Interpretive Summary: The brown citrus aphid, Toxoptera citricida, is a recently introduced pest of citrus in the United States. It is particularly important because it can develop enormous populations on citrus and it is an efficient vector of citrus tristeza virus, a potentially devastating disease of citrus. Interest in using biopesticides in such situations has increased in recent years due to their reduced adverse effects on non-target organisms and the environment in general. The biological effects of a commercially available biopesticide (Neemix. 4.5, 4.5% azadirachtin) containing extract of seeds from the neem tree (Azadirachta indica) were assessed on the brown citrus aphid (Toxoptera citricida) and its parasitoid (Lysiphlebus testaceipes). When small citrus seedlings were treated with dilute neem extract and subsequently infested with aphid nymphs, we observed 80 to 100 % mortality of nymphs after 7 days. Exposure of the adult aphid to the neem extract significantly reduced its longevity and reproduction. Neem extract sprayed onto potted citrus plants infested with aphids in the greenhouse also resulted in significant reductions of adults and nymphs of the brown citrus aphid. Embryonic mortality and failure to molt appeared to be a major cause of reproductive failure and nymphal death due to the neem treatment. The neem extract had little impact on the survival of adult parasitoids (i.e., L. testaceipes), and parasitoids developing inside parasitized aphids exposed to the neem extract emerged in numbers equal to those of untreated aphids. These properties suggest that neem extract would be compatible with integrated pest management programs in citrus.

Technical Abstract: The biological effects of a commercially available neem extract (Neemix. 4.5, 4.5percent azadirachtin (AZ)) were assessed on the brown citrus aphid (Toxoptera citricida, a recently introduced citrus insect pest in the United States) and its parasitoid (Lysiphlebus testaceipes). When small citrus seedlings were treated with the neem extract at 11 - 180 ppm AZ, 0 - 8percent of nymphs and 0 - 17.5 percent of adults survived 7 d after the treatment while 95 percent of nymphs and 42.5percent of adults in the control survived for the same period. Neem extract at all tested concentrations drastically reduced longevity of both adults and nymphs, adult fecundity, and nymph molting. Spraying neem extract (11 180 ppm AZ) onto potted citrus plants in the greenhouse also significantly reduced aphids by 20 – 100 percent; simultaneously, control aphid populations increased by 950 percent 7 d after the treatment. Application of neem extract had little impact on the survival of adult parasitoids and developing parasitoids within aphids, since emergence numbers from parasitized, treated aphids were equal to those from untreated aphids. These properties suggest that neem extract is compatible with IPM programs in citrus ecosystems.