MAIZE CHLOROTIC DWARF VIRUS-LIKE PARTICLES ASSOCIATED WITH THE FOREGUT IN VECTOR AND NONVECTOR LEAFHOPPER SPECIES

Transmission electron microscopy was used to observe viruslike particles (VLP) in thin sections of the foreguts of leafhoppers previously fed on maize plants infected with the semipersistently transmitted maize chlorotic dwarf virus (MCDV). The VLP, of size and shape similar to that of MCDV virions, were found embedded in a semiopaque matrix attached to the cuticular intima of the pharynx, cibarium, and precibarium and occasionally to the inner surface of the maxillary food canal in three cicadellid vector species (Graminella nigrifrons, G. sonora, and Amblysellus grex) and in the nonvector cicadellid Dalbulus maidis; they were not found in the nonvector delphacid peregrinus maidis. Matrix-embedded VLP were also observed in the esophagus of vectors and nonvectors, but they were mixed with food material and not attached to the intima. Attached matrix-embedded VLP were observed in cicadellids fixed immediately after a 3-day acquisition access period (AAP) on MCDV-infected maize and in those given a 1-hr fasting period or a 4- to 5-hr feeding period on healthy plants following AAP. Attached matrix but not VLP, was observed in G. nigrifrons and D. maidis leafhoppers after a 4-day feeding period on healthy plants following AAP. Neither VLP nor matrix were found in Graminella leafhoppers not exposed to MCDV; nor were they found in G. nigrifrons or D. midis exposed to the morphologically similar, cicadellid-transmitted, propagative maize rayado fino virus. We conclude that the matrix-embedded VLP are MCDV virions attached to putative retention sites on the cuticular intima of the foregut in vector leafhoppers. Occurrence of similar retention sites in a nonvector cicadellid (but not in a nonvector delphacid) suggests that, in addition to the attachment (or binding) of virions to the foregut cuticle, other factors may play a role in vector specificity of MCDV.