Selection of pepper cultivars (Capsicum spp.) for the control of bruchids Callosobruchus maculatus (F.) on stored cowpea (Vigna unguiculata (L.) Walp.) seeds

Abstract

To minimize the impact on the environment caused by indiscriminate use of synthetic chemical pesticides, four pepper cultivars were evaluated on their insecticidal activities against Callosobruchus maculatus F. on cowpea seeds. Two studies were carried out. Treatments of the first study comprised dried and ground fruits of four pepper cultivars (‘Sombo’, ‘Nsukka Yellow’, ‘Tatashi’ and ‘Tanjarawa’), one conventional storage insecticide, Actellic 2% dust (Pirimiphos-methyl), no protectant control with three rates of each protectant at all possible combinations. The treatments were arranged in a completely randomized design (CRD) with three replications. To each treatment were admixed 20 g dry cowpea seeds and six adult bruchids in the ratio of 3 males: 3 females. The second study comprised mixed proportions of a promising but expensive pepper cultivars with a less promising and less expensive cultivar from the first study. The treatments were laid in a completely randomized design (CRD) with three replications. Dried and ground fruits of ‘Nsukka Yellow’ and ‘Tanjarawa’ were therefore selected and applied in the ratios of 100:0, 80:20, 60:40, 40:60, 20:80, 0:100 and 0:0 at the rate of 5% of the treated seed weight for this second study. Efficacy of the materials used were based on the number of adult bruchid survival and reduction of oviposition rate (number of eggs laid per seed.). ‘Nsukka Yellow’ and ‘Tanjarawa’ cultivars significantly reduced number of bruchid survivors earlier than other pepper cultivars but not lower and earlier than pirmiphos-methly powder treated seeds which caused 100% adult mortality of C. maculatus within 8 days after infestation (DAI). All the materials used significantly increased adult mortality of the insect earlier than the no protectant control (p<0.05). There was no ovicidal effect of the protectants used earlier than 6 DAI. At 6 DAI all the protectants significantly reduced number of eggs by the bruchids. Differences amongst the protectant rates and protectant interaction did not produce any significant effect both on adult survivors and number of eggs deposited. Mixture of 80% ‘Tanjarawa’ +20% ‘Nsukka Yellow Pepper’ fruits caused 100% mortality of the adult bruchids earlier than the other mixtures.

Key words: selection; pepper cultvars, bruchids control, cowpea seeds.