Laboratory evaluation of Turkish entomopathogenic nematodes for suppression of the chestnut pests, Curculio elephas (Coleoptera: Curculionidae) and Cydia splendana (Lepidoptera: Tortricidae)

The lepidopteran, Cydia splendana, and the coleopteran, Curculio elephas, are the most serious pests of chestnut fruit in Turkey. We evaluated the biological control potential of three Turkish entomopathogenic nematode species, Steinernema feltiae, S. weiseri and Heterorhabditis bacteriophora, against the last instar larvae of C. splendana and C. elephas, both of which occur in the soil from fall (October-November) until mid-summer (August). The optimal temperature for infection, time to death of the hosts, and reproductive potential of the nematodes were determined at 10, 15, 20 and 25 degrees C for both pest species. Cydia splendana was more susceptible to nematode infection than C. elephas. Temperature had a significant effect on the infectivity and development of entomopathogenic nematodes. The cold-adapted S. weiseri and S. feltiae were the most virulent species at 10 and 15 degrees C, whereas the warm-adapted H. bacteriophora was the most effective at 20 and 25 degrees C. In soil pot experiments conducted at 15 degrees C, S. weiseri was the most virulent species against C. elephas and C. splendana. However, our data show that C. elephas larvae had a lower and C. splendana larvae had a higher susceptibility to the nematode species tested. Accordingly, we recommend that future efforts of using entomopathogenic nematodes, especially S. weiseri, be directed against C. splendana and that there be a continued effort to find more virulent nematode isolates against larvae of C. elephas.