An assessment of the value of dilute dust insecticides for the protection of stored maize in Kenya.
Abstract
The following is based largely on the author's summary of this account of laboratory investigations in Kenya [cf. RAE A 54 394]. Dust formulations of malathion, bromocyclen (Bromodan) or pyrethrum admixed with maize grain stored in bags each holding 200 lb. were compared as a protection against reinfestation by Sitophilus zeamais Motsch., Tribolium castaneum (Hbst.) and Cadra cautella (Wlk.) following fumigation. A mixture of 0.2% pyrethrins with 1% piperonyl butoxide at 4 oz. per bag was effective for eight months, the same formulation at 2 oz. per bag for four months, and a mixed Synergist formulation consisting of 0.2% pyrethrins, 0.5% piperonyl butoxide and 0.5% Safroxan at 4 oz. per bag for six months. Although a dust of 1 % malathion in kaolin applied at 4 oz. per bag (the measure in general use) was effective against T. castaneum, it failed to control C. cautella, allowing this species to cause considerable damage in a short period; 5% bromocyclen [cf. 55 1099] at 31/4 oz. per bag did not prove effective against either C. cautella or T. castaneum. All insecticidal treatments prevented the establishment of S. zeamais during a short period of reinfestation pressure at the beginning of the experiment. Sampling methods using paraffin flotation and visual-search techniques were tested and then used to estimate the numbers of insects per bag four times at two-monthly intervals. These estimates of insect numbers and the weights of dust sieved from the bags were used to assess the efficiency of each treatment. The weight of dust accumulated in the bags, most of which is derived from insect feeding, possibly provides the most accurate means of assessing insect numbers and hence the effectiveness of treatments [cf. 50 51].