Submitted to: Biocontrol
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2000
Publication Date: 12/1/2000
Citation: Ferkovich, S.M., Shapiro, J.P., Carpenter, J.E. 2000. Growth of a pupal ectoparasitoid, Diapetimorpha introita (Ichneumonidae), on an artificial diet: stimulation of growth rate by a lipid extract from host pupae. Biocontrol. 45:401-413.
Interpretive Summary: Effective methods are needed to mass rear high quality beneficial insects that attack pest insects as an alternative to the use of environmentally hazardous pesticides. Diapetimorpha introita, a parasitoid that attacks pupae of the army worms, Spodoptera frugiperda and S. exigua, is a potential candidate for managing these pests, especially in area wide management programs. Scientists at the Center for Medical, Agricultural, and Veterinary Entomology, ARS, Gainesville, FL are developing an artificial diet for rearing the parasitoid, but improvements still are needed as developmental time, weight of adult wasps and fecundity were inferior compared to wasps reared on natural pupal hosts. They examined the potential of supplementing the artificial diet with fats extracted from the host to optimize the diet. A fat-extract taken from host pupae of S. frugiperda stimulated the developmental rate and increased the size of adult parasitoids. Commercial sources of lipids were tested but did not work as well as the insect host-derived lipids. These results suggest that future research should focus on isolating and identifying the active component of the lipid extract in order to find a substitute for the insect lipid(s) that can be added to the artificial diet. Improving the diet will allow production of D. introita in numbers that can be used to augment other biorational measures for control of beet and fall armyworm.
Technical Abstract: An artificial diet used to rear the ectoparasitoid Diapetimorpha introita was supplemented with lipids extracted from pupae of the host, Spodoptera frugiperda (J.E. Smith). The diet also was sequentially supplemented with four fatty acids (arachidonic, linoleic, y-linolenic and oleic), flax oil and Lipid Concentrate which is used in cell culture. Pupae were homogenized dand extracted with chloroform:methanol (2:1 v/v) and after drying down the chloroform and methanol phases separately, the residues from each solvent phase were evaluated in the artificial diet. Growth- promoting activity was observed in the chloroform phase containing lipids. Diet supplemented with lipid stored at -80 C, and insects reared on diet with fresh 1 X and 2 X extracts developed significantly faster than those reared on the artificial diet but slower than those reared on host pupae. The fresh 1X and the 2 X extracts also enhanced the average weight of the males and females, respectively. Storing the lipids at -20 C resulted in a loss of activity. A lipid extract from Galleria mellonella pupae increased the average weight of male and females but did not increase their developmental rate. Adult emergence was not improved by any of the dietary additives. None of the commercial lipid treatments significantly reduced developmental time; however, the y-linolenic acid-supplemented diet significantly increased the average weight of females. TLC analyses of the lipid extract from S. frugiperda revealed lipids representing four classes of neutral lipids in the extract: triolein, cholesterol, diacylglycerol, and phospholipid. Data from this study indicate that optimization and successful utilization of an artificial diet to rear D. introita depends on identification of host factors required by the parasitoid for growth and development.