Bio-insecticidal and Grain Protectant Activities of Mixed Powder of Ocimum gratissimum and Vernonia amydalina against Callosobruchus maculatus (Coleoptera: Bruchidae) in Calabar, Nigeria

The bio-insecticidal and grain protectant activities of mixed powder of Ocimum gratissimum and Vernonia amygdalina upon Callosobruchus maculatus was carried out in Calabar, Nigeria during the dry season (August to November) of 2015. The mortality rate of cowpea weevil treated V. amygdalina: O. gratissimum at 100: 0 concentrations were 17.0%, 27.0%, and 47.0% for a period of 24hrs, 48hrs and 72hrs, respectively. Concentrations 0:100 gave a percentage mortality of 47.0%, 67.0% and 73.0% at 24hrs, 48hrs and 72hrs, respectively. 80: 20 and 20: 80 concentrations gave 33.3% and 47.0% at 24hrs and 48hrs, but 80:20 gave 47.0% while 20:80 gave 57.0% mortality rate at 72hrs. 50: 50 concentrations gave 73.0%, 77.0%, and 80.0% mortality rate at 24hrs, 48hrs and 72hrs, respectively. The 0: 0 concentrations gave 0.0%, 3.3%, and 7.0% mortality rate at 24hrs, 48hrs and 72hrs, respectively. The effect on the oviposition of cowpea weevil revealed that the mean value of eggs laid on seeds were 5.0, 2.3, 3.3, 2.8, 1.0 and 7.0 for 100:0; 0:100; 80:20; 20:80; 50:50 and 0:0 concentrations, respectively. The effects of mixture of V. amygdalina: O. gratissimum powder on the emergence of cowpea weevil gave a mean value of adult weevil emergence as 5.3, 3.0, 5.0, 3.3, 1.3 and 8.0 for 100:0, 0:100, 80:20, 20:80, 50:50 and 0:0 concentrations respectively. Mixed powder of V. amygdalina: O. grattisimun with 50:50% concentrations conferred the highest bio-insecticidal potency against C. macullatus during the experimental investigation. This was evident from the fact that treatment with V. amygdalina: O. grattisimum (50:50%) concentration attained 80.0% mortality at 72hrs of exposure, which was followed by V. amygdalina: O. grattisimum (0: 100%) concentration with 73.0% mortality.