Sex ratio variation as a function of host size in Pseudacteon flies (Diptera : Phoridae), parasitoids of Solenopsis fire ants (Hymenoptera : Formicidae)

Some Pseudacteon (Diptera: Phoridae) flies are parasitoids of Solenopsis (H ymenoptera: Formicidae) ant workers in North and South America. Laboratory studies of sex allocation revealed a pattern of sex ratio variation as a fu nction of host size, with more females arising from larger hosts. Environme ntal sex determination is a possible mechanism for the observed pattern, an d examination of Pseudacteon life history reveals several traits assumed to be important in models predicting conditions under which environmental sex determination is favoured. Sex allocation patterns of Pseudacteon are comp ared with theoretical predictions and empirical data from better-studied hy menopteran parasitoids that have haplodiploid sex determination. The patter n of sex ratio variation observed has important implications For biocontrol efforts of imported Solenopsis fire ants by the introduction of Pseudacteo n parasitoids. (C) 1999 The Linnean Society of London.