Abstract/Summary

Pears are an important crop to the UK and global fruit industry, with 17.9 thousand tonnes of pears produced in the UK and over 26.3 million tonnes produced globally in 2022. Pests pose a threat to the industry, most notably pear psyllid. Cacopsylla pyri is the dominant species within the UK, causing an estimated £5 million in damage and control per year. These phloem feeding pests damage orchards; nymphs produce honeydew, a sugary secretion that encourages the growth of black sooty mould on fruits and leaves, whilst adults are vectors of ‘pear decline’ (Candidatus Phytoplasma pyri); which can reduce shoot and fruit growth and cause tree death. Due to insecticide withdrawal and increased pesticide resistance, many growers rely on integrated pest management (IPM) for managing pear psylla. In addition, future impacts on this agroecosystem should be considered. UK Climate Projections (UKCP18) predict hotter, drier summers and warmer, wetter winters, which could have considerable impacts on pear flowering phenology, pear psyllid and natural enemy emergence and trophic interactions. The aim of this thesis was to highlight current methods used within pear psyllid management and potential changes that could occur under future climate scenarios, with emphasis on phenological shifts and trophic mismatches. Analysis of current management methods revealed the use of biorational compounds such as kaolin and the release of biological control agents was reasonably common within UK orchards. However, there were concerns whether biological control agents would continue to be effective in controlling psyllid populations, with respect to climate change. Findings indicated that all three trophic levels (pear, pest and natural enemies) are shifting with respect to climate change. Peak abundance date of first-generation C. pyri nymphs has become 14 days earlier compared to historical time periods, whilst pear flowering time has become 11 days earlier. However, natural enemies A. nemoralis and F. auricularia, are likely to remain suitable biocontrol agents under future temperature scenarios; anthocorid functional responses did not significantly differ under current temperature regimes compared to temperatures predicted for 2080 (RCP4.5 and RCP8.5 scenarios). Whilst earwigs consumed significantly more C. pyri nymphs under the RCP8.5 scenario (43.7 nymphs) compared to the current temperature scenario (36.0 nymphs) and showed synchrony with pear psyllid populations in phenological models. The importance of long-term monitoring data should be noted, this thesis recommends the collection of UK wide pear psyllid and natural enemy abundance data to assess phenological shifts.