Fully grown Philornis downsi nourish on fruit, but during larvae stage it feeds on the baby birds, generally small songbirds. While speaking about female flies, it lay their eggs in the bird nests. Once hatched fully, first-instar larvae move slowly into the nostrils of nestling birds, where they nourish on both tissue and blood. Better, second-instar larvae depart the restricted space of nostrils as well as hide out in the nest material during day time. They come out at night in order to carry on feeding on chicks. Philornis downsi plague takes a severe toll on the nestlings. In some conditions, every young in the infested nest is killed critically by the parasites. While speaking about the Philornis downsi, it is not inhabitant to the Islands of Galapagos.
These species was probable introduced unintentionally in the period of 1960s through imported fruit as well as yet has wreaked havoc on the endemic bird populations of island. Parasitism is one of the most common reasons of nestling death for minimum one species of the Darwin’s finch, as well as some think this is a root cause of decline in the number of landbirds in famous Galapagos Islands. The SIT (sterile insect technique) is a method which has been projected to control the Philornis downsi. This technique generates lots of sterilized insects that are released effective into a wild population. Females that companion with sterile males generate no offspring, therefore minimizing the mass of the next age group. SIT method has been mostly used to eradicate amount of screwworm flies and in managing some species of the fruit fly.