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

Abstract

Environmental temperature is an important factor restricting insect population dynamics. Due to the ongoing global warming, interest in the impact of heat stress on insects has grown. High temperature in summer is a key barrier for Bradysia odoriphaga (Diptera: Sciaridae), a devastating vegetable pest o in China. It is well known that moderate thermal hardening can enhance the thermotolerance of many insects, which is beneficial for adaptation to environmental thermal stress. In order to determine whether heat hardening was beneficial for B. odoriphaga to adapt to high summer temperatures, we studied the biological performance, antioxidant responses and hsp70 and hsp90 expression of B. odoriphaga 4th instar larvae and adults after pre‐exposure to mild heat hardening temperatures (30–36°C). Mild heat hardening (32–36°C) enhanced the larval thermal tolerance to extreme heat stress. 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 4th instar larvae. Mild heat hardening at 36°C weakened the heat tolerance of adults. The activity of four antioxidant enzymes in B. odoriphaga changed dramatically after heat hardening at 32–36°C. During recovery at 25°C, catalase (CAT), peroxidase (POD) and glutathione‐S‐transferase (GST) in tested larvae maintained successive higher activities after heat hardening. Simultaneously, the expression levels of hsp70 and hsp90 increased significantly after thermal hardening. Higher expression levels were also detected in larvae, pupae and adults after 48 hr recovery at 25°C. Overall, mild heat hardening played an important role in heat tolerance plasticity of B. odoriphaga larvae, and the antioxidant system and hsp70 and hsp90 genes were extremely relevant to this adaptation process.

Biological and physiological responses of Bradysia odoriphaga 4th instar larvae to long‐term mild heat stress

“…Other insects that exhibit summer diapause have similar responses, including Adelges japonicus Monzen (Tabuchi et al, 2009), Nicrophorus quadripunctatus Kraatz (Nishimura, 2010) and Chrysocharis pubicornis Zetterstedt (Larios, 2007). B. odoriphaga 4th instar larvae clearly possess the potential capacity to survive the hot summer months in a diapause-like state, which is similar to that of Adelges japonicus Monzen (Tabuchi et al, 2009) (Gou et al, 2020;Zhu et al, 2021). Furthermore, the enhanced heat tolerance due to heat hardening will help B. odoriphaga tolerate possible extreme heat stress.…”

“…The findings of the present study combined with previous studies research indicate that the 4th instar larvae of B. odoriphaga possess the strongest heat tolerance and thermal plasticity under extreme heat stress, and survive long‐term mild heat stress in a diapause‐like state. These abilities help B. odoriphaga survive the hot summer months (Gou et al, 2020; Zhu et al, 2021). Furthermore, the enhanced heat tolerance due to heat hardening will help B. odoriphaga tolerate possible extreme heat stress.…”

“…Short‐term mild heat hardening can enhance the thermal tolerance of insects to extreme heat stress (Rajamohan & Sinclair, 2008; Zhu et al, 2021). However, long‐term mild heat stress can cause increased insect mortality, while other individuals may tolerate and adapt to mild heat stress through physiological processes, such as summer diapause or dormancy (Belozerov, 2009; Liu et al, 2016).…”

“…This research confirmed that the final instar larval stage (4th) was the dominant stage in summer. In addition to adverse effects on life parameters, mild heat hardening also enhances the thermotolerance of B. odoriphaga larvae against severe heat and helps the larvae to survive hot summers (Zhu et al, 2021). This finding helps to explain why larvae are the dominant stage in the field in summer.…”

Effect of elevated CO2 and temperature on maize resistance against the Asian corn borer

“…It is well known that moderate thermal stress can enhance the activities of protective enzymes and thermotolerance for many insects (Dampc et al, 2020; Lu et al, 2014; Zhu et al, 2021). Under the conditions of elevated CO 2 , the activity of insect protective enzymes increased indirectly through the enhancement of secondary metabolism of its host plants (Xu et al, 2019).…”