Morphological variation and mating compatibility within the mealybugs Pseudococcus calceolariae and P. similans (Hemiptera: Pseudococcidae), and a new synonymy

A laboratory study of isolines of Pseudococcus calceolariae (Maskell) and P. similans (Lidgett) collected from Hawke's Bay and Auckland, two widely separated regions in the North Island of New Zealand, threw doubt on the validity of the defining characters of these species. For P. similans, the number and position of oral rim tubular ducts varied widely and sometimes fell outside the defined limits for the species, and characteristic ‘stout abdominal setae’ were lost in the F₁ generation. The morphological characters that separate one species from the other were manipulated by changing the temperature at which the mealybugs developed, such that cohorts of F₁ sisters reared in the laboratory contained phenotypes of both P. calceolariae and P. similans. No impediments were found to breeding among populations of P. calceolariae and P. similans from Hawke's Bay and Auckland. All combinations of crosses between virgin females and males produced viable progeny. Those reared at 16°C laid more eggs than those reared at 23°C. The data did not suggest the existence of cryptic or sibling species, and contrasted with experiments elsewhere which quite clearly showed species incompatibility of closely related mealybugs. Examination of 160 ‘wild’ specimens of P. calceolariae from New Zealand, Australia and California (U.S.A.) and P. similans from New Zealand and Australia showed a morphological continuum from one species to the other. It is concluded that P. calceolariae and P. similans merely represent the phenotypic extremes of one widely polymorphic species, with the morphological characters of individual adults determined by the microenvironment in which they developed. Pseudococcus calceolariae is thus the senior synonym of P. similans.