Different facets of the same niche: Integrating citizen science and scientific survey data to predict biological invasion risk under multiple global change drivers.

Citizen science initiatives have been increasingly used by researchers as a source of occurrence data to model the distribution of alien species. Since citizen science presence-only data suffer from some fundamental issues, efforts have been made to combine these data with those provided by scientifically structured surveys. Surprisingly, only a few studies proposing data integration evaluated the contribution of this process to the effective sampling of species' environmental niches and, consequently, its effect on model predictions on new time intervals. We relied on niche overlap analyses, machine learning classification algorithms and ecological niche models to compare the ability of data from citizen science and scientific surveys, along with their integration, in capturing the realized niche of 13 invasive alien species in Italy. Moreover, we assessed differences in current and future invasion risk predicted by each data set under multiple global change scenarios. We showed that data from citizen science and scientific surveys captured similar species niches though highlighting exclusive portions associated with clearly identifiable environmental conditions. In terrestrial species, citizen science data granted the highest gain in environmental space to the pooled niches, determining an increased future biological invasion risk. A few aquatic species modelled at the regional scale reported a net loss in the pooled niches compared to their scientific survey niches, suggesting that citizen science data may also lead to contraction in pooled niches. For these species, models predicted a lower future biological invasion risk. These findings indicate that citizen science data may represent a valuable contribution to predicting future spread of invasive alien species, especially within national-scale programmes. At the same time, citizen science data collected on species poorly known to citizen scientists, or in strictly local contexts, may strongly affect the niche quantification of these taxa and the prediction of their future biological invasion risk.

Tracking the invasive hornet Vespa velutina in complex environments by means of a harmonic radar.

An innovative scanning harmonic radar has been recently developed for tracking insects in complex landscapes. This movable technology has been tested on an invasive hornet species (Vespa velutina) for detecting the position of their nests in the environment, in the framework of an early detection strategy. The new model of harmonic radar proved to be effective in tracking hornets either in open landscapes, hilly environments and areas characterised by the presence of more obstacles, such as woodlands and urban areas. Hornets were effectively tracked in complex landscapes for a mean tracking length of 96 ± 62 m with maximum values of ~ 300 m. The effectiveness of locating nests was 75% in new invasive outbreaks and 60% in highly density colonised areas. Furthermore, this technology could provide information on several aspects of insect's ecology and biology. In this case, new insights were obtained about the mean foraging range of V. velutina (395 ± 208 m with a maximum value of 786 m) and flying features (ground speed), which was 6.66 ± 2.31 m s-1 for foraging individuals (hornets that are not carrying prey's pellet) and 4.06 ± 1.34 m s-1 for homing individuals.

Viability of thermal imaging in detecting nests of the invasive hornet Vespa velutina.

Vespa velutina is an invasive hornet species that is colonising Europe, generating considerable impacts on honeybees, beekeeping and biodiversity. Control and early warning strategies for this species are mainly based on monitoring plans and procedures of nest detection and destruction. Technological tools (harmonic radar, radio-telemetry) have been developed to increase the probabilities of nest detection in new outbreaks. Since hornets are able to regulate nest temperature, thermography may represent an additional technique that may be used, both alone or in support to other techniques. In this study, the viability of thermal imaging in detecting nests of V. velutina was evaluated in controlled conditions. The influence of different environmental and operative variables (time of the day, presence/absence of leaves covering the nest, distance between the nest and the operator) were tested on three nests detected during August 2018 in Italy. All the nests were detectable by thermal imaging, but environmental and operative variables affect their detectability. The temperature difference between the nests and the surrounding reaches its maximum before sunrise and without a tree canopy covering the nests. Although nests were visible in some cases from 30 m, the detectability was higher at shorter distances, even if this variable may also depend on infrared camera resolution. An increase in the environmental temperature also generates a decrease of nest detectability. Although some limitations could occur, these results show the applicability of thermography in detecting V. velutina nests before the beginning of the reproductive phase, and consequently its potentiality in control strategies.

Effectiveness and Selectiveness of Traps and Baits for Catching the Invasive Hornet Vespa velutina.

Vespa velutina is an invasive hornet that is colonising several countries worldwide, with detrimental effects on multiple components but primarily affecting honey bees and native insect species. Traps for wasps and hornets are commonly used for trapping V. velutina, both for monitoring and control purposes. In this study, we compared the performances of two typologies of traps and baits widely used for trapping this invasive hornet, by evaluating their effectiveness and selectiveness in trapping V. velutina in two sites during two different periods of the year, spring and autumn. The performance of the traps changed in relation to (i) the trap's model, (ii) the bait's typology and (iii) the period of the year. In spring, traps with common beer as bait were more effective and more selective independently of trap's model than the commercial bait that has been tested. On the contrary, in autumn, just one combination of trap and attractant (the commercial trap and bait) achieved higher effectiveness and selectiveness. Despite the underlined variations among traps and baits, overall catches of V. velutina were scanty compared to bycatches of non-target insects, since best performing traps either in term of effectiveness and selectiveness caught 3.65% of the target species in spring and 1.35% in autumn upon the total trapped insects. This highlights the urgent necessity of developing more selective trapping methods for monitoring and particularly for controlling purposes.