Metabolic mechanisms and acetylcholinesterase sensitivity involved in tolerance to chlorpyrifos-ethyl in the earwig Forficula auricularia

Limited effects of a glyphosate-based herbicide on the behaviour and immunity of males from six populations of the European earwig

The use of herbicides on crops often results in unintentional, low-dose exposure of non-target organisms, such as insects. While these exposures are increasingly known to alter the survival and physiology of insects, it remains unclear whether these effects can vary between populations and modify other fitness-related traits, such as behaviour and immunity. Here, we addressed these questions by testing the effects of sublethal exposure to a glyphosate-based herbicide (GBH) on the behaviour and immunity of European earwig males from six natural populations. We exposed each male to a dose of a common GBH (Roundup©) that was either recommended for crops, five times lower than that recommended for crops, or to a control solution. Twenty-four hours later, we measured the activity, boldness, and aggregation of each male. We then exposed them to an entomopathogenic fungus, monitored their survival for 6 weeks, and measured the immune response of the survivors. We found a condition-dependent effect of GBH exposure on male activity. Exposure to low doses induced a positive association between activity and weight, which was not observed in the high-dose and control groups. However, GBH had no effect on any of the other measured traits. All these results were consistent across the six populations tested, although we did find population-specific differences in almost all measurements on males. Further research is now needed to better understand the dose-response to GBH on male activity and its biological impact, as well as to evaluate the effectiveness of detoxification processes in this species. Overall, these results emphasise the importance of investigating the effects of herbicides on insects to expand our general understanding of the use and potential risks of plant protection products in integrated pest management programs.

Lethal and behavioural toxicity of differently aged insecticide residues on European earwigs (Forficula auricularia) in the laboratory and in the field

Pesticide residues are an important topic in many environmental studies, but little is known about the effects of pesticide residues of different ages on beneficial arthropods. Therefore, in this study the activity of residues of three different ages of several commonly used insecticides on the behaviour and mortality of European earwigs was evaluated in the laboratory and the effect of the insecticides was verified in the field. All residues of the biorational SpinTor® (spinosad), Radiant SC (spinetoram), and the conventional Steward® (indoxacarb) showed significantly faster mortality progression compared to the control in the laboratory. All the Steward® residues caused a significant wave of erratic behaviour as the earwigs went through a deep and relatively long moribund stage and resurrected. We verified the effects of SpinTor® and Steward® on changes in earwig abundance and their behaviour in the orchard. Earwigs abundance was significantly lower 16 days after application of biorational SpinTor® and conventional Steward® which had a significantly more pronounced and longer lasting effect. The earwig population stabilised by day 53 after the insecticide applications. Field applications of insecticides had no effect on earwig behaviour and sex ratio. Our results show that older residues have a negative effect on European earwigs equal to that of fresh residues, although their degradation should occur. It is interesting to note that biorational insecticides may not be safer than chemical insecticides.

The Molecular Resistance Mechanisms of European Earwigs from Apple Orchards Subjected to Different Management Strategies

To date, apple orchards are among the most treated crops in Europe with up to 35 chemical treatments per year. Combining control methods that reduce the number of pesticide treatments is essential for agriculture and more respectful of the environment, and the use of predatory insects such as earwigs may be valuable to achieve this goal. European earwigs, Forficula auricularia (Dermaptera: Forficulidae) are considered beneficial insects in apple orchards where they can feed on many pests like aphids. The aim of this study was to investigate the potential impact of orchards' insecticide treatments on resistance-associated molecular processes in natural populations of earwigs. Because very few molecular data are presently available on earwigs, our first goal was to identify earwig resistance-associated genes and potential mutations. Using earwigs from organic, integrated pest management or conventional orchards, we identified mutations in acetylcholinesterase 2, α1 and β2 nicotinic acetylcholine receptors. In addition, the expression level of these targets and of some essential detoxification genes were monitored using RT-qPCR. Unexpectedly, earwigs collected in organic orchards showed the highest expression for acetylcholinesterase 2. Four cytochromes P450, one esterase and one glutathione S-transferases were over-expressed in earwigs exposed to various management strategies in orchards. This first study on resistance-associated genes in Forficula auricularia paves the way for future experimental studies aimed at better understanding the potential competition between natural enemies in apple orchards in order to optimize the efficiency of biocontrol.

Sublethal exposure to deltamethrin stimulates reproduction and has limited effects on post-hatching maternal care in the European earwig

Although pesticides are typically used to limit pest population, the diversity and nature of their unintentional effects on non-target organisms remain unclear. Better understanding these effects requires to carry out risk assessments on key physiological and behavioral processes specific to beneficial insects. In this study, we addressed this question by exposing mothers of the European earwig (a beneficial insect) to two sublethal doses of deltamethrin (a common pesticide in agriculture) during family life and measured the short- and long-term effects on a series of behavioral, physiological, and reproductive traits. Somewhat surprisingly, our results first revealed that high and low doses of deltamethrin enhanced mothers' future reproduction by augmenting their likelihood to produce a second clutch, shortening the number of days until its production, and increasing the resulting number of eggs and their hatching rate. Conversely, the high dose of deltamethrin was detrimental, as it limited maternal brood defence, and reduced food consumption and expression of self-grooming. Finally, other traits were independent of deltamethrin exposure, such as three proxies of family interactions (i.e., distance to the brood, occurrence, and duration of mother-offspring contacts), mothers' walking distance, and mother weight gain during family life. Our study overall demonstrates that sublethal exposure to a pesticide such as deltamethrin can have both positive and negative effects on non-target beneficial insects. It thus emphasizes that focusing on narrow parameters can lead to misleading conclusions about the unintended impacts of pesticides in treated agro-ecosystems and call for better considering this parameters diversity in integrated pest management programs.

Forficula auricularia (Dermaptera) in orchards: Monitoring seasonal activity, the effect of pesticides, and the perception of European fruit growers on its role as a predator or pest

BACKGROUND

We investigated several aspects that could affect the role of the European earwig (Forficula auricularia) as a generalist predator in orchards: (i) seasonal activity in apple orchards, (ii) effectiveness of two cardboard trap types (roll vs tape) to enhance earwig densities, (iii) the effect of pesticides (chlorpyrifos-methyl, spinosad, indoxacarb, spirotetramat, pirimicarb, sulphur, fluopyram tebuconazole) on earwig survival and behaviour, and (iv) the perception of European fruit growers of the earwigs' role as a predator or pest.

RESULTS

The highest activity of earwigs in apple trees was observed in summer. Roll traps were a more effective capture method than tape traps. The roll traps also significantly increased earwig abundances in trees. Only the earwigs exposed to the insecticides indoxacarb, spinosad and chlorpyrifos-methyl had significantly higher mortality and more erratic behaviour than earwigs from the control treatment. Earwigs from orchards with long-term (>10 years) application of chlorpyrifos-methyl had significantly lower mortality when exposed to this insecticide than earwigs from nonsprayed orchards. The fruit growers perceived earwigs as natural enemies of aphids and psyllids but also as pests. However, they regarded the damage caused by earwigs as economically unimportant without the necessity for management against them.

CONCLUSION

Fruit growers can increase earwig densities by installing rolled cardboard bands around trees. The highest seasonal activity of European earwigs coincides with applications of insecticides in orchards. This could disturb the earwigs' potential to suppress pest populations because several insecticides widely used in orchards have lethal and sublethal effects on earwigs even though they seem to develop some degree of pesticide resistance over time. © 2020 Society of Chemical Industry.

How lasting are the effects of pesticides on earwigs? A study based on energy metabolism, body weight and morphometry in two generations of Forficula auricularia from apple orchards

Widespread use of pesticides to control pests is the dominant system in conventional apple orchards. To avoid adverse side effects, there is a growing interest in promoting alternative methods including biological control based on the use of natural enemies. The European earwig Forficula auricularia L. (Dermaptera: Forficuidae) is an effective predator in apple orchards. Pesticide pressure has been shown to divert energy resources which could have a negative impact on life history traits. In this study we assessed (i) whether variations in pesticide exposure could differentially impact energy reserves, body weight and morphometric parameters of F. auricularia, and (ii) whether these effects persist into the next generation reared under optimal conditions. Individuals from the first generation were collected in late October from organic, IPM and conventional orchards. The next generation was obtained under a rearing program, in the absence of pesticide exposure. Earwigs collected from conventional orchards exhibited lower values for all morphometric parameters compared to those collected in organic orchards. However, a relaxed period without pesticide exposure (in autumn) appears to have allowed the females to recover their energy reserves to ensure reproduction and maternal care. Glycogen contents were the reserves that were more easily restored. However, probably due to the rearing conditions (food ad libitum), all the earwigs from the second generation exhibited higher body weights and energy reserves than their parents.

Sublethal exposure to deltamethrin impairs maternal egg care in the European earwig Forficula auricularia

The application of pesticides typically leads to lethal and sublethal exposure of non-target insects. Whereas our current understanding of these sublethal effects typically focuses on reproductive and physiological parameters, recent works emphasize that sublethal effects on behaviors such as maternal care could be of major importance in non-target species. However, it remained unknown whether these sublethal effects occur in insects. Here, we tested if exposure to sublethal doses of deltamethrin - a pyrethroid insecticide commonly used in crops - alters the expression of maternal egg care in females of the European earwig Forficula auricularia, a predator insect and pest control. Our results first reveal that deltamethrin exposure impaired the expression of three forms of maternal egg care: It decreased the likelihood of mothers to gather their otherwise scattered clutch of eggs, increased the time during which the female abandoned the clutch after a predator attack and reduced egg grooming duration. These sublethal effects did not reflect a lower activity of deltamethrin-exposed females, as these females increased their expression of self-grooming, and deltamethrin exposure did not affect females' exploration and mobility. Finally, we found that the negative effects of deltamethrin on egg care did not modify egg development, hatching rate and juvenile weight, possibly due to the transient effects of deltamethrin on maternal behaviors. Overall, our results reveal that sublethal exposure to a pesticide may diminish maternal egg care in a natural pest control and call for the integration of this measurement in assays on pesticides application.