Context
Account must be taken of the activity of pests’ natural enemies when developing integrated pest management programmes for field crops. Analysis of data obtained for potatoes between 1994 and 2001 established the effectiveness thresholds of some natural enemies above which aphid population growth is controlled or insecticide treatment cannot be justified. These thresholds are two predator larvae or ten aphids attacked per hundred aphids.More detailed information on the diversity and activity of natural enemies serves to identify all the situations where systematic insecticide treatment can be avoided and to determine which beneficial species should be protected and encouraged by appropriate agri-environmental measures.
A biodiversity study carried out over several years also reveals any changes due to climate change or the introduction of invasive species such as the Asian ladybird.
Objectives
The aim of this study is to establish the diversity and extent of aphids’ specific enemies in cereals and potatoes, as considerable natural aphid control potential has been noted in the case of these crops.Description of tasks
This work has two separate bases:- measuring, by field entomological surveys, the diversity of the specific enemy species in situ and their impact on aphid population growth;
- using, by statistical analysis, the data previously gathered within the framework of pest warning systems.
Results obtained
With regard to aphid predators, eight syrphid species, six ladybird species and two lacewing species were found in potatoes in 2003 and 2004. Most of these species also occur in many other crops, notably cereals, and are thus part of a group of aphid-eating predators who are particularly well suited to perennial and herbaceous crops. A close relationship also appears to exist between predator populations occurring in cereals in the early summer and later populations found in other crops.A systematic study in potato crops highlighted the significance of two Aphidiidae parasite species, Aphidius ervi and Aphidius picipes. These two natural enemies alone are responsible for almost 80% of all aphid parasitism. Their broad parasitism spectrum and occurrence in many other crops suggest that natural enemies may transfer from one crop to another. Our surveys also revealed the very low level of parasitism of Aphis nasturtii which to a great extent accounts for that pest’s high reproductive potential. Investigation of species-specific parasites is one avenue to be explored for the purposes of integrated pest management programmes, especially since this pest is particularly hard to control by chemical means.
The entomological surveys in potatoes revealed the occurrence of the Asian ladybird Harmonia axyridis (Pallas), first found in Belgian field crops in 2003. The presence of eggs, larvae, pupae and adults indicates that this ladybird is successfully breeding in field crops and competing with indigenous species there. A more detailed study of this species in 2004 showed H. axyridis to occur later than other ladybirds and to be more of a potential predator upon indigenous ladybirds than an aphid predator. (link to a page on Harmonia)
Funding
- CRA-W - Walloon Agricultural Research Centre
