A large number of gall midge species are natural enemies of other crop pests. Their larvae are predatory, and some are reported as parasitic. The most common prey are aphids and spider mites, followed by scale insects, then other small prey such as whiteflies and thrips, which eat the eggs of other insects or mites. As the larvae are incapable of moving considerable distances, a substantial population of prey must be present before the adults lay eggs, and the Cecidiomyiidae are most frequently seen during pest outbreaks. One species, "Aphidoletes aphidimyza", is an important component of biological control programs for greenhouse crops and is widely sold in the United States. In South Africa, "Dasineura rubiformis" has been deployed against invasive Australian "Acacia" species.