Effect of Cowpea Seed Coat Texture on the Oviposition and Progeny Development of Callosobruchus Maculatus ( F.) ( COLEOPTERA: BRUCHIDAE ).

Abstract

The cowpea weevil, C. maculatus is a very serious pest of stored cowpeas, Vigna unguiculata.The infestation starts in the fields and continue to multiplies in storage where sometimes it causes total destructions of the cowpea seeds within a period of 3-4 months. Objectives: Present study was conducted to investigate on how cowpea seed-coat texture affects the oviposition behaviour and progeny development of C.maculatus under ambient laboratory conditions. Methods: 10 white cowpea seeds of equal size but with different seed coat texture ( 5 smooth and 5 rough-coated ) were placed in a glass vial and mixed thoroughly. These were replicated 10 times and each replicate was infested with two pairs of freshly emerged males and females adult C. maculatus for the period of 3 days after which the insects were removed. The number of eggs laid on the cowpea seeds of each type ( smooth or rough ) was counted separately per replicate and the infested cowpea seeds were kept for the assessment of F₁ adults emergence. Results: The female cowpea weevils were observed to oviposit freely on all the cowpea seed types but showed a definite oviposition preference for cowpea seeds with smooth seed coat texture.. The reproductive efficiency of the weevils was significantly ( p=0.05 ) lower on the rough-coated seeds. Conclusions: Despite the fact that females C.maculatus laid more eggs on the smooth-coated  than on rough-coated cowpea seeds, but no significant difference ( P= 0. 05 ) was observed with regards to the means of index of susceptibility between the different cowpea seed types.

Key words: Callosobruchus maculatus, Vigna unguiculata seed coat texture, oviposition, susceptibility index  reproductive efficiency.