Influence of Phaseolus vulgaris L. (Fabaceae: Fabales) varieties on oviposition behavior and susceptibility to infestation by Acanthoscelides obtectus Say (Coleoptera: Bruchidae)

Abstract

Despite beans being a vital source of cheap protein, its yield is reduced mainly by diseases, field and storage pests. An effective and sustainable control option against storage insect pests could be improving the genetic resistance of the host plant in relation to the behaviour of the pest.  A laboratory investigation was conducted to determine effects of bean varieties on oviposition behaviour and susceptibility to infestation by Acanthoscelides obtectus. The experiments evaluated oviposition site preference, number of eggs laid, and number of progeny and emergence holes of A. obtectus per bean variety. The number of progeny and duration in days taken by 50 % of progeny to emerge was determined and used to calculate susceptibility index. Seed harness index, thickness of testae and surface area of bean varieties were determined and related with susceptibility indices.  Results indicated that the number of eggs laid, progeny, and emergence holes, duration taken by progeny to emerge, susceptibility indices, seed surface area and hardness were statistically different. Mwezi moja variety was the most preferred host for oviposition whereas Mwitemania was the least preferred. Beetles laid the highest (84.5) number of eggs in Mwezi moja and the least (41.9) in Mwitemania. Number of progeny of A. obtectus emerging were the highest in Mwezi moja (73.7) and the least (36) in Mwitemania. Beetles took the shortest (36.75 days) period to emerge from Mwezi moja and the longest (38.63days) period from Mwitemania. Mwezi moja was the most susceptible variety to attack by A. obtectus with a susceptibility index of 7.43 and Mwitemania was the least susceptible with an index of 6.51. Nyayo had the highest (0.019) seed hardness index and Mwezi moja and Canadian wonder had the least (0.012) hardness index. Mwezi moja had the largest (278mm) surface area whereas Mwitemania had the lowest (171mm) surface area.