In 1958-63 and 1964-71 the life systems of four kinds of test-forming psyllid that coexist on Eucalyptus blakelyi were investigated intensively in a comparative study of insect abundance. This paper deals mainly with C. albitextura, which was kept under observation from 1950 to 1974. (The others were two species of Glycaspis, Spondyliaspis sp, and Creiis costatus.)
The results indicate that the differences in maximal abundance reached by the four kinds of psyllid are mainly the outcome of differences in their ability tg utilize the leaves of the host plant as a source of food, C. albitextura being much more effective than the other species. For the latter, it appears that the principal environmental determinant of abundance was the number of feeding places where nymphs could survive long enough to complete development. That number varied according to foliage and weather.
C. albitextura also differed from the other species by having its population densities held for long periods far below the levels at which the food supply would be limiting, by restrictions imposed upon reproduction by adverse weather and foliage conditions (the latter being due partly to poor synchronization between the emergence of adults in spring and the occurrence of foliage attractive for oviposition), and by high mortalities due to natural enemies.
The life system of C. albitextura lacks an element that can stabilize abundance at low population densities, but adverse environmental influences usually limit the rate of increase greatly when abundance is low. The magnitude of the average rate of increase to high levels of population density, and the length of time for which high average densities are maintained, depend upon the frequency with which favourable conditions of weather, foliage and predation combine to promote both survival and reproduction.
Impact of Some Weather Factors on the Population Density of Phenacoccus solenopsis Tinsley and its Natural Enemies