Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2005
Publication Date: 3/28/2005
Citation: Mahroof, R., Subramanyam, B., Flinn, P.W. 2005. Reproductive performance of tribolium castaneum (herbst)(coleoptera: tenebrionidae) exposed to the minimum heat treatment temperature as pupae and adults. Journal of Economic Entomology 98: 626-633. Interpretive Summary: Methyl bromide is the most widely used structural fumigant for managing stored-product insects in food-processing facilities; however, concerns over its stratospheric ozone-depleting effects have resulted in the phase out of this fumigant by the year 2005 in the United States. Heat treatment (50-60ºC) of a facility for 24 hours is an alternative to methyl bromide. However, a common problem with heat treatments is that homogeneous heating of the facility is rarely achieved, which allows insects in cooler locations to survive the heat treatment. We conducted experiments to determine what the reproductive effects of a sub-lethal heat treatment (50ºC) would be on red flour beetle pupae and 2-wk-old adults. We found that the number of eggs laid, egg to adult survival rate, and progeny development were approximately 50% less in treatments where either male or female pupae were exposed to 50ºC. This information will have an important impact on heat treatment recommendations for mills and food processing facilities, because it showed that temperatures need to be above 50ºC for a sufficient duration otherwise the most resistant stages (pupae and adults) will survive and produce offspring. Even though the reproductive rate of treated insects was less than untreated, their offspring can produce high numbers of insects several months later.
Technical Abstract: Managing stored-product insect pests by heating the ambient air of a food-processing facility to elevated temperatures (50-60ºC) is an old and effective technology. Horizontal and vertical stratification of temperatures within a facility during heat treatment results in non-uniform distribution of heat. Thus, some portions of a facility may be over- or under- heated. Over-heating may result in damage to heat-sensitive equipments while under-heating may result in insects surviving the heat treatment. We simulated an under-heated environment in the laboratory by exposing 1-d-old pupae and 2-wk-old adults of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) at 50ºC for the median lethal time (LT50). Such an exposure time results in 50% survival of pupae and adults. Pupae and adults exposed for the same time periods at 28ºC served as the control treatments. All possible reciprocal crosses were carried-out with treated but surviving insects and control insects. Total number of eggs produced during the first 2 weeks of adult life, and number of adults that survived from eggs during the first two weeks were determined. The total number of progeny produced after two and eight weeks, in treatments representing all reciprocal crosses, were determined in a separate experiment. Oviposition, egg to adult survival rate, and progeny development were lower in treatments where either male or female pupae or both were exposed to 50ºC. These effects were relatively more pronounced in treatments where pupae were exposed to 50ºC than adults and when females were exposed to 50ºC than males.