The khapra beetle,Trogoderma granariumEverts

Abstract

The khapra beetle, Trogoderma granarium Everts, a serious pest of stored grains and other food products in India and elsewhere, has recently been found in 23 counties of California, Arizona, and New Mexico. It thrives on hot, dry conditions and has proved exceptionally difficult to control. The State Department of Agriculture is conducting an eradication program against it in California. Studies have been conducted on factors affecting the development of this beetle and on its climatic adaptation, and tests have been carried out to find more effective control measures. The following are the principal results to date. An increase in temperature from 70°F to 93°-95° decreased the average length of a generation from 220 days to 26 days; light conditions had little effect on it. At 90° egg viability averaged 94 per cent, and 93 eggs were laid per female. The length of a generation varied widely on different foods. A few larvae survived exposures of 240 minutes to -6°F and of 51 days to temperatures fluctuating daily between 25° and 48°. Eggs and pupae were more susceptible. To obtain a 95 per cent kill (at 50 per cent relative humidity) required 960 minutes for larvae and 420 minutes for pupae at 118°, 8 minutes for both stages at 131°. These findings indicate that the species is capable of becoming a pest of grain stored in piles or sacks in the field in such ellmctes as that of Imperial Valley, California. Among ten fumigants tested (at 70°F and with 2-, 8-, and 24-hour exposures), hydrocyanic acid and acrylonitrile were the most toxic to khapra-beetle larvae and pupae. Eggs were more susceptible than the other immature stages to the majority of these fumigants. Hydrocyanic acid was the only one tested to which all three immature stages of the khapra beetle were more susceptible than granary-weevil adults. Fumigation for 12 hours with methyl bromide, hydrocyanic acid or acrylonitrile showed little evidence of reduced seed germination when moisture content of seed was less than 10 per cent. Khapra-beetle larvae were more resistant to wheat treated with a piperonyl butoxide-pyrethrin dust mixture or with a malathion dust than were the adults of the granary weevil, rice weevil, and lesser grain borer.