Dynamics of heat shock proteins and heat shock factor expression during heat stress in daughter workers in pre-heat-treated (rapid heat hardening) Apis mellifera mother queens

Honeybees have a limited capacity to control their body temperature when exposed to thermal changes in the atmosphere. Environmental changes, such as thermal climate change, have an adverse effect on honeybee survival. Insects can be pre-heat-treated (rapid heat hardening) with a mild heat stressor to induce Hsp gene expression and protect them from future stresses. Sixty accepted mother queen (MQ) larvae at the age of 7 days were selected and divided into two incubation treatment groups (n = 30). The control group (non-heat-treated mother queens, nH-T MQ) was maintained at 34.5 °C for 15 min and 70% relative humidity (RH), and the pre-heat-treated (pre-heat-treated mother queens, pH-T MQ) group was subjected to 41 °C for 15 min and 70% RH. To evaluate the effect of larval pre-heat-treatment on thermotolerance acquisition of daughter workers, about 500 workers were collected from brood combs of each treatment group. The worker bees in their cages were incubated in digital-controlled thermo-incubators for 1 h under each of the following temperatures: 35, 40, 45, 50, 55, and 60 °C. The expression of Hsp40, Hsp60, Hsp70, HSC70-3, HSC70-4, HSC70-5, Hsp83, and Hsp90 genes in both head and thorax were evaluated by relative quantitative real-time qPCR (RT-qPCR). In general, the pH-T MQ workers exhibited a higher ability to tolerate temperature than nH-T MQ workers under extreme conditions. Furthermore, we reported for the first time that pre-heat treatment of the mother queen's larvae alters the basal and dynamic expression of heat shock proteins (Hsp40, Hsp60, Hsp70, and Hsp90) and heat shock factor (HSF) during thermoneutral conditions and during heat stress of daughter workers, probably indicating a substantial improvement of honeybees' thermotolerance acquisition in arid and semi-arid regions, and improvement of honeybee longevity and management strategies.