The development of the truffle beetle Leiodes cinnamomeus at low temperature, a determining factor for the susceptibility of adults and larvae to entomopathogenic nematodes

The European truffle beetle Leiodes cinnamomeus (Panzer) (Coleoptera: Leiodidae) is the most important pest in black truffle (Tuber melanosporum) plantations. Adults and larvae feed on truffles during the cold months of autumn and winter, while during spring and summer larvae are in diapause. This study aims to test the sus-ceptibility of L. cinnamomeus adults and larvae to different entomopathogenic nematode (EPN) species at various temperatures under laboratory conditions. Different populations of Steinernema carpocapsae and Steinernema feltiae were applied against adults and mycophagous larvae at 20 degrees C, 10 degrees C and 10-15 degrees C (10 degrees C during 18 h and 15 degrees C during 6 h a day), while Heterorhabditis bacteriophora was only applied against diapause larvae at 25 degrees C. S. carpocapsae caused 100% mortality of adults three days after application at 20 degrees C. At 10 degrees C, adults were not susceptible to any EPN species seven days after treatment, while at 10-15 degrees C S. carpocapsae was the most virulent species (76.6-96.6% mortality). In the case of larvae, all EPN species were infective at 20 degrees C (43.3-83.3% mortality), despite differences among some populations. At 10 degrees C, only two populations of S. feltiae caused higher mortality of larvae (50-53.3%) than control seven days after treatment. H. bacteriophora caused 100% mortality against diapause larvae five days after application at 25 degrees C. Soil temperature was measured in a truffle plantation for each hour every day from September 2021 to April 2022 at 20 cm depth. From September to mid-October it was registered a temperature above 15 degrees C for more than 20 h a day. Temperatures were generally below 10 degrees C from November to March. An appropriate timing of field applications should be considered due to the short periods of time when temperature is optimal for each EPN species tested.

Automated summary

The European truffle beetle is a major pest in black truffle plantations. This study tested the susceptibility of the beetle to different entomopathogenic nematode species at various temperatures. The results showed that S. carpocapsae was highly effective against adults, while S. feltiae was more effective against larvae. The application of different nematode species at different temperatures can effectively control the truffle beetle.