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During the host location process, parasitoids encounter and explore a great variety of volatile and contact semiochemicals from the host-plant complex. In the system Nezara viridula and its egg parasitoid Trissolcus basalis, when wasps land on a plant, they can taste chemical footprints left by walking adult hosts. These cues represent a set of indirect host-related contact kairomones that induce arrestment and motivated searching behavior, as they drive wasps in an area where there is a high probability of finding hosts but are not able to “promise” the presence of the suitable host stage. Patch time allocation is strongly modified by experience gained during foraging on host traces. In fact, when footprint exploitation is not followed by successful oviposition, wasps gradually lose their motivated searching and move back to a more general host searching behaviour. In this work we investigated the effects of exogenous and exogenous factors that can affect the host location behaviour of T. basalis. Trials were recorded and analyzed with the aid of a video tracking and motion analysis system. The potential significance of these results in the host location behavior of T. basalis is discussed.

During the host location process, parasitoids encounter and explore a great variety of volatile and contact semiochemicals from the host-plant complex. In the system Nezara viridula and its egg parasitoid Trissolcus basalis, when wasps land on a plant, they can taste chemical footprints left by walking adult hosts. These cues represent a set of indirect host-related contact kairomones that induce arrestment and motivated searching behavior, as they drive wasps in an area where there is a high probability of finding hosts but are not able to “promise” the presence of the suitable host stage. Patch time allocation is strongly modified by experience gained during foraging on host traces. In fact, when footprint exploitation is not followed by successful oviposition, wasps gradually lose their motivated searching and move back to a more general host searching behaviour. In this work we investigated the effects of four factors, age (3days-old vs 20days-old), conspecific crowding (isolated or not for 20 days), temperature (4°C vs 25°C) and feeding status (feeding or not for 2 days), on the patch-leaving behaviour of T. basalis. Bioassays were conducted on an open arena made by a filter paper sheet; in the middle, a circular area (4·cm diameter) was defined and exposed for 30·min to a single adult of N. viridula, while the surrounding area was left untreated. Trials were recorded and analyzed with the aid of a video tracking and motion analysis system. The potential significance of these results in the host location behavior of T. basalis is discussed.

In assessing successful biological control programs by parasitoids, the knowledge of important traits, such as the host finding capability, i.e. the ability to find host and food resources, play the key role. Moreover, parasitoids in their natural environment parasitoids deal with a variable mixtures of natural cues. Some chemical cues are used by the wasps to locate their hosts, some ones drive wasps to feeding resources. The parasitoid response to these cues can fluctuate according to biotic factors and abiotic condition. This dissertation focus in details on the role of two important tools, such as selective flowering plants as food resources to add within a crop area and the traces left behind by the hosts while moving on the plant used by parasitoids to locate their host. These tools are important in order to increase the natural enemy effectiveness and thus develop successful programmes of Conservation Biological Control.

International audience; Conservation biological control programs advocate the planting of flower strips alongside crops to improve the survival and effectiveness of parasitoids. Ideally, the provided food plants are highly attractive and benefit the targeted biocontrol agents without promoting pests or intraguild competition. Previous laboratory studies showed that Trissolcus basalis, an egg parasitoid of the stink bug Nezara viridula, is highly attracted to floral odors of buckwheat and that its nectar increases the wasp’s fecundity. In the field, T. basalis competes with the co-occurring parasitoid Ooencyrtus telenomicida for host eggs. Therefore, in the present study, we explored whether O. telenomicida shows similar attraction to buckwheat volatiles. We then carried out a 2-year field experiment to assess whether the laboratory-observed olfactory behaviors of both species are reflected in changed parasitism rates of stink bug eggs. Parasitism by naturally occurring egg parasitoids was measured in tomato plots with and without a margin of flowering buckwheat. Our results showed that, unlike T. basalis, O. telenomicida was repelled by the odor of buckwheat flowers. In both years, T. basalis found more egg batches and parasitized more stinkbug eggs when flower margins were present. Egg parasitism correlated positively with proximity to the buckwheat margin. In accordance with our prediction, egg parasitism by O. telenomicida occurred almost exclusively in the control plots and for a shorter period during the season. We conclude that buckwheat strips can influence intraguild competition and hypothesize that the effect was mediated by floral volatiles.

Chemical footprints deposited by herbivorous pentatomid host bugs hosts when walking on the plant are adsorbed by leaf surfaces and perceived as substrate borne semiochemicals by scelionid egg parasitoids during host selection process. They act as indirect host-related cues, as they are not able to “promise” to parasitoid females the presence of the suitable host stage, but they drive them in the areas where their hosts are potentially present. Once in contact with host chemical footprints, scelionid wasps evidence an innate arrestment response characterized by an intense searching behaviour on host-contaminated areas. Exploiting of these cues allows the parasitoids to optimize their searching behaviour, since wasp females are able to discriminate the host gender and to distinguish associated from non-associated hosts. Here we investigated the response of Trissolcus basalis females, a natural enemy of several pentatomid species to chemical footprints left by Halyomorpha halys (Heteroptera: Pentatomidae) an herbivorous alien bug that shares the same environments as native pentatomid pests. In laboratory conditions we tested T. basalis ability to discriminate between female and male H. halys footprints. We also quantified the walking behaviour of T. basalis when they are rewarded by an oviposition experience on H. halys eggs. The outcomes are discussed by evaluating the possible consequences of alien insect spread on local parasitoid foraging behaviour.