Abstract
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.
Highlights
Climate change is the most serious concern for agriculture [1,2]
Environmental stability appears to be an essential factor that maintains the balance of population sizes threatened by global warming
At present, the biological control of S. avenae by parasitoid wasps does not appear to be significantly affected in Chile since the densities of S. avenae are still below the threshold of economic damage
Summary
Climate change (e.g., increased environmental temperature, increased atmosphericCO2 , unstable climates, and altered frequency/intensity of extreme weather events) is the most serious concern for agriculture [1,2]. Global warming, characterized by increased and extreme temperatures that will become more frequent, affects crop yields, mainly through crop pest biology and distribution changes, especially in invasive pest species [3,4,5]. A worldwide pest of cereals, the English grain aphid, Sitobion avenae (Fabricius) [9,10], originated from Europe and the Mediterranean zone and was introduced to Chile in the late 1960s, causing significant losses to cereal production [11]. Mild winters in Chile favored asexual reproduction all year round, allowing aphid populations to distribute rapidly and widely across most of the cereal production area [12]. Several Aphidiinae endoparasitoid species were introduced to Chile from different geographic origins during the late 1970s to cope with this pest as part of a governmental biocontrol program [13]. Chile is considered one of the best examples of successful aphid biological control programs to combat the English grain aphid [15]
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