Avian Predation of the Woodwasp, Sirex Noctilio F., And Its Parasitoid Complex in Tasmania.

Abstract

More than half the bird species occurring in a plantation of Pinus radiata in Tasmania were implicated in predation on the introduced woodwasp Sirex noctilio F. and its parasites, especially Ibalia leucospoides (Hochenw.), Rhyssa persuasoria (L.) and Megarhyssa nortoni nortoni (Cress.) The dusky woodswallow (Artamus cyanopterus), forest raven (Corvus tasmanicus) and spine-tailed swift (Hirundapus caudacutus) attacked mating swarms of S. noctilio at the tops of trees; an indirect effect was the abnormal sex ratios of emergent insects in the following generations, which indicate a serious disturbance of mating frequency. Estimates of predator success, through the controlled release of large numbers of woodwasps, and estimates of gross feeding, by bird census and numbers of woodwasps in the stomach contents of the major predators, indicated that avian predation supplemented the effects of other natural enemies. The behavioural response of birds to their insect prey is described, and measures are recommended which could maximise the beneficial effects of birds.