Insecticidal activities of the local entomopathogenic nematodes and cell-free supernatants from their symbiotic bacteria against the larvae of fall webworm, Hyphantriacunea

Abstract

The fall webworm (FWW), Hyphantria cunea Drury (Lepidoptera: Erebidae), is an invasive and polyphagous insect pest of many economically important crops such as hazelnuts, apple, and mulberry. Recently, there have been an increasing number of reports about the damaging activities of FWW from hazelnut growing areas of Turkey indicating that currently existing control methods fail to satisfy the expectations of growers. Entomopathogenic nematodes (EPNs) in the Steinernematidae and Heterorhabditidae (Nematoda: Rhabditida) families and the symbiotic bacteria they carry in their intestine have a great potential for the management of many agriculturally important pests. In this study, the symbiotic bacteria of local EPN species (Heterorhabditis bacteriophora AVB-15, Steinernema feltiae KCS-4S, and Steinernema bicornotum MGZ-4S) recovered from the central Anatolia region was characterized using recA gene region as Photorhabdus luminescens, Xenorhabdus bovienii and Xenorhabdus budapestensis. The contact (25, 50, 100, 200 IJs/Petri) and oral efficacies of the infective juveniles (IJs) (25, 50, 100, 200 IJs/leaf) of these EPN isolates determined on 3rd/4th instar larvae, and cell-free supernatants from the identified symbiotic bacteria were evaluated separately on the 3rd and 4th larval instars of FWW in Petri dish environment under laboratory conditions (25 ± 1 °C, 60% of RH). In the Petri dish bioassays of EPN species, the most pathogenic isolate at the 1st DAT and 4th DAT was S. feltiae which caused 50% mortality at the highest concentration (200 IJs/Petri) and the highest mortality rate (97.5%) were achieved at 4th DAT by H. bacteriophora AVB-15 isolate. Surprisingly, the mortality rates were generally higher at the lowest concentrations and 82.5% mortality were reached 4th DAT by S. bicornotum at the lowest concentration (25 IJs/leaf) in the leaf bioassays. Mortality rates were higher in both Petri dish and filter paper efficacies of cell-free supernatants at the 2nd DAT and the highest mortality (87.5%) was reached in the contact efficacy studies when applied X. bovienii KCS-4S strain. The results suggest that the tested EPN species and CFSs have good potential for biological control of the larvae of FWW and can contribute to the IPM programs of FWW. However, the efficacy of both IJs of EPNs and CFSs of their symbiotic bacteria on larvae of FWW requires further studies to verify their efficiency in the field.

Keywords: Biological control; Cell-free bacterial supernatant; Fall webworm; Hazelnut pest; Heterorhabditis bacteriophora; Steinernema bicornotum; Steinernema feltiae.