POPULATION-STRUCTURE OF RHAGOLETIS-MENDAX, THE BLUEBERRY MAGGOT

Rhagoletis mendax, the blueberry maggot, is a member of the R. pomonel la species complex, well-known as a possible example of sympatric spec iation via host race formation. Using electrophoretic data for 16 loci , I have determined that the population structure of R. mendax differs sharply from that of the well-known apple maggot fly, R. pomonella, a s follows: (i) geographical differentiation across eastern North Ameri ca is very small (F-ST=0.015 as opposed to F-ST=0.220 in R. pomonella) , (ii) no latitudinal clines in allele frequencies exist, and (iii) co nsistent differentiation with respect to individual host plant and hos t plant species was not seen (although such differentiation could not be studied as effectively in R. mendax as in R, pomonella). Fum and Ha d show strong linkage disequilibrium in two northern populations, and weak but significant disequilibrium across the entire geographical ran ge of R. mendax. The genetic uniformity of R. mendax may be a conseque nce of its restriction to a single host plant species over most of its range.