Abstract
Tomato spotted wilt virus (TSWV) is one of the most harmful plant viruses and one of its most important vectors is the western flower thrips [Frankliniella occidentalis Pergande (Thysanoptera: Thripidae)]. Recently, we reported the close association of Erwinia sp. gut bacteria with this species of thrips. The first instar larvae acquire these bacteria from their food source. A high proportion of adult western flower thrips transmit TSWV after acquiring the virus during the first larval stage when there are no bacteria in their gut. A considerably lower proportion of adults that acquire the virus early in the second instar transmit virus and none of those exposed to virus late on in the second instar do so. The highest prevalence and total number of symbiotic bacteria are recorded in the guts of second instar thrips. This leads to the hypothesis that the build up of bacteria in the gut reduces the acquisition of TSWV, resulting in a lower capacity to transmit the virus. To test this hypothesis, the transmission of this virus by symbiotic and aposymbiotic adult thrips of the NL3 population was studied. Comparison of virus transmission by adult thrips, the larvae of which either had or lacked gut bacteria and were exposed to virus in either the first or second instar, revealed no difference in the ability of symbiotic and aposymbiotic adults to transmit this virus. We conclude that virus transmission is not affected by the number of the symbiotic bacteria Erwinia sp. present in the gut of thrips larvae.
Highlights
Western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), is a small phytophagous insect, which has spread world-wide over the last 30 years from its original habitat in the western part of the United States
Thrips from population NL3 used in this study, like those from other populations, were always infested with Erwinia gut bacteria (Table 2 and De Vries et al, 2001a)
Gut bacteria were transmitted to the generation of thrips when they fed on Datura and Petunia, as previously reported for thrips feeding on bean and cucumber (De Vries et al, 2001b)
Summary
Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), is a small phytophagous insect, which has spread world-wide over the last 30 years from its original habitat in the western part of the United States. There are six steps in the transmission process: ingestion of virus into the midgut, replication in the midgut epithelium and midgut muscle cells, transfer of the virus to the salivary glands, replication in the salivary glands, release of the virus into the saliva and injection of saliva containing the virus into plants (Whitfield et al, 2005). This implies a latency period between the moment of acquisition of the virus and the first transmission of virus. The mechanism by which the virus can pass from the midgut to the salivary glands is still not fully understood
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