In laboratory studies,Copidosoma truncatellum(Dalman), a polyembryonic encyrtid that is an egg-larval parasite ofTrichoplusia ni(Hübner), was found to parasitize any age of egg. AlthoughC. truncatellumwas not an effective searcher of host eggs, even in a confined area, freshly emerged parasites showed a greater rate of parasitization than older (24-h) parasites even though both had a full complement of eggs. The parasite usually injects more than 1 egg into the host at a single insertion of the ovipositor. Temperature affects the rate of parasitization, the time taken for oviposition, and the percentage of brood that will oviposit. The parasite contains a full complement of eggs at adult emergence, which diminishes only with use; eggs are not reabsorbed. Not all individual females in a single brood are functionally fecund; many never oviposit even though they contain eggs. Those that will oviposit, oviposit most eggs early; by the middle of the adult lifespan, they have laid the final egg, and the last half of the adult lifespan is essentially nonfunctional. At certain temperatures, the parasite causes some mortality of host eggs and larvae before the 5th stage; such deaths also kill the contained parasites.