Using parasitoids to infer a native range for the obscure mealybug, Pseudococcus viburni, in South America

The co-evolutionary relationships between mealybug hosts (Hemiptera: Coccoidea) and Encyrtidae (Hymenoptera) appear to be particularly strong, and many successful classical biological control programmes against mealybugs have been carried out using these parasitoids. It is a puzzle, then, that the obscure mealybug, Pseudococcus viburni (Signoret) (Hemiptera: Pseudococcidae), is considered to be an American species but is not attacked by native parasitoids in the USA, whereas it is controlled in Europe by Acerophagus maculipennis (Mercet) (Encyrtidae) which was described from the Canary Islands (as Pseudophycus maculipennis). An examination of the biogeographical origins of both the Pseudococcus maritimus complex (to which P. viburni clearly belongs) and the genus Acerophagus Smith, coupled with historical trade records, supports the hypothesis that P. viburni and A. maculipennis are co-evolved Neotropical species, and that both were transported from S. America (probably Chile) to Europe via the Canary Islands on host plants such as potato, possibly as early as the sixteenth century. Invasion of P. viburni into the USA (and elsewhere around the world) occurred later, but without A. maculipennis (or other natural enemies). This explains why P. viburni in the USA is not attacked by native North American parasitoids and why A. maculipennis is not known to attack any mealybugs of Palaearctic origin. The hypothesis adds confidence that well conducted classical biocontrol programmes involving these taxa pose a low environmental risk to native, non-target fauna.