Host Behavioural Manipulation of Spiders by Ichneumonid Wasps

Abstract

Modified webs constructed by spiders parasitized by Ichneumonid wasps were first mentioned in literature in 1771. These initial observations were restricted to the description of the cocoon web spun by an unidentified spider species presenting a cocoon attached. Only in the year 2000 was the subject intensively studied in another host/parasitoid system. The interaction between Leucauge argyra (Tetragnathidae) and Hymenoepimecis argyraphaga (Ichneumonidae) was carefully described by W. G. Eberhard in Costa Rica. Web modifications, in this case, are even more extensive than those previously recorded. Cocoon webs spun by L. argyra are composed of just a few strong lines. Spirals are absent, and the cocoon remains suspended attached to the hub of the structure. From these studies up to now, several other cases have been described in the Neotropics. The initial doubt about the generality of host manipulation involving the Polysphincta genus-group was solved, but many questions arise from the subsequent studies. We still know almost nothing about the mechanisms involved in manipulation, for example. Recent studies suggest that it involves the injection of some substance by the parasitoid onto its host because the removal of the attached larva leads to a restoration of the original web patterns. Another interesting aspect is the investigation of how the structure of normal webs affects the design of cocoon webs. Finally, it is important to demonstrate that specific alterations in normal webs result in benefits to the manipulative wasp. The objectives of this chapter are to present an overview of recent discoveries involving these interactions, a brief historical summary of the researching efforts in the Neotropical region, and perspectives for future studies.