Sex ratio variation as a function of host size inPseudacteonflies (Diptera: Phoridae), parasitoids ofSolenopsisfire ants (Hymenoptera: Formicidae)

Abstract

SomePseudacteon(Diptera: Phoridae) flies are parasitoids ofSolenopsis(Hymenoptera: Formicidae) ant workers in North and South America. Laboratory studies of sex allocation revealed a pattern of sex ratio variation as a function of host size, with more females arising from larger hosts. Environmental sex determination is a possible mechanism for the observed pattern, and examination ofPseudacteonlife history reveals several traits assumed to be important in models predicting conditions under which environmental sex determination is favoured. Sex allocation patterns ofPseudacteonare compared with theoretical predictions and empirical data from better-studied hymenopteran parasitoids that have haplodiploid sex determination. The pattern of sex ratio variation observed has important implications for biocontrol efforts of importedSolenopsisfire ants by the introduction ofPseudacteonparasitoids.