Oecophylla smaragdina ants provide pest control in Australian cacao

Ecosystem service‐driven methods of agricultural production that make optimal use of an ecosystem's natural services are often effective in smallholder crops, leading increases in habitat heterogeneity at large spatial scales that encourage beneficial species. Pollination services in cacao farms can be enhanced through efforts to conserve pollinator habitats, such as adding cacao fruit husks underneath trees to provide habitat and food resources for midge pollinators. However, it remains unclear how this habitat manipulation affects pest densities or biological control. Here, we evaluated the effects of the predaceous ant Oecophylla smaragdina on three major pests of Australian cacao (Helopeltis spp., Amblypelta spp., and Rhyparida nitida) in an Australian cacao farm, in the presence and absence of cacao fruit husks. We also evaluated the effect of O. smaragdina on their potentially plant‐damaging, mutualistic mealybug (Pseudococcidae) partners in the presence and absence of cacao fruit husks. Oecophylla smaragdina reduced the combined densities of Helopeltis spp. and Amblypelta spp., regardless of cacao fruit husk addition. The ants also reduced the densities of R. nitida in the absence of cacao fruit husks, but R. nitida densities were naturally low in the experimental plots that received the addition of cacao fruit husks, regardless of ant presence. In contrast, ants generally increased the densities of mealybugs. These data suggest that O. smaragdina ants provide pest control services for three major insect pests in Australian cacao farms. Furthermore, this control may be compatible with habitat manipulations (i.e., the addition of cacao fruit husks) to improve pollinator habitat.