Search Results (7)

Diaeretiella rapae (McIntosh, 1855) is a cosmopolitan koinobiont endoparasitoid of aphids, occurring mainly on crucifers and cereals. From description, it has changed several genera and has about 20 synonyms. The specimens for this study were collected between 1989 and 2023 from sites across Europe and the Middle East. For molecular analysis, the barcode mitochondrial gene COI was used, and morphological analysis was conducted with other Aphidius species. Morphologically, D. rapae falls within the determined variability of the same characters of the genus Aphidius. Dieretiella rapae comprised 23 haplotypes with a mean genetic distance between haplotypes of 0.8%. Phylogenetically, D. rapae is nested within Aphidius species with a genetic distance of 2.1% to 11.3%, which is within the range of other Aphidius species. Our results on morphological and molecular level confirm that D. rapae belongs to the genus Aphidius. Full article

Agricultural land use and its disruption of natural landscapes threaten the provision of ecosystem services, such as biological control by natural enemies, because of habitat simplification and management intensification. However, most studies that evaluate the effect of local management practices rarely identify and include other important predictors such as landscape compositional values. We studied the effect of adding flower strips at farms on the control of aphids in a seminatural habitat (SNH) gradient. We found significantly less aphids on farms with flower strips and more SNH at the second sampling date as well as a greater proportion of mummies with flowers early in the season, with a greater proportion of mummies at a greater %SNH at the end of the season. Foraging predators responded to the %SNH of farms without flowers only on the second sampling date, which coincided with their highest mean abundances. Our data suggests that aphid parasitism was enhanced by flowers, having a potential effect early in the season, which ultimately explained the reduction in aphid numbers thereafter. On the other hand, the effects perceived on predator abundances seemed to be more date- and landscape-sensitive. Flower strips of faba beans and buckwheat in the field as well as the %SNH surrounding farms positively affected Diaeretiella rapae and could therefore be an important management strategy to decrease Brevicoryne brassicae densities in brassica crops. Full article

Despite the known benefits of integrated pest management, adoption in Australian broadacre crops has been slow, in part due to the lack of understanding about how pests and natural enemies interact. We use a previously developed process-based model to predict seasonal patterns in the population dynamics of a canola pest, the green peach aphid (Myzus persicae), and an associated common primary parasitic wasp (Diaeretiella rapae), found in this cropping landscape. The model predicted aphid population outbreaks in autumn and spring. Diaeretiella rapae was able to suppress these outbreaks, but only in scenarios with a sufficiently high number of female wasps in the field (a simulated aphid:wasp density ratio of at least 5:1 was required). Model simulations of aphid-specific foliar pesticide applications facilitated biological control. However, a broad-spectrum pesticide negated the control provided by D. rapae, in one case leading to a predicted 15% increase in aphid densities compared to simulations in which no pesticide was applied. Biological and chemical control could therefore be used in combination for the successful management of the aphid while conserving the wasp. This modelling framework provides a versatile tool for further exploring how chemical applications can impact pests and candidate species for biological control. Full article

Plants use a variety of secondary metabolites to defend themselves against herbivore insects. Methyl salicylate (MeSA) is a natural plant-derived compound that has been used as a plant defence elicitor and a herbivore repellent on several crop plants. The aim of this study was to investigate the effect of MeSA treatment of Brassica rapa subsp. chinensis (‘Hanakan’ pak choi) on its interactions with peach potato aphids, Myzus persicae, and their natural enemy, Diaeretiella rapae. For this, we selected two concentrations of MeSA (75 mg/L and 100 mg/L). Our results showed that aphid performance was significantly reduced on plants treated with MeSA (100 mg/L). In a cage bioassay, the MeSA (100 mg/L)-treated plants showed lower adult survival and larviposition. Similarly, the MeSA (100 mg/L)-treated plants had a significantly lower aphid settlement in a settlement bioassay. In contrast, the M. persicae aphids did not show any significant difference between the MeSA (75 mg/L)-treated and control plants. In a parasitoid foraging bioassay, the parasitoid D. rapae also did not show any significant difference in the time spent on MeSA-treated and control plants. A volatile analysis showed that the MeSA treatment induced a significant change in volatile emissions, as high numbers of volatile compounds were detected from the MeSA-treated plants. Our results showed that MeSA has potential to induce defence in Brassica against M. persicae and can be utilised in developing sustainable approaches for the management of peach potato aphids. Full article

Aphid alarm pheromones, as important semiochemicals, not only mediate behavioral response of aphids, but can also act as kairomones to attract their natural enemies. The sesquiterpene (E)-β-farnesene (EβF), the major alarm pheromone component of most aphid species, has been shown to have a kairomonal effect on the predators of aphids, but other alarm pheromone components, especially the monoterpenes and analogs, are rarely investigated. Here, two EβF analogs were successfully synthesized via the nucleophilic substitution reaction, and we then examined the kairomonal effects of four alarm pheromone components and two EβF analogs on the aphid parasitoid, Diaeretiella rapae. In olfactory bioassays, D. rapae females generally showed no significant behavioral response to these alarm pheromone components and analogs under low concentrations (0.1 μg/μL). Nevertheless, their olfactory response to these compounds gradually enhanced with increasing concentrations. Among the four pheromone components, EβF showed the highest attractive activity, but the parasitoid preferred blends over single compounds. Moreover, the response time decreased as the concentration increased. We confirmed the kairomonal effect of monoterpene alarm pheromone components and their blends, in addition to EβF, on the natural enemies of aphids. This is the first report that the blend of alarm pheromone components and their analogs has a stronger kairomonal effect than do the single components on the natural enemies of aphids. This study contributes to our understanding of the mechanisms involved in the regulation of parasitoid behaviors by kairomones and provides a promising opportunity for designing kairomones for the aphid parasitoid to mediate aphid populations in the field. Full article

The reproduction of aphids depends to a great extent on their host plants, an integration that impacts on the successful expansion of overwintering populations. Therefore, a survey was conducted to evaluate the globally distributed Capsella bursa-pastoris as an overwintering host of economically important aphid species, their parasitoids and hyperparasitoids in the southern and western regions of Turkey from November to March in 2006 to 2013. During this survey, 395 samples of C. bursa-pastoris were collected with 25 aphid species recorded. Among aphids that feed on this host, Myzus persicae, Aphis gossypii, Rhopalosiphum padi, Aphis fabae, Aphis craccivora, Lipaphis erysimi, and Brevicoryne brassicae were the most frequently recorded. In total, 10,761 individual parasitoids were identified. Binodoxys angelicae, Aphidius colemani, Aphidius matricariae, Diaeretiella rapae, Ephedrus persicae, and Lysiphlebus confusus were the most abundant aphidiines that emerged from the aphids collected from C. bursa-pastoris. Alloxysta spp. (Hymenoptera: Cynipoidea), Chalcidoidea (unidentified at genus level), and Dendrocerus spp. (Hymenoptera: Ceraphronoidea) were identified as hyperparasitoids on the parasitoids. These findings indicate that C. bursa-pastoris is a key non-agricultural plant that significantly contributes to the overwintering of numerous aphids and their parasitoids, which should be given serious consideration when biological control strategies are designed. Full article

In grain crops, aphids are important pests, but they can be suppressed by hymenopteran parasitoids. A challenge in incorporating parasitoids into Integrated Pest Management (IPM) programs, however, is that parasitoid numbers can be low during periods within the season when aphids are most damaging. Understanding the population dynamics of key aphid species and their parasitoids is central to ameliorating this problem. To examine the composition and seasonal trends of both aphid and parasitoid populations in south-eastern Australia, samples were taken throughout the winter growing seasons of 2017 and 2018 in 28 fields of wheat and canola. Myzus persicae (Sulzer) was the most abundant aphid species, particularly within canola crops. Across all fields, aphid populations remained relatively low during the early stages of crop growth and increased as the season progressed. Seasonal patterns were consistent across sites, due to climate, crop growth stage, and interactions between these factors. For canola, field edges did not appear to act as reservoirs for either aphids or parasitoids, as there was little overlap in the community composition of either, but for wheat there was much similarity. This is likely due to the presence of similar host plants within field edges and the neighbouring crop, enabling the same aphid species to persist within both areas. Diaeretiella rapae (M’Intosh) was the most common parasitoid across our study, particularly in canola, yet was present only in low abundance at field edges. The most common parasitoid in wheat fields was Aphidius matricariae (Haliday), with field edges likely acting as a reservoir for this species. Secondary parasitoid numbers were consistently low across our study. Differences in parasitoid species composition are discussed in relation to crop type, inter-field variation, and aphid host. The results highlight potential focal management areas and parasitoids that could help control aphid pests within grain crops. Full article