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

Published online by Cambridge University Press:  09 March 2007

H. Barari
Affiliation:
Plant and Invertebrate Ecology Division, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK
A.W. Ferguson*
Affiliation:
Plant and Invertebrate Ecology Division, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK
R.W. Piper
Affiliation:
Plant and Invertebrate Ecology Division, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK
E. Smith
Affiliation:
Plant and Invertebrate Ecology Division, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK
D.L.J. Quicke
Affiliation:
Division of Biology and NERC Centre for Population Biology, Imperial College London, Silwood Park Campus, Ascot, Berkshire, SL5 7PY, UK, and Department of Entomology, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK
I.H. Williams
Affiliation:
Plant and Invertebrate Ecology Division, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK
*
*Fax: +44 (0)1582 760981 E-mail: andrew.ferguson@bbsrc.ac.uk

Abstract

Tersilochus obscurator Aubert and Tersilochus microgaster (Szépligeti) are larval endoparasitoids of economically-important stem-mining pests of winter oilseed rape (Brassica napus L.) in Europe. They are difficult to separate morphologically. Their hosts are Ceutorhynchus pallidactylus (Marsham) and Psylliodes chrysocephala Linnaeus, 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 from C. pallidactylus, 20 reared from P. chrysocephala and individuals from two outgroups, Tersilochus heterocerus Thomson and Phradis interstitialis Thomson. Distinct and invariable COI sequences corresponded exclusively to each parasitoid group, confirming that T. obscurator and T. microgaster are 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, adult T. microgaster emerging from winter diapause by 29 March 2000, T. obscurator emerging between 12 April and 24 May 2000. The value of molecular techniques in the identification of closely-related parasitoid species is discussed.

Information

Type
Research Article
Copyright
Copyright © Cambridge University Press 2005

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