DISTRIBUTION OF PARASITISM BY MACROCENTRUS-GRANDII (HYMENOPTERA, BRACONIDAE) IN MAIZE INFESTED BY OSTRINIA-NUBILALIS (LEPIDOPTERA, PYRALIDAE)

Macrocentrus grandii Goidanich is a braconid parasitoid of the European corn borer, Ostrinia nubilalis (Hubner). Over a 3-yr period, we collected corn borer larvae from maize fields in Illinois to determine how host density and other factors influence the distribution of parasitism. The proportion of parasitized larvae was not density dependent at the single-stalk and field scales. Parasitism was always higher in the first generation of the bivoltine population. Proportion of parasitized larvae was correlated with the proportion of stalks that had at least one parasitized larva and with the frequency of infested stalks. These correlations indicated that searching and oviposition by the female parasitoid may be random among maize stalks. The apparent inefficiency of this parasitoid is discussed.