Biology and Immature Stages of Megaselia aequalis, a Phorid Predator of Slug Eggs

TLDR: The egg, 3 larval instars, and puparium are described and illustrated and the female oviposits directly onto the slug eggs or occasionally onto nearby vegetation.

Abstract: Megaselia aequalis (Wood) apparently is restricted to feeding on the eggs of the slug Deroceras laeve (Muller). The female oviposits directly onto the slug eggs or occasionally onto nearby vegetation. The newly hatched larva penetrates the outer covering of the egg, passes through the gelatinous matrix, and begins feeding on the perivitelline fluid. It does not attack the developing embryo. The 1st larval stadium lasts 1 or 2 days, and molting occurs within the egg. The 2nd-instar larva also remains within the egg, but unlike the 1st instar it usually destroys the embryo of the slug. The 2nd stadium lasts 2 days, with molting taking place outside the egg. The early 3rdinstar larva feeds within the gelatinous matrix surrounding the egg-capsule. Later it becomes more predatory and usually destroys at least 4 additional eggs. When fully grown, the larva abandons the cluster of eggs and pupates. The prepupal period lasts about 24 hours, the pupal period, 10–12 days. The earliest collecting record for adults in northeastern Ohio is May 27; the latest, September 10. There are at least 3 generations a year. Overwintering occurs as pupae. The egg, 3 larval instars, and puparium are described and illustrated.