Entomopathogenic nematodes in pecan orchards in Georgia and their virulence on selected pecan pests.

Abstract

Several insect pests prevalent in pecan orchards cause considerable damage to foliage and nuts, including fall webworm (Hyphantria cunea Drury) (Lepidoptera: Erebidae), walnut caterpillar (Datana integerrima Grote and Robinson) (Lepidoptera: Notodontidae), and nut curculio (Curculio hicoriae) (Coleoptera: Curculionidae). Synthetic insecticides are commonly used to manage these pests. However, developing effective biological control methods is essential to reduce reliance on chemical insecticides and their associated impacts. Entomopathogenic nematodes (EPNs) are effective biocontrol agents used against various lepidopteran and coleopteran pests in different cropping systems. The objectives of the current study were to identify the naturally abundant EPNs in pecan orchards and evaluate their effectiveness against fall webworm, walnut caterpillar, and nut curculio. EPNs were recovered from all sampled orchards. However, 46.43% of the samples were positive for the presence of EPN, which were identified to 5 EPN species, Heterorhabditis indica, H. zealandica, Metarhabditis rainai, Oscheius myriophilus, and Steinernema glaseri. Additionally, the effectiveness of these local EPNs was compared with 2 commercial EPN strains, H. bacteriophora (HP88) and S. carpocapsae (All). Laboratory assays indicated that H. indica and H. zealandica have high virulence against both the larvae and pupae of fall webworm, walnut caterpillar, as well as larvae of nut curculio. In contrast, M. rainai, O. myriophilus, and S. glaseri exhibited low virulence against the larvae of fall webworm and walnut caterpillar. Therefore, H. indica and H. zealandica could be potential biological control agents for managing fall webworm, walnut caterpillar, and nut curculio in pecan orchards.