Abstract
About 25% of 63 microorganisms known to be pathogenic to insects (7 of 38 viruses, 5 of 8 bacteria, 2 of 6 fungi, 1 of 11 protozoans) were sufficiently active (induced greater than 30% mortality) against larvae of Agrotis ipsilon (Hufnagel) to warrant additional testing to obtain an estimated LC50. The LC50 for the protozoan, Vairimorpha necatrix (Kramer) was 68 spores/mm2 Nomuraea rileyi (Farlow) Samson and Metarrhizium anisopliae (Metchnikoff) Sorokin, both fungi, had LC50,s of 219 and 807 conidia/mm2, respectively. The LC50 for viruses ranged from 260 inclusion bodies/mm2 for the nucleopolyhedrosis virus (NPV) of Mamestra brassicae (L.) to 7263 inclusion bodies/mm2 for the NPV of Pseudopluisa includens (Walker). The LC50 for 5 preparations of the bacterium Bacillus thuringiensis Berliner ranged from 7.3 to 55.9 ng/mm2