Field assessment of insecticidal efficacy of some plant aqueous extracts in reducing cowpea pod-sucking bug Acanthomia tomentosicollis Stâl (Hemiptera: Coreidae) infestation and damage

Abstract

Array of pest complex and yield reduction due to insect pests is one of the major constraints for low productivity of cowpea. The insecticidal efficacy of Spondias mombia, Momordica charantia, Mitrocarpus villosus and Chenopodium ambrosioides crude aqueous extracts was assayed for suitability in controlling the pod-sucking bug Clavigralla tomentosicollis Stâl (Hemiptera: Coreidae) on cowpea. The field experiment was laid out in a randomised complete block design with two treatments replicated three times at the Teaching and Research Farm of Rufus Giwa Polytechnic, Owo, Ondo State, in 2012. One kilogram of plant leaves was pounded using mortar and pestle and soaked in 3 L of cold water overnight. The extracts were applied at 10% (v/w) and sprayed every week for four weeks and a synthetic insecticide (Lambda cyhalothrin) was used as reference to compare the effectiveness of the plant extracts. Results of the experiment show that the plant extracts caused considerable reduction in the insect population; similarly, yield attributes corresponded positively with the effectiveness of the treatment and were at par with the synthetic insecticide. However, among the plots treated with aqueous plant extracts, the plot treated with S. mombia performed better than other plant extracts in terms of number of uninfested pods (55.34), plots treated with C. ambrosioides, having least number of damaged (infested) pods (6.0), and plots sprayed with S. mombia, having highest number of harvested pods (62.67), uninfested pods (55.34) and seed weight (0.18 kg). This study is probably the first reported case of the potential of the evaluated plant extracts for the control of insect pests of field crops. Therefore, the present study suggests the use of all the tested plant extracts, as they have been found to be very promising biopesticides in the control of cowpea pod-sucking insect pests. Thus, the extracts could be a good alternative to the synthetic insecticides on organically managed farms as well as on farms of limited-resource farmers in the tropics and subtropics.