Life histories of two predaceous beetles, Bembidion lampros and Tachyporus hyponorum, in the agroecosystem

Polyphagous predators are important for natural control of insect pests in arable fields. This study has focused on mortality, fecundity and seasonal movements which were expected to influence predator field densities. It has been suggested that increased number of predators in arable fields could lead to an increased natural control of insect pests. Investigations were primarily made under controlled conditions. Priority was given to mortality factors out of farmer's control such as influence from weather and soil types, as these factors will define the limits for effects of man-made manipulations. The carabid Bembidion lampros and the staphylinid Tachyporus hypnorus were selected due to their abundance and activity during the period of aphid establishment in cereal crops. Both species overwinter as adults. In spring they disperse into arable fields where they reproduce. Juvenile mortality was high in different soil types which were irrigated regularly and had prey occuring in excess. Mortality of T. hypnorum was lower in sandy soil (51%) than clayey soil (80%). Mortality of B. lampros was, on average, 70% and independent of soil type. In general adult B. lampros were more robust, less fecund and less mobile compared to T. hypnorum. Adult mortality during winter and early spring is of minor importance as long as temperatures during the winter are stable and the beetles are protected by a cover of vegetation. However, some winters might have a temperature regime that will cause a higher mortality. In the post-winter period both species have the capacity to survive periods of starvation. B. lampros starts movement into the field a month before T. hypnorum. Two single-species simulation models were constructed using the concept of metabolic pool models. The models contain all quantified data on B. lampros and T. hypnorum found in the literature or obtained in this study. Increase of populations of B. lampros and T. hypnorum should be concentrated to enhancement of the conditions for the juvenile stages during development in the soil surface. Specific recommendations cannot be given before optimal conditions are determined in detail and compared to effects of different potential changes in agricultural practices.