| Methyl bromide, a fumigant traditionally used in mills for insect management, is an ozone depleter and may be phased out in the United States by 2005. The use of elevated temperatures, or heat treatment, is gaining popularity as a methyl bromide alternative. Heat treatment involves raising the ambient temperature of a flour mill to 50 to 60°C and holding these temperatures for 24 to 36 h. The purpose of this study was to characterize temperature profiles within a facility during heat treatment and to investigate stage-specific susceptibility, mechanisms of heat tolerance, and effects of elevated temperatures on reproduction in the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), an economic pest commonly associated with flour mills in the United States.; Temperature profiles at 20 different locations in the Kansas State University pilot flour and feed mills subjected to heat treatment were described using nonlinear regressions. Mortality of eggs, young larvae, old larvae, pupae, and adults of T. castaneum exposed at these locations showed that temperatures ≥50°C were necessary for complete mortality. Time-mortality relationships at 42, 46, 50, 54, 58, and 60°C showed that young larvae were the most heat tolerant of all five life stages. It is hypothesized that heat shock proteins (HSP) may be involved in the thermotolerance observed. Western blotting using anti-bovine brain HSP 70 monoclonal antibody from mouse indicated that the expression of HSP 70 significantly increased by about 33% after the heat shock in young larvae. To understand the molecular basis of heat tolerance, three different cDNA fragments of heat shock proteins were developed by semi-nested PCR using degenerate primers. These three different hsp70 genes were named as tchsp70 I, tchsc70 II, and tchsp III. Northern blotting and real-time quantitative PCR analyses suggested that tchsp70 I encoded a heat-inducible HSP, tchsc70 II a constitutively expressed HSP, and tchsp70 III a developmentally regulated HSP in T. castaneum that is over-expressed in young larvae.; The fecundity, fertility, and progeny production of T. castaneum were adversely affected when exposed as pupae and adults to 50°C for ≤60 min. The quantitative information generated in this study will aid in effective management of T. castaneum in flour mills subjected to heat treatments. |
