| With the global temperature rising,the frequency and severity of extreme drought events have increased in recent years.Extreme drought events can affect the plant performance,thus alter the interaction between plants and aboveground insects,which lead to changing the community structure of plants and insects.Extreme drought not only affects the interaction between plants and insects during drought,but also has a long-lasting(legacy)effect during rewetting.There have been several studies on the effects of extreme drought events and its legacy on plant-herbivorous insect interactions.However,few studies have focus on the effects of extreme drought event and its legacy on plant-herbivorous insect-natural enemies tri-trophic interactions.In this study,we selected the tri-trophic system of Asteraceae plant-aphidpredator/parasitoid,and explored the effects of extreme drought and its legacy on plantherbivorous insect-natural enemies tri-trophic interactions,we investigated plant growth performance,aphid density,and the number of predators and parasitoid by field experiment and common garden experiment in eastern Qinghai-Tibet Plateau(Hezuo,Gansu)after summer drought and subsequently rewetting.In this study,we selected 10 plant species of Asteraceae(Cosmos bipinnatus,Ligularia virgaurea,Ligularia sagitta,Senecio dubitabilis,Taraxacum mongolicum,Saussurea parviflora,Saussurea nigrescens,Cirsium arvense,Picris hieracioides,Sonchus brachyotus).We found that:(1)Extreme drought decreased the aphid density and the predator number but increased the parasitoid attack rate of aphids of Picris hieracioides in the field.(2)Extreme drought decreased the shoot biomass of plants,which varied among different species.Moreover,for plants that flowering,extreme drought significantly decreased the flowering height,but had no significant effect on flowering time.(3)In the common garden experiment,our study showed that the content of plant defense compounds(tannins)was varied among different species,and extreme drought had no significant effect on plant tannin content.(4)In the common garden experiment,we found that extreme drought had no significant effect on the aphid density,predator number,and parasitoid attack rate of aphids,which varied among plant species: extreme drought reduced the aphid density of Picris hieracioides and Ligularia virgaurea,reduced the number of predators of Picris hieracioides and Ligularia virgaurea,increased the parasitoid attack rate of aphids of Picris hieracioides.(5)Extreme drought had a positively legacy effect on the density of aphids,which varied among plant species: the legacy effect of extreme drought significantly increased the aphid density of Ligularia virgaurea and Saussurea nigrescens,significantly reduced the aphid density of Picris hieracioides,but had no effects on the aphid density of Sonchus brachyotus and Senecio dubitabilis.Moreover,the legacy effect of extreme drought reduced the number of predators of Picris hieracioides,and increased number of predators of Ligularia virgaurea,and increased the parasitoid attack rate of aphids of Ligularia virgaurea and Picris hieracioides.(6)The aphid density was different in different years of the experimental stage.The above results show that extreme drought and its legacy effects significantly change plant performance and plant-aphid-natural enemies tri-trophic interactions.The effects of extreme drought and its legacy effects have different effects on aphid density.Extreme drought decreased aphid density,while the legacy effect of extreme drought increased aphid density.The change of aphid density will further have an upward effect on predators and parasitoids,but the direction of the effect is different,showing that with the decrease of aphid density,the number of predators decreases,while the parasitoid attack rate of aphids increases.This may change the competition between predators and parasitoids of aphids and enhance the control of parasitoids on aphids.This study demonstrated that complex effects of extreme drought events on the interaction between aboveground multitrophic populations among aphids,predators,and parasitoids.Understanding the effects of extreme drought and its legacy on plantaphid-natural enemies interactions are helpful for better understanding of insect community responses to climatic extremes,and are very important for improving the ability of biological control of aphids,and are of great significance for predicting the response of communities and ecosystems under future global climate change. |
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