Changes in biochemical contents and survival rates of two stored product moths under different thermal regimes

Plodia interpunctella (Hiibner) and Ectomyelois ceratoniae (Zeller) (Lepidoptera: Pyralidae) are two destructive pests of stored products. Survival and physiological changes of last instar larvae were investigated under different thermal regimes [i.e. control (optimal temperature), cold-acclimation (CA), fluctuating-acclimation (FA) and rapid cold-hardiness (RCH)]. Our results indicate a relationship between supercooling points, carbohydrate contents, enzyme activities and survival rates of the larvae under different thermal regimes. Glycogen content was greatest for control and RCH regimes whereas the greatest trehalose level was recorded for the CA regime. The supercooling points of control larvae of P. interpunctella and E. ceratoniae were - 14 and - 10 degrees C, respectively, and decreased to - 16 and - 18 degrees C under the CA regime. Thermal regimes had no significant effect on the survival of the larvae after 24 h exposure at 0 degrees C, but when larvae exposed to - 5 degrees C for 24 h, the highest and lowest survival rates were recorded in the CA and RCH regimes, respectively. Protein phosphatases 1 and cAMP-dependent protein kinase (AMPK) were found to have the highest enzyme activity. The activity of AMPK varied between different thermal regimes and was greatest under the CA regime. CA considerably increased lower lethal times of the larvae compared with the control regime. RCH showed the highest impact on lower lethal temperature limits of the larvae. Our results indicated a characteristic enhancement of the survival rates of the larvae of P. interpuntella and E. ceratoniae under the CA regime. This enhancement is likely related to elevated contents of low molecular weight carbohydrates under the CA regime.