UC San Diego

In San Diego County, a major economic impact of the Argentine ant occurs in citrus agroecosystems, where ants interfere with biological control of key insect pests, especially California red scale. Ant control is considered a critical component of integrated pest management (IPM) of several citrus pests, but IPM recommendations fail to consider quantitative relationships between levels of Argentine ant abundance and those of the economic pests. This serious gap in understanding impedes development of economically and environmentally sustainable strategies for the management of these agricultural pests. In this study, we manipulated key members of a citrus food web to discover direct and indirect effects of a commonly- occurring mutualism. We found that there was a positive correlation between ants and red scale and an increase in parasitism on red scale when ants were removed. We also found that when ants were not present, key honeydew- producing insect abundance was reduced, as well as the converse : when honeydew-producing insects were removed, ant abundance was depressed. This study provides mechanistic and quantitative information required to engineer improved IPM strategies. For example, farmers could save money and labor by only applying pest control measures when ants reach the threshold level at which they positively affect hemipteran pests. Such ecologically informed strategies would reduce management costs while minimizing negative environmental effects resulting from existing, chemically intensive management practices