Einfluß von Zuchttemperatur und Vorbehandlung auf die Giftempfindlichkeit von Khaprakäfer-Larven (Trogoderma granarium Everts) gegen Methylbromid

Abstract

Effect of rearing and preconditioning temperature as well as type of pre-treatment on the susceptibility of Khapra Beetle Larvae (Trogoderma granarium Everts) to methyl bromide

The effect of two different rearing temperatures (25 and 28°C) on the susceptibility of Khapra Beetle Larvae to methyl bromide was investigated in the laboratory at 15 and 5°C. It was found that the exposure time needed for a given mortality is significantly longer for the larvae reared at 25°C than for the larvae reared at 28°C. However, these differences were abolished if the cultures of T. granarium bred at 25°C were transferred to 28°C and kept for 1 or 2 months at this temperature before the larvae were exposed to methyl bromide.

The effect of different types of pre-treatment on the susceptibility of the larvae was also tested at 0°C. Experimental results showed that the susceptibility of the larvae increased, when the Trogoderma cultures bred at 28°C were transferred directly to 20, 10 or 0°C and then kept for 1–2 months at one of these pre-conditioning temperatures before the larvae were exposed to the fumigant: at the test temperature.

No significant differences in the susceptibility of the larvae were found, when the cultures were transferred progressively from the rearing temperature (28°C), to 20, 15, 10, 5 and 0°C, then kept at each temperature for 2 days before the larvae were fumigated at 0°C. In this case a decrease in the susceptibility of the larvae was obtained if the pre-conditioning time at 0°C was extended to 8–10 days. Moreover, if the T. granarium cultures reared at 28°C were transferred to 25°C and kept for 1 month before the larvae were examined at 12° C. It was found that the larvae pre-conditioned at 25°C were less susceptible than those bred at 28°C. Anyhow, the same keeping-period at 20, 10 or 0°C caused an increase in the susceptibility of the larvae fumigated at the test temperature (12°C).