Growth of a pupal ectoparasitoid, Diapetimorphaintroita, on an artificial diet: stimulation of growth rate by a lipid extract from host pupae

Abstract

An artificial diet used to rear the ectoparasitoid,Diapetimorpha introita, was supplemented withlipids extracted from pupae of the host, Spodoptera frugiperda (J. E. Smith). The diet alsowas sequentially supplemented with four fatty acids(arachidonic, linoleic, γ-linolenic and oleic),flax oil and Lipid Concentrate^® which is used in cellculture. Pupae were homogenized and extracted withchloroform:methanol (2:1 v/v) and after drying downthe chloroform and methanol phases separately, theresidues from each solvent phase were evaluated in theartificial diet. Growth-promoting activity wasobserved in the chloroform phase containing lipids. Diet supplemented with lipid stored at −80 °C, andinsects reared on diet with fresh 1× and 2× extractsdeveloped significantly faster than those reared onthe artificial diet but slower than those reared onhost pupae. The fresh 1× and the 2× extracts alsoenhanced the average weight of the males and females,respectively. Storing the lipids at −20 °C resultedin a loss of activity. A lipid extract from Galleria mellonella pupae increased the averageweight of male and females but did not increase theirdevelopmental rate. Adult emergence was not improvedby any of the dietary additives. None of thecommercial lipid treatments significantly reduceddevelopmental time; however, the γ-linolenicacid-supplemented diet significantly increased theaverage weight of females. TLC analyses of the lipidextract from S. frugiperda revealed lipidsrepresenting four classes of neutral lipids in theextract: triolein, cholesterol, diacylglycerol, andphospholipid. Data from this study indicate thatoptimization and successful utilization of anartificial diet to rear D. introita depends onidentification of host factors required by theparasitic for growth and development.