Persistence of Cameroonian neem seed oil on Callosobruchus maculatus and Sitophilus zeamais and the degradation of its Azadirachtin A on treated maize and cowpea
2014
Tofel, H.K. | Nukenine, N.E. | Stähler, Matthias | Adler, Cornel
The cowpea beetle Callosobruchus maculatus and the maize weevil Sitophilus zeamais are considered in many tropical countries as important pests of legumes and cereals. Botanicals are considered a good alternative to chemical insecticides, as they are often less toxic for users and more biodegradable. Products from the neem tree have long been used in many parts of the world for the control of various insect pests. The tree is common in North Cameroon. Therefore, it is an interesting source of insecticide for smallholder farmers. The degradation of Azadirachtin A in treated grain was determined with HPLC-MS between 0 and 180 days. Neem oil caused a significant day-dependent mortality of the insects and its effectiveness decreased with time. There was 100% mortality of C. maculatus (5 ml/kg) and S. zeamais (6 ml/kg) after treatment but for all dosages, there was less than 10% mortality 180 days after treatment. With 3 ml/kg, neem oil strongly inhibited the progeny production (100 %) of C. maculatus and S. zeamais. The tested oil was more persistent for inhibiting progeny production than on adult mortality. Azadirachtin A degraded slowly on treated grain from 1.31 mg/kg (0-day) to 0.31 mg/kg (180-day). The quality of treated grain could be examined at different storage times before recommending neem oil to smallholder farmers.
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