Thermal tolerance of the rosy apple aphid Dysaphis plantaginea and its parasitoids: Effect of low temperatures on some fitness activities of Aphidius matricariae.

Understanding the thermal tolerance of insect herbivores and their natural enemies is crucial for biological control programs. The rosy apple aphid Dysaphis plantaginea is one of the most problematic pests of apple orchards, causing economic losses of up to 30% due to damage to fruits. Dysaphis plantaginea is highly adapted to low temperature, enabling it to appear early in the season. This study aimed at evaluating the critical thermal minimum of D. plantaginea and of two parasitoid species: Aphidius matricariae and Ephedrus cerasicola. For the generalist parasitoid A. matricariae we also evaluated the fitness traits of flight, walking, and oviposition, at four temperatures: 20, 15, 10 and 8 °C. We found that both males and females did not fly at the two lowest temperatures. Walking, parasitism rate and sex ratio (proportion of female progeny) were reduced at 8 °C. In addition, the parasitism rate was significantly lower at 8 and 10 °C compared to 15 and 20 °C. The progeny emerging from the oviposition experiment at 8 °C were significantly larger compared with other temperatures, possibly attributed to longer development time. The fact that the parasitoids were unable to fly at 8 and 10 °C, in combination with a more male-biased sex ratio, could reduce their efficiency at low temperature, even though they may still be able to walk and parasitize aphids.