Bioefficacy of single and mixed applications of Citrus paradisi Maef and Citrus aurantifolia Swingle peel extracts against seed beetle, Callosobruchus maculatus (F.) (Coleoptera:Chrysomelidae).

The present study was conducted to determine the effects of grapefruit, Citrus paradisi Maef and lime, Citrus aurantifolia Swingle peel extracts on the storability of cowpea seeds. Cowpea samples were treated with various concentrations of single application (0.6, 0.8 and 1.0%) of extracts and their mixtures in the ratios of 1:1; 1:2; 2:1; 1:3; 3:1; 3:2 and 2:3 was applied at 5% level of concentration. Increasing extract concentrations resulted in better cowpea protection as recorded in oviposition where the control had mean number of 4.33 eggs, while oviposition was inhibited in 0.6 and 0.8% lime-treated sample at 7 days after treatment (DAT). Generally, better results were obtained with higher extract concentrations in single application. The bioassay revealed that grapefruit : lime mixture (1:2) gave 27.8% adult mortality at 24 hours post treatment (HPT) which increased to 50% 72 HPT. However, peel extracts applied in the ratios of 2:1 and 1:1 also gave 50% adult mortality during the same period. Adult emergence of Callosobruchus maculatus in the seeds showed significant differences while the percentage emergence of beetle was highest in seeds treated grapefruit : lime applied at 3:2 (12.67%), lowest percentage emergence of beetle was obtained in extracts mixture at 2:1 (0.33%). The mean fecundity in the mixtures showed that C. maculatus was most fecund (27.00 eggs) in the ratio (3:2) and least fecund in the ratio of 2:1(0.67 eggs). Maximum deterrent activity in oviposition, adult emergence and seed damage was observed at 2:1 (grapefruit : lime) peel extracts in all the treatment mixtures. Based on this study, grapefruit : lime ratio (2:1) peel extracts could be suggested for the use to suppress populations of C. maculatus for short period of storage.