First formulation of a botanical active substance extracted from neem cell culture for controlling the armyworm.
Neem (Azadirachta indica) produces several of compounds known as limonoids, which have an antifeedant effect on insects. These compounds are extremely sensitive to some environmental factors that cause their degradation. Despite this, they are widely used in many formulations of commercial bioinsecticides. We evaluated the photodegradation of the crude extract from A. indica cell culture and designed the formulation of a botanical active substance for controlling insects. The crude extract was subjected to 368 nm UV light for 24 h, and its degradation was examined. Limonoids present in the crude extract were analyzed via high-performance liquid chromatography (HPLC). The composition of some compounds in the extract decreased by 55% after 214 min and 83% after 1440 min. For the insect bioassay, we prepared six formulations containing ethanolic extracts from A. indica cell culture as the active ingredient. The formulation also contained a photoprotector and two stabilizers, emulsified with water, castor oil, and Tween 80. Formulations were subjected to stability tests, and the relative phase separation was assessed. To evaluate their biological activity, the antifeedant index and the affected leaf area on corn infested with Spodoptera frugiperda were determined using laboratory- and field-scale bioassays. Three formulations showed good stability, and two presented the highest antifeedant indices (98.5 and 99.7%) in laboratory-scale bioassays. They provided the greatest field-level protection (leaf areas affected were 0.6 and 1.9%, respectively). Therefore, the emulsion containing 0.76% p/p ethanolic extract, 0.72% 8-hydroxyquinoline, 1.00% anthraquinone and epichlorohydrin, 0.20% Tween 80, and 50/50 aqueous phase/oil phase was selected as the best formulation for the insect biocontroller. This thus addresses the problem of metabolite degradation in the field. To our knowledge, this is the first effective formulation of a botanical active substance for controlling insects using A. indica cell culture extract.