Effects of malathion and Staley's bait on the behavior and survival of parasitic Hymenoptera

A wasp parasite of ice plant scale, Encyrtus saliens Prinsloo and Annecke, was studied to determine the effect of simulated malathion-Staley's bait spray residue on the walking speed of the parasite and whether the bait alone was attractive or repellant. Trioxys pallidus (Haliday), a parasitic wasp of walnut aphid, and Euderauphale flavimedia (Howard), a parasitic wasp of iris whitefly, were similarly tested for response to the bait. Walking speeds of intoxicated wasps and controls were determined with a video camera-microcomputer tracking system. Baseline data on the effect of temperature and time of day were established. The three wasp species demonstrated neutral or negative responses to Staley's bait in all but 1 of 45 cases. The net impact of a toxicant-bait spray program on parasitic wasps needs to be determined under field conditions, but this study identifies the phenomena that may contribute to that net result.