Studio di comunità di insetti visitatori di alcune specie di orchidee del Piemonte e Valle D'Aosta: ruolo della strategia di impollinazione e piante nettarifere adiacenti.

Orchidaceae are a heterogeneous family, with peculiar biological traits such as the two-way symbiosis with mycorrhizae and insects both essential for their reproductive success. The majority of orchid species are entomophilous, requiring insects for their pollination. Orchids have evolved two main strategies to attract their pollinators. Rewarding orchids provide insect visitors with satisfying signals, as nectar or warm shelters; in this case plants and insects get mutual benefit from the interaction. On the other hand, deceptive orchids attract pollinators without giving any rewards. Orchids are the most representative plant group adopting various deceptive strategies, since one third of species are indeed deceptive; the most common is food-deception in which orchids exploit insects foraging behaviours via mimicking true signals of nectar-bearing plants like colour, smell, tactile cues, spur. Orchidaceae share unique traits that guarantee high pollination success, such as the presence of pollen clumped in organised structures (pollinia), the stylus, filament of pistil and stamens fused in a single organ (column), and the labellum being an enlarged sepal acting as a landing spot for pollinators. Most of the orchid pollinators belong to three main orders, i.e. Hymenoptera, Lepidoptera and Diptera. In this work, we studied ten orchid species with different pollination strategies in five sites distributed in Piedmont and Aosta Valley during summer 2023. At each locality, we collected data by direct observations via standardised plots and transects. During plot surveys, we recorded the number of nectariferous plants, colour and number of flowers, to investigate the relationship between the orchids’ strategy and the neighbouring nectar plants, trying to establish if they are friends or foes. We also recorded the abundance of insects (total and divided per orders) interacting with nectariferous plants and orchids and the durations of interaction events, to explore the effect of orchid strategies and nectariferous plants on insect visitors and pollinators. Deceptive orchids are associated with a higher abundance of white and yellow flowering plants, and abundance of white flowers. These colours suggest that deceptive orchids benefit from high diversity in plant species with flowers having attractive colours. We can deduce that food deceptive generalist orchids need such diversity to deceive insect recognition, while generalist rewarding species hold minor species variability, since they need to be remembered and distinguished from other plants. Other more specialised or selective orchids of both strategies are less community-friendly and avoid competition. In addition, we observed that rewarding orchids attract a higher abundance of insects, mainly Lepidoptera, which are the most reward-seeking as stated in previous research. We also noticed that the number of insect feeding events do not differ between rewarding orchids and the nearby flowers, while deceptive species were more visited than their vicinal plants, mostly by Diptera and Hymenoptera. Thus, we could hypothesise that deceptive orchids tend to grow in the vicinity of plants, which can attract insects but are unable to support insect feeding. The present study also allowed us to enlarge our knowledge on orchid pollinator networks, and biological interactions of a group of plants which are considered very important from a conservational point of view.