ASPECTS OF SEED RESISTANCE IN SELECTED VARIETIES OF COWPEA TO DAMAGE BY CALLOSOBRUCHUS MACULATUS (FABRICIUS) (COLEOPTERA: BRUCHIDAE)

Abstract

Three experiments were used to assess the relative susceptibilities of three known resistant, one known susceptible and seven other varieties of cowpea available locally ill Akure (Nigeria) markers under laboratory conditions (30+ 1C and 50+ 10% r. h.). In the first experiment. a known susceptible and three resistant varieties of cowpea were subjected to three different levels of initial larval infestation (one, five and tell larvae per seed). A beetle colony derived from infested cowpea seeds in a local market in Akure was employed. In the second experiment. the susceptibility of seven varieties of cowpea commonly sold in local markets, to seed damage by C. maculatus were compared with that or three known resistant varieties and a well-known susceptible variety. The development and survival of C. maculatus in two of the known resistant varieties over five successive generations of the beetle was further monitored ill the third experiment. Speed of beetle development and larval survival to adult emergence in the cowpeas, were used y) measure performance of the beetle ill the cowpeas, Results of the first experiment showed that in the resistant cowpeas, development time was not affected by level of larval infestation. Percentage adult emergence decreased significantly (P < 0.05)) with increase in level of larval infestation in the resistant cowpeas. In the second experiment, beetle development was generally slower and fewer individual survived to adulthood in the known resistant cowpea compared to others. Development tie was significantly longer and percentage adult emergence was significantly lower in the locally sold varieties, TVx 3436, White Drum and Oloo than in the well-known susceptible variety. In the third experiment, there were no significantly differences in the development time of C. maculatus in the resistance cowpeas (IT851-2205 and IT90K391) between five successive generations. The percentage of hatched beetle eggs which produced adults in the cowpea increased significantly from one generation to the next. The significance of the observations in the experiments is discussed.