EFFICACY OF NIGERIA-DERIVED DIATOMACEOUS EARTH, BOTANICALS AND RIVERBED SAND AGAINST Sitophilus oryzae AND Rhyzopertha dominica ON WHEAT

Powdered seeds of Dennettia tripetala (Baker f.) and Piper guineense Schumach, Bularafa diatomaceous earth (DE), Riverbed Sand, and combinations of the two botanicals with Bularafa DE and Riverbed Sand were evaluated as protectants of wheat seed against Sitophilus oryzae (L.) and Rhyzopertha dominica (F.). Insecto®, a commercialised DE, was tested as a standard check. The rates tested were 60 g kg-1 of wheat (for botanicals) and 1 g kg-1 of wheat (for other dusts). The botanicals singly and in combination with Bularafa DE and sand induced 100% mortality and total progeny suppression of both species in 7 days. Insecto and Bularafa DE treatments each induced 69% mortality and 78% progeny suppression against R. dominica, respectively. Sand was ineffective, inducing 10 and 13% mortality and progeny suppression, respectively. In S. oryzae assay, Insecto and Bularafa DEs singly caused ~ 100% mortality and 87% progeny suppression; while Riverbed Sand caused 9% mortality and 14% progeny suppression. Micrographs of dusted S. oryzae cuticle showed Bularafa and Insecto DEs to be abrasive. The relatively larger size of sand particles compared to DE particles probably contributed to its poor activity.