DISCRIMINATION BY HYSSOPUS THYMUS (HYMENOPTERA: EULOPHIDAE) AGAINST ORGILUS OBSCURATOR (HYMENOPTERA: BRACONIDAE), AN INTERNAL PARASITE OF THE EUROPEAN PINE SHOOT MOTH, RHYACIONIA BUOLIANA (LEPIDOPTERA: OLETHREUTIDAE)

Abstract When given a choice of large, unparasitised sixth-instar larvae of the European pine shoot moth, Rhyacionia buoliana, and small sixth instars containing developing Orgilus obscurator, Hyssopus thymus selected the former. This discrimination does not exist when the host larvae are in the third or fourth instars. The size of the contained O. obscurator larva is related to this change in behaviour. H. thymus shows no cleptoparasitic tendencies and is recommended as a safe candidate for introduction where O. obscurator exists.

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