Improving biological control in UK organic vegetable growers

温室香草和蔬菜是英国的高价值作物。在过去的二十年里，这些作物的产量大大增加，许多生产者是有机的或正在考虑转向有机生产。目前，非有机生产者的病虫害防治严重依赖于传统的化学农药。由于最近的欧盟安全法规，其中许多正在被撤销。欧盟的一项新政策（农药可持续使用指令，2009/128/EC）旨在促进环境友好型、基于生物的虫害防治方法。政策环境的这种变化，加上最近的科学和技术进步，为基于生物的防治剂创造了真正的机会。然而，新的生物防治剂的开发受到了一种规避风险的老式方法的阻碍，这种方法基于传统化学农药商业化的系统。现在有机会以一种新的思维方式来处理这个问题，评估目前的方法，并用新的生物制剂来改进或取代它们。在这个项目中，我们将重点研究两种重要作物的生物防治，草本植物，如欧芹和有机辣椒。欧芹通常受到两种蚜虫的攻击，一种是Cavariella aegopodii，另一种是山楂欧芹蚜虫Dysaphis apiifolia。有机辣椒的主要问题是叶蝉（Empoasca deciens）。蚜虫通常用市售的寄生蜂（拟寄生蜂）来处理，寄生蜂最初是单一物种，但最近是多达六种不同物种的混合物。尽管如此，控制通常不够充分，种植者报告了不可接受的损失。另一方面，在培养皿和实验室试验中，类寄生虫似乎非常有效。在有机辣椒栽培中，推荐的防治叶蝉的生物制剂是卵类寄生蜂小夜蛾（Anagrus atomus）。更复杂的是，辣椒也会受到蚜虫的侵害，尤其是桃子马铃薯蚜虫，桃蚜和温室马铃薯蚜虫。通常使用市售的拟寄生虫可以成功控制这些疾病。不幸的是，使用灰蚜控制叶蝉通常是不成功的，种植者必须使用化学农药来拯救他们的作物，从而失去了有机的优势，破坏了成功的蚜虫生物防治剂。有人建议使用银行作物，即一种非商业作物，寄主另一种害虫的种群，原子蚜可以在其上取食和发育，并积累足够多的数量，使叶蝉的种群保持在较低的水平，但只取得了不同的成功。本博士将研究影响香菜和辣椒害虫生物防治成功的因素。例如，假设商业欧芹生产的间距使拟寄生物难以找到蚜虫宿主，此外，极快的生产进度，从萌发到收获欧芹3-4周，虽然足够长的时间使蚜虫种群达到破坏性水平，但不足以使拟寄生物有效地发挥作用。因此，我们将测试种植密度和间距对蚜虫种群生长发育和寄生蜂搜索效率的影响。此外，我们还将研究早期释放寄生蜂的效果。在辣椒中，原子蝽很难找到寄主的位置，因为辣椒可能没有足够早地激活它们的防御系统（众所周知，这些防御系统可以吸引天敌）来应对叶蝉产卵，或者是银行植物没有正确放置或质量不够。我们将测试使用顺式茉莉酸是否会刺激植物防御系统，从而改善生物防治。对庄家植物的分布和种类也将进行调查。

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 Due to recent EU safety regulations many of these are being withdrawn.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 reportunacceptable 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 bankerplants 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.