Stored product pests infest buildings, packaging, and spillage of grain products, leading to destruction and loss of product. Urban environments that house these stored product pests create a new environment where the insects are rarely exposed to cold. Cold stress can be used as an alternative treatment for killing insects in packaged or stored materials. However, insects may adapt to their man-made or geographic environments, creating strains that can be resistant to thermal stresses. Warehouse beetles, Trogoderma variabile, have been shown to be tolerant to extreme cold stress, especially in the larval stages, but their ability to adapt to cold stress is not known. We selected late instar larvae for an increase and decrease in tolerance to cold stress using chill coma recovery, a non-lethal cold stress treatment, at two different temperatures (0oC and -10oC) and two different time points (3 and 5 hours). We also test our three replicates for each time-temperature combination for cross-tolerance to a chronic cold stress (-10oC for 48 hours) and effects on body length in our selection lines.
Results/Conclusions
For warehouse beetles, temperature is the most significant factor in chill-coma recovery time. By generation 7 of selection, warehouse beetles show significant differences between those selected for quick (increased tolerance) and slow (decreased tolerance) recovery time for all selection regimes. After four generations of inbreeding, beetles selected at -10oC for 5 hours and 0oC for 3 hours maintain differences between quick and slow recovery. Beetles show cross-tolerance to chronic cold stress with increased survival for beetles selected for quick recovery at 0oC for 3 hours and increased survival for beetles selected for slow recovery at -10oC for 5 hours. Body length for males and females decreased for slow compared to quick selected beetles at -10oC for 3 hours. These results show that these insect pests can undergo adaptations to thermal stress and that temperature and time of cold treatment have a large impact on adaptation, recovery, and survival. Managers using cold stress as a treatment should use the prescribed cold treatments to ensure all insects are killed. This research also shows that these pests maintain the genetic underpinnings to adapt to thermal stress even when they are found indoors, and further analysis could provide genetically-based integrated pest management tools.