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Herbivores walking over the epicuticular wax layer of a plant may leave tracks that disclose their presence to hunting predators or parasitoids. The braconid wasp Cotesia marginiventris is a solitary parasitoid of young noctuid caterpillars. It can locate potential hosts from a distance by orienting toward the scent of herbivore-damaged plants. Upon landing on the caterpillars' food plant, the female parasitoid searches for further cues (kairomones) that confirm the presence of a suitable host. In a previous study, we showed that C. marginiventris recognizes the chemical footprints of absent Spodoptera frugiperda caterpillars on a leaf. Here, we report on the persistence and chemical nature of this host location kairomone. In a series of behavioral assays, we confirmed that caterpillars of S. frugiperda leave chemical tracks that elicit characteristic antennation behavior in C. marginiventris for up to 2 days. Both hexane extracts of caterpillar footprints and of the larvae's ventral cuticle induced antennation and contained almost identical long-chain hydrocarbons, thus suggesting the prolegs and claspers as the kairomones' main source. A series of linear C(21) to C(32) alkanes accounted for ca 90% of all identified compounds. Female wasps showed significant antennation responses on leaves treated with a reconstructed blend of these n-alkanes. However, wasp responses were relatively weak. Therefore, we presume that minor compounds, such as monomethyl-branched alkanes, which were also found, may contribute additionally to host recognition.

Isolated fragments of semi-natural habitats are often embedded in a landscape matrix that is hostile to organisms of conservation concern. Such habitat islands are prone to changes in their biota over time. For insects, few studies on long-term trends in species richness within conservation areas are available, mainly due to the lack of historical data. We here use moths in the coastal pine wood reserve Pineta san Vitale (Ravenna, NE Italy) to assess how local fauna has changed over the last 85 years. This reserve has experienced massive changes in vegetation structure due to secondary succession. We compared historical collections (1933–1976: 107 species; and 1977–1996: 157 species) with our own samples (1997–2002: 174 species; and 2011+2012: 187 species). Over the last 85 years, the proportion of habitat generalists in relation to all recorded moth species increased from 20 to 33%. The fractions of woodland and open habitat species concomitantly decreased by 10 percentage points, respectively. Amongst woodland and habitat generalist species, gains outnumbered losses. In contrast, 18 species of open habitats and 10 reed species were lost over the decades. We attribute these changes to vegetation succession and to the isolation of the reserve. Generalist species are presumably better able to pass through anthropogenically exploited landscapes and colonise isolated habitat fragments than habitat specialists.

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