Natural History And Larval Behavior Of The Parasitoid Zatypota Petronae (hymenoptera: Ichneumonidae)

—The koinobiont ectoparasitoid Zatypota petronae Gauld (Ichneumonidae) parasitizes medium-sized immatures of the cobweb spider Theridion evexum Keyserling (Theridiidae). Zatypota petronae apparently attacks the spider inside its retreat. An egg is glued on the antero-lateral dorsal section of the spider’s abdomen. First-instar larvae remain partially inside the egg chorion which is attached to the spider’s abdomen. In later instars, a layer of a brownish material (saddle), to which the 7 and 8 abdominal segments of the larva adhere ventrally, anchors the larva to the spider. In the last instar the saddle includes the egg chorion and the shed exoskeletons of previous instars. A row of retractile, dorsal protuberances, crowned with hooklets, is present on abdominal segments 1 to 8 of the final-instar larva. The larva uses the hooklets to grab silk lines of the retreat of the spider’s web. Hanging on the spider’s web the larva kills the spider and sucks out its body tissues. Then the larva pushes vigorously laterally with its head against the spider’s corpse, and alternately presses the corpse against the saddle. These movements, in combination with peristaltic movements, free the larva from the saddle that falls to the ground with the dead spider. The larva then constructs its pupal cocoon. Prior to cocoon construction, the larva induces the spider to reinforce the retreat by adding more threads. Parasitism rate and host behavior are also described. __________________________________________________________________________________________________________________________________________________________ The polysphinctine pimplines are koinobiont ectoparasitoids of spiders in several families (Nielsen 1923, 1932, Fincke et al. 1990, Hanson and Gauld 1995, Gauld et al. 1998). Nielsen (1923, 1932) described in detail the behavior of the larvae and hosts of several European polysphinctine species. The parasitism rates and life cycle of Hymenoepimecis robertsae Gauld on the neotropical tetragnathid Nephila clavipes (L.) was described by Fincke et al. (1990). However, larval behavior of neotropical polysphinctine wasps has been described in detail for only one species, H. argyraphaga Gauld on the tetragnatid Plesiometa argyra (Walker) (Eberhard 2000a, 2000b, 2001). Parasitoid wasps of the cosmopolitan speciose polysphinctine genus Zatypota Förster parasitize spiders in at least five families (Dictynidae, Agelenidae, Tetragnathidae, Araneidae and Theridiidae) (Shaw 1994, Gauld et al. 1998). In the neotropics the only two host records were Theridion species: T. contreras Levi for an unidentified Zatypota species (Jiménez 1987) and T. evexum Keyserling for Z. petronae Gauld (Barrantes and Weng in press). The larval behavior of Zatypota sp. (Jiménez 1987) differs in some aspects from that of European polysphinctine species (Nielsen 1923, 1932) and H. argyraphaga (Eberhard 2000a). The larva of Zatypota sp. was said to hold on to the spider by biting the dorsum or sides of the anterior section of the spider’s abdomen. This description is likely wrong as detailed descriptions of the behavior of the larva of Z. albicoxa Journal of Hymenoptera Research hyre-16-02-09.3d 25/7/07 18:04:53 327 * Current address: Department of Entomology, Kansas State University, Manhattan, Kansas, USA 1 Author for correspondence J. HYM. RES. Vol. 16(2), 2007, pp. 327–336