Preservation of an artificial diet for rearing the predator Orius laevigatus

The use of an artificial meat diet for Orius laevigatus lacking antimicrobial agents, resulted in rapid contamination of the medium especially by (unidentified) bacteria when stored in the rearing cages at 23 degrees C. Meat spoilage was detrimental for the insect and negatively affected the developmental parameters depending on the time between two feeding intervals. Two antibiotics (chortetracycline and gentamycin sulfate) were screened for their potential to extend the shelf life of the diet. The efficiency of the preservatives to control bacterial growth was tested by using a plate count method. Results showed that both agents were able to suppress growth of the bacteria in the diet but the sensitivity of the predator to 0.05% chlortetracycline was high: growth, survival rate and size of the insect were seriously affected by this antibiotic. When diet containing 0.05% gentamycin sulfate was left in the cages for 2 to 3 days, it yielded similar development to that on fresh antimicrobial-free diet. Gentamycin sulphate at a concentration of 0.05% can thus be considered as a safe antibiotic for O. laevigatus.