The Chemical Diversity of Midge Pheromones

Dates: 2006-2009

FUNDING: Horticultural Development Council, Worshipful Company of Fruiterers, laxoSmithKline Blackcurrant Growers Research Fund

COUNTRIES: UK

SCIENTIFIC COLLABORATORS: East Malling Research (EMR)

INDUSTRIAL COLLABORATORS: GlaxoSmithKline Blackcurrant Growers Research Fund

NRI PROJECT LEADER: David Hall

BACKGROUND

Many horticultural crops, especially perennial fruit crops, are subject to pest attack by various species of leaf curling or other gall midges. Some species are currently controlled with the broad-spectrum organophosphate (OP) chlorpyrifos or with pyrethroid insecticides but use of these insecticides is undesirable because they are harmful or toxic and because they disrupt Integrated Pest Management. These midges are thus likely to continue as significant pests and will affect the economic viability of their host crops. For other species, such as the apple and pear leaf midges, there are currently no effective control methods and they already cause extensive damage, especially in nurseries and young orchards. Alternative, non-pesticidal control methods need to be identified.

Pear midge female © University of Greenwich

Plant-feeding midges are typically very short-lived as adults and highly specific for their host-crop. In several species there is evidence for production of highly potent sex pheromones by virgin female adults and strong attraction of mated females to volatiles from host plants. Identification of these attractants could provide means of manipulating pest behaviour at critical stages in their life cycle. However, identification of the attractants has proved extremely challenging due to the very small amounts of chemical involved and the difficulties of carrying out laboratory bioassays with the small and delicate insects.

OBJECTIVES

The overall aim of this project is to explore the chemical diversity in female sex pheromones of herbivorous midges and whether patterns exist within and between genera. In particular it will aim to further knowledge on how widespread is the novel type of structure recently found in the pheromone of the apple leaf curling midge in comparison with the diester pattern found in most midge pheromones identified to date. Specific objectives will be to identify the female sex pheromones of three midges of significance to the UK horticultural industry, those of the pear midge, the pear leaf midge and the blackcurrant gall midge.

RESULTS

© University of Greenwich

This work is being carried out by Lakmali Amarawardana as the basis for her PhD thesis. The main component of the female sex pheromone of the pear leaf midge, Dasineura pyri, has been detected by linked GC-EAG (right) and identified as a novel 17-carbon unsaturated diester. The four isomers have been separated by chiral hplc and one has been shown to be attractive to male midges in the field. Two components of the female sex pheromone of the pear midge, Contarinia pyrivora, have been identified and synthesised and the isomers are being separated for field trials during 2008. A structure for the major component of the female sex pheromone of the blackcurrant leaf midge, D. tetensi, has been proposed and synthesis is in progress.