ASSESSMENT OF FOUR PLANT EXTRACTS AS MAIZE SEED STORAGE PROTECTANTS AGAINST Sitophilus zeamais AND Prostephanus truncatus IN GHANA.
ABSTRACT:
Sitophilus zeamais and Prostephanus truncatus are two most important storage insect pests of maize in Ghana and Africa as a whole. These insects cause weight loss of about 20 to 90 % of the untreated stored maize seeds. The control of post-harvest pests largely depends on the use of pesticides. Because of the adverse effects of insecticides on humans and the environment, attempts are being made to discover remedies pest management. This study was to assess four plants (Lantana camara, Moringa oleifera, Citrus sinensis and Hyptis suaveolens) extracts as maize seed storage protectants against Sitophilus zeamais and Prostephanus truncatus in Ghana. The study was laid out in a Completely Randomized Design (CRD) with three replications. Dried powders at (5 and 10%) and aqueous extracts (0.05 and 0.1 g/mL) of botanicals were prepared and evaluated for their insecticidal activity against P. truncatus and S. zeamais in treated maize seed. Untreated control and seed maize grains treated with Actellic were included as checks. There was decrease in oviposition and survivorship of insects was lowest when grains were treated with plant extracts at egg stage compared to the control. There was reduction in the number of adult insects that emerged at all developmental stages of the insects in treated maize seeds with methanol extracts of botanicals. All plant extracts at 0.1 g/ mL showed significant (P<0.001) difference in repellency compared to the control; however, H. suaveolens recorded the highest repellent activity to P. truncatus and S. zeamais at 93.3 and 96.7% respectively. Maize seeds treated with L. camara and M. oleifera recorded a percentage germination of 94.0 each followed by Actellic (93.0%), C. sinensis and H. suaveolens (86.0%) and the control (82.0 %). Maize seeds treated with methanol extracts of the botanicals after 10 weeks in cribs, recorded a reduction in percentage seeds damaged and weight loss caused by the two insects as compared to the untreated seeds which recorded higher number of damaged seeds and percentage weight loss. The phytochemical analysis revealed that compounds such as alkaloids, saponins, tannins and phenolic, steroids, flavonoids, anthroquinones, phlobatinins, cardiac glycosides and terpenoids were recorded in all the four plant extracts. These compounds may have caused lower progeny emergence, inhibitory effect, repellent action and antifeedant effect to S. zeamais and P. truncatus in grains treated with the botanicals.The study proposes that the botanicals tested have the potential in the growth of the seed industry to enhance quality seed production. It is therefore recommended to be used by farmers to control P. truncatus and S. zeamais in stored maize seed.