The role of acoustic experience in host song preference of the phonotactic parasitoid fly, Ormia ochracea (Diptera: tachinidae)

Ormia ochracea is a phonotactic parasitoid fly that attacks field crickets, locating hosts by their mating call. While the natural history of this fly is known, seasonal population dynamics in southern California have not been characterized. In this thesis, a population of flies were censused in the Santa Monica Mountains (CA) in 2008. This population of flies was active beginning in early August, peaking in abundance in mid-September, and disappearing entirely by end of November. Outside of the active season, the status of this species is not known. A possible pupal overwintering strategy was tested by burying and monitoring lab-propagated pupae in the field. Most pupae in this study did not emerge, but a few pupae had protracted development and incomplete adult emergence. A variety of field cricket species occur within the range of this parasitoid, which stretches across the southern United States and into Hawaii. Previous research has demonstrated that there is a regional preference for the primary local host song over nonlocal host songs. This study examined whether acoustic experience (learning) plays a role in host song preference in O. ochracea. Flies were raised in controlled acoustic environments where they were exposed daily to one of two host songs, and then tested for host song preference. Flies showed a significant preference for their treatment song over the novel song, indicating that host song preference is due at least in part to learning. In a second protocol where flies were treated with silence the day prior to their test, flies showed no significant preference for either song. This rapid loss of song preference allows the fly to respond to changes in host population density, i.e. when the preferred host becomes scarce, flies will drop their preference and respond to any host song. This switching behavior may facilitate rapid range expansion. In addition to the manipulated studies of host preference, host fidelity of wild flies was tested using a mark-and-recapture technique. Two host songs were broadcast for seven consecutive nights, and flies were marked for the song they were initially caught at. Returning flies were highly likely to return to their initial song. This individual consistency supports the learning model of host preference, and explains at least some of the variation in fly populations as a result of different acoustic experience