Seasonal History and Host Synchronization of Lydella grisescens (Diptera: Tachinidae) in Minnesota1

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Abstract
Seasonal history of Lydella grisescens Robineau-Desvoidy was studied in its primary host, the European corn borer, Ostrinia nubilalis (Hübner) and an alternate host, the stalk borer, Papaipema nebris (Guenée). Results show that the seasonal development of the parasite is poorly synchronized with that of the corn borer host. If only the European corn borer is available as the host, most of the Lydella adults emerged in the spring will find the borer larvae too young to be parasitized. The parasite adults will die before larvipositing. The very few adults which emerge very late may find the borer larvae old enough. The parasite will then carry on 3 generations in the year with a rather low initial population. If stalk borers are present, they are usually more advanced in development than corn borers. Larvae old enough for parasitization are available during the entire period of Lydella emergence. The parasite then carries out 1 or 2 generations in stalk borers, depending upon the host plants on which the stalk borers feed. The parasite will then complete 2 or 3 generations in the corn borer, making a total of 4 generations in the year. Thus, the presence of the stalk borer is beneficial to the preservation of the Lydella parasite in this area. Other relationships between Lydella and its hosts are discussed.

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