Localization of Virus-like Particles in the Foreguts of Viruliferous Graminella nigrifrons Leafhoppers Carrying the Semi-persistent Maize Chlorotic Dwarf Virus

Abstract

SUMMARY The leaf hopper Graminella nigrifrons transmits maize chlorotic dwarf virus(MCDV) in a semi-persistent manner and loses its ability to inoculate plants following ecdysis. Virus-like particles (VLP) resembling MCDV in purified preparations and in MCDV-infected plants were observed by electron microscopy adhering to the cuticula lining the precibarium, cibarium (sucking pump), pharynx and fore-oesophagus in viruliferous leaf hoppers carrying MCDV. No VLP were observed in the alimentary canal beyond the cardiac valve, in any organ or tissue in the haemocoele, or in the maxillary salivary duct. No VLP were observed associated with the stylet tips or anywhere on the cuticula surfaces of either the mandibular or maxillary stylets. The VLP were not found associated with the cuticula lining of the foregut in a similarly treated non-vector species, Dalbulus maidis, or in vector or non-vector species given either a 48 h acquisition access feeding period on MCDV-infected source plants followed by a 48 h post-acquisition feeding on healthy plants (renders inoculative leaf hoppers non-inoculative) or solely a 48 h feeding on healthy plants. No differences were observed between MCDV-inoculative and non-inoculative Graminella given similar access to virus. The VLP occurred in thin layers or small to large clusters embedded in a lightly stained matrix material (m-material) or a densely stained substrate which, in turn, were apparently attached by m-material to the cuticula. It is thought that the VLP are those of MCDV and that the m-material, which resembles materials previously reported in association with virus-binding sites in the fore alimentary canals of aphid and nematode vectors, functions in binding virus to retention sites on the vector’s cuticula.