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Abstract |
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Heitland, W. & H. Pschorn-Walcher (2005): Biology and parasitoids of the peculiar alder sawfly, Platycampus luridiventris (Fallen) (Insecta: Hymenoptera, Tenthredinidae). Senckenbergiana biologica 85(2): 1-17. |
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Platycampus luridiventris (Fall?n 1808) is an outsider among the European sawflies, characterized by crepuscular, sluggish, wood-louse shaped larvae (Fig. 1) with an unusually long feeding period, and by an impoverished complex of larval parasitoids. The biology and parasitism of this nematine species has been studied between 1986 and 1989 in Schleswig-Holstein, with additional samples from western and southern Germany, Austria and Switzerland. Three foodplant races have been identified, specific to Alnus glutinosa, A. incana, and A. viridis, respectively (Heitland & Pschorn-Walcher 1992a). The univoltine life cycle of the species is as follows (Fig. 4): Adults are on the wing from May to mid-June. Oviposition into the leaf stalk or the mid-rib, up to 3 eggs per leaf. Embryonic development in the field in 3 to 4 weeks. Males with 5, females with 6 instars; larvae are solitary and almost sedentary on the underside of a leaf. Young larvae make shot holes, older larvae punch holes. Feeding is restricted to a total of 3 to 4 hours per day, mostly at dawn and dusk (Fig. 2), with long resting phases in an angle between mid-rib and a side-vein. Total period of feeding around 2 months in the laboratory (Fig. 3); under field conditions 3 months in the male and 2 to 3 weeks longer in female larvae (i.e. from late June to late September/mid-October). Hibernation as cocooned eonymphs in the soil; pupation in April. Pupal stage lasts about 2 to 4 weeks; adults appear in May-June. A total of 7 species of larval parasites have been reared: 6 ichneumonids and 1 tachinid (Tab. 1). Their biology is briefly described. Remarkable are the high rates of superparasitism in Hypamblys albopictus (Heitland & Pschorn-Walcher 1992b) as well as the immigration of the first instar larvae of Olesicampe vexata into the head capsule of their hosts, possibly in order to avoid hyperparasitism by Mesochorus or competition with other parasitoids in cases of multiple parasitism. Rates of parasitism were high in all regions and years; around Kiel between 40 and 70 percent (Fig. 7, 8), in the other regions between 30 and 60 percent (Fig. 9, 10). Of special interest is the low species diversity of the parasitoid complex of P. luridiventris (only 7 species of larval parasites compared with, on average, 11 to 12 species in other nematine hosts with free-living larvae). The absence of several species of typical sawfly parasitoids (e.g. Tryphoninae) in the parasitoid list from Platycampus is probably due to the aberrant and highly cryptic form and behaviour of the host larvae. Finally, the implications of the life-cycle strategy of this peculiar alder sawfly are briefly discussed. |
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Keywords: Platycampus luridiventris, sawflies, life-cycle, parasitoids. |
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modified: wh
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