Investigating the association of Tetranychus urticae Koch (Acari: Tetranychidae) with raspberry viruses

Abstract: Red raspberry (Rubus idaeus) is known to be host plant of 22 plant viruses belonging to several families and genera. Among them, 8 were known to be transmitted by arthropods, namely aphids and eriophyid mite Phyllocoptes gracilis (Nalepa). The two-spotted spider mite, Tetranychus urticae Koch, is commonly found infesting the raspberry but is often assumed to cause only physical damage and, so far, not associated with any raspberry viruses. Therefore, in this study the association of T. urticae with two raspberry viruses, black raspberry necrosis virus (BRNV) and raspberry leaf blotch virus (RLBV) was investigated. Adult T. urticae females were fed with either RLBV-infected or BRNV-infected leaves for at least 48 hours. The presence of viruses in both plants and spider mites were tested by molecular methods. Subsequently, dual-choice leaf disc tests were conducted to assess the effects of these raspberry viruses on T. urticae host plant preference. A T. urticae female was presented with half leaf disc either RLBV-infected or BRNV-infected leaf while the alternative half leaf disc being from healthy plant, acting as control. The position of these mites was monitored daily for a duration of 4 days. The number of eggs laid on respective half areas were also recorded. The results indicate that T. urticae was able to acquire RLBV but not BRNV. In addition, they significantly preferred RLBV-infected leaf over healthy raspberry leaf, while no such preference was found in experiments with BRNV-infected plants. This suggests that the state of association of virus with the arthropod affects host plant preference behavior. Therefore, further studies to understand this interaction of virus with potential arthropod vectors is recommended. In addition, T. urticae potential as vector of RLBV should be assessed.