Microbial Contamination in Spodoptera littoralis Nuclear Polyhedrosis Virus Produced in Insects in Egypt

Spodoptera littoralis nuclear polyhedrosis virus produced in Egypt, for use in field trials for the control of S. littoralis on cotton, was subject to microbiological examination to quantify microbial contamination. Bacteria were found to be present at 10(6)-10(9) colony-forming units/ml in virus suspensions containing 2.1 x 10(9) polyhedral inclusion bodies/ml. Batches were found to contain between 2 and 11 different species of contaminant microbes. No primary human pathogens of medical importance were found. The dominant species were fecal Streptococci and two Bacillus species, B. cereus and B. sphaericus. The Streptococci were derived from the normal gut flora found in healthy insects; the Bacillus species were common opportunistic saprophytes which gained access to the product by colonizing dead larvae and diet waste. Purification methods based on centrifugation were found to be ineffective in removing bacteria and improved methods of hygiene and harvesting appeared to be of more value in reducing contamination.