Date of Award

Summer 8-30-2018

Semester of Degree


Document Type

Open Access Dissertation

Degree Name

Ph.D. in Environmental and Forest Biology


Environmental and Forest Biology

Major Professor

Stephen A. Teale

Steering Committee Member

James P. Gibbs

Steering Committee Member

Charlotte C. Causton

Steering Committee Member

Dong H. Cha

Steering Committee Member

Margaret A. Voss


Larvae of the parasitic fly Philornis downsi (Diptera: Muscidae) feed on the blood and tissues of passerine chicks. Parasitism by P. downsi contributes to increasing mortality and population declines in several bird species in the Galapagos Islands. This dissertation focuses on the identification of chemical attractants (food odors, sex or aggregation pheromones) for P. downsi. These attractants are important for increased trapping efficiency in the management of P. downsi. Dipteran mating and reproductive success are dependent on chemical communication, yet little is still known about the chemical ecology of most Diptera, with the exception of some agricultural pests and vectors of pathogens. My studies of chemical communication in P. downsi found some food odors, such as the volatile fermentation products (ethanol and acetic acid) produced by the yeast Saccharomyces cerevisiae, to be attractive. Maximal attraction was attained by a mixture of 3% ethanol and 0.3% acetic acid. The addition of 250 ml of this solution to an external reservoir that dispensed into a McPhail trap prolonged the effectiveness of these compounds in the field. Sex and aggregation pheromones are also important in this system; experiments identified males as the attractive sex. GC-EAD and GC-MS analyses on crude and photo-oxidized cuticular lipids of both sexes identified 18 photo- oxidation compounds produced by males as potential attractants for females. Genitalia extracts of each sex had markedly different volatile compounds. Extracts from male genitalia were significantly attractive to females in y-tube olfactometer assays (p= 0.02). Based on data presented here, I hypothesize that P. downsi mating begins with feeding behaviors, followed by location of host nests by male and female flies. Male flies then emit pheromones to attract the females. Mating occurs after mate location by visual identification and sexual or contact pheromones. Mating and communication systems in the calyptrate muscoids are poorly understood in general. In addition to identifying attractants specific to P. downsi, some of the work presented here may be broadly applicable to the chemical communication of muscoid flies in general.