A51 Hyperthermia and thermal shock

Topic

Hyperthermia damages the insect through several mechanisms acting in parallel within its body: it is not just a single component of the insect that suffers from excessive heat; rather, its proteins, cell membranes, and muscles are all affected simultaneously, albeit through distinct pathways.

The first of these pathways is the denaturation of the insect's enzymatic proteins, a process that follows the Arrhenius equation with a very high activation energy; consequently, the rate of damage to these proteins does not increase gradually with temperature but instead roughly doubles with each additional degree. Between 35°C and 45°C, this damage to the insect's proteins accelerates drastically.

To counter this protein denaturation, the insect possesses an innate defense mechanism: chaperone proteins known as HSP70 are activated above a certain temperature threshold and work to refold proteins that have undergone only partial denaturation, acting as a protective system that attempts to reverse some of the heat-induced damage.

The second pathway of damage—independent of the first—affects the insect's cell membranes: at high temperatures, the lipids constituting these membranes become more fluid, and once the temperature exceeds the lipids' specific melting point, the membranes lose the structural integrity required for proper function.

The third pathway of damage affects the insect's muscles and is the first to manifest, occurring even before the heat actually kills the insect: when muscle temperature exceeds the optimal range for the catalytic activity of its myosin and actin, the insect loses its ability to move, entering a state of immobility known as "knockdown"—a condition that precedes death but does not yet signify it. Ultimately, just how lethal this entire combination of mechanisms proves to be for the insect depends not only on the peak temperature reached but also on the duration of exposure; the lethal temperature model integrates temperature and exposure time into a single cumulative damage calculation, meaning that a moderate temperature maintained for a long period can be just as lethal to the insect as a much higher temperature sustained only briefly.

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