Compatibility of Biological Control Agents and Agrochemicals to Entomopathogenic Nematodes,Steinernema yirgalemense and Heterorhabditis zealandica

Abstract

The compatibility of two endemic entomopathogenic nematodes (EPNs) with biological control agents and agro-chemicals, likely to be used in an integrated pest management programme for citrus in South Africa was investigated. This is the first report on the possible negative effect of EPNs against Cryptolaemus montrouzieri, a commercially produced biocontrol predatory insect, used against mealybugs. Bioassays were conducted to determine the susceptibility of the mealybug predatory coccinellid beetle, C. montrouzieri, to both nematode species. Results showed the beetle larvae to be highly susceptible to a concentration of 80 IJ/insect of H. zealandica and S. yirgalemense, obtaining 80 % and 92 % mortality, respectively. Adult beetles were found to be twice as susceptible to S. yirgalemense with 64 % mortality, as to H. zealandica with 30 % mortality recorded. Tolerance of both species of infective juveniles to aqueous solutions of Cyperfos 500 EC®, Cryptogran™, Helicovir™, Nu-Film-P® and Zeba®, for infectivity and survival was evaluated. Heterorhabditis zealandica proved to be highly compatible to all products tested, with no significant increase in nematode mortality. The formulations also did not affect the ability of H. zealandica to infect Tenebrio molitor, after exposure to products over a 24-h period. Significant increase in mortality of S. yirgalemense was recorded after 12 hours of exposure to Nu-Film-P® and Cyperfos 500 EC®, and after 6 hours of exposure to Nu-Film-P®. However, results for S. yirgalemense infectivity showed no decrease in the ability of the nematodes to infect insect hosts. Results indicated that nematodes should possibly be applied before the release of C. montrouzieri in citrus orchards.