Exploitation of underexplored physiological, metabarcoding and evolutionary aspects to enhance invasive insect pest management

Invasive pests threaten agriculture and ecology of the invaded countries. To contrast and reduce their impact, entomologists develop specific and sustainable control strategies, which should target the pest and should not affect the surrounding environment. Therefore, a profound knowledge of pest biology and ecology is necessary to afford this task. During my PhD, I delved into three underexplored approaches that hold the potential to unveil crucial biological information and develop more effective pest management strategies tailored to specific species: metabolic rate, microbiota shifts and molecular divergences. Although these three aspects might sound secondary in the context of pest management, they are important descriptors of the insect biological processes as they determine both the internal balance and the external interaction of the organism. I analyzed these three aspects for three case studies on three invasive pests diffused on the Italian territory. None of these investigated topics had been previously examined in relation to the studied species, and the findings I obtained hold promise for advancing species-specific control strategies. The overarching objective of my PhD research was to demonstrate the significance of exploring overlooked aspects of pest species biology, thereby augmenting the wealth of information necessary to enhance control strategies. The metabolic rate aspect (Chapter 2) was addressed considering the spotted wing drosophila (Drosophila suzukii), an invasive species from eastern Asia that particularly threatens soft fruit crops. The study focused on measuring metabolic and water loss rates of D. suzukii flies captured at different sites located on an altitudinal gradient in Val dei Mocheni (Trentino, Italy) from early summer to fall. Respirometry was used to quantify the emission of carbon dioxide (CO2) and water (H2O) from individual flies, with the obtained CO2 values serving as a proxy for the metabolic rate. The study aimed to compare the metabolic and water loss rates among Drosophila populations, aiming to enhance the ecological understanding of this species and shed light on the metabolic and water management implications of living at different altitudes. Consequently, the results would provide insights into survivability, adaptability, pest distribution, and habitat suitability, offering valuable perspectives for management considerations. Concerning the microbiota aspect (Chapter 3), I analyzed the brown marmorated stink bug (Halyomorpha halys), an invasive polyphagous insect from Asia that threatens most crops. Populations of this bug are able to survive severe winters, although during this period of the year they don’t feed and they are subject to severe abiotic conditions, such as freezing. It is well known that, in general, bacterial microbiota can shift due to severe and prolonged conditions, but I find out that this is not the case for H. halys. Thus, targeting the bacterial microbiota could be a key factor for the management of this species. Moreover, I also searched for the presence of the microsporidian Nosema maddoxi and the overwintering consequences on its infection. The role of this microsporidian is still not clear, but it is supposed to be a parasite that negatively affects the ecology of H. halys. Findings of this study are also interesting for the sterile insect technique (SIT), since it has been suggested to be performed on overwintering wild males to overcome mass-rearing limitations in laboratory conditions, and therefore it is important to unravel microbial communities that characterize them to avoid accidental spreading of deleterious microbes. Ultimately, the molecular divergence aspect (Chapter 4) was tackled studying the molecular clock of a newly invasive species of leafhoppers, Arboridia dalmatina, that was very recently found in Puglia (Apulia, Italy). This species might be a threat for vineyards, since it can feed on grapevines’ leaves causing their decay. A phylogenetic and molecular clock analysis on the COI gene was performed to attempt to trace back the origin of this invasion and to understand the threats of this species. Overall, the three approaches I used unveiled under-explored aspects of the three studied species, pointing out key information on their biological processes that can be exploited to further improve their pest-specific management strategies. The work presented in this thesis further proves the importance of using these approaches to deeply figure out pests’ biology that can serve agricultural entomology purposes.