Warming impact on the population size and structure of a crop pest (soybean aphid) and its consequence for pest colonization
The soybean aphid, Aphis glycines Matsumura, a native species to Asia, has been widespread across eastern and southeastern Asia. It has also invaded northern America and caused a serious impact on soybean production. The optimal temperature for soybean aphids is between 25°C and 30°C. Increasing temperature could enhance aphid population growth (e.g., outbreak), yet it could also reduce the production of alates (winged aphids), potentially impeding the colonization of aphids on new host plants. Giving that global temperature is predicted to increase about 2 – 4 oC by the end of this century (Intergovernmental Panel on Climate Change 2013), this study is aimed to explore how this upcoming warming may ultimately affect the population growth and colonization of soybean aphids living near their optimal temperature. We first conducted a warming experiment in the laboratory to examine the impact of a 2 and 4 oC warming on aphid population size and structure (e.g. alate proportion), using soybean aphids collected from three field sites. The control temperature was set at 24.5 oC based on field data. We then set up a colonization experiment in the field to investigate how the impact of warming on aphid population size and structure (based on the first experiment) may consequently affect aphid colonization under the appearance of ladybugs (predators and biocontrol agent). Our warming experiment revealed that warming reduced the production of alate aphids, but had no effect on overall aphid population size. The colonization experiment showed that the presence of ladybugs (predators) failed to control the colonization of aphids (preys) when alate proportion was high (i.e. ambient temperature scenario), but succeeded when alate proportion was lowered (i.e. warming scenario). The results above suggest that warming may limit the colonization of soybean aphids around their optimal temperature, by reducing the production of alate aphids and facilitating the biocontrol by ladybugs.
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