Assessing the optimal frequency of early parasitoid releases in an apple orchard to control Dysaphis plantaginea: a proof of concept study

Abstract

Alternative measures to pesticides to control the rosy apple aphid Dysaphis plantaginea are being developed. Naturally occurring predators and parasitoids often fail to reduce aphid abundance below the economic threshold in orchards, because they are active too late after the aphid first infestation. We tested the efficiency of mass release of two parasitoid species, Aphidius matricariae and Ephedrus cerasicola, early in the season to match the presence of aphid fundatrix (sensitive stages). In this trial focusing on an organic apple orchard, three releases were done either every week or every two weeks to test the effect of the release frequency, during two consecutive years. The number of aphid colonies and aphid number per tree were monitored from late March to late May. Degree-days necessary for parasitoid emergence in the field after release were calculated. We show that a sufficient level of aphid control by parasitoids is reached during the first month of the survey, but control mostly fails during the second part of the monitoring session, for both release treatments, and compared to the neem oil control treatment. The relative effects of release frequencies were different between years probably because of interannual differences in aphid population dynamics and initial infestation in orchards. The field survey and the degree-day model suggest that parasitoid releases, at either frequency, are promising candidates for biological control of the rosy aphid, although the method still needs proper calibration. This conclusion needs to be reinforced by repeating the study in more orchards, but our case study lays the first empirical basis that will help to develop future control methods of aphids by parasitoid releases in apple orchards. We argue that releases should be done one to two weeks before first aphid detection to account for long development times of parasitoids at relatively low temperatures.

Flower strips increase the control of rosy apple aphids after parasitoid releases in an apple orchard

“…Three parasitoid releases were done at 10-day intervals, according to a preliminary study that showed that these two species are complementary in terms of emergence timing in the orchards (Ferrais et al, 2022). For each release, the mix of parasitoid species was provided by Viridaxis SA (Belgium) in cardboard tubes, each containing ≈675 A. matricariae and ≈570 E. cerasicola at the final development stage (mummies) and placed directly on each tree.…”

“…For each release, the mix of parasitoid species was provided by Viridaxis SA (Belgium) in cardboard tubes, each containing ≈675 A. matricariae and ≈570 E. cerasicola at the final development stage (mummies) and placed directly on each tree. This allowed obtaining a minimum emergence per release of 114 A. matricariae and 135 E. cerasicola per tree (Ferrais et al, 2022). In 2018, releases were done on 13 April, 24 April and 4 May.…”

“…A cocktail of two solitary parasitoid species, Aphidius matricariae and Ephedrus cerasicola (Hymenoptera: Braconidae), was developed in previous projects to control D. plantaginea in apple orchards (Boivin et al, 2012;Dumont et al, 2011;Ferrais et al, 2021;Nicolas et al, 2013). Parasitoid cocktails are used in inundative biological control strategies in several crop systems, because each species can complement the others on their host spectrum, on activity timing, and on behavioral and physiological specificities (Boivin et al, 2012).…”

“…Therefore, augmentative releases of beneficial insects in early spring have been proposed to complement the impact of the naturally occurring natural enemies of aphids (Dib et al, 2016; Kehrli & Wyss, 2001). The aim is to target aphid fundatrix, the wingless aphids hatching from overwintering eggs, because they are relatively few in number, but at the starting point of an exponential and massive parthenogenetic reproduction in early spring, which will be damaging to trees (Ferrais et al, 2022).…”

“…The aim is to target aphid fundatrix, the wingless aphids hatching from overwintering eggs, because they are relatively few in number, but at the starting point of an exponential and massive parthenogenetic reproduction in early spring, which will be damaging to trees (Ferrais et al, 2022).…”