Submitted to: Journal of American Society for Mass Spectrometry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 23, 1997
Publication Date: N/A
Interpretive Summary: Parasitic wasps are an important method of biologically-based control of insect pests, and may provide an alternative to the use of pesticides. Several wasps currently used for the control of filth flies are members of the genus Muscidifurax. These small wasps do not sting or bite humans; moreover, they are host-specific and attack only fly pupae. Correct identification of these wasps using presently available methods is difficult. Seeking a simple and accurate method for identifying the wasps, scientists at the USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology have analyzed the hydrocarbon compounds present in surface cuticle of the wasps using gas chromatography and mass spectrometry techniques. The results showed that the patterns of observed hydrocarbons in all four members of the genus are similar and that all species, and sexes within species, can be differentiated by the abundance and identity of the hydrocarbons. Both females and males contain unique and rare hydrocarbons and can be distinguished based on the methyl-branch locations of the hydrocarbons. This method of wasp identification will enable detection of cross-contamination of species in laboratory colonies, before wasps are released in the field, and will be useful for entomologists, scientists, and companies concerned with quality control in the production of wasp parasites.
Technical Abstract: Parasitic Hymenoptera can be difficult to identify by conventional taxonomic techniques. Examination of the cuticular hydrocarbons (CHCs) provides a basis for chemotaxonomic differentiation, which may lead to the discovery of pheromones, and can be a means of examining colonies for species cross-contamination. The parasitic wasps examined were Muscidifurax raptor, M. zaraptor, M. uniraptor, and the gregarious form of M. raptorellus. Species within the genus Muscidifurax, as well as the sex, can clearly be differentiated by examining the gas chromatograms of the CHCs. Identification of the alkanes by mass spectrometry shows similar 11-methylene interrupted dimethylalkanes and 3/7-methylene interrupted trimethylalkanes for all members of the genus except M. uniraptor. Methylalkanes with this interruption pattern are rare compared to those found on insects reported in the literature, but is found in significant amounts on these insects. Additionally, sexual dimorphism is observed in long chain alkanes (C21-C39) present on male and female cuticular surfaces for these species. Females tend to have methyl branches located externally on the carbon chain for dimethyl-, trimethyl-, and tetramethylalkanes, whereas males tend to have dimethyl- and trimethylalkanes located internally on the hydrocarbon backbone chains. Mass spectra of novel and rare methyl branched compounds identified on these parasitoids are presented.