Interaction between cyromazine and the entomopathogenic nematode Heterorhabditis bacteriophora Poinar “GPS11” for control of onion maggot, Delia antiqua (Meigen)

Abstract

Cyromazine seed treatments, which affect insect cuticle formation, and entomopathogenic nematodes, which must pass through openings in the insect cuticle, were applied independently and in combination to test for synergism between the two in their effects on onion maggots. In preliminary assays with Heterorhabditis bacteriophora, rates of 10–160 nematodes per larva caused significant mortality in both first and second stadium onion maggots. Cyromazine treatments, applied as a film-coated seed treatment at rates ranging from 0.78 to 50 g ai/kg seed, were tested alone and in combination with 5 and 10 nematodes per larva for first and second instars, respectively, to examine interactions between the insecticide and biological control. No significant interactions between cyromazine and nematode treatments were observed. Differences among rates of cyromazine in plant and larval mortality, however, were statistically significant, and differed for the two larval stadia examined. Although cyromazine and entomopathogenic nematodes could be used independently for onion maggot control without negative interactions, no synergistic effects should be expected from their combined use.