Differences in the reproductive durations of Myzus persicae (Hemiptera: Aphididae) parasitized by three aphidiid parasitoids

The reproductive durations of Myzus persicae (Sulzer) after parasitization by three species of Aphidiinae were compared and the mechanisms for differences in duration were examined. The lifetime fecundities of adult aphids parasitized by Aphidius colemani Viereck, Aphidius gifuensis Ashmead, and Diaeretiella rapae (McIntosh) were 3.96, 6.40, and 6.48, respectively. These values were much smaller than that of healthy adults (61.43 nymphs). The time of termination of reproduction by the aphids coincided with the time that the parasitic wasp larvae reached second instar. We infer that first-instar larvae of all three species initially attack conspecific and/or heterospecific competitors and that consumption of the aphid’s ovaries and other reproductive organs commences in the second instar. The modified intrinsic rates of natural increase (r ₚₐᵣₐₛᵢₜᵢzₑd) calculated from post-parasitized fecundity were 0.185 by A. colemani, 0.233 by A. gifuensis, and 0.234 by D. rapae. Parasitization of 100 % of the adult aphids by A. gifuensis or D. rapae decreased the growth rate to a minimum of 24.4 % while A. colemani more moderately suppressed the growth of the aphid population (39.9 %). We propose the possibility that the effectiveness of species of Aphidiinae as biological control agents is influenced by differences in the duration of aphid reproduction following parasitization.