Abstract
The invasive Asian hornet, Vespa velutina, threatens the already declining honey bees and their pollination services, and presents a cost to the environment and the economy. Eradication campaigns are ineffective and damaging to biodiversity, calling for the development of more selective traps. In North America, the pitcher plant, Sarracenia leucophylla, traps many flying prey, and in France its horticultural hybrids trap the Asian hornet. While no pheromone trapping is emerging, this thesis explores the possibility of drawing inspiration from the natural trap of these carnivorous plants to fight against the hornet.The objectives were (1) to characterize the visual and olfactory signals of 4 species of pitcher plants with a gradient of relatedness to S. leucophylla, (2) to identify and test the signals and other trap features most effective in attracting and capturing the hornet. The colours of the pitchers were measured using spectrophotometry and their contrasts modelled for the hornet's visual system. The odours of the pitchers (n=39) and plants (n=31) were collected by headspace and analysed in GC-MS. They were tested in olfactometry, with the odours of honey and bee, on the hornet (406 tests). The capture efficiency of these plants (12 plants / 96 pitchers) was measured and filmed during a laboratory experiment and evaluated during 3 years in the field (n=223).The 4 species of pitcher plants revealed to have a generalist odorant signal including terpenes, benzenoids and fatty acid derivatives. However, they present specificities in their visual and olfactory lures, which explain an important part of the differences in their prey composition. We observe real trapping syndromes with species with short pitchers, with few contrasts, the odours of which are rich in fatty acid derivatives that trap mainly ants, like S. purpurea, and those with long and narrow pitchers, with contrasting white areoles, important odour emissions rich in monoterpenes, that trap mainly flying hymenoptera, like S. X leucophylla.These pitcher plants also differ in their attractiveness and capture efficiency for the Asian hornet. S. purpurea attracts neither visually nor olfactory and never captures them, whereas S. X leucophylla and S. X Juthatip soper frequently capture them in autumn. S. mitchelliana, which together with S. X Juthatip soper emits the most attractive odours to hornets, has intermediate capture rates, which is explained by low retention rates. These two species also have the most similar plant odour profiles. As for the highly concentrated odours of S. X leucophylla, they could elicit attraction at large distance and repulsion at close range, based on the all-then-nothing behaviours observed in olfactometry. Its high visitation and capture rates in laboratory and field suggest that its odour is never as concentrated and therefore potentially repulsive as in the olfactometer. The laboratory experiment and the measurement of the pitchers’ features highlighted other traits effective in attracting the hornet such as the white areoles of the operculum and the nectar secretion at the trap entrance, and those related to its capture, such as the long and narrow shape of the trap and the presence of microstructures responsible for a slippery texture that favours the fall of insects in the trap. The comparison of odour profiles of attractive and non-attractive species allowed us to identify volatile organic compounds to be tested in the future for the development of an attractive bait. The brightness contrasts, the microstructures responsible for the slipperiness of the surfaces are sources of inspiration for the development of a biomimetic, biodiversity-friendly and effective trap.