Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 12, 2004
Publication Date: October 1, 2005
Citation: Arthur, F.H. 2005. Initial and delayed mortality of late-instar larvae, pupae, and adults of Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae) exposed at variable temperatures and time intervals. Journal of Stored Products Research 42: 1-7. Interpretive Summary: When commercial facilities are heated to control insect infestations, there is lag time before the target temperature is achieved, which could affect insect mortality. Different life stages of the red flour beetle and confused flour beetle were exposed for short time intervals to increasing temperatures by gradually exposing them to the target temperature. As temperatures increased, the time required to kill the beetles correspondingly decreased, especially as temperatures approached 120 to 130°F. However, the acclimation period increased the time required to kill both insect species at this range, as compared to previous laboratory studies in which insects were suddenly exposed to similar temperature levels. During a commercial treatment, this acclimation period may have consequences for insect control, particularly when target temperatures are achieved at different times for various locations within a facility.
Technical Abstract: Late-instar larvae, pupae, and adults of Tribolium castaneum (Herbst), the red flour beetle or T. confusum (Jacqueline DuVal), the confused flour beetle, were exposed for variable durations at 36 to 54°C. Beetles were placed in laboratory ovens set at a baseline of 27°C, the temperature was increased by 0.1°C per minute until the target temperature was achieved, and beetles were held for specified exposure durations. There was no mortality after initial exposure or after a one-week holding period of any life stage of T. castaneum or T. confusum exposed for 32 hours to 36, 39, or 42°C. At 45°C, there was no initial mortality of either species exposed for different time intervals except for those exposed for 28 hours. However, there was a significant increase in mortality after the 1-week holding period of those beetles exposed initially for at least 16 hours to 45°C. There was a sharp increase in mortality after the initial exposures of 4 hours at 48°C; mortality of T. confusum larvae was 90.0 ± 5.7% but was only 10.0 ± 10.0% for larvae of T. castaneum, and no pupae of either species were dead. All life stages of both species were killed after the initial exposure of 12 hours, and 1-week mortality of beetles exposed for 4 and 8 hours was generally greater than initial mortality. At 51 and 54°C, two and one-hour exposures, respectively, killed all life stages of each species. Mortality at conditions of gradual temperature increase was less than previous studies with sudden temperature increases.