Variation in tospovirus transmission between populations of Frankliniella occidentalis (Thysanoptera : Thripidae)

Fourteen populations of the western flower thrips Frankliniella occidentali s Pergande, originating from different hosts and countries in Asia, Europe, North America and New Zealand, were analysed for their competency and effi ciency to transmit tomato spotted wilt virus (TSWV). All populations acquir ed and subsequently transmitted the virus, and were thus competent to trans mit. They show marked differences in their efficiency, expressed as the per centage of transmitting adults. Efficiencies varied from 18% for a F. occid entalis population from the USA (US2) to 75% for a population from Israel ( IS2). The differences between populations were not affected by the amount o f virus ingested or by the host plant used. However, the tospovirus species studied and age at which the larvae acquired the virus affected the effici ency to transmit. First instar larvae of the NL3 population from The Nether lands were able to acquire tomato spotted wilt virus, whereas second instar larvae failed to do so. However, both instars of this population acquired impatiens necrotic spot virus (INSV), another tospovirus. This and tomato s potted wilt virus were both acquired by both larval stages of the populatio ns IS2 and US2, although their ability to acquire virus decreased with thei r age. Hence, it is likely that, in general, both instar larvae of most F. occidentalis populations are competent to acquire both tospoviruses. These results show that large differences exist in the efficiency by which tomato spotted wilt is transmitted by the various F. occidentalis populations and that the ability to acquire tospovirus decreases with the age of the larva e.