Sniff and shout and let it all out: Investigating the ability of SCM larval olfaction

Most insects use volatile organic compounds (VOCs) to search for food, mates, or oviposition sites. VOCs research is typically performed on adults rather than immature stages. Even when immature stages are used, the work focuses mostly on above-ground caterpillars- overlooking damaging underground pests such as Delia platura (Meigen), or seedcorn maggot (SCM). Adults rely on VOCs to search for oviposition sites, while the larval stage of the SCM consumes germinating seeds. It remains unclear whether larval choice or adult oviposition choice dictates resource finding. Our question remains: Do SCM larva use VOCs to locate food sources?

To test SCM larva’s food searching ability, filter discs were pressed against a germinating seed in a glass container with moist SiCO₂ sand for 72 hours. Control discs were placed in moist sand without seeds. Maggots were presented with two filter discs (a control and a seed exposed treatment) on either extreme end of a glass petri dish. The maggots were released in the center of the petri dish, with their orientation and treatment location changed after each choice. A choice was recorded once the maggot (n = 10) encountered a filter disc within five minutes.

Maggots consistently chose treated discs over control discs, demonstrating that SCM larva can sense its surroundings based off available resources. Volatiles were collected using a thin film SPME fiber which were analyzed using a GC-MS. Volatile profiles suggested that compounds emitted from germinating lima bean seeds serve as attractants for SCM larva.