Improving biological control in UK organic vegetable growers

Glasshouse herbs and vegetables are high value crops within the UK. Production of these crops has increased greatly over the last twenty years and a number of producers are organic or contemplating the switch to organic production. Currently, pest control in non-organic producers is heavily reliant on conventional chemical pesticides. Due to recent EU safety regulations many of these are being withdrawn. A new EU policy (the Sustainable Use Directive on pesticides, 2009/128/EC) is to promote environmentally friendly, biologically based pest control methods. This change in the policy environment, combined with recent scientific and technological advances, creates real opportunities for biologically-based control agents. The development of new biological control agents has, however, been hampered by a risk-averse, oldfashioned approach based on the system in which conventional chemical pesticides were commercialized. There is now an opportunity to approach the problem with a fresh mind-set and to evaluate current methods and to improve or replace them with novel biological agents.
In this project we will focus on biological control within two important crops, herbs, such as parsley, and organic peppers. Parsley is commonly attacked by two aphid species, Cavariella aegopodii and the hawthorn-parsley aphid, Dysaphis apiifolia. In organic peppers the major problem is the leafhopper Empoasca decipiens. The aphid species are commonly treated with commercially available parasitic wasps (parasitoids), originally as single species but more recently in mixtures of sometimes as many as six different species. Despite this, control is commonly less than adequate and growers report
unacceptable losses. On the other hand, in Petri dish and laboratory trials the parasitoids appear to be very effective.
In organic pepper cultivation the biological agent recommended against leafhoppers is the egg parasitoid Anagrus atomus. To further complicate matters, peppers are also attacked by aphids, in particular the peach-potato aphid, Myzus persicae and the glasshouse potato aphid, Aulacorthum solani. These are usually successfully controlled using commercially available parasitoids. Unfortunately, control of the leafhopper using A. atomus, is often unsuccessful and growers must then use chemical pesticides to save their crop, thus losing the organic premium and disrupting the successful aphid biological control agents. The use of banker crops, i.e. a non-commercial plant hosting populations of another pest insect on which A. atomus can feed and develop and build up to high enough numbers to keep the leafhopper populations at low levels on the crop, has been suggested, but with mixed success only.
This PhD will investigate the factors affecting successfully biological control of the pests of parsley and peppers. It is for example, hypothesized that the spacing in commercial parsley production is making it difficult for the parasitoids to locate their aphid hosts and that in addition, the extremely fast production schedule, 3-4 weeks from germination to harvest in parsley, whilst long enough to allow aphid populations to reach damaging levels is insufficient to allow parasitoids to act effectively. We will thus test the effects of planting density and spacing on the growth and development of aphid populations and parasitoid searching efficiency. In addition we will investigate the effect of earlier parasitoid release. In the peppers it is possible that A. atomus is finding host location difficult as the peppers are possibly not activating their defence systems (these are known to attract natural enemies) early enough in response to leafhopper egg laying or that the banker
plants are not correctly placed or of sufficient quality. We will test if applying cis-jasmonate will stimulate the plant defence system and result in improved biological control. The placement and species of banker plants will also be investigated.