Aphids out of control
Aphids are major crop pests, both in greenhouses and in the field, and are usually controlled using pesticides. Chemical control of aphid outbreaks is not environmentally friendly, nor sustainable because of the evolution of aphid insecticide resistance. Furthermore, key chemicals for aphid control have been banned, further increasing the urgency of implementing alternatives such as biocontrol.
Aphid biocontrol is most effective through the use of parasitoids that prevents early-stage aphid population expansion. Unfortunately, the effectiveness of biocontrol is sometimes failing. Endosymbionts associated with aphids can confer resistance against parasitoid attacks thus playing a role in this failure. However, information is scarce for endosymbiont variation and research about its functionality and the specificity of aphid-endosymbiont associations, and the role that the symbiont community plays in resistance is mostly lacking. In this project, we will provide this essential information through, (i) monitoring and establishing the extent of aphid-endoysmbionts associations, aphid resistance, and parasitoid virulence, (ii) unravelling the aphid-symbiont interactions and mechanisms of defence, (iii) determining the aphid-parasitoid interactions and variation in virulence, in order to (iv) deliver advice on biocontrol resource development and biocontrol application strategies.
Our project will provide key insights into the role of aphid-associated endosymbionts in the interactions between aphids and parasitoids at greenhouse levels, which, in close-collaboration with world-leading biocontrol experts from Koppert, can be implemented in the production of many important greenhouse crops. Our programme thus contributes to increasing the resilience and sustainability of crop production and contributes to technology development in the field of biocontrol.
Our research program has the following objectives:
1. To monitor and establish the extent of aphid-endosymbiont associations, aphid resistance, and parasitoid virulence;
2. To unravel aphid-symbiont interactions and mechanisms of defence;
3. To determine aphid-parasitoid interactions and variation in virulence;
4. To deliver advice on biocontrol resource development and application strategies.
These objectives are addressed in two separate PhD projects, one focusing on aphids (Beekman) and another on parasitoids (Donner).
Beoogde resultaten 2021
Expected delay caused by the Covid-19 situation
Because of Covid-19 both PhD candidates were forced to work less hours in the lab and more hours from home. This has resulted in:
- Sampling of fewer strawberry greenhouses than planned
- Suboptimal surveillance of living aphid lines in the laboratory. As a result, lines collected in the strawberry greenhouses were lost due to very low reproductive rates.
- This caused a delay in the testing of strawberry-aphid resistance against parasitoid wasps.
- None of the planned symposia and congresses happened in 2020. As a result, both PhD candidates were not able to disseminate their work to scientific peers.
All together we are expecting that the Covid-19 situation has, up until the end of 2020, caused this project a delay of approximately three months.
Plans for 2021:
Monitoring of aphid communities in pepper greenhouses (Beekman & Donner)
• Perform parasitism experiment with Aphidius ervi parasitoids on 6 Aulacorthum solani aphid lines from bell pepper greenhouses.
• Test the DNA samples of the aphids gathered from bell pepper greenhouses in 2019 for parasitoid presence. We will use published parasitoid-specific primer sets for this.
• Publish our work on aphid species and microbiomes of aphids sampled in bell pepper greenhouses in 2019
Monitoring of aphid communities on strawberry (Beekman & Donner)
• Finish testing aphid samples from the second sampling point for endosymbionts.
• Test resistance of most common strawberry aphid lines (Macrosiphum euphorbiae and Acyrthosiphon malvae) with different endosymbiont infections against Aphidius and Praon parasitoids to determine the effects of endosymbiont infections on resistance against biocontrol agents.
• Nanopore sequencing of the strawberry aphid microbiomes to: i) check if no known endosymbionts are missed with the diagnostic PCR methods, ii) if there might be currently unknown new endosymbiotic bacteria present in strawberry aphids, and iii) if microbiome composition differs between aphids collected from greenhouses using different control strategies and between different species of aphids.
Monitoring of aphid field populations in the Netherlands (Donner)
• Publish the dataset on aphid field populations.
Aphid population genetic structure (Beekman)
• Multiplex the cross-species, and newly developed primers targeting microsatellites in A. solani, and use this set of microsatellites to analyze the population genetic structure of A. solani collected from bell pepper (2019) and strawberry (2020) greenhouses.
• Sample and analyze the population genetic structure of aphids from conventional bell pepper greenhouses in 2021, to add the population genetic data to the 2019/2020 dataset we collected so far.
• Deep sequencing of M.persicae lines from different bell pepper greenhouse, with same microsatellite-genotypes, to check if microsatellite analysis shows enough depth to be able distinguish between different aphid clonal lines.
• Make a start determining the population genetic structure of strawberry aphids, apart from A. solani. Most importantly M.euphorbiae–using pre-existing microsatellite markers, and A.malvae-using ddRAD-seq or SNP analysis.