stressor (e.g. insecticides). Although the concept of insecticide-induced hormesis often does not receive sufficient attention, or has been subject to semantic confusion, it has been reported in many arthropod pest species and natural enemies, and has been linked to pest outbreaks and potential problems with insecticide resistance. The study of hormesis remains largely neglected in entomology and acarology. Here, we examined the concept of insecticide-induced hormesis in arthropods, its functional basis and potential fitness consequences, and its importance in arthropod pest management and other areas.

Beyond selectivity: are behavioral avoidance and hormesis likely causes of pyrethroid-induced outbreaks of the southern red mite Oligonychus ilicis?

Secondary pest outbreak is a counterintuitive ecological backlash of pesticide use in agriculture that takes place with the increase in abundance of a non-targeted pest species after pesticide application against a targeted pest species. Although the phenomenon was well recognized, its alternative causes are seldom considered. Outbreaks of the southern red mite Oligonychus ilicis are frequently reported in Brazilian coffee farms after the application of pyrethroid insecticides against the coffee leaf miner Leucoptera coffeella. Selectivity favoring the red mite against its main predatory mites is generally assumed as the outbreak cause, but this theory has never been tested. Here, we assessed the toxicity (and thus the selectivity) of deltamethrin against both mite species: the southern red mite and its phytoseid predator Amblyseius herbicolus. Additionally, behavioral avoidance and deltamethrin-induced hormesis were also tested as potential causes of red mite outbreak using free-choice behavioral walking bioassays with the predatory mite and life-table experiments with both mite species, respectively. Lethal toxicity bioassays indicated that the predatory mite was slightly more susceptible than its prey (1.5×), but in more robust demographic bioassays, the predator was three times more tolerant to deltamethrin than its prey, indicating that predator susceptibility to deltamethrin is not a cause of the reported outbreaks. The predator did not exhibit behavioral avoidance to deltamethrin; however insecticide-induced hormesis in the red mite led to its high population increase under low doses, which was not observed for the predatory mite. Therefore, deltamethrin-induced hormesis is a likely cause of the reported red mite outbreaks.

Transgenerational shifts in reproduction hormesis in green peach aphid exposed to low concentrations of imidacloprid

Hormesis is a biphasic phenomenon that in toxicology is characterized by low-dose stimulation and high-dose inhibition. It has been observed in a wide range of organisms in response to many chemical stressors, including insects exposed to pesticides, with potential repercussions for agriculture and pest management. To address questions related to the nature of the dose-response and potential consequences on biological fitness, we examined transgenerational hormesis in the green peach aphid, Myzus persicae, when exposed to sublethal concentrations of the insecticide imidacloprid. A hormetic response in the form of increased reproduction was consistently observed and a model previously developed to test for hormesis adequately fit some of our data. However, the nature of the dose-response differed within and across generations depending upon the duration and mode of exposure. Decreased reproduction in intermediate generations confirmed that fitness tradeoffs were a consequence of the hormetic response. However, recovery to levels of reproduction equal to that of controls in subsequent generations and significantly greater total reproduction after four generations suggested that biological fitness was increased by exposure to low concentrations of the insecticide, even when insects were continuously exposed to the stressor. This was especially evident in a greenhouse experiment where the instantaneous rate of population increase almost doubled and total aphid production more than quadrupled when aphids were exposed to potato plants systemically treated with low amounts of imidacloprid. Our results show that although fitness tradeoffs do occur with hormetic responses, this does not necessarily compromise overall biological fitness.

Laboratory tests of insect growth regulators as bait sprays for the control of the olive fruit fly, Bactrocera oleae (Diptera: Tephritidae)

BACKGROUND

Insect growth regulators (IGRs) act specifically on arthropods. This selectivity makes them an interesting alternative to traditional insecticides for pest control. The aim of this work was to test the IGRs azadirachtin, cyromazine, flufenoxuron, lufenuron and pyriproxyfen as useful pesticides for the control of the olive fruit fly, Bactrocera oleae (Rossi), a key pest of olive crops.

RESULTS

Of the products tested, the chitin-synthesis inhibitor lufenuron showed the highest efficacy. The life parameter showing the strongest effect was the egg hatch, because lufenuron caused nearly 100% egg mortality 7 days after treatment. However, sterility was not transmitted from the treated males to the untreated females. The LC50 and LC90 values for a 7 day evaluation period were 19.3 and 86.2 µg AI mL(-1) respectively. Azadirachtin, cyromazine and flufenoxuron also caused significant increases in egg mortality. However, these increases were less than those produced by lufenuron. Pyriproxyfen had a stimulatory effect on B. oleae fecundity.

CONCLUSION

Applied as a bait treatment, a procedure used frequently in the field for the control of B. oleae, lufenuron is potentially useful against this important pest.

Insects, insecticides and hormesis: evidence and considerations for study

Insects are ubiquitous, crucial components of almost all terrestrial and fresh water ecosystems. In agricultural settings they are subjected to, intentionally or unintentionally, an array of synthetic pesticides and other chemical stressors. These ecological underpinnings, the amenability of insects to laboratory and field experiments, and our strong knowledgebase in insecticide toxicology, make the insect-insecticide model an excellent one to study many questions surrounding hormesis. Moreover, there is practical importance for agriculture with evidence of pest population growth being accelerated by insecticide hormesis. Nevertheless, insects have been underutilized in studies of hormesis. Where hormesis hypotheses have been tested, results clearly demonstrate stimulatory effects on multiple taxa as measured through several biological endpoints, both at individual and population levels. However, many basic questions are outstanding given the myriad of chemicals, responses, and ecological interactions that are likely to occur.

Sublethal effects of Cry 1F Bt corn and clothianidin on black cutworm (Lepidoptera: Noctuidae) larval development

Black cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae), is an occasional pest of maize (corn), Zea mays L., that may cause severe stand losses and injury to corn seedlings. The efficacy of the neonicotinoid seed treatment clothianidin at two commercially available rates and their interaction with a transgenic corn hybrid (Bt corn), trait expressing the Bacillus thuringiensis variety aizawai insecticidal toxin Cry 1Fa2, against black cutworm larvae was investigated. Clothianidin at a rate of 25 mg kernel(-1) on Bt corn increased larval mortality and reduced larval weight gains additively. In contrast, weights of larvae fed non-Bt corn seedlings treated with clothianidin at a rate of 25 mg kernel(-1) increased significantly, suggesting either compensatory overconsumption, hormesis, or hormoligosis. Both Bt corn alone and clothianidin at a rate of 125 mg kernel(-1) applied to non-Bt corn seedlings caused increased mortality and reduced larval weight gains. In two field trials, plots planted with Bt corn hybrids consistently had the highest plant populations and yields, regardless of whether they were treated with clothianidin at the lower commercial rate of 25 mg kernel(-1) The use of Bt corn alone or in combination with the low rate of clothianidin (25 mg kernel(-1)) seems suitable as a means of suppressing black cutworm in no-tillage cornfields, although rescue treatments may still be necessary under severe infestations. Clothianidin alone at the low rate of 25 mg kernel(-1) is not recommended for black cutworm control until further studies of its effects on larval physiology and field performance have been completed.

Insecticide survival and behavioral avoidance in the lacewings Chrysoperla externa and Ceraeochrysa cubana

Insecticide impact on non-target species, such as insect predators and parasitoids, is an ever-growing concern in agriculture and recent studies have been shifting focus from lethal to sub-lethal effects since they may prevail in field conditions, although more difficult to assess. Synthetic insecticides are the main concern, but the recent spread of biopesticide use in agriculture draws attention, particularly the main botanical insecticide currently in use - azadirachtin. Here we assessed the lethal and behavioral sub-lethal response of predatory larvae of the lacewing species Chrysoperla externa and Ceraeochrysa cubana to two frequently used synthetic insecticides, malathion and permethrin, and to the bioinsecticide azadirachtin. The recommended field concentration of the synthetic insecticides led to low survival time of lacewing larvae from both species, in contrast with azadirachtin. However, all three compounds led to 100% mortality of the lacewing larvae from both species. Insecticide repellence (i.e., avoidance without contact) was similar for both synthetic insecticides in both species, but azadirachtin was a stronger repellent for C. externa, but not C. cubana. In addition, insecticide irritability (i.e., avoidance after contact) occurred in both lacewing species to all three insecticides tested. The notion that natural compounds are safer than synthetic compounds to non-target species is refuted in the present study, which also detected significant irritability to all of the insecticides regardless of their origin, and species-specific repellence elicited particularly by azadirachtin. Therefore, bioinsecticides should not be exempted from risk assessment, and non-target sub-lethal effects should not be neglected when considering potential insecticide use in agriculture.