Enhancing the biological control potential of Steinernema feltiae with protection from desiccation and UV radiation

Abstract

Entomopathogenic nematodes (EPNs) are obligate parasites of insects. EPNs generally have a broad host range, are easily mass reared, and can kill some insects within 48 h. EPNs are safe for vertebrates, plants, and other non-target organisms. However, EPNs have disadvantages that make them less effective against foliar insect pests such as sensitivity to desiccation, ultraviolet (UV) radiation, and high temperatures. The goal of this research was to improve the efficacy of aboveground application of Steinernema feltiae by protecting the nematodes against desiccation and UV radiation. The objectives were to evaluate the effect of UV chemical protectants on S. feltiae viability and demonstrate enhanced insect control with S. feltiae formulated to protect them against UV radiation and desiccation. The UV radiation protectant chemicals P-amino benzoic acid (PABA), octyl methoxycinnamate (OMC), Congo red, titanium dioxide, and zinc oxide were not toxic to mealworm larvae nor the EPNs. PABA, OMC, Congo red, titanium dioxide, and zinc oxide protected Infective Juveniles (IJ) of S. feltiae exposed to UV light for 0, 4, 8 and 12 hrs. After 48 hrs exposure, PABA afforded the greatest protection to S. feltiae compared to other chemicals. OMC provided the second greatest protection to the S. feltiae compared to other chemicals. The UV protectants PABA and OMC were individually combined with Barricade® fire gel, a desiccant protectant, and IJs of S. feltiae were added to the mixture. The IJs were exposed to full spectra UV light in the laboratory for up to 12 hrs before introduction of a mealworm host. The subsequent number of dead mealworm larvae on filter paper or on detached leaves was greatest in the combination treatments of OMC + Barricade and PABA + Barricade and lowest in water controls demonstrating the protection afforded to S. feltiae. The survival of S. feltiae can be enhanced when applied with a desiccant protectant such as Barricade and a chemical such as PABA or OMC to protect against UV radiation. The protection afforded to the IJ by these chemicals allows for greater infection and mortality of target insect pests. The formulation of IJs with desiccant and UV radiation protection will allow the greater use of S. feltiae for the management of foliar insect pests.