Reproductive system and activity patterns of Philornis downsi (Diptera: Muscidae).

This article focuses on the reproductive morphology and activity patterns of *Philornis downsi* (Dodge & Aitken), known as the avian vampire fly, a major threat to land bird conservation in the Galapagos Islands. It provides the first detailed description of the male and female reproductive systems of this species, revealing structures such as peanut-shaped testes and accessory glands in males, and ovaries with three spermathecae in females. The study also compares locomotor activity between lab-reared and wild flies, finding that both exhibit peak activity in the morning and at dusk, with lab-reared flies more active at dusk and females generally more active in the morning as they age. These findings offer foundational knowledge for developing laboratory rearing protocols and quality control measures, which are critical for implementing environmentally friendly control strategies against this invasive pest.