Azadirachtin avoidance by larvae and adult females of the tomato leafminer Tuta absoluta.
The tomato leafminer Tuta absoluta is a serious worldwide threat to tomato production and its control in open-field tomato has relied heavily on synthetic insecticides, which however are not allowed in organic tomato cultivation. Furthermore, insecticide resistance to synthetic insecticides is already a major concern in populations of the tomato leafminer. Azadirachtin is one of the main biorational pesticides in use today, particularly in organic farming, and has potential as an alternative to conventional insecticides for such use. However, the effects of neem-based products of high azadirachtin content on the tomato leafminer have been little studied and very little is known of their sublethal behavioral effects on this pest species. Here we assessed the insecticidal effect of a commercial neem-based formulation (as a source of azadirachtin) against two populations of the tomato leafminer and its behavioral effects on egg-laying preferences, walking by larvae and leaf-mining. Azadirachtin caused heavy mortality in insect larvae allowing only 2.5-3.5% survival at the Brazilian recommended field-concentration (i.e., 27 mg a.i./L) with negligible difference between the populations tested. Azadirachtin also caused egg-laying avoidance (under free-choice conditions, but not in no-choice conditions) and affected walking by larvae, but not leaf-mining. These results indicate the potential of azadirachtin not only as an insecticide potentially important for organic farming, but also as an egg-laying deterrent minimizing T. absoluta infestation although it may also favor escape by larvae to exposure since it sparks behavioral avoidance.