Effects of soil application of neem (NeemAzal®-U) on different life stages of Liriomyza sativae (Diptera: Agromyzidae) on tomato in the humid tropics

Abstract

NeemAzal®-U, a formulation containing 17% azadirachtin developed for soil treatments, was tested in air conditioned laboratories and net greenhouses in Thailand to control Liriomyza sativae Blanchard (Diptera: Agromyzidae) on tomatoes (Lycopersicon esculentum). The substrates of potted tomato plants were drenched with set volumes of neem solutions of altered concentrations. All tested neem concentrations had very low effects on oviposition and egg hatching. Strong systemic effects however were recorded in the larval stages attaining mortalities up to 100% when high dose drenching solutions containing 3 g NeemAzal®-U l–1 water equivalent to 0.5 g l–1 azadirachtin A were implemented. First instar larvae were found to be most susceptible to all dosages tested. Activity of NeemAzal®-U was persistent since application of even seven days before infestation resulted in mortalities extending between 40 to 70%. Leafminer late 3rd instar surviving on treated plants and moving as so called prepupa to pupate in treated soils endured a very high mortality during pupal stage ensuing in few adult emergences even when the lowest NeemAzal®-U concentration of 0.75 g l–1 water was used. The direct effects of soil treatment were elucidated by rearing leafminers on untreated plants but treating the substrate used for pupal development. Significant mortalities were only obtained when soil treatment was performed immediately before prepupa moved to the soil.