The Role of Predators and Attendant Ants in the Regulation and Persistence of a Population of the Citrus Mealybug Pseudococcus citriculus in a Satsuma Orange Orchard

Abstract

The role of predation in regulating a population of the citrus mealybug, Pseudocuccus citriculus, and the effects of ant-attendance on the predator-prey interactions were studied in a pesticide-reduced Satsuma orange orchard in Wakayama Prefecture, Japan. The population of the first generation increased by more than 5 fold when predaceous insects were excluded, whereas it did not show a notable change in size under natural conditions where enemies naturally attacked mealybugs and some mealybugs were well protected by a honey-dew-collecting ant, Lasius niger. The mealybug population showed a drastic decrease by 94% when the attendant ants (L. niger) were excluded. Attending ants (L. niger) were observed to protect P. citriculus by aggressive behaviour towards its natural enemies, the common coccidophagous ladybird beetle Chilocorus kuwanae and a lacewing species (Chrysopidae sp.). Field censuses and laboratory rearing suggested that the two abundant predaceous insects are the effective agents regulating the mealybug population at low density. These result demonstrate that predators regulate the population of P. citriculus and that ant-attedance is indispensable to the persistence of the mealybug population.