Hoverfly preference for high honeydew amounts creates enemy‐free space for aphids colonizing novel host plants

Abstract

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 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.

Neonicotinoids in excretion product of phloem-feeding insects kill beneficial insects

“…We selected hoverflies and parasitic wasps of honeydew-producing insects because it is known that they feed on honeydew in the field and also use honeydew as cues to locate their hosts (25–27, 40–43). Therefore, they are extensively in contact with honeydew in the field.…”

“…Most of these parasitic wasps would die in less than 2 d without feeding on honeydew (20). Bees, as well as other pollinators, also feed on honeydew when nectar is scarce (27, 28).…”

Elevated CO2 Concentrations Impact the Semiochemistry of Aphid Honeydew without Having a Cascade Effect on an Aphid Predator

“…The plants were covered with 35 µL fresh honeydew that had been collected from the corresponding CO 2 treatment (see Section 2.2 ). This amount was previously shown to induce oviposition in hoverflies [ 16 , 17 ]. According to our quantification assays, this volume represents a quantity of honeydew excreted by 50 adult aphids over 24 h. After honeydew deposition, plants were left over for 30 min to let the honeydew dry.…”

Ant–hemipteran association decreases parasitism of Phenacoccus solenopsis by endoparasitoid Aenasius bambawalei

“…Honeydew produced by aphids is an important oviposition cue for hoverflies. Episyrphus balteatus showed an obvious oviposition preference for the site with a larger amount of honeydew produced by pea aphid Acyrthosiphon pisum , and when the honeydew production was reduced, pea aphids showed a lower predation rate (Vosteen et al ., ). In addition, abundant honeydew is collected and removed by the tending ants in ant–hemipteran mutualism (Degen & Gersani, ; Helms & Vinson, ).…”