Potential of sorghum and physic nut (Jatropha curcas) for management of plant bugs (Hemiptera: Miridae) and cotton bollworm (Helicoverpa armigera) on cotton in an assisted trap-cropping strategy

The cotton bollworm (CBW) Helicoverpa armigera andto a lesser extent plant bugs (PB) (Hemiptera: Miridae)are important pests of cotton in Africa. For sustainabilityreasons, it is necessary to reduce use of chemical controlmeasures for these pests. A promising alternative tochemical control of both CBW and PB is trap cropping,assisted with botanical pesticides sprays, if needed. Wereport studies conducted from 1995–98 on sorghumattractiveness to PB and CBW, on the potential of physicnut (Jatropha curcas) extracts [particularly the phorbolester (PE) fraction of the oil] for sorghum protection fromPB damage, and on the insecticidal activity of Jatrophaextracts on CBW. At the ICRISAT research station(Samanko, Mali), infestation by the five main species ofPB (accounting for 96% of total) was much higher onsorghum than on cotton. In the Kolokani region, CBWinfestation was negligible on the Guinea loose-panicledsorghum cultivar Bibalawili, while it was significant onboth compact-panicled PB susceptible ICSH 89002 andPB resistant Malisor 84-7. At Samanko, Jatropha oilapplication on sorghum panicles showed some effect onPB when damage level was high, better than Jatrophaand neem aqueous extracts. However, it did not competewith pyrethroid protection level. PE contact toxicity onCBW larvae was too low to determine a LC 50. Aningestion insecticidal activity of PE was found on alltested larval instars. Contact toxicity LC 50 of PE on eggswas 1.66 g ml-1. Development of larvae and reproductiveability of adults derived from new-laid eggs treated with solutions of 0.35 g ml-1 PE and above were considerablyaffected. Prospects for using sorghum and Jatrophaextracts for cotton protection against insect pests in anassisted trap-cropping strategy are discussed.