Conditional vector preference aids the spread of plant pathogens: results from a model

Vectors of several economically important plant viruses have been shown to feed or settle preferentially on either infected or noninfected host plants. Recent research has revealed that the feeding or settling preferences of insect vectors can depend on whether a vector is inoculative (carries the virus). To explore the implications of such changes in vector preference for the spread of the pathogen, we create a basic model of disease spread, incorporating vector preferences for infected and noninfected plants dependent on whether the vector is inoculative. Previous modeling work assumed that vector preferences remain unchanged with vector infection status and showed that vector preference for infected host plants promotes disease spread when infected hosts are rare, whereas preference for noninfected hosts promotes spread once infected hosts become abundant. In contrast, our model shows that a change in preference following acquisition of the pathogen can increase pathogen spread throughout the epidemic if noninoculative vectors prefer infected plants and inoculative vectors prefer noninfected plants, as has been detected experimentally in two pathosystems. Our results show that conditional vector preference can substantially influence plant pathogen spread, with implications for agricultural and natural systems. Conditional preference as a component of virus manipulation of vector behavior is potentially more important for the understanding of plant disease spread than previously recognized.