Personality in the parasitic avian vampire fly (Philornis downsi)

Personality, i.e., consistent and repeatable differences in behaviour between individuals, has been documented and studied across taxa. However, relatively little research attention has been given to personality in invertebrates, particularly in parasitic species. The avian vampire fly Philornis downsi (Diptera: Muscidae) is a semi-hematophagous ectoparasite that feeds on the blood of nestling birds during its larval phase and on decaying vegetable matter as an adult. Invasive to the Galápagos Islands, the avian vampire fly causes permanent deformation and high mortality in its avian hosts. To better understand the behaviour of adult flies, we aimed to determine whether avian vampire flies have short-term individual repeatability for three personality traits, and whether these three traits covary. We collected avian vampire fly pupae from wild nests of small landbird species on Floreana Island, Galápagos, reared the pupae to adulthood, and individually marked the adult flies. On days 5–7 post-eclosion, we tested the behavioural responses of each individual fly once per day, using (1) a walking test (activity), (2) a novel environment test (exploration) and (3) a back test (boldness). We found significant repeatability at the individual level for all three traits, and no evidence for a behavioural syndrome between the traits. These findings are the first step towards understanding the role of parasite personality within host-parasite dynamics, and how personality differences may affect the avian vampire fly and its novel hosts on the Galápagos.