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During the host location process, egg parasitoids can eavesdrop on chemical cues released from immature and adult hosts. These indirect host-related cues are highly detectable, but of low reliability because they lead egg parasitoid females to an area where oviposition is likely to occur rather then providing wasps with direct information on the presence of eggs and their location. In the host-parasitoid associations between true bugs and their scelionid egg parasitoids, female wasps perceive the chemical residues left by host adults walking on substrates as contact kairomones, displaying a characteristic arrestment posture. In this study, we demonstrated that epicuticular waxes of leaves of two vegetable crops, broad bean, Vicia faba, and collard greens, Brassica oleracea, mediate the foraging behavior of Trissolcus basalis (Wollaston) by adsorbing contact kairomones from adults of Nezara viridula (L.). Trissolcus basalis females showed no response when released on the adaxial leaf surface of broad bean or collard green plants with intact cuticular wax layers that had not been exposed to bugs, whereas wasps displayed the arrestment posture when intact leaves were contaminated by chemical residues from host females. Adaxial leaf surfaces that were dewaxed with an aqueous solution of gum arabic and afterwards contaminated by N. viridula females elicited no arrestment responses from wasp females. Similarly, leaves contaminated by host females and subsequently dewaxed did not elicit responses from female wasps. These findings reveal the important role of plant waxes in N. viridula - T. basalis semiochemical communication

Chemical footprints left behind by true bugs are perceived as contact kairomones by scelionid egg parasitoids. Female wasps encountering a contaminated artificial substrate display a characteristic arrestment posture, holding the body motionless and antennating the surface. In the system Nezara viridula (L.) and its egg parasitoid Trissolcus basalis (Wollaston), previous studies have shown that the kairomone mediating such behavior is part of N. viridula's cuticular hydrocarbons (CHC) and furthermore that the wasp's ability to discriminate host male and female footprints is mainly based on the presence/absence of nonadecane (nC(19)). In this study, the effect of epicuticular waxes of leaves of broad bean, Vicia faba, on wasp responses to footprints of N. viridula females were investigated. Approximately 20% of T. basalis females displayed an arrestment posture when released on the adaxial leaf surfaces of broad bean plants with intact wax layer and without host chemical contamination; whereas approximately 70% of wasps displayed the arrestment posture when intact leaves were contaminated by host female footprints. Adaxial leaf surfaces of broad bean plants dewaxed with an aqueous solution of gum arabic and afterwards contaminated by N. viridula females induced arrestment responses in about 10% of female wasps; the same percentage of arrestment (10%) was observed when the wasps were released on leaves contaminated by host females and subsequently dewaxed. The side of the polymer film that was appressed to the leaf surface, peeled from the contaminated leaves, induced an arrestment posture in about 95% of observed wasps. Scanning electron microscopy (SEM) revealed that the epicuticular waxes occurred as a film densely crystallized as irregularly shaped platelets with spherical granules randomly distributed. These findings demonstrated that epicuticular waxes of broad bean leaves can mediate the foraging behavior of T. basalis females by absorbing contact kairomones of the host.

Chemical footprints left behind by true bugs are perceived as a contact kairomones by scelionid egg parasitoids. In the system Nezara viridula and its egg parasitoid Trissolcus basalis, previous studies have shown that the kairomone mediating such behavior is part of N. viridula’s cuticular hydrocarbons. In this study, the effect of epicuticular waxes of leaves of broad bean, Vicia faba, on wasp response to footprints of N. viridula females are investigated. Plants with intact waxes layer were used (1) without host chemical contamination, or (2) contaminated by host female footprints. Mechanically de-waxed plants were tested (3) without host chemical contamination, or (4) de-waxed a few minutes after being contaminated, or (5) de-waxed about 30 min before being contaminated by host female footprints. And, finally, female wasps were tested on the side of the gum arabic film that had been appressed to (6) the adaxial leaf surface of plants without host chemical contamination, and (7) to plants contaminated by host footprints. Direct contact solid-phase microextraction of the adaxial leaf surface of broad bean plants analyzed by GC/MS showed that epicuticular waxes contained high concentrations of hydrocarbons and alcohols, and low concentrations of aldehydes and esters. Scanning electron microscopy revealed that the epicuticular waxes occurred as a film densely crystallized as irregularly shaped platelets with spherical granules randomly distributed. These findings demonstrated that epicuticular waxes of broad bean leaves can mediate the foraging behaviour of T. basalis females by absorbing host adult footprints contact kairomone.

La localizzazione dell’ospite nei parassitoidi oofagi è il risultato di un complesso comportamento di foraggiamento influenzato prevalentemente da stimoli di natura fisica e chimica. I segnali chimici (semiochimici) possono derivare dall’interazione tra la pianta e l’uovo ospite (sinomoni indotti dall’ovideposizione), dall’uovo tal quale (cairomoni diretti) e/o da stadi diversi da quello di uovo, come per esempio l’adulto (cairomoni indiretti). I sinomoni indotti con l’ovideposizione, capaci di richiamare i parassitoidi delle uova ancor prima che il fitofago possa causare danni, sono un efficace esempio del coinvolgimento “diretto” della pianta nel processo di localizzazione dell’ospite da parte dei parassitoidi oofagi. La pianta può inoltre influenzare “indirettamente” l’attività di ricerca di tali parassitoidi grazie alle proprie caratteristiche chimico-fisiche. Un valido esempio è offerto dal ruolo che possono svolgere le cere epicuticulari, molecole apolari (idrocarburi, chetoni, alcooli, aldeidi, esteri, acidi grassi etc.) che ricoprono la superficie delle parti aeree delle piante superiori. Le cere epicuticulari rappresentano un’interfaccia tra la pianta e l’esterno e svolgono importanti ruoli funzionali e fisiologici. In questa presentazione saranno passati in rassegna gli studi che riguardano l’influenza di tali cere sull’efficacia dei parassitoidi oofagi. Inoltre saranno forniti, per due sistemi tri-trofici, dati sperimentali sul ruolo che le cere hanno nell’influenzare la percezione dei sinomoni indotti dall’ovideposizione [Brassica oleracea L. var. sabauda - Murgantia histrionica Hahn - Trissolcus brochymenae (Ashmead)] e dei cairomoni di contatto rilasciati dagli adulti delle cimici [Vicia faba var. luz de otoño e Brassica oleracea L. var. marathon - Nezara viridula (L.) - Trissolcus basalis (Wollaston)] da parte dei loro principali parassitoidi oofagi. Le prove sono state condotte con biosaggi in vivo, mentre le cere epicuticulari sono state studiate morfologicamente, con l’ausilio di un microscopio elettronico a scansione (SEM), e chimicamente, mediante rimozione meccanica, estrazione in cloroformio o microestrazione in fase solida (SPME), e successiva analisi in cromatografia gassosa accoppiata alla spettrometria di massa (GC-MS). I risultati hanno permesso di evidenziare l’importante ruolo svolto dalle cere nel modulare il comportamento di foraggiamento dei parassitoidi, interferendo sul rilascio dei sinomoni indotti e adsorbendo i composti cairomonali prodotti dagli ospiti, svolgendo dunque una funzione “ponte” tra fitofago e antagonista. Nella discussione saranno analizzati i possibili contributi che queste conoscenze possono avere nel potenziare l’efficacia di programmi di controllo biologico mediante ooparassitoidi.

Chemical footprints left behind by true bugs act as contact kairomones inducing an arrestment response in scelionid egg parasitoids. Once in contact with contaminated substrates, female wasps display a characteristic arrestment posture followed by an increase of the host searching time. Previous studies were conducted on artificial substrates as filter papers, so that little is known about the effects of natural substrates on behavioural response by wasps. In field, the substrate where these interactions occur, i.e. the surface of plants, is covered by wax layers that can have a role in trophic interactions between insects. In this study, we investigated the influence of plant surfaces on absorbing chemical footprints of the true bug Nezara viridula (L.) and on influencing the host location behaviour of the scelionid Trissolcus basalis (Wollaston). Nezara viridula males and females were allowed to walk on leaves artificially dewaxed and leaves with intact superficial layers of three different plants, broad bean, sweet pepper and cabbage. Bioassays suggest that leaf waxes absorb chemical footprints of N. viridula, so that the response of T. basalis females was less pronounced on leaves where superficial waxes were removed using an aqueous solution of arabic gum. Furthermore, a chemical investigation was conducted on the polimer film peeled off from leaves contaminated by N. viridula. In conclusion, our findings demonstrated that surface of studied plants mediates interaction between N. viridula chemical footprints and T. basalis.

Role of oophagous parasitoids in the natural control of hazelnut bugs inducing the “cimiciato seeds” in Nebrodi Park (ME) Oophagous parasitoids of bugs collected on hazelnut cultivations and seasonal parasitism on eggs of Gonocerus acutengulatus (Goeze) were studied from 2004 to 2006 in the Nebrodi Park (ME). Samples of bug eggs were collected in three altitude areas, 300-590, 600-890 and 900-1100 m above sea level, and examined in laboratory. Parasitoid adults obtained from all eggs were identified. Parasitization levels, detected on G. acuteangulatus in all areas showed a similar trend with the most value on August. Significant regression between the total number of eggs and the number of parasitized eggs was found (R2=0.75). Parasitoid species detected were Anastatus bifasciatus (Geoffroy), Gryon muscaeformis (Nees), Telenomus viggiani Mineo and other three species not yet identified.