PHONOTAXIS IN FEMALE ORMIA-OCHRACEA (DIPTERA, TACHINIDAE), A PARASITOID OF FIELD CRICKETS

Gravid females of Ormia ochracea locate their hosts by homing on their hosts' calling songs. At Gainesville, Florida, O. ochracea females we re attracted in greatest numbers to broadcast sounds that simulated th e calling song of Gryllus rubens. Other candidate hosts and the attrac tiveness of their songs relative to the simultaneous song of G. rubens were G. fultoni (9%), G. integer (4%), G. firmus (3%), Orocharis lute olira (1%), Scapteriscus borellii (1%), and S. vicinus (0%). The respo nse of female O. ochracea to simulated G. rubens songs that have diffe rent pulse rates changes with temperature in parallel with temperature -induced changes in the pulse rate of natural songs. Speaker stations less-than-or-equal-to 16 m apart in an apparently uniform environment produced strikingly different fly counts (e.g., 852 and 2163). The son g of G. rubens al 21-degrees-C approximates a continuous sequence of 4 .6-kHz pulses at a rate of 45 s-1 and with a duty cycle of 50%. When t wo of these parameters were held constant and the third systematically varied in steps of 0.4 kHz, 10 s-1, and 10-20%, maximum attraction oc curred at 4.4 kHz, 45 s-1, and 20-80%. Omitting as many as half the pu lses in a rubens simulation (e. g., 1, 2, 4, or 16 pulses followed by an equivalent silence, and repeat) did not significantly reduce the co unts of O. ochracea, proving that chirping (producing pulses in brief groups) is no safeguard from call-seeking 0. ochracea. Phase shifting of pulses in successive chirps sometimes decreased fly counts. When so ngs were first broadcast, flies came within seconds. Flies that landed at sound often stayed for minutes, even when the sound was turned off .