Phonotaxis in femaleOrmia ochracea (Diptera: Tachinidae), a parasitoid of field crickets

Abstract

Gravid females of Ormia ochracealocate their hosts by homing on their hosts' calling songs. At Gainesville, Florida, O. ochraceafemales were attracted in greatest numbers to broadcast sounds that simulated the calling song of Gryllus rubens.Other candidate hosts and the attractiveness of their songs relative to the simultaneous song of G. rubenswere G. fultoni(9%), G. integer(4%), G. firmus(3%), Orocharis luteolira(1%), Scapteriscus borellii(1%), and S. vicinus(0%). The response of female O. ochraceato simulated G. rubenssongs that have different pulse rates changes with temperature in parallel with temperature-induced changes in the pulse rate of natural songs. Speaker stations ≤ 16 m apart in an apparently uniform environment produced strikingly different fly counts (e.g., 852 and 2163). The song of G. rubensat 21 °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 two of these parameters were held constant and the third systematically varied in steps of 0.4kHz, 10s ⁻¹,and 10–20%, maximum attraction occurred at 4.4 kHz, 45 s ⁻¹,and 20–80%. Omitting as many as half the pulses in a rubenssimulation (e.g., 1, 2, 4, or 16 pulses followed by an equivalent silence, and repeat) did not significantly reduce the counts of O. ochracea,proving that chirping (producing pulses in brief groups) is no safeguard from call-seeking O. ochracea.Phase shifting of pulses in successive chirps sometimes decreased fly counts. When songs were first broadcast, flies came within seconds. Flies that landed at sound often stayed for minutes, even when the sound was turned off.