| Summary: | <i>Sitodiplosis mosellana</i>, a periodic but devastating wheat pest that escapes temperature extremes in summer and winter by undergoing obligatory diapause. To determine the roles of small heat shock proteins (sHsps) in diapause of <i>S. mosellana,</i> we characterized two <i>sHsp</i> genes, <i>SmHsp17.4</i> and <i>SmHsp20.3</i>, from this species. Both SmHsps contained the conserved α-crystallin domain and the carboxy-terminal I/VXI/V motif of the sHsp family. <i>SmHsp17.4</i> had one intron while <i>SmHsp20.3</i> had none. Quantitative PCR revealed that <i>SmHsp17.4</i> expression decreased after diapause initiation, but substantially increased during transition to post-diapause quiescence. In contrast, <i>SmHsp20.3</i> expression was not affected by entry of diapause, but was clearly up-regulated during summer and winter. Short-term more severe heat-stress (≥35 °C) of over-summering larvae or cold-stress (≤−5 °C) of over-wintering larvae could stimulate higher expression of both genes, and <i>SmHsp17.4</i> was more responsive to cold stress while <i>SmHsp20.3</i> was more sensitive to heat stress. Notably, transcription of <i>SmHsp17.4</i>, but not <i>SmHsp20.3</i>, in diapausing larvae was inducible by 20-hydroxyecdysone (20E). Recombinant SmHsp17.4 and SmHsp20.3 proteins also displayed significant chaperone functionality. These findings suggest that both <i>SmHsps</i> play key roles in stress tolerance during diapause; and 20E-regulated <i>SmHsp17.4</i> was also likely involved in diapause termination.
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