Abstract
Understanding warming impact on herbivores facilitates predicting plant/crop dynamics in natural/agricultural systems. However, it remains unclear how warming will affect herbivore population size and population composition, consequently altering herbivore colonization in a tri-trophic system (plant-herbivore-predator or crop-pest-biocontrol agent). We studied a soybean-aphid-lady beetle system, by conducting (1) a laboratory warming experiment to examine warming impact (+2 °C or +4 °C) on the aphid population size and composition (alate proportion), and (2) a field colonization experiment to examine whether the warming-induced effect subsequently interacts with predators (lady beetles) in affecting aphid colonization. The results showed that warming affected the initial aphid population composition (reduced alate proportion) but not population size; this warming-induced effect strengthened the top-down control by lady beetles and slowing aphid colonization. In other words, biocontrol on crop pests by predators could improve under 2–4 °C warming. Furthermore, aphid colonization was affected by an interaction between the alate proportion and predator (lady beetle) presence. This study suggests that warming affects herbivore population composition and likely mediates top-down control on herbivore colonization by predators. This mechanism may be crucial but underappreciated in climate change ecology because population composition (wing form, sex ratio, age/body size structure) shifts in many species under environmental change.
Highlights
Herbivores exert top-down control on plant growth, development, and production in natural and agricultural systems[1,2,3]
Many studies have focused on warming impact on herbivore population size[8,9,10], and less is known about (1) whether warming affects population size and population composition in herbivores, and (2) how this warming impact may subsequently affect herbivore colonization on plants in the presence or absence of predators
Given that average global surface temperature may increase from 1.9 to 3.7 °C by 2100 (RCP 4.5 and 8.5)[11], is it possible that this degree of warming will be just sufficient to change one but not another herbivore population trait? In addition, will this warming impact on herbivore population subsequently interact with predator effect in influencing herbivore colonization? Answering these questions can advance our understanding in basic ecology, as well as applied ecology
Summary
Herbivores exert top-down control on plant growth, development, and production in natural and agricultural systems[1,2,3]. (2) How would this warming impact on the initial population size and composition subsequently interact with lady beetle (predator) effect in influencing aphid colonization? Because alates have a better migration ability[15, 16], warming impact on the aphid population composition (alate proportion) likely affects subsequent aphid colonization This study included both laboratory and field experiments (warming and colonization experiments, respectively; Fig. 1a), focusing on soybean (Glycine max), soybean aphids (Aphis glycines), and seven-spotted lady beetles (Coccinella septempunctata) because they represent a typical plant-herbivore-predator system, as well as an important crop, crop pest and biocontrol agent, respectively. On the basis of these results, a colonization experiment (without active warming) was conducted in the field with a 2
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