Oviposition behavior of Zatypota albicoxa (Hymenoptera, Ichneumonidae), an ectoparasitoid of Achaearanea tepidariorum (Araneae, Theridiidae)

Abstract

Oviposition behavior of Zatypota albicoxa (Walker) is described. This wasp parasitizes the house spider Achaearanea tepidariorum (Koch), which weaves irregular, three-dimensional webs. Based on field observations, two modes of oviposition behavior were recognized. In one, the wasp hung on the web, pulling the thread with its fore leg, until the spider lifted it up (ambush-style). In the other mode, the wasp climbed the web (climbing-style). Under laboratory conditions in an aquarium, the wasp hung on the web in mid height of the gumfoot thread as in the former style, then flew toward unaware spider and paralyzed it. After paralyzing, the wasp usually rubbed the spider's abdomen with its ovipositor and tip of metasoma repeatedly at short intervals for several minutes. In all cases they adopted the same posture in which they grasped the spider abdomen with fore and mid legs during oviposition. As female wasps emerged from larger hosts and male wasps emerged from smaller ones, the ovipositing wasp apparently assesses the size of the spider and chooses whether to lay a fertilized or an unfertilized egg. In addition, it was confirmed that Z. albicoxa expelled the eggs not from the tip of the ovipositor but from the tip of its abdomen, as in other species of the Polysphincta group (e.g. Hymenoepimecis argyraphaga, Reclinervellus tuberculatus and Schizopyga circulator).

Lying on the dorsum: unique host-attacking behaviour of Zatypota albicoxa (Hymenoptera, Ichneumonidae)

“…In addition, we observed much behaviour perching on the web motionlessly apart from the gumfeet by the other three wasps (individuals A, B, and D) in the aquarium (alternative ambush style). Zatypota albicoxa thus also seems to avoid the gumfeet of the vertical threads in both modes because the climbing wasp would choose the non-sticky frame thread and the ambushing wasp perched between a host spider and gumfoot (Takasuka et al 2009;Takasuka 2009a, b, c;Fig. 1a-c).…”

“…Three of Fig. 1 Schematic diagram of attack styles adopted by Z. albicoxa (a-c were schematized by reference to Takasuka et al 2009). Star indicates where the attack occurs and three black circles lying at the far end of each vertical thread indicate gumfeet.…”

“…The female of Brachyzapus nikkoensis (Uchida), a parasitoid of Agelena silvatica Oliger (Agelenidae) forming a funnel web with a tunnel as a refuge but with no sticky masses, hovers over the funnel web, drops into it, and attacks the enticed spider at the moment of encounter (Iwata 1942;Matsumoto 2009). Takasuka et al (2009) observed a total of seven sequences of oviposition behaviour of Z. albicoxa and recognized two modes of attack, ambush and climbing styles, seemingly an adaptation to the host spider being in an irregular, three dimensional web (Fig. 1a-c).…”

“…About half of the prey items of P. tepidariorum are wingless insects, for example ants and isopods, whereas winged prey items are mainly dipterans, hemipterans, coleopterans, and winged ants (Tanaka 1989). Takasuka et al (2009) described two modes of oviposition behaviour in Z. albicoxa to attack host spiders in the irregular, three dimensional web of P. tepidariorum. In one, the wasp hangs on one of the vertical gumfoot threads between a host spider and gumfoot, pulling the thread with its fore leg until the spider lifts it up (ambush-style: Takasuka 2009a; Fig.…”

Biology, early stages and description of a new species of Adelognathus Holmgren (Hymenoptera: Ichneumonidae: Adelognathinae)

“…However, the egg not passing down the ovipositor appears to be typical of all groups of koinobiont ectoparasitoid Ichneumonidae so far observed. It is universal in the large subfamily Tryphoninae (Kasparyan 1973) and almost certainly Lycorininae (Coronado-Rivera et al 2004, Shaw 2004, in which only a non-embryonic part of the egg passes down the ovipositor with the bulk of the egg remaining external to it; and in the Polysphincta genus-group of the ephialtine Pimplinae the egg issues from the genital opening onto a pre-glued patch of the host integument (see Takasuka et al 2009 for a brief review of known occurrence) without involving the ovipositor, much as in Adelognathus. These groups of Ichneumonidae are by no means all close relatives (Quicke et al 2009, A.M.R.…”