Effect of Tasmanian blue gum (Eucalyptus globulus Labill.) leaf extract on cowpea weevil (Callosobruchus maculatus [Fabricius, 1775], Coleoptera: Chrysomelidae)

Abstract

A laboratory study was carried out to examine the efficacy of solvent extract of Eucalyptus globulus leaves in reducing post-harvest losses caused by cowpea weevil (Callosobruchus maculatus) on cowpea seed variety RSH 256. 450 g of E. globulus leaf powder were put in 1000 ml flask and 450 ml of n-hexane was used as the solvent. The extract was tested at dosages of 50, 100 and 150 µl 50 g-1 of cowpea grains on the weevil in stored cowpea. The different rates of treatment recorded significant differences (p < 0.05) in causing adult mortality compared to the untreated control. The different rates of treatment also recorded significant differences (p < 0.05) in emergence of F1 adults of each treatment compared to the control. The percentage masst loss and grain damage were also suppressed as a result of treatment with the plant material compared to the untreated control. However, among the treatments 150 µl 150 g-1 cowpea recorded the highest adult mortality rate and lowest emergence while control had the lowest mortality rate and the highest emergence of the insect. The rates of application were indicative of bioactive characteristics of the plant extract.

Keywords

• cowpea
• Callosobruchus maculatus
• Eucalyptus globulus
• leaf exctracts
• biopesticides