Effects of a Bulking Agent on the Protein:Carbohydrate Ratio, Bioconversion, and Cost-effectiveness of a Larval Diet for Anastrepha ludens (Diptera: Tephritidae).

Although the bulking agent is categorized as 'inert', it could modify protein bioavailability and nutritional quality. In this study, the main goal was to determine if the bulking agent modified the protein:carbohydrate (P:C) ratio and bioconversion from diet biomass to larval biomass of Anastrepha ludens. The diet was altered only by modifying the type of bulking agent (corncob powder, coconut fiber, carrot fiber, oatmeal) added without changing the composition and concentration of the other components in the formulation. This allowed reclassification of the food matrices according to P:C ratios of 1:30, 1:35, 1:64, and 1:93. A food matrix with a high P:C ratio promoted a high protein and carbohydrate content in the larval hemolymph and immediately influenced the life-history traits of the larva or delayed them in the adult. The present study indicated a positive relationship between the P:G+T (glucose+trehalose) ratio in the larval hemolymph and the P:C ratio in the larval diet. Our results highlight the importance of including the optimum and real P:C ratio in whole fresh larval diets, since considering only the theoretical concentration of the formulation is not enough to understand the variation in key life-history traits. In addition, the bioconversion index should be included as an indicator of the efficacy of larval diets for mass rearing insects. A diet with high cost-effectiveness should be evaluated by taking into account flying flies as the end product of the mass rearing process to enhance operational SIT programs.

Effect of larval nutrition on the hemolymph protein composition during metamorphosis of Anastrepha obliqua.

Few studies have focused on how nutrition affects the bioavailability and investment of protein during the metamorphosis of tephritids. Our study allowed us to observe how the type and particle size of the bulking agent affected the protein composition in the hemolymph of the larva and adult of Anastrepha obliqua. Results indicated that, true protein bioavailability and protein profile was greatly modified by the bulking agent and its particle size. The physical structure of the food matrix affected the content of crude fiber (F), crude protein (P), F/P ratio, non-protein nitrogen, ammoniacal nitrogen, and α-amylase and trypsin inhibitors. Results from SDS-PAGE revealed 45 fractions with well-defined bands ranging from ~28 to ~401 kDa in larvae and adults, we found the main differences between the samples from different food matrices within the 75-100 kDa range. Hemolymph of adults from the coarse coconut fiber food matrix treatment showed a single band with a molecular weight close to 250 kDa, probably associated with a storage protein such as lipophorins. The food matrix with a coarse bulking agent had a high concentration of ammoniacal nitrogen, suggesting high microbial activity. In conclusion, the particle size of the bulking agent of the food matrix changes the bioavailability of protein in hemolymph in the adult regardless of the total concentration of protein. Also, when the particle size of the bulking agent favored the F/P ratio, higher larval density resulted in higher individual larval weight, larval yield, and adult emergence.

Big particles, best nutrition? Absorption and excretion of protein by Anastrepha obliqua larvae (Diptera: Tephritidae).

For purposes of mass-rearing fruit flies, nutrient intake through artificial diets is a challenge, artificial food content and processing should promote sufficient absorption and availability to ensure fly fitness. Bulking agents play an essential role in creating a quality diet, but its physical characteristics, such as particle size, may establish a better microenvironment for feeding and development. Currently, there is a lack of information about protein metabolism in mass-reared fruit flies. Therefore, we evaluated whether the particle size of the bulking agent affects the absorption and excretion of the proteins, as well as their effect on the life-history traits of Anastrepha obliqua. We determined the protein content of hemolymph and feces, as well as the presence of nitrogen end-products as indicators of their level of absorption in a diet elaborated with coarse and fine corn cob particles as a bulking agent. The bromatological composition showed that coarse particles increased the bioavailability and content of crude, digestible, and soluble protein for the diet and hemolymph protein of larvae alike. We found an inverse relationship between the protein content of the hemolymph and feces of the larvae. Ammonium was determined to be a product of the catabolism of proteins. Also, A. obliqua improved its development (yield and pupal weight) and fitness (adult emergence and flight ability) when larvae were reared on a coarse particle diet. In conclusion, a diet elaborated with a coarse bulking agent features increased protein bioavailability and nutritional quality, which, in turn, increases the life-history traits of A. obliqua.

A Novel, Low-Cost Coconut Fiber Larval Diet for Mass Rearing Anastrepha (Diptera: Tephritidae).

Mass rearing fruit flies of the genus Anastrepha for the sterile insect technique involves the use of artificial larval diets that commonly contain corn cob powder as a bulking agent. Corn cob powder varies in quality, and larval diets that contain it can be reaching at high temperatures (>34°C), which subsequently has a negative effect on pupal weight and adult survival. In addition, corn cob powder is susceptible to contamination by mycotoxins, which can inhibit larval development and cause high larval mortality. The objective of this work was to develop a low-cost artificial larval diet for mass rearing Anastrepha spp. fruit flies using coconut fiber, a nonconventional bulking agent, and to evaluate its effects on the quality parameters for A. ludens wild-type, A. ludens Tap-7 GS-strain, A. obliqua, A. serpentina, and A. striata. The coconut fiber diet resulted in an increase in the larval and pupal weight of A. ludens Tap-7 GS-strain and A. obliqua, an increase in the larval weight of A. ludens wild-type, an increase in the flight ability of A. obliqua and A. serpentina and an increase in adult eclosion in A. ludens Tap-7 GS-strain. The coconut fiber diet resulted in increased production and quality of the mass-reared flies, reduced the cost of the diet by 15 and 20% for A. ludens and A. obliqua, respectively, and led to further cost savings through reduced labor processes.