Arable: Yellow Wheat Blossom Midge - an emergent threat to UK wheat production

Yellow Wheat Blossom Midge (YWBM) is a poorly understood and often under-reported insect pest of wheat, the UK's most widely grown crop. Midge larvae feed on the wheat flower, preventing grain formation and leading to significant yield losses. All wheat varieties are reported to be susceptible to this pest. In some years, the ideal conditions required for adult midges to emerge from dormancy in the soil, mate and lay eggs occur just as the wheat is at its most vulnerable to attack. However, YWBM damage varies from year-to-year and is currently difficult to predict. This project aims to further our knowledge of this pest and its impact on the wheat crop.

In related pest midges, adult females produce a volatile sex pheromone which allows adult males to locate females prior to mating. Synthetic versions of these pheromones released from simple traps are widely used in many crops to monitor midge pests and identify when and where control strategies must be applied. By identifying the sex pheromone of YWBM in this project, we will have completed the necessary first step in developing an appropriate monitoring tool for use in UK wheat crops.

We have previously identified experimental NIAB wheat lines that showed no YWBM damage in seasons when midge levels were high in adjacent varieties. With help from plant breeding companies, we will test these promising lines more thoroughly. We will grow them in small field plots at several locations across the UK, and measure YWBM levels in resistant NIAB lines and in susceptible commercial varieties. We will collect unripe wheat ears containing live YWBM larvae, and soil samples containing dormant pupae, from these and other sites to provide a source of midges.

Young midges will be reared individually at NIAB East Malling until they emerge as adults. NIAB and NRI specialists will collect the volatile chemicals produced by groups of adult males and females. Through electrophysiological experiments at NRI, we will identify which chemicals produced by female midges can be detected by the males as likely components of the sex pheromone.

Using chemical analysis and our experience in identifying other midge pheromones, we will begin identification of the YWBM sex pheromone components. If supply of midges and time allows, we will synthesize these likely components for further testing. NIAB will also explore the feasibility of maintaining a laboratory colony of YWBM for future work into the life cycle of this important pest.

Yellow Wheat Blossom Midge (Contarinia tritici; YWBM) is a poorly understood pest of wheat, with no reported host resistance. Its larvae feed on wheat anthers and stigmas, leading to significant yield losses. The complex control of both adult midge emergence and wheat flowering time means that YWBM outbreaks can be sporadic and difficult to predict. We aim to further our knowledge of this pest and its impact.

Previously, some NIAB experimental wheat pre-breeding lines have shown consistently little YWBM damage, in contrast to nearby varieties at matching developmental stages. Partners will grow promising NIAB lines alongside susceptible commercial varieties at several field locations and monitor YWBM levels. Samples of unripe ears containing live larvae and soil containing dormant pupae from these trials will be used as a source of midges.

At NIAB East Malling, midges will be reared individually until they emerge as adults, with sex determined through differences in genital and antennal morphology. Volatiles will be collected from groups of virgin adult males and females through headspace entrainment onto Porapak.

At NRI, potential pheromone components will be determined through GC coupled to electroantennographic recording (GC-EAG), and their possible structure determined by gas chromatography - mass spectrometry. Identification will be informed by differences in volatiles produced by males and females, and by our experience with related species (e.g., the newly discovered oilseed rape pest Contarinia brassicola). We will begin synthesis of potential pheromone components, and if supply of midges allows, confirm their detection by males through GC-EAG.

Future possible work includes investigations into the genetic control of host resistance, the optimisation of synthetic pheromone lure traps, and the feasibility of maintaining laboratory colonies of YWBM to further understand its life cycle and host interactions.