Physic nut (#Jatropha curcas#) oil as a protectant against field insect pests of cowpea in Sudano-Sahelian cropping systems

摘要

Cowpea is a profitable food and fodder crop in the Sudano-Sahelian region of Africa. Unfortunately, it is extensively damaged in the field by a range of insect pests. The use of locally available insecticidal plant extracts is a promising alternative to chemical crop protection, which is the most popular management strategy but shows many drawbacks. In this respect, oil extracted from seed of the physic nut shrub (Jatropha curcas) showed promise. The insecticidal properties of J. curcas oil were thus assessed against cowpea insect pests at the ICRISAT research station, Sadoré, Niger. In 2002, four concentrations of physic nut oil extract, formulated as an emulsifiable concentrate (EC) (namely 2.5%, 5%, 7.5% and 10%), were evaluated as field sprays along with an untreated control (water spraying) and a conventional insecticide (Deltamethrin Decis® EC) treatment. In 2009, these latter two checks were evaluated alongside four concentrations of a "blank" formulation consisting of only the adjuvants of the 2002 EC formulation (namely 1.25%, 2.5%, 3.75% and 5%). In 2002, application of Deltamethrin and physic nut oil at 7.5% gave the highest seed yields, with more than 1000 kg ha-1. Both treatments, alongside the one with 10% oil, sustained significantly lower thrips (Megalurothrips sjostedti) infestation than the water-sprayed control. All oil extract treatments and the Deltamethrin treatment sustained significantly lower infestation by Clavigralla tomentosicollis bugs than the untreated control, with the lowest infestation occurring with 7.5% oil. Furthermore, correlations between oil concentration and thrips and bug infestation were negative and significant, while correlation between oil concentration and seed yield was not significant, due to a phytotoxic effect of oil at high concentrations. The follow-up studies in 2009 confirmed that effects of Jatropha oil on cowpea insect infestation and seed yield observed in 2002 could be ascribed to the physic nut oil fraction alone. (Résumé d'auteur)