The effects of pathogens, used singularly or synergistically with other pathogens on the European corn borer larvae, Ostrinia nubilalis (Hubner), were studied. Pathogens used in this research were Perezia fumiferananae, Nosema disstriae, Nosema bombycis, Bacillus thuringiensis, and Beauveria bassiana. The egg masses were dipped into a vial containing a suspension of a single pathogenic species or combination of two pathogenic species. The egg masses were then incubated and hatched in a growth chamber with a temperature of 29°C, a relative humidity of 639, and constant light conditions. Observations were made concerning the mortality rates of each pathogen group.It was observed that the known pathogens, Bacillus thuringiensis, and Beauveria bassiana, caused high mortality rates in the corn borer larvae and could serve as effective biological controls. The Microsporidia, Perezia,fumiferanae, Nosema disstriae, and Nosema bombycis caused low mortality rates in corn borer larvae and therefore would not be considered as effective biological control agents for the European corn borer.The mortality rate for Bacillus thuringiensis treated larvae or Beauveria bassiana treated larvae, used in combination with other Microsporidia was not as high as when Bacillus thuringiensis,or Beauveria bassiana was used singularly. There may have been some interference or antagonism between the two combined pathogens, whether these pathogens be fungi, bacteria, or microsporidia.

The use of Clostridium species as possible pathogens of the European corn borer, Ostrinia nubilalis (Hubner) was arrived at by using screening criteria derived from studying the environment of the insect mid-gut and correlating these criteria to known physiological factors of bacteria. European corn borer larvae were treated by placing one drop of bacterial suspension on a corn borer egg mass. The newly-hatched larvae were then transferred to sterile, individual vials with synthetic food medium and observed daily. Clostridium putrefaciens (McBryde) treated larvae showed a significant reduction in hatching, slowed growth rate and a mortality of 50%.

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