Does the imported cabbageworm,Pieris rapae, use an oviposition deterring pheromone?

Area of Science:

• Chemical ecology
• Insect behavior
• Chemical communication

Background:

• The cabbage butterfly (Pieris rapae) utilizes chemical cues for egg-laying decisions.
• Oviposition-deterring pheromones (ODPs) are known in some insect species, but their precise role and perception in P. rapae require clarification.

Purpose of the Study:

• To investigate the presence and nature of oviposition-deterring pheromones in Pieris rapae eggs.
• To identify the sensory mechanisms involved in ODP perception.
• To compare ODP production and perception between North American and European populations.

Main Methods:

• Choice experiments presenting females with treated and untreated cabbage leaves.
• Analysis of water and methanol extracts from P. rapae eggs and female accessory glands.
• Contact chemoreceptor stimulation assays using foretarsal sensilla.
• Electroantennogram (EAG) recordings to assess antennal responses to egg volatiles.

Main Results:

• P. rapae eggs contain a water- and methanol-soluble ODP that deters oviposition.
• Water extracts from female accessory glands also exhibit ODP activity.
• Egg washes and gland extracts stimulate contact chemoreceptors on the fore tarsi.
• Antennal receptors respond to volatiles from conspecific eggs but not from Mamestra brassicae eggs.
• No significant differences in ODP production or perception were found between North American and European P. rapae.

Conclusions:

• Pieris rapae produces and perceives an oviposition-deterring pheromone (ODP) present in its eggs and female accessory glands.
• ODP perception involves both contact chemoreception (tarsi) and potentially olfactory reception (antennae).
• Methodological differences likely explain discrepancies with previous field-based studies on P. rapae ODP behavior.