Azadirachtin soil drenches show increased mortality of avocado lace bug nymphs (Hemiptera: Tingidae), in Hawai’i with evidence of multiweek residual activity

Avocado lace bug, Pseudacysta perseae (Heidemann) (Hemiptera: Tingidae), is a sap-feeding insect that feeds on avocado leaves. Injury from P. perseae is indicated by areas of leaf chlorosis/necrosis. Large areas of injury can lead to premature leaf drop, and severe infestations can lead to large proportions of leaves dropping, adversely affecting fruit development and quality. Since its establishment in Hawai'i, P. perseae has become a ubiquitous pest across the islands and is correlated with yield decline. Due to the challenging topography of Hawai'i, lack of biocontrol agents, and mixed fruit tree orchards, effective management strategies are limited to pesticide use. Even so, routine foliar sprays of pesticides are not economically or logistically feasible for controlling P. perseae in Hawai'i. While synthetic systemic pesticides can be used as soil drenches, many show toxicity to nontarget animals and have limited application frequencies. However, research shows azadirachtin, an active component in the organic pesticide neem oil, has some systemic properties. This study investigated soil drenches of varying concentrations of azadirachtin in avocado seedlings on P. perseae nymphal mortality over eight weeks. Results showed mortality had an 85% to 98% probability of occurrence in the first week following drenching for nymphs feeding on azadirachtin-treated trees compared to 14% for untreated trees. Mortality for treated trees decreased through time but remained significantly higher than untreated trees 3 to 6 weeks following drenching. The findings from this study will aid in developing a more practical and economically reasonable management strategy for P. perseae in Hawai'i.