Efficacy of Heterorhabditis bacteriophora Against Diapausing Larvae of the Truffle Beetle, Leiodes cinnamomeus

Abstract

The truffle beetle, Leiodes cinnamomeus, is the most important pest in black truffle (Tuber melanosporum) plantations. Adults and mycophagous larvae are active during autumn and winter, while diapausing larvae are not. Previous laboratory studies demonstrated the high virulence of the entomopathogenic nematode (EPN) Heterorhabditis bacteriophora against diapausing L. cinnamomeus larvae when exposed without their earthen cocoons. However, the efficacy of EPNs against soil-dwelling insects may be affected by the low metabolic rate of diapausing insects and the potential barrier posed by earthen chambers. Therefore, the aim of the present study was to evaluate the efficacy of H. bacteriophora in targeting diapausing larvae within their earthen cocoons under laboratory simulated natural conditions. The experiment was conducted in cardboard tubes (30 × 8 cm) filled with truffle soil, into which 15 L. cinnamomeus larvae were introduced at three different depths in February. In June, two applications of H. bacteriophora were conducted to the tubes, spaced 7 days apart. Eight days after the second application, the number of living larvae at each depth was counted. Our results showed that H. bacteriophora can locate and kill diapausing L. cinnamomeus larvae within their earthen aestivation cocoons at different soil depths. Future efficacy assays should focus on field applications to corroborate the efficacy of this nematode.