Egg-laying-site preferences of Pterostichus melanarius in mono- and intercrops

Increased vegetational diversity influences the behaviour of carabid beetles by changing plant-related abiotic factors. These abiotic factors (light, humidity and habitat structure) affect the selection of oviposition sites and egg survival of carabid beetles. In a field experiment, more larvae of Pterostichus melanarius (Illiger) (Coleoptera Carabidae) were caught in Brussels sprout intercropped with barley than in Brussels sprout alone. The influence of the presence of living barley and Brussels sprout plants on oviposition was studied in the laboratory. Also, the effects of wet/dry substrate, light/shadowed and structured/unstructured environment on the number of eggs laid were investigated under laboratory conditions. Results indicate a preference for moist, shadowed, structurally complex environments as egg laying sites. This preference results in significantly higher numbers of eggs laid by beetles in barley compared to Brussels sprout. Vegetation characteristics by themselves may influence egg-laying-site preferences, in addition to the availability of prey for adults and larvae in the different cropping systems. Vegetables intercropped with cereals provide a more favourable microclimate for the reproduction of P. melanarius than vegetables grown alone