Unraveling the mating secrets of the invasive parasitic fly Philornis downsi

Abstract

Understanding the reproductive behaviour of invasive species is crucial for developing control techniques. This study investigated the mating behaviour and reproduction of Philornis downsi, an invasive parasitic fly that is threatening the survival of endemic birds in the Galapagos Islands. An observational study describing the mating behaviour of P. downsi was combined with experimental studies examining factors (feeding on a hormone analogue that influences sexual maturity, density and sex ratio, and body size) that could increase the low reproductive success in the laboratory. Males actively pursue females in flight, mount them, land, and copulation occurs when the male inserts the aedeagus and the female extends her ovipositor toward the male. Copulation duration ranged from 2 to 13 min. Male–male interactions were observed and point to a behaviour that defends access to females. The addition of methoprene to the diet did not increase copulation frequency or mating success (sperm stored) and reduced female fecundity and survival. No effect of density or sex ratio was found in copulation frequency or mating success; however, females laid more eggs at higher densities with a male biased sex ratio, and more fertile eggs were found at high densities regardless of sex ratio. Additionally, we found no influence of body size of wild or laboratory-reared male or females on mating success in the laboratory. These results bring us closer to understanding the mating behaviour of P. downsi.