Degradation of azadirachtin A on treated maize and cowpea and the persistence of Azadirachta indica seed oil on Callosobruchus maculatus and Sitophilus zeamais

Azadirachta indica seed oil has long been used in many parts of the world for the control of various insect pests. The quantification of its known insecticidal compound Azadirachtin A on treated commodities remains a challenge. The degradation of Azadirachtin A in treated cowpea and maize was determined with HPLC-MS as well as the toxicity of A. indica seed oil on their respective major pests is storage between 0 and 180 days. Azadirachtin A degraded slowly on treated maize from 1.31 mg/kg (0-day) to 0.38 mg/kg (180-day) while on cowpea it degraded from 1.14 mg/kg (0-day) to 0.43 mg/kg (180-day). A. indica oil caused a significant day-dependent mortality of adults Callosobruchus maculatus and Sitophilus zeamais and its effectiveness decreased with time. The tested oil was more persistent for inhibiting progeny production than on adult mortality. Further studies are needed to evaluate the quality of treated grains at different storage times.