GENETIC ENHANCEMENT OF NEMATICIDE RESISTANCE IN ENTOMOPATHOGENIC NEMATODES

Entomopathogenic nematodes are highly effective bioinsecticides. Their efficacy may be reduced due to the various pesticides they encounter in the soil. These include insecticides as well as nematicides used ag ainst plant-parasitic nematodes. The purpose of this study was to exam ine the feasibility of genetic selection as means of enhancing resista nce of the entomopathogenic nematode Heterorhabditis bacteriophora str ain HP88 to the nematicides: Fenamiphos (an organophosphate), Oxamyl ( a carbamate) and Avermectin (a biological product). Estimates of herit ability (h(2)) of resistance to the three nematicides were obtained fr om analysis of inbred lines derived from the base population. The heri tability estimate for Fenamiphos was h(2) = 0.31, for Oxamyl h(2) = 0. 71 and for Avermectin h(2) = 0.46. Five rounds of selection were perfo rmed. Thereafter, each line was divided into two: for one subline sele ction continued for six additional rounds. The other subline was reare d without selection for the six additional rounds. After the eleventh round, resistance to the nematicides was examined as were several trai ts relevant to biocontrol efficacy including virulence, heat tolerance and reproduction potential. Selection resulted in an 8-9-fold increas e in resistance to Fenamiphos and Avermectin and a 70-fold increase in resistance to Oxamyl. The enhanced resistance Oxamyl and Avermectin, and to a lesser extent to Fenamiphos, was stable and continued after s election was relaxed. No deterioration in traits relevant to biocontro l efficacy was observed in the selected lines as compared with the bas e population. The selected lines displayed enhanced cross-resistance t owards some, but not all, of the nematicides tested. These results dem onstrate that genetic selection can be used to enhance resistance of e ntomopathogenic nematodes to certain environmental stresses. The selec ted lines will be useful bioinsecticides in the context of integrated pest management.