Protectant Efficacy of Dennetia Tripetala Bak. (F) (Annonaceae) Extracts and Deltamethrin Against Sitophilus Zeamais Motsch (Coleoptera: Curculionidae) in Stored Maize

Abstract

The use of plant products has shown great potentials as alternatives to synthetic insecticides. The present studies investigated the efficacy of Dennetia tripetala and Deltamethrin as grain protectants against adult Sitophilus zeamais in stored maize. Acetone extracts of D. tripetala and Deltamthrin 12.5EC were evaluated in the laboratory based on insect mortality, progeny production and grain damage. Five concentration levels of each toxicant were prepared including 20mls, 15mls, 10mls, 5mls and 1ml for D. tripetala and 1ml, 0.5ml, 0.25ml, 0.1ml and 0.01ml for Deltamethrin. Controls with no toxicants were included. The design of the experiment was a CRD and each repeated 4 times. Twenty grams of insect-free maize were measured into each replicate vial and infested with ten, 1-5-days old adult insects. Mortality was recorded at 12, 24, 48- and 72-hours post-treatment. After 35 days, progeny production and number of damaged grains were recorded. Data obtained were statistically analyzed using SPSS version 13. The results indicated that Deltamethrin was more toxic than Dennetia tripetala, however, at 10mls-20mls, D. tripetala showed moderate toxicity against S. zeamais. Comparative mortalities of the two toxicants indicated that Deltamethrin was significantly (P < 0.05) more toxic than D. tripetala at all levels. The studies however, revealed that the application of D. tripetala in controlling S. zeamais could be effective at higher concentrations. Therefore, it was suggested that D. tripetala should be applied at higher concentrations for effective control of maize weevil.