ABSTRACT
Assuring the quality of artificial diet ingredients is the first step to ensure the mass production of quality insects for the sterile insect technique (SIT). Ingredients used as a bulking agent for larval diets, such as corncob fractions, are vulnerable to chemical or microbiological contamination that can make the diet toxic to larvae. Traditional methods of physicochemical and microbiological testing of diet ingredients have been inefficient at guaranteeing the safety of ingredients, making quality assurance of the material a challenge. Thus, we developed a toxicological test to detect the presence of pathogenic bacteria and fungi and their mycotoxins. Sixteen batches were evaluated. Each batch was composed of 26 pallets containing 40 packages of corncob fractions of 20 kg each. The bacteria and fungi were isolated from a sample of 2.6 kg of corncob fractions per batch, which was obtained by sampling three packages per pallet to complete 100 g for each of the 26 pallets of a batch. The toxicological tests involved four steps: (1) identification of bacteria and fungi, (2) toxicological test for larval survival, (3) mycotoxin determination, and (4) effect of the incorporation of mycotoxin sequestrants on larval yield. The toxicological test of the corncob fractions allowed to classify a batch as 192acceptable or non-acceptable. A nonacceptable batch presented at least a colony of any these species: Morganella morganii, Serratia marcescens, Fusarium oxysporum, F. graminearum, or Aspergillus spp., or any of these mycotoxins: aflatoxin, fumonisin, ochratoxin, or T2-HT2. Fungi contamination by F. oxysporum, F. graminearum, and Aspergillus spp. caused high mortality either in single contaminations/alone or in association with the bacteria M. morganii or S. marcescens. The addition of Aflaban™ to a contaminated diet reduced the effects of mycotoxins and increased larval yield. A toxicological test should be included during quality control evaluations of diet ingredients to classify diets as acceptable or non-acceptable.
