Diel Calling Activity and Field Survival of the Bushcricket, Sciarasaga quadrata (Orthoptera: Tettigoniidae): A Role for Sound-locating Parasitic Flies?


School of Agricultural Science, University of Tasmania, GPO Box 252-54, Hobart, TAS, 7001, Australia. E-mail: Geoff.Allen@utas.edu.au


In this study I examine the variability in calling activity of Sciarasaga quadrata over both the short (4 d) and long term (life span), and the temporal pattern to host searching by its most significant natural enemy, the ormiine fly Homotrixa alleni. Indeed, few male S. quadrata survive the entire calling season as this acoustically orienting parasitoid fly continually ‘culls’ calling males out of the population. I found that male S. quadrata commence calling over 1 h before sunset, cease around midnight and call, on average, for over 3 h within this period (range 0–11 h 09 min). There was significant concordance and repeatability in calling activity over both the short and long term, enabling me to conclude that relative differences in calling activity among males persist throughout a male's life span. There was a distinct peak to host searching by gravid female flies, with 82 % of all flies collected at acoustic traps between sunset and midnight. A positive association between call duration (time spent calling) and fly attraction was evident from multiple collections of flies at single traps. Counter to expectation, there was no significant decline in average call duration across successive collections of males, indicating that long-call-duration males were not being selectively culled by flies from the calling population. Males at the end of the calling season, when their remaining reproductive potential is low, allocate the majority of their calling time between sunset and midnight despite the high risk of fly attack. The distribution of call durations within the population was not skewed, which if heritable, indicates a lack of history of directional selection acting on call duration. Limited evidence suggests that encounters with females are rare in S. quadrata so that males may be selected, irrespective of natural selection pressure, to call for long periods of time to optimize their chance of attracting mates. The above findings are further discussed in relation to parasitoid foraging and acoustic reproductive strategies.