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United States Department of Agriculture

Agricultural Research Service

Research Project: DEVELOPMENT OF ADVANCED TECHNOLOGIES FOR THE SCREWWORM ERADICATION PROGRAM

Location: Screwworm Research

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

Authors
item CHAUDHURY, MUHAMMAD
item SKODA, STEVEN

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 18, 2008
Publication Date: April 1, 2009
Citation: Chaudhury, M.F., Skoda, S.R. 2009. Diet pH, and viscosity affect development and survival of screwworm larvae (Diptera:Calliphoridae). Journal of Economic Entomology. 102(2):799-803.

Interpretive Summary: Eradication programs for the new world screwworm using the sterile insect technique depend on successful mass rearing of the insect. We studied the pH and viscosity of the standard diet used to rear immatures and evaluated the effects on larval development and survival to determine if manipulating these characteristics improved the yield of screwworms. In the pH studies, gel-based and cellulose fiber-based diets were used. The standard gel-based diet had normal initial pH (6.5) lower than the standard cellulose fiber-based diet (6.8). These values gradually decreased as the larvae grew in the media, probably due to the accumulation of the acidic metabolic waste. Diets were also formulated with higher than normal initial pH (7.5) and lower than normal initial pH (4.0). Diets with an initial pH at 7.5 produced significantly larger and greater number of insects while diets with initial pH of 4.0 produced significantly smaller and lower numbers of insects when compared to the standard diets. The effects of viscosity were studied using only cellulose fiber-based diet at six different initial viscosity levels ranging from 2000 to 7000 cP. The viscosity level of the diet increased as larval growth progressed due to gradual loss of moisture from the diet. Diet viscosity levels of 4000 and 5000 cP proved superior for larval development showing significantly higher yield and size. It is recommended that for mass rearing the cellulose fiber-based diet should be formulated to give an initial viscosity reading of 4000-5000 cP for normal growth of insects. Further study is needed before adoption of a diet formulated at a higher initial pH, such as 7.5, to determine the economic as well as biological advantages in mass rearing of screwworms.

Technical Abstract: The effects of dietary pH and viscosity on larval development of the new world screwworms, Cochliomyia hominivorax (Coquerel), were studied in the laboratory using standard rearing procedures for screwworms. The effects of pH were studied in two different screwworm diets – a gelled-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 possibly due to the accumulation of acidic metabolic waste. Diets were also formulated with higher than normal initial pH (7.5) and lower than normal initial pH (4.0). Diets with higher initial pH produced a slightly larger and greater number of pupae; differences were significant when compared with those obtained from the standard diet. The diets with lower than normal initial pH produced significantly smaller and lower numbers of pupae compared to those produced by the standard diets. The effects of viscosity were studied using the cellulose fiber-based diet at six different initial viscosity levels ranging from 2000 to 7000 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 4000 and 5000 cP proved superior for larval development showing significantly higher yield and larger pupae when compared with those obtained from diets with initial viscosities of 2000-3000 or 6000-7000 cP. It is recommended that the cellulose fiber-based diet used for mass rearing should be formulated to give an initial viscosity reading of 4000-5000 cP for normal larval growth and development. Adoption of a diet formulated to provide a higher initial pH such as 7.5 for the mass rearing of screwworm may produce better quality insects and may prove economical.

Last Modified: 9/10/2014
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