<I>Diaeretiella rapae</I> Limits <I>Myzus persicae</I> Populations After Applications of Deltamethrin in Oilseed Rape

Abstract

In fall, Myzus persicae (Sulzer) (Homoptera: Aphididae) may exhibit population resurgence in winter oilseed rape in France. This resurgence may arise from pyrethroid treatments against Coleoptera (Psylliodes chrysocephala L.) that either kill parasitoids present during treatment or prevent recolonization by off-crop parasitoids. We studied the impact of Diaeretiella rapae (M'Intosh) (Hymenoptera: Braconidae) on populations of M. persicae when parasitoids were introduced on deltamethrin-treated plants at increasing intervals after treatment. Parasitoids were introduced 1, 2, 7, or 14 d posttreatment on individually caged plants infested with established populations of M. persicae. Aphids were counted 7, 14 and 21 d after parasitoid introduction. First, we observed that both the pesticide and the parasitoid reduced aphid population growth and that their effects were additive. Second, there was no mortality of parasitoids exposed to treated leaves in a device with a refuge area, and only 20% of mortality without the refuge area. Furthermore, deltamethrin residues had no effect on the reproduction of D. rapae females. Compared with the known toxicity of deltamethrin to D. rapae on glass, this low mortality may have been due to both the high liposolubility of deltamethrin (leading to a rapid diffusion of residues in the oilseed rape leaf cuticle) and to the existence of a refuge area. This work suggests that D. rapae could limit populations of M. persicae in the fall, even after pyrethroid treatment, because the presence of deltamethrin residues had little impact on the parasitoid.

Transcriptomic analysis of pea aphids (Acyrthosiphon pisum) treated with plant extracts from endophyte‐containing drunken horse grass

“…The pea aphid mortality was examined after the exposure for 24 hr, 48 hr and 72 hr. Pea aphids were regarded to be dead when no movements were observed after being tenderly touched (Moores et al, 1996;Desneux et al, 2005). Also, after 24 hr, 40 surviving adult wingless pea aphids (whole individual) were collected from each treatment, respectively.…”