Effects of heat hardening on life parameters and thermostability of Bradysia odoriphaga larva and adults

High temperature in summer is a key barrier for <i>Bradysia odoriphaga</i> (Diptera: Sciaridae), a serious pest of vegetables in China. Because mild heat hardening can enhance the thermotolerance of many insects, we determined if heat hardening was beneficial for <i>B. odoriphaga</i> adaptation to high summer temperatures. We studied the biological performance, antioxidant responses and <i>hsp70</i> and <i>hsp90</i> expression of <i>B. odoriphaga </i>4^th instar larvae and adults after pre-exposure to mild heat hardening temperatures (30-36°C). The tolerance of larvae to severe heat stress was enhanced after mild heat hardening (32-36°C). However, life parameters were significantly inhibited, development was delayed, longevity was shortened and fecundity was decreased. Mild heat hardening (30-34°C) caused serious adverse effects on life parameters and less enhancement of heat resistance for 4^th larvae. Mild heat hardening at 36°C weakened the heat tolerance of adults. The activity of four antioxidant enzymes in <i>B. odoriphaga</i> changed dramatically after heat hardening at 32-36°C. CAT and GST maintained successive higher activities, and POD also had higher activities in larvae after 48 h recovery at 25°C, pupae, and adults. Simultaneously, the expression levels<i> </i>of<i> hsp70</i> and <i>hsp90</i> increased significantly upon thermal hardening. Higher expression levels were also detected in larvae after 48 h recovery at 25°C, pupae, and adults. Mild heat hardening played an important role in heat tolerance plasticity of <i>B. odoriphaga</i> larvae. The antioxidant system and <i>hsp70</i> and <i>hsp90</i> genes were relevant to this adaptation process.