A novel mechanism for disease dilution: Differences in vector production among host species

Background/Question/Methods The dilution effect in disease ecology posits that disease burdens in richer ecological communities tend to be lighter than in simpler, less diverse communities. For vector-borne diseases, at least two mechanisms might underlie this pattern: (i) more widespread and abundant species are more “competent” hosts that efficiently pass on infection to vectors, and (ii) more widespread and abundant species are the most effective vector producers. The first mechanism has received some previous attention, but to our knowledge the hypothesis that widespread / abundant hosts produce more disease vectors has not been investigated to date. We sampled grass communties along the US west coast measuring local abundance (% cover) of grass species and their distribution across a latitudinal gradient of 15 degrees or 2000 kilometers. We conducted field experiments quantifying the reproductive rate of aphids, which act as vectors for plant viruses, on eight of the grass species.

Results/Conclusions

The species distribution of grasses was strongly nested among sites, with the least diverse communities composed largely of widespread species, and the rarer species occurring only at the richest sites. More widespread species also yielded the highest aphid reproductive rates, but local abundance had no effect on vector production. Our data thus corroborate the hypothesis that disease dilution may in part be driven by differences among hosts in vector production.