Data from: Hoverfly preference for high honeydew amounts creates enemy-free space for aphids colonizing novel host plants

The existence of an enemy-free space can play an important role in aphid host race formation processes, but little is known about the mechanisms that create an area of low predation pressure on particular host plants. In this paper we identify a mechanism generating lower predation pressure that promotes the maintenance of the different host races of the pea aphid (Acyrthosiphon pisum) complex, a well-studied model for ecological speciation. The pea aphid consists of at least 15 genetically distinct host races which are native to specific host plants of the legume family, but can all develop on the universal host plant Vicia faba. Previous work showed that hoverfly (Episyrphus balteatus) oviposition preferences contribute to the enemy-free space that helps to maintain the different pea aphid host races, and that higher amounts of honeydew are more attractive to ovipositing hoverflies. Here we demonstrated that aphid honeydew is produced in large amounts when aphid reproduction rate was highest, and so is an important oviposition cue for hoverflies under field conditions. However, on less suitable host plants, where honeydew production is reduced, pea aphids enjoy lower predation rates. A reduction in enemy pressure can mitigate the performance disadvantages of aphids colonizing a novel host, and probably plays an important role in pea aphid host race formation.

无天敌空间（enemy-free space）的存在可在蚜虫寄主宗（host race）形成过程中发挥关键作用，但目前学界对特定寄主植物上形成低捕食压力区域的机制仍知之甚少。本文针对豌豆蚜（Acyrthosiphon pisum）复合种群——一类被广泛研究的生态物种形成模型——的不同寄主宗维持机制展开研究，明确了一种可降低捕食压力的调控途径。豌豆蚜复合种群至少包含15个遗传分化显著的寄主宗，它们天然寄生于豆科植物的特定物种，但均可在广谱寄主蚕豆（Vicia faba）上完成生长发育。既往研究表明，食蚜蝇（黑带食蚜蝇Episyrphus balteatus）的产卵偏好可构建无天敌空间，进而助力豌豆蚜不同寄主宗的维持；且蜜露（honeydew）含量越高，对产卵期食蚜蝇的吸引效果越强。本研究证实，当蚜虫繁殖速率达到峰值时会大量分泌蜜露，因此蜜露是田间条件下食蚜蝇产卵的重要定位线索。然而，在蚜虫适应性较差的寄主植物上，蜜露分泌量会显著降低，此时豌豆蚜面临的捕食压力也随之减弱。捕食压力的缓解可抵消蚜虫定植新寄主时的适合度劣势，该过程可能在豌豆蚜寄主宗形成过程中发挥核心作用。