Effects of constant and variable temperature extremes on sex ratio and progeny production by Aphytis melinus and A.lingnanensis (Hymenoptera: Aphelinidae)

Abstract. 1. Aphytis melinus DeBach and A.lingnanensis Compere were exposed to temperature extremes during development, mating, preoviposition, and opposition to assess the effect of these exposures on the progeny per female and F 1 sex ratio. 2. Both species showed a significant reduction in the expected proportion of F 1 females when the male parent was exposed to 32°C during its development. 3. The proportion of females was further reduced when mating and/or oviposition occurred at 32°C and these effects on sex ratio appeared cumulative. 4. Preovipositional exposure of the females of both species to 38°C, 2°C or ‐2°C for 1 5, 4 or 7 h in most cases significantly reduced the expected proportion of females. 5. In general our results showed that the sex ratios of A.melinus was less severely affected by these exposures than were those of A.lingnanensis. 6. It is suggested that this difference may be one factor explaining the ability of A.melinus to exclude A.lingnanensis from the climatically more extreme areas of southern California.