Impact of heat stress on the development of egg and adult coccinellid Serangium japonicum: evidence for cross-stage and cross-generation effects

Arthropod biological control agents are at risk due to climate change, since heat stress negatively impacts their life history traits. Here, we investigated ontogenetic variation of thermal sensitivity in an important whitefly predator, Serangium japonicum Chapin (Coleoptera: Coccinellidae). In particular, we evaluated the impact of heat shock on survival rate, development, and reproduction of S. japonicum, and checked whether the negative effects resulting from heat stress are stage-related. The two most heat-tolerant stages of S. japonicum (egg and adult) were exposed to heat shock treatments at 36, 39, and 42 degrees C for 2 h, and 36 and 39 degrees C for 4 h. We found that heat shock significantly reduced egg-to-adult survival rate, extended egg-to-adult development time, and decreased fecundity and oviposition period compared to control (27 degrees C). The sex ratio however was not affected. Eggs exposed to heat shock led to adults whose weight and longevity were considerably reduced. The detrimental effects that resulted from heat shock were carried over to later life stages and even the next generation. Those carry-over effects were independent of stage except for egg-to-adult development time and adult weight. Our results suggest that releasing eggs or adults into fields or greenhouses makes little difference in reducing any negative impact on the developmental performance of S. japonicum induced by heat stress in a warming climate.