The general bioloy of Cardiaspina albitextura (Psyllidae) and its abundance in relation to weather and Parasitism.

Abstract

Cardiaspina albitextura Taylor is a test-forming psyllid which inhabits the foliage of redgums, particularly Eucalyptus blakelyi Maiden, in inland southeastern Australia. In warmer areas, as on the South-West Slopes of New South Wales, this psyllid usually completes three generations per year, whereas in the cooler Southern Tablelands region it normally takes about 18 months to do so. It is a small insect with limited powers of dispersal. The majority of females oviposit within 100 yd of where they originated. The average number of eggs laid per female varies greatly even when individuals are not crowded, the observed range being 14-289. The reproductive rate appears to be influenced by weather conditions, especially by temperature. A few individuals of E. blakelyi are unfavourable to the psyllid and therefore resistant to attack. The susceptible majority exhibit considerable differences and variability in favourableness. In general, however, although there may be marked differences between individuals within stands, average favourableness does not differ greatly from place to place. When the numbers of C. albitextura become very high, i.e. when outbreaks occur, susceptible E. blakelyi suffer severe foliage damage. Where high psyllid numbers occur repeatedly at intervals of less than 3 years, they cause increasing "die back" and host plants produce progressively less new foliage. If outbreaks continue for years, trees are destroyed at an increasing rate. For the 15-20 years prior to 1950 it appears that localized outbreaks of C. albitextura were not uncommon, particularly on the Tablelands, but did not persist for long. Since then extensive outbreaks have occurred in both the Tablelands and Slopes regions. Some have persisted for 10 years and show no signs of ending. Others have lasted only for several psyllid generations. They have been more numerous and persistent in cooler areas than in the Slopes region.