Field Response of Cowpea, Vigna unguiculata Walper to Four Insecticidal Compounds and Their Residual Toxicity to Callosobruchus maculatus (F.) [Coleoptera: Chrysomelidae] in The Laboratory

Abstract

There have been paradigm shift to the use of biopesticides as alternative to synthetic pesticides in recent years due to its environment friendliness and non-toxic to the non-target organisms. Therefore, three synthetic insecticides and water extract from neem back powder were evaluated on cowpea in the field and their residual toxicity tested against C. maculatus in the laboratory. The insecticides were applied at the rate of 2ml in 2L of water and 2L of extract from neem back powder on the field. The harvested seeds were infested with C. maculatus to evaluate the residual toxicity of the insecticides. Data on growth and yield parameters were taken on the field while data on adult mortality, oviposition, adult emergence and weight loss were recorded for the laboratory experiment. The results showed positive response of cowpea to the applied chemicals as they had higher values for the number of leaves, branches and reduced number of holes. Number of holes was significant (p< 0.05) at the 8^th week with the control having highest number of holes. Cowpea treated with cypermethrin had highest number of pods at both 7^th and 8^th week and showed significant difference at 7^th week. Highest weight of seeds per pod was obtained from the cowpea treated with water extract from neem back powder and was significantly different (p< 0.05) from other treatments. Seeds treated with the three insecticides had the same number of mortality while neem extract had highest but was not significantly different (p> 0.05). There was a reduction in number of eggs laid, adult emergence, seeds with holes and weight loss in the seeds treated with the four insecticide compounds. It was concluded that application of the insecticidal compounds positively enhanced the performance of cowpea on the field and could protect the seeds against C. maculatus in the laboratory. This study revealed that water extract from back powder of neem could be used as a botanical in the protection of cowpea against seed beetles.