Within food webs, vectors of plant pathogens interact with individuals of other species across multiple trophic levels, including predators, competitors, and mutualists. These interactions may in turn affect vector‐borne pathogens by altering vector fitness and behavior. Predators, for example, consume vectors and reduce their abundance, but often spur movement of vectors as they seek to avoid predation. However, a general framework to predict how species interactions affect vectors of plant pathogens, and the resulting spread of vector‐borne pathogens, is lacking. Here we developed a mathematical model to assess whether interactions such as predation, competition, and mutualism affected the spread of vector‐borne plant pathogens with nonpersistent or persistent transmission modes. We considered transmission mode because interactions affecting vector–host encounter rates were expected to most strongly affect nonpersistent pathogens that are transmitted with short feeding bouts; interactions that affect vector feeding duration were expected to most strongly affect persistent pathogens that require long feeding bouts for transmission. Our results show that interactions that affected vector behavior (feeding duration, vector–host encounter rates) substantially altered rates of spread for vector‐borne plant pathogens, whereas those affecting vector fitness (births, deaths) had relatively small effects. These effects of species interactions were largely independent of transmission mode, except when interactions affected vector–host encounter rates, where effects were strongest for nonpersistent pathogens. Our results suggest that a better understanding of how vectors interact with other species within food webs could enhance our understanding of disease ecology.

The vine mealybug, Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae), is a major pest of vineyards. Here, we tested the efficacy of the mating disruption method against the pest when applied during one or two successive years in high and low infestation levels. Following 1 year of treatment, at low initial infestation levels a shutdown of pheromone traps was observed, along with a significant reduction in infested vines. With initially high infestation levels, a gradual reduction in infested vines was observed, with a trap shutdown seen only after the second year of pheromone application. We discuss the implications of the male mating disruption method for this pest in which the wingless females are aggregated with limited movement among vines, offering multiple mating opportunities for the flying male.

Hyalesthes obsoletus Signoret (Homoptera: Cixiidae) is a polyphagous planthopper that transmits stolbur phytoplasma (a causative agent of "yellows" disease) to various weeds, members of the Solanaceae, and wine grapes (Vitis vinifera L.) in Europe and the Middle East. Planthoppers were collected by hand vacuuming eight native plant species. Vitex agnus-castus L., a shrub in the Verbenaceae, hosted the largest number of H. obsoletus, although Olea europaea L. also served as a host for adults. Using a Y-olfactometer, we compared the planthoppers relative preference for V. agnus-castus, Convolvulus arvensis, and V. vinifera. V. agnus-castus was more attractive to both male and female H. obsoletus than the other plants. H. obsoletus antennal response was stronger to volatiles collected from V. agnuscastus than from Cabernet Sauvignon variety of V. vinifera. To determine if V. agnus-castus would serve as a reservoir for the pathogen, H. obsoletus were collected from leaf and stem samples of native V. agnus-castus, and were tested by polymerase chain reaction (PCR) for the presence of phytoplasma DNA. While 14% and 25% (2003 and 2004, respectively) of the insects tested positive for phytoplasma DNA, none of the plant samples tested positive. To determine if V. agnus-castus could serve as a host plant for the development of the planthopper, we placed emergence cages beneath field shrubs and enclosed wild-caught H. obsoletus in a cage with a potted young shrub. We found adult H. obsoletus in the emergence cases and planthopper nymphs in the soil of the potted plant. We concluded that V. agnus-castus is attractive to H. obsoletus, which seems to be refractory to phytoplasma infections and warrants further testing as a trap plant near vineyards.

Species from three subfamilies of Cicadellidae and one species of Cixiidae, all potential vectors of phytoplasmas, were trapped in vineyards over the course of two years. These insects were caught on yellow sticky traps during the spring; virtually none were trapped during the summer months. Molecular analysis (PCR) of selected samples of the leafhoppers and planthoppers for presence of phytoplasma DNA was conducted on most species. Neoaliturus fenestratus was the most abundant known vector species and was positive for stolbur (Stol) and aster yellows (AY) phytoplasma. Circulifer haematoceps complex, which were also positive for Stol and AY, were about 10-fold fewer than N. fenestratus. Hyalesthes obsoletus, also a known phytoplasma vector, occurred in substantial numbers only late in the season when the vines and leaves were dehiscing and turning brown, but was positive for Stol and AY. A species whose vector status is unknown (Megophthalmus scabripennis) was also caught in large numbers and was shown, by PCR analysis, to be positive for AY. Other known vector species trapped included: Anaceratagallia laevis (positive for AY), Austroagallia sinuata, Dryodurades sp. (dlabolai ?) (positive for AY), Macrosteles quadripunctulatus (positive for Stol), and Orosius orientalis. The spatial dispersion pattern of the four most abundant species were investigated by using Moran's I spatial statistic; N. fenestratus and M. scabripennis showed significant spatial patterns, whereas C. haematoceps and H. obsoletus did not.

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