Phytophagous Mite Control in Raspberry: Integrating Top-Down and Bottom-Up Approaches

Phytophagous mites are major agricultural pests in annual, perennial and horticultural crops. In UK raspberry plantations, two mite species are particularly problematic, causing foliar damage, fruit malformation and yield loss: two-spotted spider mite (TSSM, Tetranychus urticae); and raspberry leaf and bud mite (RLBM, Phyllocoptes gracilis), whose damage is associated with transmission of a recently-discovered virus, Raspberry leaf blotch virus (RLBV). Mite control currently relies on pesticides with variable efficacy, and there is increasing pressure to identify alternative control methods that reduce reliance on chemical inputs. Previous research at the institute has identified varietal differences in raspberry susceptibility to TSSM and RLBM linked to the deterrent effects of high leaf trichome densities. Other plant traits, such as release of deterrent plant volatiles, are also likely to contribute to resistance. These traits might influence the efficacy of predatory mites for phytophagous mite control on raspberry, and this needs to be tested on different raspberry varieties. Identifying optimal combinations of resistant germplasm and biocontrol organisms could form the basis of integrated pest management (IPM) for mites in raspberry that would be relevant to other fruit and horticultural crops.

The project aims to identify raspberry varietal traits that reduce susceptibility to TSSM and RLBM and facilitate mite control by predatory mites. The specific objectives are:
1) to understand the mechanisms, and underlying plant trait(s), that lead to TSSM and RLBV disease resistance in raspberry using varieties that show differential susceptibility to RLBM and TSSM;
2) to investigate the chemical ecology of host attraction of mites to volatiles from different raspberry varieties and predator attraction to volatiles from infested plants; and
3) to test the effect of plant resistance traits on the efficacy of predatory mites as part of an IPM approach.

To achieve the project aims and objectives, the student will use a combination of methods ranging from arthropod husbandry and whole plant resistance testing of raspberry varieties against TSSM and RLBM, to chemical ecology and molecular diagnostics, and will include assessment of mite behaviour and fitness in relation to plant traits, biochemical and physical analyses of plant surface characteristics and diagnostic RT-PCR-based tests for the presence of RLBV. Volatile collection, olfactometer bioassays and chemical analysis (GC-MS) will be used in chemical ecology studies. Experimental work will be conducted in glasshouse (variety resistance testing) or controlled environment conditions (mechanistic studies of plant resistance traits and mite behaviour) and in small-scale field trials (predatory mite biocontrol). The project will also benefit from collaboration with Dr Tom Pope at Harper Adams University who has established expertise in integrated pest management.