The lifecycle and development of Agrilus biguttatus, and mechanisms of host resistance and annual growth in relation to Acute Oak Decline

Reed, K. (2017) The lifecycle and development of Agrilus biguttatus, and mechanisms of host resistance and annual growth in relation to Acute Oak Decline. Doctoral thesis, Harper Adams University.

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Acute Oak Decline (AOD) affects thousands of UK oaks. The two spotted oak buprestid, Agrilus biguttatus, shares a similar distribution with AOD, and its larval galleries are almost always present on symptomatic trees. To determine whether the beetle is thermally limited in the UK, and collect data for lifecycle modelling, its thermal requirements were experimentally investigated, and its life history studied. To determine whether robust host defences explain the irregular emergence of adults from symptomatic trees, wound closure, a proxy for defensive ability, was measured, in monitored trees across the range of severity of AOD decline. To investigate the nature of predisposition before, and growth after AOD onset, the trees’ annual increment was analysed. 2. The developmental data calculated for eggs, larvae, and pupae suggest climate limits the beetle’s current UK distribution, which is likely to be further restricted to warmer microsites. Its distribution, and, potentially, that of AOD, may change under a warming climate. Beetles appeared to have an obligatory prepupal diapause at all temperatures studied. 3. After two years, wound closure was most, and least, efficient in asymptomatic trees, and trees with long-term symptoms, respectively. Adult exit hole presence was strongly correlated with reduced wound closure, suggesting robust host resistance, and particularly wound response, may result in a cessation of larval development on more vigorous hosts. 4. Trees with long-term AOD symptoms seemed predisposed by poorer growth throughout their lifespans. Surprisingly, there was no evidence of growth divergences between asymptomatic and symptomatic trees after AOD onset, although trees that experienced recent growth declines were less likely to recover when beetle exit holes were present. 5. Thinning severely declined trees may increase the vigour of remaining trees and decrease beetle emergence. Improved understanding of the role of A. biguttatus in AOD is urgently needed to inform management efforts.

Item Type: Thesis (Doctoral)
Divisions: Crop and Environment Sciences (to 31.07.20)
Depositing User: Ms Kath Osborn
Date Deposited: 16 Nov 2018 11:59
Last Modified: 16 Nov 2018 11:59

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