Untersuchungen zur Wirkung von Methylbromid besonders bei niedrigen Temperaturen gegen Khaprakäfer-Larven (Trogoderma granarium Everts (Dermestidae, Coleoptera)

Abstract

Tests on the efficiency of methyl bromide especially at lower temperatures in controlling Khapra Beetle Larvae (Trogoderma granarium Everts), Dermestidae, Coleoptera

In the laboratory, experiments were carried out to investigate the efficiency of methyl bromide in controlling the Khapra Beetle (Trogoderma granarium Everts) in a specially developed fumigation apparatus at 30, 25, 20, 15, 10, 5, 0, −6, and −10 °C as well as 40 – 70% relative humidity. The lethal dosis as c. t. products in mg.h/l were estimated at different temperatures from the dosis-mortality regression lines. The treated larvae were divided after the fumigation into two series (1 and 2). The larvae of serie 1 were held immediately after the fumigation time at 28°C, while the larvae of serie 2 were kept for another 10 days at the same fumigation temperature, then removed to 28°C until final control. Experimental results of both series showed that, for a given mortality the c. t. product required at low temperatures considerably increased and accordingly the tolerance of the larvae decreased with a rise in temperature (in range 0–30°C). A maximum in the tolerance of the larvae to methyl bromide was found at 0°C. At lower trial temperatures −6 and −10°C the required c. t. product subsequently decreased. This result was caused through the combined harmful effect of the low temperatures and the methyl bromide. It is evident from the estimated values that the c. t. products of methyl bromide required for a given mortality in serie 2 especially at lower temperatures (from +10 to −10°C) are lower than that in serie 1. For example in serie 2 the c. t. product required to kill the larvae decreased at 5°C to less than 50%. This effect of the post-treatment temperature was also examined to obtain the shortest holding time for maximum mortality, which was observed after 3–4, 7–8, 7–8 and 8–9 days at 10, 5, 0, and −6°C respectively. From a practical aspect this result is of great importance, because it proves the influence of the factors prevailing after a quarantine fumigation.