Hosts of a Phonotactic Parasitoid and Levels of Parasitism (Diptera: Tachinidae: Ormia Ochracea)

T. J. Walker, S. A. Wineriter


In central Texas, females of Ormia ochracea (Bigot) find hosts, Gryllus integer Scudder (Orthoptera), by homing on the hosts' calling songs. O. ochracea is abundant each fall in Alachua County, Florida, where G. integer does not occur. Gryllus rubens Scudder and G. firmus Scudder were collected by three methods and held for emergence of O. ochracea. Of 185 G. rubens and 100 G. firmus collected during January to August, none were parasitized. Levels of parasitism during the remaining months never exceeded 10% except at sound-baited traps--but these attracted larvipositing O. ochracea as well as G. rubens. For specimens collected in pitfall traps and by searching under objects, levels of parasitism of G. rubens and G. firmus and of males and females were unexpectedly similar--though O. ochracea is not attracted to firmus calls and female Gryllus do not call. When muted and nonmuted reared males of G. rubens were experimentally exposed in the field in the fall for 5 days, no muted males were parasitized but 7 of 13 nonmuted males were.

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