ENTRY OF INGESTED PLANT-VIRUSES INTO THE HEMOCOEL OF THE BEETLE VECTOR DIABROTICA-UNDECIMPUNCTATA-HOWARDI

Southern bean mosaic sobemovirus (SBMV) and the cowpea strain of tobac co mosaic tobamovirus (CP-TMV) are found in the hemocoel of some beetl e vectors after they have fed on infected plants. The location in the alimentary canal through which ingested plant viruses enter the hemoco el of the spotted cucumber beetle Diabrotica undecimpunctata howardi w as studied. Immunofluorescent and electron microscopy were used to det ect the presence of ingested viruses in the gut lumen and the epitheli al cells lining the midgut of the spotted cucumber beetle. Virus-speci fic immunofluorescent microscopy detected bean pod mottle virus and to bacco ringspot virus only in the lumen of the gut; these two viruses c annot be detected in the hemocoel. In beetles from which virus was rec overed from the hemocoel, SBMV and CP-TMV were found both in the lumen of the gut and in the epithelial cells of the midgut. CP-TMV was obse rved by electron microscopy both in the epithelial cells of the midgut and in the hemocytes of the beetles that had acquired the virus. This suggests that plant viruses enter the hemocoel of the beetle through the peritrophic membrane-lined midgut but not through the cuticle-line d foregut or hindgut.