Habitat use and activity patterns of larval and adult Cantharis beetles in arable land

Generalist predators play a key role in agriculturally and environmentally sustainable systems of pest control. A detailed knowledge on their ecology, however, is needed to improve management practices to maximize their service of pest control. The present study examines the habitat use and activity patterns of larval and adult Cantharis beetles that are abundant predators in arable land. Laboratory experiments revealed that sixth instar larvae of Cantharis fusca and Cantharis livida significantly preferred high relative humidity levels of 85–90% to lower ones. This can explain their preference for meadows over fields due to the more favorable microclimatic conditions in the former habitats. Surface activity of sixth instar Cantharis larvae during autumn, winter and early spring occurred at soil temperatures above 0 °C. However, no correlation between surface activity and soil temperature, air temperature or relative humidity was found above 0 °C. Catches of sixth instar Cantharis larvae within fenced pitfall traps were higher in a meadow (Mean ± S.D.; 13.8 ± 7.63 individuals m−2) than in a field (4.60 ± 2.89 individuals m−2). Mark-recapture density estimations for sixth instar larvae indicated mean densities of 25.9 ± 5.63 (field) and 42.8 ± 16.0 individuals m−2 (meadow). The same pattern was found for adult emergence rates in the field (0.17 ± 0.39 adults m−2) and meadow (1.83 ± 1.17 adults m−2) as well as for adult densities in the vegetation (field 4.89 ± 3.62 adults 60 m−2; meadow 12.5 ± 11.2 adults 60 m−2). It is concluded that especially in winter elements that provide plant cover should be incorporated in arable fields to enhance larval cantharid population densities and to attract them from their prime grassland habitats into arable sites.