Submitted to: International Plant Virus Epidemiology Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 10/19/2007
Publication Date: 12/18/2007
Citation: Castle, S.J. 2007. Testing of the vector dependency hypothesis with aphids and whiteflies. International Plant Virus Epidemiology Symposium. October 15-19, 2007, Patancheru, India, P.47.
Technical Abstract: The concept of ‘vector dependency’ by viruses was proposed as a way to better understand the outcomes of interactions among viruses, vectors and plants from the standpoint of the vector species involved. The fitness of a vector is closely linked to host plant quality, which in turn may be influenced by virus-mediated changes that affect plant nutritional attributes for the vector. Because viruses vary considerably in their relations with vectors, from complete dependence upon a principal vector species for dispersal to complete independence, i.e. a non-vectored virus, the relative dependency of a virus on one or more vector species may be important to understanding outcomes from a vector performance perspective. The vector dependency hypothesis posits that viruses that are more dependent upon vectors will indirectly benefit those vectors through favorable changes in the quality of their host plants. Conversely, less dependent viruses do not have as much at stake from an evolutionary perspective, and therefore are not under as much selection pressure to mediate changes in host plant quality that benefit vector species. In addition, the relative complexity of the virus-vector relationship will likely correspond to degree of dependency as a virus that exhibits a more complex mode of transmission (e.g. circulative) will be more specific in its relationship with a particular vector and therefore more dependent. To test this hypothesis, three potato viruses that vary in their dependency on the aphid vector Myzus persicae were tested in potato plants to determine if putative virus-mediated changes in plant quality affected various life history traits of M. persicae. The three viruses were potato leafroll (PLRV), transmitted circulatively by its principal vector M. persicae; potato virus Y (PVY), transmitted nonpersistently by numerous aphid species; and potato virus X (PVX), a non-vectored virus. All life history traits including rate of increase, longevity and fecundity were significantly greater for M. persicae on PLRV-infected plants compared to plants infected by either of the other two viruses or the virus-free plants. A second virus-vector combination is presently being investigated to test the robustness of the vector dependency hypothesis. This system consists of Bemisia tabaci as the insect vector of the cotton leaf crumple virus (CLRV) on two different host plants, Gossypium hirsutum and G. thurberi. Initial tests on CLRV-infected vs. uninfected upland cotton (G. hirsutum) failed to detect any benefit to B. tabaci on CLRV-infected plants. However, the nature of the G. hirsutum/CLRV relationship is a recent one, dating back to the mid-20th century when cotton was first cultivated in the southwestern USA. In contrast, interactions among G. thurberi, B. tabaci and CLRV probably date back well before the 20th century as all are indigenous to the southwestern USA. Evidence of this long association is apparent in the mild symptoms that occur in G. thurberi relative to the severe symptoms observed in G. hirsutum. Tests currently in progress will measure life history traits of B. tabaci on virus-infected and virus-free G. thurberi as well as relative attractiveness of plants to B. tabaci according to virus status.