Plant volatiles (odors) are known to mediate diverse interactions among plants and insects.  Yet, the chemical ecology of insect-vectored disease transmission remains relatively unexplored, even though plant odors are key foraging cues for herbivorous insects and thus likely targets for manipulation by vector-borne pathogens.  Current research in our laboratory explores the effects of viral and bacterial pathogens on host plant phenotypes, including volatile emissions and nutritional quality, the influence of these effects on insect vectors, and implications for disease transmission. This presentation addresses recent work on pathosystems involving cultivated and wild squash (Cucurbita pepo).
Results/Conclusions

Field and laboratory experiments revealed that the widespread plant pathogen Cucumber mosaic virus (CMV) significantly reduces the quality of cultivated squash (C. pepo cv. Dixie) for two aphid vectors (Myzus persicae and Aphis gossypii): Aphid population growth was slower on infected plants, while dispersal rates were elevated. But, surprisingly, aphids were preferentially attracted to the odors of infected plants despite their poor quality—apparently because CMV induces elevated emissions of a volatile blend similar to that of healthy plants. The overall pattern of effects described here (vector attraction to the odors of infected plants followed by rapid dispersal) appears conducive to CMV’s non-persistent mode of transmission and is different from that previously reported for other (persistent) viruses that require more sustained aphid feeding for efficient transmission. In the wild gourd C. pepo ssp. texana—believed to be the progenitor of cultivated squash—we found that infection by the bacterial pathogen Erwinia tracheiphila, which causes a fatal wilt disease, results in elevated emissions of foliar volatiles (including the production of novel compounds) and reduced emissions of floral volatiles. Field and laboratory studies further indicated that the cucumber beetles (Acalymma vittatum) that vector E. tracheiphila are preferentially attracted to wilting leaves compared to healthy leaves and to flowers on healthy plants compared to those on wilting plants. As with CMV, the overall pattern of pathogen-induced effects appears conducive to disease transmission, as cucumber beetles are known to aggregate and feed on wilting leaves (where they presumably acquire the pathogen) and previous work from our collaborators indicates that the bacteria can be introduced through floral nectaries. These studies together with other recent results suggest that pathogen infection may often have significant effects on plant-insect interactions with potentially important implications for disease transmission and ecology.