The separation of two hymenopteran parasitoids,Tersilochus obscuratorandTersilochus microgaster(Ichneumonidae), of stem-mining pests of winter oilseed rape using DNA, morphometric and ecological data

Abstract

AbstractTersilochus obscuratorAubert andTersilochus microgaster(Szépligeti) are larval endoparasitoids of economically-important stem-mining pests of winter oilseed rape (Brassica napusL.) in Europe. They are difficult to separate morphologically. Their hosts areCeutorhynchus pallidactylus(Marsham) andPsylliodes chrysocephalaLinnaeus, respectively. The parasitoids' taxonomic status, identification, host range and phenology were studied using genetic, morphometric and ecological data. The study used 527 female parasitoids from the UK and Germany, either field-collected in emergence traps or reared from field-collected host larvae. Two morphometric characters, the ovipositor sheath to first metasomal tergite ratio and the percentage of the mesopleuron spanned by the sternaulus, were measured. A 440 bp section of mitochondrial DNA cytochrome oxidase subunit I (COI) gene was sequenced from 35 parasitoids reared fromC. pallidactylus, 20 reared fromP. chrysocephalaand individuals from two outgroups,Tersilochus heterocerusThomson andPhradis interstitialisThomson. Distinct and invariable COI sequences corresponded exclusively to each parasitoid group, confirming thatT. obscuratorandT. microgasterare discrete species. Measurements of host-reared and COI-sequenced specimens indicated that the ranges of both morphometric characters overlapped between species. Using these ranges as criteria, all but 3.6% of UK specimens and 2% of German specimens were identifiable to species without reference to host or phenology. There were differences in emergence phenology in the UK, adultT. microgasteremerging from winter diapause by 29 March 2000,T. obscuratoremerging between 12 April and 24 May 2000. The value of molecular techniques in the identification of closely-related parasitoid species is discussed.