SUMMARYThe egg parasitoid Trissolcus basalis (Wollaston) (Hymenoptera:Scelionidae) responded to synomones emitted by leguminous plants induced by feeding and oviposition activity of the bug Nezara viridula (L.)(Heteroptera: Pentatomidae). This was shown by laboratory bioassays using a Y-tube olfactometer. Broad bean leaves (Vicia faba L.) damaged by feeding activity of N. viridula and on which host egg mass had been laid produced synomones that attracted T. basalis. By contrast,undamaged leaves or feeding-damaged leaves without eggs did not attract wasp females. French bean plants (Phaseolus vulgaris L.) also emitted attractive synomones when they were damaged by host feeding and carrying egg masses. Thus, release of feeding- and oviposition-induced synomones does not seem to be plant-specific. Synomone production was shown to be a systemically induced plant physiological response to feeding damage and oviposition. Also,parts of the plant that were left undamaged and did not carry host eggs emitted attractive synomones when other parts of the plant were damaged by feeding and carrying eggs. Furthermore, wasps were not attracted by N. viridula egg masses offered alone or combined with damaged broad bean leaves. Thus, the attractiveness of feeding-damaged leaves carrying eggs is due to induction by feeding and oviposition rather than due to a combined effect of attractive volatiles released from eggs and damaged leaves. The production of synomones was influenced by the age of the host egg mass,because feeding-damaged leaves bearing egg masses attracted the parasitoid until the eggs were ∼72-96 h old but not once the larvae had hatched from the eggs (∼120 h old). These results show that annual plants are able to produce synomones as a consequence of feeding and egg mass oviposition by a sucking insect.

The eggs of the southern green stink bug, Nezara viridula (L.) (Hemiptera: Pentatomidae), are successfully attacked by Trissolcus basalis (Woll.) (Hymenoptera: Scelionidae) and are recognized as hosts by a secretion applied to the egg chorion. This secretion is produced by the follicular cells in the proximal region of the ovanole of the female pentatomid and functions as an adhesive for attaching the eggs to the oviposition substrate. The adhesive and kairomone activity could be partially removed with water. This water extract elicited host recognition behaviour in T. basalis when applied to glass beads which stuck together as the extract dried. The adhesive and kairomonal activity was removed completely with acetone since acetone-washed host eggs were not recognized by T. basalis. Application of the acetone extract to glass beads stimulated ovipositional probes by T. basalis. The adhesive appeared to be composed of a mucopolysaccharide-protein complex.

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In parasitic wasps, various kinds of antennal plates have been interpreted as olfactory organs due to the presence of numerous pores. However, on the basis of ultrastructural investigations, some of these multiporous plates were revealed as being release sites of exocrine glands while others were postulated to have a gustatory function. Such sensilla, present only on female antennae, show unique features, found exclusively in Platygastroidea, with some differences between Scelionidae and Platygastridae. The cuticular apparatus consists of a short basiconic shaft with an apical multiporous area, the pores of which are covered by movable structures. The cellular components are made up of a remarkable number of sensory neurons, from 200 to 220, and an undefined number of sheath cells. These multiporous sensilla have tubular accessory glands that release their secretion through the socket sensillum only in scelionids. These morphological characters, combined with behavioral observations, strongly suggest a gustatory function, although electrophysiological studies are still needed to confirm this. A new terminology for antennal multiporous plates is discussed in relation to their different functions.

Colazza et al., 2004a;Colazza et al., 2004b).The egg parasitoids might also respond to short-range induced synomones that are perceived after they have alighted on the plant. Oviposition by Pieris brassicae L. (Lepidoptera: Pieridae) on Brussels sprouts (Brassica oleracea var. gemmifera) and on Arabidopsis thaliana induces changes in the chemistry of the leaf Accepted 24 August 2010 SUMMARY Oviposition-induced plant synomones are semiochemical cues used by egg parasitoids during host selection, and are therefore considered important elements of plant defence. In this paper we show that, in the tritrophic system Brassica oleracea-Murgantia histrionica-Trissolcus brochymenae, the latter responded in a closed arena and in a static olfactometer to induced chemicals that are perceived from a very short range and after parasitoid contact with the leaf surface opposite the treated surface. An additive or synergistic effect due to (1) egg deposition, (2) feeding punctures and (3) chemical footprints of M. histrionica was observed. When all three phases were present, the parasitoid reacted to the induced synomone locally on the treated leaf area, at a close distance to the treated area, and on the leaf above the treated one, showing that there is also a systemic effect. When plants with host footprints combined with feeding punctures or with oviposition were tested, responses were obtained both locally and at a close distance, whereas in the remaining assays only local responses were observed. Induction time was less than 24h, whereas signal duration was apparently related to the suitability of the host eggs, as parasitoids did not respond to plants carrying old or hatched eggs. These oviposition-induced short-range plant synomones might have an important role in the host location process after parasitoid landing on the plant, in different combinations with the host kairomones involved in the system studied here.