Mobile parasitoids may restrict the spatial spread of an insect outbreak

摘要: 1. The western tussock moth Orgyia vetusta, a defoliator with flightless adult females, forms localized outbreaks within larger areas of its habitat. These may persist for several (> 10) years little tendency to spread. 2. According reaction-diffusion models, spatial patterns in population density arise from the interaction between mobile predator and less-mobile prey. This occurs because predators 'spill over' around edges prey populations, creating zones which ratios are elevated. 3. To test this 'predator diffusion' hypothesis moths, we placed their eggs larvae along 500-m transect leading away edge outbreak. through suitable but sparsely occupied We measured attack rates by wasp egg parasitoid four species tachinid fly larval-to-pupal parasitoids on these experimental immature moths. 4. As predicted parasitism were elevated zone surrounding For some species, relationship distance outbreak was linear; others it parabolic. 5. results compatible explanations, including diffusion hypothesis. Whatever mechanism, suggest that restricts distribution therefore global abundance host insect system.