Potential Vectors of Xylella fastidiosa On Citrus and Coffee In Puerto Rico

Two of Puerto Rico’s principal agricultural commodities, coffee and citrus, are highly susceptible to diseases caused by the xylem-limited bacteria Xylella fastidiosa (Xf).  In addition, the Caribbean Basin is a potential gateway for the Xf disease citrus variegated chlorosis for Florida citrus via northern spread from South America.  We surveyed Homoptera in citrus and coffee plantings for 18 months at 3 month intervals throughout western Puerto Rico to detect potential vectors of Xf.  Sampling was done by sweep and trap sampling of coffee, citrus and adjacent habitats.  Only insects that feed on xylem fluid, sharpshooter leafhoppers (Cicadellidae:Cicadellinae) and froghoppers (Cecropidae), can vector Xf.  Over 5,000 Homoptera were collected; roughly 5% of these were xylem feeding insects. However, 4 of the 6 sharpshooter species that have been previously documented in Puerto Rico were shown to be insects frequently collected in citrus and coffee plantings.  Two of these species, Hortensia similis and Caribovia coffeaphila, are primarily grass feeders and rarely feed directly on coffee and citrus. Apoganallia sp. were infrequently collected, and often on herbaceous host plant species.  Caribovia coffeacola poses the greatest potential threat, commonly being found feeding directly on coffee densities in plantings at high elevations.  Citrus had many fewer potential vectors, as C. coffeacola and H. similis were only rarely found on citrus. Locally high populations of C. coffeacola occurred on coffee grown in proximity to the common shade legume Inga vera, including high populations of immatures rarely noted on coffee.  Within farms, we documented that populations of C. coffeacola increased with proximity to I. vera.  Field collected C. coffeacola were subjected to choice and no-choice tests to establish insect preference and performance.  Caribovia coffeacola preferred both coffee and I. vera over other hosts on which they had been collected including citrus, milkweed (Asclepias spp.) and grasses.  In no-choice tests, C. coffeacola confined on I. vera outperformed similar insects with survivorship, male and female weights significantly exceeding C. coffeacola confined to other hosts including coffee.  We are currently investigating leafhopper utilization of I. vera and other shade species in order to develop management strategies for shade coffee that do not increase the possibility of Xf infection.