Dynamics of heat shock protein responses to thermal stress changes after metamorphosis in a lepidopteran insect

In the last decade, unexpected high temperatures have been frequent in spring and early summer. Numerous studies have shown that such thermal stress has substantial effects on life-history traits that influence fitness of insects, but few have examined expression dynamics of heat shock proteins (Hsps) across developmental stages, especially as regards potential carry-over effects at the transcriptional level across metamorphosis. We exposed pupae of the oriental fruit moth ("OFM," Grapholita molesta Busck) to mild heat stress (38°C, 6 h) and then quantified expression patterns of six Hsps (Hsp90, 70, 60, 40, 21, and 11) from pupal through adult stages. Almost all Hsps showed a higher expression immediately after pupae were heat-stressed, but later dropped to normal levels after metamorphosis. Although upregulation of Hsps is transient and the effects carry over longer to early adult stage, upregulation will nonetheless have positive effects on adult fitness. The fitness of some insects may benefit from higher expression of chaperon genes after mild stress, in the form of higher fecundity and longer lifespan, as a carry-over effect. These results suggest that mild thermal stress can change genetic expression that later boosts adult fitness through a cascade effect.