Novel formulations improve the environmental tolerance of entomopathogenic nematodes

Abstract

Entomopathogenic nematodes (EPN) are susceptible to environmental factors such as ultraviolet (UV), for which formulations of EPN infective juveniles (IJs) were explored. In the screening test for Steinernema carpocapsae, liquid starch displayed the greatest UV protection, followed by white kaolin clay (WKC), watergel and Barricade. In concentration tests, after 20-min UV S. carpocapsae IJs mixed in WKC caused 100% mortality of Galleria mellonella larvae at ≥5% concentration and had lower IJ mortality than aqueous IJs at 0.5%-10% WKC. Liquid starch showed increased UV tolerance with concentrations up to 30% and 50% for IJ viability and virulence, respectively. The WKC, liquid starch, Barricade and watergel were further compared to water using S. carpocapsae and Heterorhabditis floridensis. H. floridensis was more susceptible to UV radiation than S. carpocapsae. Liquid starch provided the strongest protection of both EPNs in IJ viability and virulence, with more prominent effects for S. carpocapsae than H. floridensis. The WKC and Barricade improved the viability of both EPNs after UV treatment, but only WKC enhanced S. carpocapsae virulence. The number of invading S. carpocapsae decreased as UV exposure time increased for WKC and only decreased at 20-min UV for liquid starch. Very few H. floridensis invaded insects after UV exposure regardless of treatments. In outdoor soil tests, liquid starch and WKC protected S. carpocapsae but were inferior to Barricade and watergel, probably associated with anti-desiccation. Overall, liquid starch and WKC improved the UV tolerance of EPNs, although the effects were less pronounced in soil involving other factors.