Sovereign sojourners: Investigating dispersal of invasive blowflies

Abstract

Understanding what drives insect dispersal is essential for predicting species spread, persistence, and the ecological impacts of invasive species, particularly as climate change accelerates range expansions. My thesis investigates the dispersal behaviour of several invasive blowfly species in Aotearoa New Zealand, focusing both on species-specific traits and environmental context. Specifically, I aimed to assess how conspecific density, sex, species identity, and group composition influence movement patterns, and how these patterns differ across contrasting urban and rural environments. My research combined two approaches: controlled laboratory assays and a large-scale field trial. In the lab, I used multi-patch arenas and automated video tracking to assess dispersal rate, exploration, and social spacing in two invasive blowfly species (Calliphora vicina and Calliphora stygia) under varied social conditions (densities of n = 1, n = 5, and n = 10). In the field, I dusted ~4,000 wild-caught blowflies with fluorescent powder and released them at a central location at the University of Waikato. I then monitored 28 baited traps placed along a radial transect (0.5 km to 3 km) for 10 days to track dispersal across the landscape. In the lab, I found that dispersal increased significantly under group conditions (n = 5), regardless of species or sex, and that C. vicina, especially females, exhibited higher exploration and movement metrics than C. stygia. Mixed-sex groupings further enhanced exploratory behaviour in C. vicina. In contrast, my field experiment yielded no marked fly recaptures. However, unmarked trap catches revealed that Lucilia spp. and Chrysomya spp. (both globally invasive) were the most frequently captured species across urban and rural sites, while C. vicina and C. stygia were less common and more restricted to urban areas. Together, these findings provide novel insights into both the behavioural ecology and spatial dynamics of invasive blowflies. By combining behavioural assays with field-scale observations, my thesis offers a foundation for improving dispersal prediction models and informs future research design in the context of biosecurity and invasive species management.