Efficacy of Piper guineense (Shum and Thonn), Dennettia tripetala (G. Baker), and Ocimum gratissimum (Linnaeus) powders admixed with selected excipients for the control of Callosobruchus maculatus (Fabricus) infesting cowpea, Vigna unguiculata (L. Walp), seed

Abstract

The use of synthetic insecticides to control stored product insects causes various health and Ecological challenges to man. Therefore, there is a need for alternative formulations like plant materials with the least possible side effects for the effective control of cowpea bruchid, Callosobruchus maculatus (Fabricius), a cosmopolitan pest of pulses. This study evaluated the efficacy of insecticidal dust formulations using three botanicals (Piper guineense, Dennettia tripetala and Ocimum gratissimum), three excipients (rice bran, maize husk and cowpea pod husk), admixed at ratios 70:30, 60:40, 50:50, 40:60 and 30:70 botanical to an excipient, for the control of C. maculatus. Four particle sizes (212, 300, 500 and 1000 µm) applied at dosages of 0.1- 0.5 g / 20 g cowpea seeds were assayed and untreated cowpea seeds served as controls. Ten C. maculatus adults (sex ratio 1:1) were used to infest the treated and untreated cowpea seeds separately in Petri dishes. Data were collected on mortality, Oviposition, F1 progeny emergence and damaged cowpea seeds. The data were subjected to analysis of variance and means were separated with Least Significant Difference at a 5% significance level. All dosage ratios of the formulated dusts caused significantly (p˂ 0.05) higher mortality of bruchids, reduced the number of laid eggs, F1 progeny emergence and damaged cowpea seeds due to C. maculatus infestation. Regardless of the assayed botanical, 212 µm particle size was outstanding and the formulation ratio of 70:30 (botanical: excipient) was significantly (p˂ 0.05) better than other formulation ratios. The formulation with P. guineense with any excipient at 0.5 g/ 20 g cowpea seeds using 212 µm was superior to other formulations as cowpea protectant against C. maculatus. Therefore, it is recommended as an alternative to over-dependence on synthetic insecticides.