Cardamom bushy dwarf virus (CBDV) causes foorkey disease of large cardamom (Ammomum subulatum Roxburgh) in the eastern sub-Himalayan mountains. Although the aphid Micromyzus kalimpongensis Basu (Hemiptera: Aphididae) is known as a vector of CBDV, its behavior in dissemination of CBDV has not been investigated. In the present study, M. kalimpongensis was observed to colonize in higher number on CBDV-infected large cardamom plants compared with the healthy plants in the several plantations in Sikkim and Darjeeling hills. The affinity of M. kalimpongensis to the diseased large cardamom plants was further confirmed in a contained field experiment with intact plant as well as in a laboratory bioassay with the plant extract, where significantly higher number of aphids settled on the diseased plants or extracts compared with the healthy counterparts. Aphids grown on CBDV-infected large cardamom plants had shortened nymphal period and increased longevity and fecundity compared with those grown on the healthy plants. In the contained field experiment, M. kalimpongensis migrated to the CBDV-infected plants, colonized there, acquired CBDV, and once the diseased plants withered, migrated to healthy plants, which eventually became diseased. Our results suggest a general pattern of spread of CBDV by M. kalimpongensis where CBDV-infected plants attract or arrest and stimulate emergence and migration of viruliferous aphids that otherwise are sedentary in the underground plant parts of large cardamom. To our knowledge, this is the first study that shows the influence of a plant virus from the family Nanoviridae in altering behavior of its insect vector that favors its dissemination.
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Vol. 45 • No. 1