Novel formulations improve the environmental tolerance of the entomopathogenic nematodes

Authors: WU, SHAOHUI - University Of Georgia; LI, YINPING - Fort Valley State University; TOWES, MICHAEL - University Of Georgia; MBATA, GEORGIA - Fort Valley State University; Shapiro Ilan, David

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/13/2023
Publication Date: 8/20/2023
Citation: Wu, S., Li, Y., Towes, M.D., Mbata, G., Shapiro Ilan, D.I. 2023. Novel formulations improve the tolerance of the entomopathogenic nematodes to ultraviolet radiation. Biological Control. Vol 186:105239. https://doi.org/10.1016/j.biocontrol.2023.105239.
DOI: https://doi.org/10.1016/j.biocontrol.2023.105239

Interpretive Summary: Entomopathogenic nematodes (also known as beneficial nematodes) are small round worms that are biopesticides that are used to control a wide variety of economically important insect pests. These biopesticides are advantageous compared to most chemical insecticides because the nematodes do not harm humans, the environment or beneficial insects (such as lady beetles). However, entomopathogenic nematode use can be limited, especially when applied to crops aboveground, because the worms are sensitive to UV radiation and desiccation (drying out); excessive exposure to these elements will kill the nematodes. Therefore, formulations are needed to protect the nematodes. In this study, we investigated a variety of formulations for their ability to protect the nematodes from UV radiation. Among 16 different formulations initially tested, three showed the most promise and were tested further: Barricade (a firegel), kaolin clay, and liquid starch. These formulations exhibited UV protection. Liquid starch exhibited the greatest protection to the nematodes from UV radiation. However, when nematodes were applied under field conditions, the Barricade gel was superior to the other formulations in enhancing nematode survival. The Barricade was probably the best because it protected against both UV radiation and desiccation. Studies on improving beneficial nematode formulations will continue and lead to enhanced pest control efficacy.

Technical Abstract: Formulations of entomopathogenic nematode infective juveniles were tested for relative resistance to ultraviolet (UV) radiation in indoor and outdoor tests. In the screening test for Steinernema carpocapsae, liquid starch displayed the greatest UV protection, followed by white kaolin clay, watergel and Barricade. The white kaolin clay and liquid starch were then tested at different sprayable concentrations for S. carpocapsae. The IJs mixed in white kaolin clay caused 100% insect mortality at = 5% concentration of white kaolin clay even after 20-min UV exposure and had lower nematode mortality than aqueous IJs after 20-min UV exposure at all concentrations. The UV tolerance level of liquid starch increased with concentrations, at = 30% concentrations for nematode viability and = 50% for IJ virulence. The white kaolin clay, liquid starch, Barricade and watergel were further compared to water control using S. carpocapsae and Heterorhabditis floridensis. H. floridensis was more susceptible to UV radiation than S. carpocapsae. Liquid starch provided the strongest UV protection of both EPNs in both IJ viability and virulence, with more prominent effects exhibited for S. carpocapsae than H. floridensis. The white kaolin clay and Barricade improved the viability of both EPNs after UV treatment, but only white kaolin clay enhanced the virulence of S. carpocapsae. The number of invading S. carpocapsae in white kaolin clay decreased at longer UV exposure times, and invading nematodes in liquid starch decreased at 20-min UV exposure. Very few H. floridensis invaded insects after UV exposure regardless of treatments. In outdoor soil tests, liquid starch and white kaolin clay protected S. carpocapsae but were inferior to Barricade and watergel, probably associated with anti-desiccation of the latter formulations.