Postharvest Losses And Evaluation Of The Bioefficacy Of Chromolaena Odorata And Jatropha Gossypiifolia Against Sitophilus Zeamais Motsch And Tribolium Castaneum Herbst In The Awutu-Senya District Of The Central Region Of Ghana

Abstract

A survey was conducted within five maize farming communities namely: Ahentia, Bontrase, Chochoe, Kroebogyir and Kwai-Blagu in the Awutu-Senya District in the Central Region of Ghana to determine the perception of maize farmers with respect to grain losses in their storage structures. The two major insect pests of maize encountered in the district namely Sitophilus zeamais Motschulsky and Tribolium castaneum Herbst were used as test insects. Bio-efficacies of diethyl-ether and methanol extracts of dried Jatropha gossypiifolia L. and Chromolaena odorata (L.) King and Robinson leaf and bark were evaluated as bio-insecticidal agents against the beetles using topical application and grain treatments under laboratory conditions. A conventional grain storage insecticide, pirimiphos-methyl (Actellic 25 EC) was used as a reference product. The assays were run in complete randomized design with three replications. The effect of the methanol and diethyl-ether leaf and bark extracts of the two plant species at different concentrations (20%, 50% and 100%) on the adult insects in grain treatment was also determined in the laboratory. The survey showed that about 80%, 12% and 8% of farmers reported insects, rodents and moulds, respectively, to cause damage to maize grains stored in these traditional storage structures. Sitophilus zeamais was the major insect pest identified by farmers and ranked as the most destructive, followed by T. castaneum. Most of the farmers (52%) applied either chemicals such as actellic or phostoxin or dried the maize frequently (28%) to control maize grains against pest infestation. Other post-harvest practices such as dehusking and shelling (8%) to prevent further damage were also commonly used by farmers. The laboratory assays of the two plants‘ parts showed varying levels of toxicity to the two insects, but comparatively the leaf extracts were more toxic than the bark extracts against S. zeamais and T. castaneum. Both plant products were not as effective as Actellic 25 EC. The methanolic leaf extracts of C. odorata and J. gossypiifolia were effective at 20% and significantly increased the mortality of T. castaneum and S. zeamais to 66.1% and 77.7%, respectively. Percentage mortality of the insects was significantly increased at higher concentration of the extracts. The highest mortality of 90% was recorded at 4 ml/L of Actellic for S. zeamais. A repellency of 83.3% was recorded for 20% diethyl-ether leaf extract of J. gossypiifolia against both insects compared to 100% repellency produced by Actellic against T. castaneum. The methanolic leaf extracts of C. odorata, diethyl-ether leaf extracts of J. gossypiifolia at 20% and reference product completely inhibited the development of both insects (0.0%) as no adults emerged in these treatments. Grains treated with the plant extracts significantly reduced damage caused by S. zeamais and T. castaneum compared with the untreated grains. The current findings showed that extracts of C. odorata and J. gossypiifolia could potentially be used in IPM programmes as environmentally friendly products for the management of stored-product beetles and may be exploited for the development of botanical insecticides for grain protection. This would, however, require further field studies to establish levels that would produce consistent and acceptable results.