Entomopathogenic nematodes as biological control agent against Bactrocera zonata and Bactrocera dorsalis (Diptera: Tephritidae)

We evaluated ten different species of entomopathogenic nematodes (EPNs) Heterorhabditis bacteriophora, H. megidis, H. georgiana, H. floridensis, H. indica, Steinernema carpocapsae, S. riobrave, S. feltiae, S. rarum and S. glaseri against different developmental stages i.e. larvae, pupae and adults of fruit flies species Bactrocera zonata and Bactrocera dorsalis. In addition to this broad virulence screening in the laboratory, we also conducted the first field tests measuring the potential for EPNs to control B. zonata and B. dorsalis. In a Petri plate assays targeting adult insects, all EPN species caused different levels of mortality with maximums of 81.18% and 73.64% caused by H. bacteriophora 72 h after exposure in B. zonata and B. dorsalis, respectively. All the EPN species caused infection with the lowest survival levels observed in H. bacteriophora treatments against B. zonata and B. dorsalis. In a long-term exposure bioassay, both larvae and pupae were susceptible to all the EPN species with maximum mortalities caused by H. bacteriophora at 93.06% and 85.93% and 66.71% and 58.50% against larvae and pupae of B. zonata and B. dorsalis, respectively. In a potted soil bioassay, both developmental stages were found susceptible to the different EPN species, but again H. bacteriophora caused the highest levels of mortality; 95.74% and 86.88% in larvae and 71.27% and 67.65% in pupae of B. zonata and B. dorsalis, respectively. Clear dose response relationships were found in four EPNs (H. bacteriophora, S. carpocapsae, S. riobrave, S. feltiae) against larvae, pupae and adult B. zonata and B. dorsalis; the dose-response assays also confirmed superior virulence in H. bacteriophora relative to other EPN species. In a fruit exposure bioassay under laboratory condition, all EPN species were lethal towards larvae even inside the fruit and also in soil with maximum mortalities caused by H. bacteriophora in both fly species. Under greenhouse conditions, the lowest adult emergences (ranging from 19% to 52%) were observed in H. bacteriophora treatments when EPNs were exposed as larvae and pupae of B. zonata and B. dorsalis. Under field conditions, the same EPN species were tested and all the species significantly reduced adult fly emergence, but the lowest adult emergence was observed when using H. bacteriophora (25.06% and 31.53% in B. zonata and B. dorsalis, respectively). In the field, EPNs performed better in artificially infested fruit with mortalities of 47.18% and 42.03% as compared to natural infested fruit with mortalities of 36.88% and 30.86% in B. zonata and B. dorsalis, respectively. Our results indicate that EPNs could be part of an integrated pest management program for control of soil inhabiting stages of fruit fly complexes in orchard systems of Pakistan.

Automated summary

Our study demonstrated that Heterorhabditis bacteriophora exhibited the highest levels of virulence against different developmental stages of fruit flies Bactrocera zonata and Bactrocera dorsalis, showing strong and consistent efficacy under various experimental conditions.