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

Area of Science:

• Ecology
• Evolutionary Biology
• Entomology

Background:

• Enemy-free space is crucial for aphid host race formation.
• Mechanisms creating low predation pressure on specific host plants are poorly understood.
• Pea aphids (Acyrthosiphon pisum) exhibit distinct host races, with Vicia faba as a universal host.

Purpose of the Study:

• Identify mechanisms generating reduced predation pressure that support pea aphid host race maintenance.
• Investigate the role of aphid honeydew as an oviposition cue for hoverflies.
• Determine how host plant suitability influences aphid-host interactions and predation.

Main Methods:

• Field observations and data collection on aphid reproduction and honeydew production.
• Assessment of hoverfly (Episyrphus balteatus) oviposition preferences in relation to honeydew.
• Correlation analysis between honeydew levels, host plant suitability, and aphid predation rates.

Main Results:

• Aphid honeydew production is highest during peak aphid reproduction and serves as a key oviposition cue for hoverflies.
• Reduced honeydew production on less suitable host plants leads to decreased hoverfly-mediated predation.
• Lower enemy pressure on novel hosts can offset performance disadvantages for colonizing aphids.

Conclusions:

• Aphid honeydew acts as a critical factor in mediating predator-prey dynamics and maintaining host-specific aphid populations.
• Reduced predation on less suitable hosts, facilitated by lower honeydew, is a significant driver of pea aphid ecological speciation.
• Understanding these mechanisms provides insight into the processes of ecological speciation in insects.