The toxicity of methyl chloroform to stored product insects

Abstract

The susceptibility to methyl chloroform of all developmental stages of Cryptolestes ferrugineus, Ephestia kuehniella, Oryzaephilus surinamensis, Rhyzopertha dominica, Sitotroga cerealella, Sitophilus granarius, S. oryzae and Tribolium confusum, diapausing larvae of Ephestia elutella, E. cautella, Plodia interpunctella and Trogoderma granarium and adults of Tribolium castaneum, was studied. Tests were conducted at 15, 20 and 25°C, 55–75% r.h. with concentrations ranging from 25 to 200 mg/l and exposure times from 8 h to 16 days. The toxicity of methyl chloroform was in general similar to that of carbon tetrachloride. Immature stages of R. dominica, S. cerealella and Sitophilus spp, and diapausing larvae of T. granarium, showed the highest levels of tolerance. Methyl chloroform was more effective at the higher temperatures but a concentration of 50 mg/l was below the threshold level for full toxicity against 5 species at 25°C. Depending on the species concerned, the concentration × time (CT) product required for control varied from 3,700 mgh/l at 25°C to 60,000 mgh/l or more at 20°C. At 15°C fewer species were tested but five out of nine survived CT products in the region of 30,000 mgh/l. There was no appreciable difference between the susceptibility of the immature stages of malathion-resistant and susceptible strains of O. surinamensis. Neither were any consistent differences observed between adults of normal susceptibility and those resistant to methyl bromide or phosphine.