My Enemy's Enemies: Recruiting Hemipteran-Tending Generalist ants for Biological Control in Citrus Orchards by Spatial Partitioning of Foraging Webs

Abstract

Generalist predators are contentious biocontrol agents, especially ants that protect pestilent hemipterans from specialist predators and parasitoids. We attempted to force generalist, hemipteran-tending ants into a degree of dietary specificity by spatially partitioning and simplifying their trophic web. Pupae of Helicoverpa armigera, Thaumatotibia leucotreta and Ceratitis capitata introduced into a citrus orchard survived significantly better in plots where all nests of two pestilent, generalist ant species namely Anoplolepis custodiens and Pheidole megacephala had been poisoned compared with untreated control plots. In some plots the ants' foraging environments were partitioned into arboreal and epigaeic trophic webs using sticky barriers to prevent ground-nesting ants from ascending the trees. Plots partitioned this way showed suppressed levels of survival of emplaced pest pupae that were similar to those in unpartitioned control plots. Pest survival was significantly lower for T. leucotreta than for H. armigera and C. capitata, implicating prey body size or life cycle duration as factors in predation by ants. Pheidole megacephala and the predator complex as a whole can be valuable agents in the natural control of soil-pupating citrus pests if they are restricted to the ground. Trunk banding, rather than poisoning, is therefore recommended as part of managing ecologically mercenary ants in citrus orchards.