Diet pH, and viscosity affect development and survival of screwworm larvae (Diptera: Calliphoridae)

The effects of dietary pH and viscosity on larval development of the New World screwworm, Cochliomyia hominivorax (Coquerel) (Diptera: Calliphoridae), were studied in the laboratory using a gel-based and a cellulose fiber-based media. The mean initial pH of the standard gelled diet was lower (6.5 +/- 0.3) than that of the standard cellulose fiber-based diet (6.8 +/- 0.6). As larval development progressed, these values decreased to below 6.0 possibly due to the accumulation of acidic metabolic waste. Diets formulated with higher initial pH (7.5) produced a slightly larger and greater number of pupae compared with those for untreated standard diets. The diets with lower than normal initial pH (4.0) produced significantly smaller and lower numbers of pupae compared with those produced by the untreated standard diets. The effects of viscosity were studied using the cellulose fiber-based diet at six different initial viscosity levels ranging from 2,000 to 7,000 cP. The viscosity level of the diet increased as the larval development progressed due to gradual loss of moisture from the diet. The diet viscosity levels of 4,000 and 5,000 cP proved superior for larval development showing significantly higher yield and larger pupae compared with those obtained from diets with initial viscosities of 2,000-3,000 or 6,000-7,000 cP. The cellulose fiber-based diet used for mass rearing should be formulated to an initial viscosity reading of 4,000-5,000 cP for optimal larval growth and development. Adoption of a diet formulated to provide a higher initial pH such as 7.5 may produce better quality insects.