An exploratory study of energy reserves and biometry as potential tools for assessing the effects of pest management strategies on the earwig, Forficula auricularia L

Abstract

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.

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

“…Our previous study reported contrasting results for measurements on earwigs sampled in the same orchards in July. In that latter study, earwigs from organic orchards were the heaviest and females were lighter than males (Suchail et al, 2018).…”

“…A single person carried out all measurements to avoid user bias. For adults (males and females) and nymphs, we measured the maximum width of the prothorax, inter-eye and telson and the length of the left femur of the third pair (Suchail et al, 2018). The growth of earwig nymphs was assessed through the increase in body weight, femur length and prothorax width by calculating the ratio between two successive life-stages (N4/N3 or adult/N4).…”

“…After the morphometric assessment, the whole earwig body was homogenized on ice in 10% (w/v) low-salt buffer containing 10 mM Tris-HCL (pH 7.3) and 10 mM NaCl and centrifuged for min at x g according to Suchail et al (2018). The supernatant was used for further glycogen, lipid and protein measurements.…”

“…Total lipids were determined according to Frings et al (1972) adapted to a 96-well microplate format (Suchail et al, 2018). Concentrated sulfuric acid (298 µL) was added to either 2 µL of sample or 2 µL of standard solution (olive oil).…”

“…Recently, we reported a severe depletion in energy reserves associated with lower weights and lower values for morphometric parameters in the earwig F. auricularia sampled in IPM orchards compared to those sampled in organic apple orchards (Suchail et al, 2018). However, further points remain to be addressed to accurately assess the impact of pesticide pressure on F. auricularia.…”