Ormia ochracea

In 1975, William H. Cade experimentally demonstrated that Ormia ochracea uses the mating call of the field cricket as a means to locate its host. Cade placed dead crickets on top of speakers playing cricket songs and various control sounds and recorded the amount of time the fly spent on either the control or test speaker. He found that flies spent more time on the speakers playing cricket songs and observed that the flies would always deposit larvae on and around the speaker which was playing cricket songs.[1]

O. ochracea have been shown to adjust their preference for host songs after exposure to different songs in the laboratory. In a 2011 study, flies that were previously exposed to the G. lineaticeps song chose the G. lineaticeps song over the G. integer song, and vice versa.[9] This preference was very short term. O. ochracea's flexible learning capabilities may have been critical in expanding its host and geographical range.

O. ochracea infestation has been shown to affect the behavior and reproduction of host field crickets.[7][10] Early in the infestation period, non-reproductive behavior is largely unimpaired because the parasitic larvae do not consume the digestive system or central nervous system of the host.[7] After the larvae migrate to the host’s abdomen, the host’s mating, egg-laying, and fighting ability decline, most likely due to tissue damage caused by the larvae.[7] Additionally, infestation of female crickets alters their mating preferences. Gryllus lineaticeps females normally prefer to respond to male songs with intermediate chirp rates over those with slow chirp rates, but females parasitized by O. ochracea show no preference between chrip rates.[10] Reduced selectivity in infested female G. lineaticeps may be adaptive, as a female may be more likely to reproduce before being killed by the parasitoids if they are less selective.

Some species of cricket which are parasitzed by O. ochracea have evolved methods to avoid infestation. For example, some members of the prey cricket Teleogryllus oceanicus have a mutation called flat wing, in which the sound-producing structures of the male forewings are erased.[11] The flat wing was first observed in 2003 on the Hawaiian island of Kauai, and was also found on neighbouring Oahu two years later. Genetic studies of crickets from each island show that the mutations arose from different genomic variations.

In order for an animal to localize sound, it must be able to detect minute differences in intensity and time between the arrival of the sound to the ear closer to the source and the ear further from the source. O. ochracea displays a remarkable ability to localize sound despite the incredibly small distance (450-520μm) between its acoustic sensory organs.[13] Its sound localization ability is facilitated by a cuticular structure which joins its ears, mechanically coupling their motion and magnifying interaural differences by a factor of about 20.[13] Prior to O. ochracea no similar mechanism of auditory localization had been described.