Apple orchards are heavily treated crops and some sprayed insecticides are recognized to have toxic effects on non-target arthropods. Earwigs are important natural enemies in pip-fruit orchards and contribute to the biological control of aphids. In addition, due to their ease of capture and identification, they are an interesting potential bioindicator of the possible detrimental effects of different orchard management strategies. In this study, we measured the energy reserves and some morphological traits of Forficula auricularia L. sampled in apple orchards under management strategies (organic versus integrated pest management (IPM)). We observed a significant decrease in mass (22 to 27%), inter-eye width (3%), and prothorax width (2 to 5%) in earwigs from IPM compared to organic orchards. Energy body reserves also confirmed these results with a significant decrease of 48% in glycogen and 25 to 42% in lipid content in earwigs from IPM compared to organic orchards. However, the protein content was approximately 70% higher in earwigs from IPM than in organic orchards. Earwigs sampled in IPM orchards may adapt to minimize the adverse toxic effects of pesticide treatments using a large number of strategies, which are reflected in changes to their energy reserves. These strategies could, in turn, influence the population dynamics of natural enemies and impair their role in the biological control of pests in apple orchards.
Widespread use of pesticides to control crop pests is still the dominant system in apple orchards. Therefore, to avoid adverse side effects, there is a growing interest in promoting alternative methods such as 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 last or not in 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 are the reserves that were more easily restored. However, 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. They finally reached the same level in these parameters regardless of the protection system from which their parents were collected. Sex-specific responses appeared to depend on earwig life cycle.
Fluctuating asymmetry (FA), defined as the random non-directional deviation from perfect bilateral symmetry, is considered to reflect developmental instability in bilaterally symmetrical organisms. It has been commonly used as a reliable biomarker of environmental stresses in natural populations. In agroecosystems, FA may arise through transgenerational influence of insecticides. We measured fluctuating asymmetry on unexposed progeny of Forficula auricularia mothers sampled in orchards that used no to frequent insecticides’ applications. Seven morphometric traits were measured on both right and left side and fluctuating asymmetry was calculated. Among these seven traits, four were more asymmetric when the progeny was born from a mother who lived in conventional orchards that used insecticides frequently compared to a mother who lived in insecticide free orchards. Males were more asymmetric than females for all traits but pest management strategy influenced FA in a similar way for both sexes. Measuring FA on unexposed daughters and sons of individuals originating from natural ecosystems may thus be a reliable easy-to-use tool to monitor mid-term effects of insecticides in the environment.
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