Is what you see what you get? The relationship between field observed and laboratory observed aphid parasitism rates in canola fields

Abstract

Background: Estimating parasitoid abundance in the field can be difficult, even more so when attempting to quantify parasitism rates and theecosystemserviceofbiologicalcontrol thatparasitoidscanprovide.Tounderstandhow'field observed'parasitismrates(in-field mummy counts) of the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae) translate to 'laboratory observed' parasitism rates (laboratory-reared parasitoid counts), field work was undertaken in Australian canola fields, over the winter growing season.Results: Overall, laboratory observed parasitism was on average 2.4 times higher than field observed parasitism, with rates an average of four-fold higher in fields from South Australia. Total field observed and laboratory observed parasitism rates (OPRs) of M. persicae varied considerably across regions, but less so among fields within regions. As crop growth stage progressed, the incidence of field observed mummies increased. The incidence of total parasitoids reared also increased with crop growth stage, averaging 3.4% during flowering and reaching 14.4% during podding/senescing. Although there was a greater diversity of reared parasitoid species at later crop growth stages, the laboratory OPR was unaffected by parasitoid species. Diaeretiella rapae was the most commonly reared parasitoid, increasing in absolute abundance with crop growth stage.Conclusion: These findings indicate that field mummy counts alone do not provide a clear representation of parasitism within canola fields.

A rapidly spreading deleterious aphid endosymbiont that uses horizontal as well as vertical transmission

“…Our findings suggest that Rickettsiella can rapidly spread through aphid populations despite asexuality under cool conditions, and this can happen through both vertical and horizontal transmission. Given aphids in winter grain crops often build up from a low population density ( 72 ), deliberate releases of transinfected aphids early in the crop development stage and their subsequent rapid spread could lead to the collapse of the aphid population later in the crop stage when conditions become warmer due to the fecundity costs of Rickettsiella and their impact on heat resistance. In this way, Rickettsiella could impact aphid population dynamics in novel ways and persistent Rickettsiella infections could even have impacts across multiple years, increasing in frequency as conditions become cooler during the establishment phase of winter crops.…”

Application of a Mechanistic Model to Explore Management Strategies for Biological Control of an Agricultural Pest

“…During the dry summer months, M. persicae in Australia take refuge on secondary host plants within the landscape [28]. Diaeretiella rapae is similarly distributed across the Mediterranean-type climate zone of Australia, although relatively little is known about its life-history and phenology [14,15,29,30].…”

“…The model describes a population of aphids that occupy a 1 m 2 "patch" within a canola paddock [16] and assumes that all M. persicae individuals are virginoparae [27]. While many models integrate spatial and temporal components, here we focus on the temporal patterns in population dynamics within a small area, given the lack of knowledge of the M. persicae and D. rapae spatial distribution and association across field crop environments [15].…”

“…A promising candidate species for biological (and augmentative) control of M. persicae, is the wasp Diaeretiella rapae (M'Intosh) (Hymenoptera: Braconidae: Aphidiinae). Laboratory studies confirmed that D. rapae readily parasitises M. persicae [14], and its potential as a biological control agent in grain crops across Australia has recently been recognized [15]. A number of studies have already modelled the population dynamics of M. persicae [16][17][18][19].…”

Low prevalence of secondary endosymbionts in aphids sampled from rapeseed crops in Germany

“…One avenue that is being explored is the promotion of natural enemy populations, such as parsitoid wasps, that can provide natural pest regulation services (Ali et al, 2023;Elliott et al, 2023). The main parasitoids of M. persicae and B. brassicae include Aphidius ervi Haliday (Hymenoptera: Braconidae), A. colemani Viereck (Hymenoptera:Braconidae), and Diaeretiella rapae McIntosh (Hymenoptera:Braconidae) (Mehrparvar et al, 2019;Ward et al, 2022). By promoting the abundance and activities of these parasitoids farmers could increase the provision of natural pest regulation services and reduce reliance on chemical-based pest control methods.…”