Effect of Vernonia amygdalina, Ocimum gratissimum and their combination on Callosobruchus maculatus in cowpea varieties

This research emphasizes the possible benefits of powdered Vernonia amygdalina and Ocimum gratissimum as environmentally friendly substitutes for chemical pesticides in the post-harvest control of Callosobruchus maculatus; as their availability, affordability, and effectiveness make them promising options for resource-poor farmers in reducing storage losses of Cowpeas. The experiment was conducted in the laboratory of Crop Production Department, Faculty of Agriculture, Prince Abubakar Audu University Anyigba, Kogi State, Nigeria. The location is on Latitude 7⁰61N and Longitude 7⁰43¹E, which falls within the southern Guinea savannah zone of Nigeria. The daily temperature range is between 25⁰C - 35⁰C, relative humidity is moderately high varying between 65 – 80 percent. The experiment consisted of four pest control measures: Bitter leaf powder (3g), Scent leaf powder (3g), 1.5g Bitter leaf powder + 1.5g Scent leaf powder mixture, in addition to control treatment apportioned to three varieties of Cowpea grains (brown, black and black eyed), replicated three times resulting in a total of thirty-six (36) experimental units. Twenty (20) apparently healthy seeds of these three Cowpea varieties and five (5) life adults Callosobruchus maculatus (2 males, 3 females) were introduced into each of the plastic containers, measuring 7cm in depth and 4.5cm in diameter with each plastic container covered with white mesh sieve and tied with rubber band. The trial was a 4 x 3 Factorial Experiment with three replications. Generally, the application of Vernonia amygdalina, Ocimum gratissimum powders and their combination had significant effect on egg laid, weevil multiplication, live weevils, weevil mortality as well as Cowpea damage, with the best controls obtained in the mixture of Vernonia amygdalina and Ocimum gratissimum, thus recommended for the control of Cowpea weevils, Callosobruchus maculatus. However, better performance was observed in grains treated with Ocimum gratissimum over those treated with Vernonia amygdalina. Brown cowpea variety suffered the most damage to grains compared with other varieties, while the least damage was in black-eyed cowpea variety; an indication that Brown cowpea grains need the most protection, while Black-eyed required the least protection.