INSECTICIDAL AND GRAIN-PROTECTING PROPERTIES OF A PYRETHRUM-BASED PRODUCT AGAINST STORED MAIZE WEEVIL, SITOPHILUS ZEAMAIS (COLEOPTERA: CURCULIONIDAE).

In Rwanda, management of stored maize insect pests is based on conventional chemical insecticide applications with high residues. Organic pesticides containing pyrethrins like Agrothrin® (Dusting powder, Agropharm Ltd., Kigali, Rwanda) containing 0.11% pyrethrins, 1.1% piperonyl butoxide (PBO) synergist (w/w), a natural extract from the African pyrethrums with no side effects, can be a suitable option for managing stored maize. The present study was conducted to determine insecticidal and grainprotecting properties of Agrothrin against the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), under both laboratory (controlled) and warehouse (non-controlled) conditions. The product was tested at seven different doses ranging from 0.9 kg/ton to 2.1 kg/ton and compared with an untreated control (control^-) and a conventional chemical insecticide control (malathion, control⁺). The results from the study revealed that insecticidal activity of Agrothrin was low and not quick but it was more than doing nothing because it caused mortalities more than 95% of artificially introduced insects after 5 and 6 weeks. However, higher doses superior to 1.7 kg/ton and/or longer exposures than 4 weeks were needed to obtain an adult mortality more than 95%. In addition, Agrothrin gave effective grain protection against S. zeamais and the insects were predominantly present in positive and negative controls but absent or in low number in grains treated with Agrothrin. This indicates that the product can be used as an effective grain protectant for newly harvested maize grains before storage. Overall results suggest that Agrothrin may be a very effective alternative to the existing conventional chemical insecticides in stored maize protection at doses equal to or higher than 1.7 kg/ton of grain. [ABSTRACT FROM AUTHOR]