Life in the leaf-litter: a novel metal detector technique to investigate the over-wintering survival of rare, case-bearing beetle larvae

Investigating the ecology of leaf-litter dwelling insects is very difficult without destructive sampling of their habitat. Here, we describe the use of a metal-detector technique to study the overwintering survival of the case-bearing, leaf-litter dwelling larvae of Cryptocephalus coryli (Coleoptera: Chrysomelidae). Three-hundred and thirty captive-reared larvae of this RDB-1 species were released at three sites and recovered on three occasions over a 6 month period. The number of recovered larvae at the three release sites was generally high and was always over 50 % of those remaining to be found. The technique also enabled predation to be investigated. After a period of 180 days, 50, 79 and 89.8 % of the released larvae that were known to have died had been preyed upon at the three study sites. Feeding tests (using baited larval cases), mammal trapping and pitfall trapping suggest the wood mouse (Apodemus sylvaticus) was the principal predator. This study also suggests that open areas with abundant bare ground may be optimal for the over-wintering survival of C. coryli larvae. The adult beetles make no known selection of the ground characteristics when ovipositing from their perches in host trees. Therefore, the remaining populations of this species may be dependent on the dynamic occurrence of suitable host trees on ground that is coincidentally suitable for larval development.