Factors affecting host plant selection in alfalfa aphids.

Area of Science:

• Ecology
• Entomology
• Chemical Ecology

Background:

• Alfalfa (Medicago sativa L.) is a host plant for multiple aphid species, including Acyrthosiphon pisum, Aphis craccivora, and Therioaphis trifolii.
• Previous observations indicated distinct habitat preferences among these aphid species on alfalfa, with single species typically colonizing individual plants.

Purpose of the Study:

• To investigate the host plant selection behavior of three alfalfa aphid species.
• To determine if aphid species actively avoid each other during host selection through olfactory cues.
• To understand the role of plant volatiles in mediating interspecific competition avoidance.

Main Methods:

• Field and laboratory experiments were conducted to assess aphid preferences for plant density and condition (healthy vs. infested).
• The effect of volatiles from healthy and aphid-infested alfalfa plants on aphid attraction was tested.
• Interspecific competitive ability was assessed, with A. pisum showing the weakest and A. craccivora the strongest traits.

Main Results:

• Aphis craccivora was repelled by dense alfalfa crops and volatiles from plants infested with A. pisum or T. trifolii.
• Acyrthosiphon pisum and Therioaphis trifolii preferred dense plant stands and were repelled by volatiles from plants infested with A. craccivora.
• Aphid species exhibited distinct preferences, leading to spatial segregation on alfalfa plants and weeds.

Conclusions:

• Aphid species utilize olfactory cues from plants to avoid interspecific competition.
• Competition avoidance begins at the host selection stage, mediated by plant volatiles, rather than solely occurring after co-infestation.
• Understanding these behaviors is crucial for managing aphid populations in alfalfa ecosystems.