Earthworm mucus stimulates oviposition in a predatory fly (Diptera: Anthomyiidae)

Coenosia tigrina larvae feed on earthworms. We hypothesized that earthworm mucus contains a kairomone that stimulates oviposition behavior in adultC. tigrina females, thus minimizing the search area in the soil required for newly eclosed larvae to find earthworms. In bioassays, adult females responded with extension of the ovipositor 25-43% of the time to earthworm-mucus-soaked filter paper disks compared to 6-7% in response to water-soaked disks. Ovipositor extension on mucus-soaked disks was followed by egg-laying 29% of the time and 0% of the time on water-soaked disks. Egg-laying byC. tigrina followed a diurnal periodicity, with most eggs laid in the latter half of the photophase even in the absence of earthworm mucus. More eggs were deposited from 1600 to 1800 hr by females given access to earthworm mucus during that period than were deposited by females not given access. There was no difference in the number of eggs deposited from 0600 to 0800 hr, by females given access to earthworm mucus or not. This is a time of day when few eggs are normally laid. This paper is the first report of an earthworm-produced kairomone in an insect-earthworm interaction. The kairomone may have potential for enhancing biological control of the onion maggot,Delia antiqua, which is a prey of adultC. tigrina.