Transgenerational responses to heat and fasting acclimation in the Angoumois grain moth

Transgenerational plasticity (TGP) is a physiological mechanism where environmental experiences of parents affect phenotypes of the offspring, and potentially facilitates organisms' survival in stressful environments. The Angouimois grain moth, Sitotroga cerealella (Olivier), is a dominant primary grain pest in Africa, particularly affecting sorghum and maize staples. Despite its widely known economic significance, little is known on its thermal responses, particularly how acclimation in one generation impacts fitness in successive generations. We tested how heat (acute and dynamic) as well as fasting acclimation in one generation affects physiological tolerance (i.e., critical thermal maxima [CT_max] and heat knock down time [HKDT]) using laboratory-reared S. cerealella populations. Specifically, we assessed whether pre-exposure to heat or fasting stress confers fitness costs or benefits in subsequent generations (i.e., through TGP). Results showed acclimation had significant effects in interaction with temperature ramping rates on CT_max. Moderate acute heat (34 °C) and dynamic temperature (28–38 °C) acclimations reduced F₁ CT_max and HKDT, particularly at low ramping rates (for CT_max). We did not find fasting acclimation to significantly affect CT_max, indicating a lack of evidence for cross tolerance and/or susceptibility. For HKDT, all acclimation treatments (including fasting) showed significantly lower HKDT compared to controls, and mostly so, for the 38 °C and dynamic acclimation (28–38 °C) treatments, indicating a transgenerational fitness cost of acclimation. This is the first report of the costs of transgenerational plasticity in a stored product pest of economic significance and has implications in designing heat-based phytosanitary grain treatments.