Sitotroga cerealella (Olivier) resilience to extreme temperature and desiccation may explain its increasing pest status in changing climates

The mechanisms underlying Sitotroga cerealella survival under variable and increasing mean thermal and desiccation environments typical under global change is currently unknown. To understand how S. cerealella survives extreme abiotic stressors typical of stored-grain environments, we measured S. cerealella tolerance temperature and desiccation. The results showed that to survive desiccating grain storage environments, S. cerealella relied more on high body water content (BWC) (70.2 ± 3.72%) compared to lipid reserves (9.8± 0.81%). In desiccating environment, S. cerealella showed a reduced water loss rate (0.056mg/h) (equivalent of 1.81% of body water/hour) which would require 19.31 h to reduce the insect body water to its critical minimum (35.23% body water content at death), which is 50.20% of normal initial body water. Similarly S. cerealella exhibited high basal heat tolerance with critical thermal maximum of 46.09 ± 1.042°C and a heat knockdown time of 7.97 ± 1.64 minutes. Basal cold tolerance was relatively compromised (critical thermal minima of 4.52 ± 1.06°C and chill coma recovery time of 5.80 ±1.17 minutes), following 1h at 0°C. We found no significant correlation (P > 0.001) between BWC and the measured thermal tolerance traits. Low water loss rates reported here may be an evolutionary resistance mechanism for desiccation tolerance. Observed abiotic stress tolerance may explain the ubiquitous distribution of S. cerealella in Africa which is likely to enhance its survival and increase its pest status under global change.