Discrimination between Asian populations of the parasitoid wasp Ganaspis cf. brasiliensis using a simple MALDI-TOF MS-based method for use with insects

The fruit fly Drosophila suzukii has recently become an invasive pest insect of significant economic impact in Europe and the USA. In contrast to other Drosophila species, D. suzukii is able to infest intact fruit by means of a saw-like ovipositor, which allows females to deposit eggs beneath the skin of the fruit. Classical biological control using the parasitoid wasp Ganaspis cf. brasiliensis is currently being researched as an environmentally sustainable option for the control of D. suzukii. In particular, the host specificity of this parasitoid has been assessed for populations from different regions in China and Japan. In order to study the relationship between the differences in specificity and molecular variations, we have adapted a matrix-assisted laser-desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS)-based method, originally developed for use with plant material, to discriminate between example populations of G. cf. brasiliensis. We have employed a combination of principal component analysis and blind-tested comparison between reference sample MALDI-TOF MS spectra and test sample spectra to discriminate, on the basis of the acid-soluble insect protein spectra generated, between four populations of G. cf. brasiliensis (originally collected from Tokyo and Hasuike in Japan and Dali and Ximing in China). MALDI-TOF MS analysis is able to discriminate with 100% accuracy between populations G. cf. brasiliensis. The Chinese populations were observed to be similar, but the Tokyo population is slightly different and the Hasuike population is significantly different from the other populations. The Tokyo population appears more closely related to the Chinese populations than the Hasuike population, even though both originate from Japan.