Two methods for determining the resistance of strawberry cultivars to two-spotted mite (Acari: Tetranychidae)

Five strawberry cultivars (Hapil, Pegasus, Rhapsody, Elsanta and Symphony) were evaluated for resistance to two-spotted spider mite (Tetranychus urticae Koch.). Two methods of assessing the resistance of leaves to two-spotted mites were compared by determining the number of eggs laid and mites which developed. The first method involved a detached leaf being placed upside down on a moistened filter paper in a covered petri dish, however leaves were liable to dry out after a week. The other method, also using detached leaves, involved maintaining the cut leaf stem in water but supporting the leaf clear of the water on a floating polystyrene raft with the lower side of the leaf facing downwards. Using the polystyrene raft method leaves remained turgid for 4 weeks. 'Hapil' and 'Pegasus' were shown to be significantly more susceptible to two-spotted mite than the cultivars Rhapsody, Symphony and Elsanta. The floating polystyrene raft method of assessing two-spotted mite resistance may be of potential use for studying population dynamics of both two-spotted mite and possible predators over extended periods of time.