The long-tailed mealybug, Pseudococcus adonidum (L.) in South Australia

Abstract

The numbers of the long-tailed mealybug, P. adonidum (L.), on irrigated orange trees in South Australia rise and fall in a fairly regular sequence throughout the year. They are always low in summer, rise in autumn and early winter, and begin to fall gradually in late winter and spring. There is a sudden sharp rise in November followed almost at once by an equally sharp fall to the numbers characteristic of summer. This sequence may be explained in terms of the influence of weather on the survival and multiplication of the mealybugs in relation to the place where they happen to be living, the influence of predatory insects, and the behaviour pattern of the species. Food seems to play no part in this sequence except as its quality may influence behaviour. During summer the majority of the mealybugs on the leaves are to be found in specially sheltered places, such as under spider webs. There is evidence that the special quality of these places that makes them suitable for mealybugs is the greater humidity there than elsewhere. Young mealybugs on hatching are active in summer and tend to leave the shelter in which they originated and are likely to perish before they find another suitable place. At this time there are relatively few predatory insects. As autumn approaches the becomes cooler and less desiccating, and although the reproductive rate may fall the chance that young mealybugs will survive increases. This continues until the cold of winter reduces the reproductive rate to the point where it can no longer compensate for deaths and the population begins to fall. At the same time predatory insects become more numerous and take a greater toll of the population, forcing numbers still further down. In early spring the insects stop feeding and seek a sheltered place in which to reproduce. The migration from the leaves to the trunk and ground gathers momentum during September and October until the numbers left on the leaves are very low. At this time predatory insects become more numerous than they have been and the numbers of sheltering mealybugs may be greatly reduced. Then in November a new generation is produced which invades the leaves but most of these are killed quite soon by the hot dry winds which are common at this time of the year. The population falls to a low level and remains so until autumn.