Overwintering Sites ofIris yellow spot virusandThrips tabaci(Thysanoptera: Thripidae) in Colorado

Abstract

Iris yellow spot virus (family Bunyaviridae, genus Tospovirus) and its insect vector, onion thrips, Thrips tabaci Lindeman, are of economic concern worldwide in regions where onions (Allium cepa L.) are grown. Several weed species have been described as additional hosts and likely green bridges for survival of Iris yellow spot virus, however, there is little work regarding the overwintering habits and potential of onion thrips as a source of inoculum during the following season. The results of this work confirm onion thrips and Iris yellow spot virus presence near three Colorado onion fields throughout the winter, onion thrips reproduction on six non-allium plant species, and larval acquisition of Iris yellow spot virus from two non-allium plant species. Thrips were monitored by sticky traps during the winter months from 2011 to 2013. Thrips activity seemed to cease when the average temperature was cooler than 0°C and resumed once the average temperature warmed above 0°C. Onion cull piles were constructed and were apparently conducive to survival of thrips, but no live thrips were collected from the piles after onion bulbs began to decay. Iris yellow spot virus was detected by RTPCR in live adult and larval thrips from onion; common mallow, Malva neglecta Wallr.; dandelion, Taraxacum officinale Weber in Wiggers; flixweed, Descurainia sophia (L.) Webb. Ex Prantl; prickly lettuce, Lactuca serriola L.; and salsify, Tragopogon dubius Scop. during the winters from 2010 to 2013. Iris yellow spot virus was detected in prickly lettuce and flixweed. The five weed species were grown from seed in a greenhouse and exposed to viruliferous thrips to elucidate their potential as green bridges. Of the five weeds, Iris yellow spot virus was detected in eight of 15 salsify leaf samples and in three of six thrips larval samples reared on the plant. Winter annuals play a role in overwintering survival of onion thrips and Iris yellow spot virus, providing inoculum the next growing season, and weed management during the winter might be warranted.