Effect of intercropping selected pesticidal plants with common bean on aphids infestation and natural enemies abundance in Arusha, Tanzania

Abstract

A Randomized Complete Block Design experiment was laid out in four replications to evaluate abundance of natural enemies (NEs) and aphid infestation on common bean (Phaseolus vulgaris L) when intercropped with pesticidal plants (PPs) namely Tagetes minuta, Bidens pilosa, Ageratum conyzoides, Ocimum suave and Hyptis suaveolens. The results showed that PPs attracted NEs and pollinators and reduced aphid infestation with no or little negative effect on bean actual yield. Increased NEs and pollinators was probably attributed to plant diversity created by intercropping system, which provide a greater number of opportunities for NEs and pollinators to survive in agricultural systems. However, the degree of abundance of NEs and pollinators differed among treatments. H. suaveolens and O. suave attracted high proportion of pollinators compared with other treatments, while B. pilosa, T. minuta and A. conyzoides attracted high proportion of NEs compared with H. suaveolens and O. suave. Likewise, abundance, incidence and severity of aphids was lower in the intercropped plots implying positive effects of the PPs-bean intercrop in reducing number of aphids. On repelling effects, all PPs repelled aphids in comparison with the control (unintercropped common bean). Further work is required to determine the exact cause of the yield variability in common bean intercropped with H. suaveolens and O. suave compared with the yield of the same common bean when intercropped with other treatments in the same study.