We are investigating the efficacy of generalist predators – carabid and staphylinid beetles – for biocontrol of dipteran pests. In field experiments we found that egg predation increased as activity-density of beetles increased, but only when our study was conducted with young plants. Egg predation did not increase with beetle activity-density when plants were larger and supporting high aphid populations. Subsequent experiments confirmed that as aphid density increased, egg predation by beetles decreased. Currently, we are investigating if the presence of coccinelid larvae in the foliage further exacerbate disruption of egg predation by epigeal beetles.