Anatomy of an outbreak : the biology and population dynamics of a Cardiaspina psyllid species in an endangered woodland ecosystem

1. Climate, resource availability and natural enemies are pivotal factors influencing population fluctuations of insects. However, the principal factors underlying insect outbreaks, particularly in natural ecosystems, are still debated and may vary between species. 2. We assessed the role of these factors on psyllid population dynamics during the peak and decline of a Cardiaspina psyllid outbreak in a critically endangered eucalypt woodland in Australia. Initially, this involved describing the field biology and ecology of a newly reported Cardiaspina species on grey box (Eucalyptus moluccana Roxb.). 3. Within 1 year, the psyllid completed four generations. Its biology and parasitoid complex were similar to other Cardiaspina species during outbreaks. 4. Minimum winter temperature was a key driver of psyllid development and density. Natural enemies did not prevent or control this outbreak. 5. The outbreak resulted in area-wide and chronic defoliation of host trees. Resource depletion and summer heat waves impacting critical developmental stages of psyllids were the major factors responsible for the significant reduction of psyllid populations in early 2013. However, ongoing regeneration of trees in the highly fragmented woodlands may allow recolonization of new foliage and chronic infestations to continue.