Predicting the ecological impacts of invasive alien insects at multiple levels: from genes to communities

Biological invasions are global phenomena that impact ecosystems, the economy and human, animal and plant health. The rate at which biological invasions occur has grown exponentially in recent times, due to global trade that has increased the pathways for organisms to be transported across the globe at unprecedented speed. It is therefore of high importance to understand in advance the impact that alien organisms might pose to the ecosystems that they invade.

Among invasive animals, top predators are of particular interest, as they directly impact on a wide range of organisms that they prey upon, and also cascade their effects indirectly through, for example, enemy release.

In this PhD project, the student will adopt a series of experimental approaches, that span from molecular methods to behavioural and community analyses, to characterize whether key traits of insect top predators have shifted after biological invasions and also their actual and predicted impacts on ecosystems. The student will comparatively analyse two high profile insect invaders: the Asian hornet Vespa velutina (a recent invader) and the harlequin ladybird Harmonia axyridis (established in Europe).

Hence, the two systems present a great opportunity to compare key ecological traits associated with a relatively 'old' invasion (Harmonia) vs. a more recent one (Vespa), with an enhanced potential to predict the type of impact that these two insects might have across invaded ecosystems.

The student will perform field work in the UK, Europe and North America to sample insects of the two species from different populations representing a gradient in their history of invasion, and the will perform experiments in the lab to test behavioural and physiological traits that could be associated with successful invasions. Two traits will be prioritised: feeding behaviour/ecology and immunocompetence.

Feeding analyses will combine density dependent patterns of prey consumption and preference with stable isotope analyses and DNA metabarcoding, to characterize the composition of the diet of the two insects at a broader scale, and also with a high-throughput metagenomic approach to identify prey items at the highest resolution. For immunocompetence, a candidate gene approach will be used to characterize the expression patterns of key genes associated with constitutive and induced responses.

This experimental approach will lay the ground for a statistical analysis to model the impact that Vespa and Harmonia are having on the ecosystem. This will be followed by another modelling approach to predict how top predators could impact UK ecosystems over time.