Homogeneity of agriculture landscape promotes insecticide resistance in the ground beetle Poecilus cupreus

Mortality Pattern of Poecilus cupreus Beetles after Repeated Topical Exposure to Insecticide─Stochastic Death or Individual Tolerance?

The mortality of organisms exposed to toxicants has been attributed to either stochastic processes or individual tolerance (IT), leading to the stochastic death (SD) and IT models. While the IT model follows the principles of natural selection, the relevance of the SD model has been debated. To clarify why the idea of stochastic mortality has found its way into ecotoxicology, we investigated the mortality of Poecilus cupreus (Linnaeus, 1758) beetles from pesticide-treated oilseed rape (OSR) fields and unsprayed meadows, subjected to repeated insecticide treatments. We analyzed the mortality with the Kaplan-Meier estimator and general unified threshold model for survival (GUTS), which integrates SD and IT assumptions. The beetles were exposed three times, ca. monthly, to the same dose of Proteus 110 OD insecticide containing thiacloprid and deltamethrin, commonly used in the OSR fields. Kaplan-Meier analysis showed that the mortality of beetles from meadows was much higher after the first treatment than after the next two, indicating the IT model. Beetles from the OSR displayed approximately constant mortality after the first and second treatments, consistent with the SD model. GUTS analysis did not conclusively identify the better model, with the IT being marginally better for beetles from meadows and the SD better for beetles from OSR fields.

Effects of agricultural landscape structure and canola coverage on biochemical and physiological traits of the ground beetle Poecilus cupreus

The intensifications in the agricultural landscape and the application of pesticides can cause adverse effects on the fitness of organisms in that landscape. Here, we investigated whether habitats with different agricultural pressures influenced acetylcholinesterase (AChE) activity - a biomarker for exposure to pesticides, respiration rate, and resistance to starvation in the ground beetle Poecilus cupreus. Two differently structured landscapes were selected for the study, one dominated by small (S) and another by large (L) fields. Within each landscape three habitat types were selected: in the S landscape, these were habitats with medium (M), small (S) and no canola (meadow, 0) coverage (i.e., SM, SS, S0), and in the L landscape habitats with large (L), medium (M) and no canola (meadow, 0) coverage (i.e., LL, LM, L0), representing different levels of agricultural pressure. The activity of AChE was the highest in beetles from canola-free habitats (S0 and L0), being significantly higher than in beetles from the SM and SS habitats. The mean respiration rate corrected for body mass was also the highest in S0 and L0 beetles, with significant differences between populations from L0 vs. SS and from S0 vs. SS. Only beetles from S0, SS, L0, and LM were numerous enough to assess the resistance to starvation. Individuals from the LM habitat showed better survival compared to the canola-free habitat in the same landscape (L0), whereas in S landscape the SS beetles survived worse than those from S0, suggesting that characteristics of L landscape may lead to developing mechanisms of starvation resistance of P. cupreus in response to agricultural pressure.

Species composition and ecological structure of ground beetles (Coleoptera, Carabidae) communities as biological indicators of the agro-environmental sustainability

Intensification of crop cultivation can have detrimental environmental consequences that however can be prevented by monitoring of the specific biological indicators sensitive to changes in the ambient environment. In this study the impact of crop type (spring wheat and corn) and cultivation intensity on the community of ground beetles (Coleoptera: Carabidae) in the forest-steppe of Western Siberia was investigated. A total of 39 species from 15 genera were collected. Ground beetles' community was characterized by a high evenness of species distribution across the agroecosystems. The average Jaccard's similarity index for species presence/absence was 65%, and for abundance it was 54%. The significant difference in the distribution of predatory and mixophytophages ground beetles in wheat crops (U test, P < 0.05) can be justified by the constant suppression of the weed component and the use of insecticides that lead to the dominance of the predators. Fauna of wheat crops was more diverse than that in corn (Margalef index, U test, P < 0.05). No significant differences in biological diversity indexes, except for the Simpson dominance index (U test, P < 0.05, wheat), were found in ground beetle communities in crops at different levels of intensification. A certain differentiation of predatory species was caused by the selective occurrence of the litter-soil species, especially abundant in the row-crop. The specificity of the ground beetle community of corn crops may have been caused by repeated inter-row tillage, which influenced the increase in porosity and topsoil relief and contributed to the creation of favorable microclimatic conditions. In general, the applied level of agrotechnological intensification had no significant effect on the species composition and ecological structure of beetle communities in agrolandscapes. The use of bioindicators made it possible to assess the environmental sustainability of the agricultural environment and also creates the prerequisites for the development of ecologically directed correction of agrotechnological operations in agroecosystem management.