Lignin-based compounds for the microencapsulation of neem extract for the control of Diabrotica speciosa (Coleoptera: Chrysomelidae) larvae on maize roots

Diabrotica speciosa (Germar) larvae have been considered one of the major subterranean pests of several crops, including maize (Zea mays L) in South America. Currently, there are limited options for managing this pest in maize, and botanical insecticides are a potential option that could provide additional modes of action against D. speciosa. One of the major barriers to using botanical insecticides is their instability due to their rapid degradation in the environment. Lignin extracted from sugarcane bagasse, a byproduct which is largely produced in the Brazilian sugarcane industries, was tested for encapsulating neem (Azadirachta indica A. Juss) extract with and without additional additives to provide stability in some formulations. Thus, this research aimed to evaluate the effect of neem extract in different microencapsulated formulations and doses to control D. speciosa. In addition, effects on maize plant development were assayed. In low-dose neem testing, the microencapsulated formulations with the additives Tinogard®, Silicone, Styleze® and Styleze® + Tinogard® were the most efficient in controlling D. speciosa larvae. Most of the formulations delayed the larva to adult period, which could lead to fewer generations per year. Moreover, LigN + silicone caused reduction in the weight of adults. All additives were not toxic to D. speciosa. Overall, the low doses of neem had no negative effect on the development of maize plants. In high-dose neem testing all the insects died, but the high-doses were toxic to plants. The aforementioned low-dose formulations seem a promising tool for controlling D. speciosa in maize fields.