The Host-Parasite Relationship of the European Corn Borer, Ostrinia nubilalis, and the Protozoan, Perezia pyraustae, in Delaware1

Abstract

A high incidence of Perezia pyraustae was found in European corn borer larvae collected in the Autumn of 1959. Four hundred additional larvae were collected in April 1960 and subjected to controlled laboratory studies of the host-parasite relationship. Of the 114 adults that emerged from these larvae, P. pyraustae was found in 85%. Eighty per cent of a sample of 50 dead larvae examined contained spores of this pathogen. P. pyraustae significantly reduced adult longevity in both males and females. The fecundity of infected females was greatly lowered as compared with no infected females. The number of viable eggs laid by infected females was somewhat lower, suggesting that the pathogen may also have adversely infuenced embryonic development. The results of this investigation, coupled with recent findings of workers in other areas of the country, suggest that P. pyraustae may be an important biotic factor in the regulation of the population density of the European corn borer in Delaware.