Entomopathogenic nematodes for the biological control of stored product insect pests

Entomopathogenic nematodes are lethal endoparasites of insects. They have been used as biological controls for many insect pests, but their potential to control stored product insects has not been investigated. Research presented here focused on two aspects of entomopathogenic nematodes as biological control agents: an applied aspect studying pathogenicity and survival under different environmental conditions encountered in the field, and a basic aspect evaluating nematode/host infection dynamics. The pathogenicity of three nematode species, Steinernema carpocapsae, S. feltiae and S. riobrave, was tested against a range of insects that attack stored products. Steinernema riobrave was selected based on its high pathogenicity and tolerance to temperatures encountered in storage facilities. Experiments under field conditions demonstrated that this nematode species could cause high mortality of late instar larvae and pupae of T. castaneum and all stages of P. interpunctella. Pathogenicity under field conditions may be less than predicted due to a variety of factors, including differences in attraction and infection of hosts based on their infection status. Carbon dioxide has been reported as a cue used to find hosts. Changes in CO2 released over time by Galleria mellonella and Tenebrio molitor after infection by either S. carpocapsae, S. feltiae, S. riobrave or S. feltiae were measured. Infected G. mellonella showed two distinct peaks of CO2 production higher than levels produced by uninfected insects, while infected T. molitor showed one. Behavioral assays were conducted to test for changes in nematode attraction that could be related with the timing of the CO2 peaks. Steinernema glaseri was highly attracted to uninfected and infected hosts and S. riobrave and S. carpocapsae did not respond positively to either host type. There was no relation between nematode behavior and CO 2 peaks. Nematode composition inside the infected host, and presumably the quality of the host, changed over time, but the attraction response measured in behavioral assays did not show any trends over the infection period. Additional research is needed to determine if other factors such as close range attraction and penetration rate are impacted by these changes in CO2 production.