Spatial and Temporal Variation in the Aphid–Parasitoid Interaction under Different Climates

Global warming will increase pest insect population sizes and diminish the effectiveness of biological control. This biological control failure scenario appears to be of particular concern for areas with a significant increase in maximum temperatures, such as the increase experienced in the Central Valley of Chile over the last 40 years. We assessed the impact of different climatic zones and maximum temperatures along the coast and the Chilean Central Valley on the grain aphid (Sitobion avenae) density, parasitism rate, and facultative endosymbionts in wheat fields during the growing season in the springs of 2017 and 2018. A significant effect on aphid density due to zones and maximum temperatures was detected; however, this depended on the zone and year analyzed. Changes between zones and seasons were observed for parasitism rates, while maximum temperatures only significantly affected the parasitism rate in 2017. The main parasitoid wasp found was Aphidius ervi in both zones and seasons. Regiella insecticola infected 95% of the samples in both zones, although it does not seem to have a protective role at the field level. Our findings suggest that, at present, global warming does not significantly affect the grain aphid outbreaks and their biological control in Chile. However, this study points out the importance of pre-emptive monitoring to detect aphids and the synchrony loss of their parasitoid wasps.