Dis-service Management Protocols

As indicated in the warning triangle at point 4 in the spiral, although attempts to enhance and manage ecosystem services (ES) in agriculture and horticulture have had some dramatic successes, ecosystem dis-services (EDS) may be occurring at the same time and researchers are not always aware of this possibility. The photograph of a car and the video of ants attacking a parasitoid which are part of the EDS warning triangle are two good examples of EDS occurring. We therefore need dis-service management protocols (DMP) to at least improve the ratio between ES and EDS, favouring the former. A further example of where EDS needs to be managed is the invasion of commercial glasshouses in the UK by an aphid hyperparasitoid which attacks the aphid parasitoid biocontrol agents (see image below). The proportion of hyperparasitoids compared with the primary parasitoids was high for much of the growing season (see graph below; Jacobson 2011). In that work there was no apparent selection management in favour of the primary parasitoids. Historically, the only management intervention was insecticide use, which was certainly not selective in favour of the main biological control agent.

An example of hyperparasitism. The photograph shows a broken mummy of the cabbage aphid (Brevicoryne brassicae (L.)) containing an empty pupa of a parasitoid, probably of Diaretiella rapae M’Intosh. Two eggs of a hyperparasitoid can be seen on the empty parasitoid pupa. Photo Yann-David Varennes (Lefort et al. 2017).

Proportion of primary parasitoids to hyperparasitoids throughout the season (from Jacobson 2011).

More recently, work by Dr David Foster and colleagues of Koppert Biological Systems, U.K., in glasshouse capsicums tends to slow the build-up of the aphid mummies by using Aphidius matricariae Haliday as a biological agent in the first part of the year instead of Aphidius colemani Viereck.A. matricariae performs better as an aphid biocontrol agent at lower light levels early in the northern hemisphere year and has a lower aphid density oviposition threshold. That leads to low aphid and mummy populations, so the hyperparasitoids then tend to appear later, around July, which is late summer in the northern hemisphere. When hyperparasitism eventually reaches 25%, further introductions of parasitic wasps ceases and an aphid predator (the midge Aphidoletes aphidimyza Rondani) is deployed at ‘curative rates’ of 2/m2.

It is of interest to consider other ways that managing an EDS such as this could be designed. Perhaps nectar-bearing plants that favour the primary parasitoid more than the hyperparasitoid could be used, thereby enhancing the fecundity and longevity of the third trophic level more than that of the fourth. There is some evidence that a fifth trophic level may exist in some systems in which hyperparasitoid guilds may attack the larvae or the pupae of the hyperparasitoid inside the primary parasitoid host (Araj et al. 2010). The extent to that this modifies the EDS caused by hyperparasitoids is unknown.

It is of interest to consider other ways that managing an EDS such as this could be designed. Perhaps nectar-bearing plants that favour the primary parasitoid more than the hyperparasitoid could be used, thereby enhancing the fecundity and longevity of the third trophic level more than that of the fourth. There is some evidence that a fifth trophic level may exist in some systems in which hyperparasitoid guilds may attack the larvae or the pupae of the hyperparasitoid inside the primary parasitoid host (Araj et al. 2010). The extent to that this modifies the EDS caused by hyperparasitoids is unknown.

Another example of of enhancement of ES that could generate EDS is the use of particular flower species to provide nectar and pollen to beneficial insects. For example the annual brassica, sweet alyssum (Lobularia maritima (L.) Desv.) that is deployed to reduce aphid populations in lettuce (see Gillespie et al. 2011 and the first photograph in Ecosystem Services (4). If such a plant became a weed, a dis-service management protocol would be required. This could comprise deploying an alternative nectar-bearing plant species or a brassica-specific herbicide to be deployed after the harvest of the lettuce crop. As brassicas habour many insect pests, alyssum could become a host for them.

References

Araj, S., Wratten, S., Lister, A., Buckley, H. and Ghabeish, I. 2011. Searching behavior of an aphid parasitoid and its hyperparasitoid with and without floral nectar. Biological Control, Vol. 57:79-84.

Gillespie, M., Wratten, S., Sedcole, R. and Colfer, R. 2011. Manipulating floral resources dispersion for hoverflies (Diptera: Syrphidae) in a California lettuce agro-ecosystem. Biological Control, Vol 59:215-220. Doi 10.1016/j.biocontrol.2011.07.010.

Jacobson, R. 2011. Sweet pepper: Further development of IPM solutions for aphid infestations. Final Report, Project PC 295b, Agriculture and Horticulture Development Board 2011.

Lefort, M. C., Wratten, S., Cusumano, A., Varennes, Y. D., & Boyer, S. (2017). Disentangling higher trophic level interactions in the cabbage aphid food web using high-throughput DNA sequencing. Metabarcoding and Metagenomics, 1, e13709.