Development and deployment of rapid molecular diagnostic tools to assess biocontrol strategies of the highly-invasive oak processionary moth for integrated pest management

Abstract

Oak Processionary Moth (Thaumetopoea processionea - OPM) is a serious forestry pest and risk to public health in the UK. The unsustainable nature and spiralling cost of chemical pesticides in managing OPM has driven the need for sustainable, integrated pest management including the use of novel biocontrol methods. The challenges posed by the health risks of OPM make many morphological methods impractical. Molecular methods offer a solution to this by reducing contact between humans and OPM material. Here the use of molecular methods for the discovery and surveillance of biocontrol prospects, such as Carcelia iliaca, in OPM is implemented. A field applicable molecular approach to diagnosing parasitism in OPM was successfully developed and validated with diagnostic sensitivity (91%) and specificity (75%) that is considered suitable by industry standards. This was then applied to OPM samples from the Greater London area over a two-year study to reveal parasitism rates of C. iliaca. Parasitism rates were found to be variable with no spatial pattern that could be linked to environmental covariates and the data set being too short in duration to infer reliable temporal trends. To investigate the possibility of pathogen control of OPM, tagged nested metabarcoding was used to characterise the bacterial and fungal communities associated with diseased and healthy OPM samples. Overall, species richness and diversity were higher in diseased samples which was either caused by opportunistic coloniser species in diseased samples or a reduced species richness and diversity in healthy samples driven by a bacterial symbiont. Non-metric multidimensional scaling analysis found little overall community difference although the presence of Wolbachia, Beauveria, and Fusarium, do drive some differences. These results demonstrate how novel molecular methods can be adapted for use in informing the management of an invasive pest species. The successes and lessons from this work will be applicable to the next generation of forestry pests that are predicted to arrive in the UK.