Cockchafer larvae smell host root scents in soil

Area of Science:

• Chemical ecology
• Insect olfaction
• Below-ground ecosystems

Background:

• Olfaction is crucial for many insects, but below-ground chemical ecology is understudied.
• Limited evidence exists for insect behavioral responses to soil chemical cues beyond carbon dioxide (CO2).
• The role of olfaction in soil-dwelling larvae locating host plants remains unclear.

Purpose of the Study:

• To investigate olfactory perception and behavioral responses in soil-dwelling larvae of Melolontha hippocastani to host plant roots.
• To determine if larvae can detect volatile compounds released by damaged host plants.
• To understand the mechanisms used by larvae to locate host plants below ground.

Main Methods:

• Electrophysiological recordings from larval antennae.
• Behavioral assays in natural soil to assess directed movement.
• Analysis of olfactory apparatus structure, including pore plates and glomeruli.

Main Results:

• Melolontha hippocastani larvae exhibit a well-developed olfactory system with specialized antennae.
• Larvae responded electrophysiologically and behaviorally to volatile compounds from damaged oak roots (e.g., eucalyptol, anisol).
• Detection of volatiles occurred at concentrations as low as 5 parts per billion by volume (ppbv) in soil air, eliciting directed movement.

Conclusions:

• Soil-dwelling larvae possess the olfactory capability to perceive plant root volatiles.
• These volatiles guide larvae towards host plants, similar to adult beetles.
• Larvae utilize olfactory cues for locating below-ground food sources, despite challenging soil conditions.