Vector attraction and host exposure mediated by pathogen effects on plant volatiles

Synopsis by Lori Shapiro

Transmission of insect-vectored diseases depends on the ability of infective vectors to interact with both infected and healthy hosts in ways that promote disease transmission. However, the factors affecting vector foraging and the consequences for host exposure are often poorly understood, especially in natural systems with multiple co-circulating pathogens.

Penn State researchers Lori Shapiro, Consuelo De Moraes, Andrew Stephenson, and Mark Mescher investigated volatile responses of the wild gourd Cucurbita pepo spp. texana to infection with either of two co-occurring plant pathogens, the bacterial wilt pathogen Erwinia tracheiphila, transmitted by the striped cucumber beetle Acalymma vittatum, or Zucchini Yellow Mosaic Virus (ZYMV), which is transmitted by a variety of generalist aphids. They found that wilting, symptomatic leaves of E. tracheiphila-infected plants produce a unique volatile blend that is attractive to cucumber beetle vectors, while E. tracheiphila infection suppressed the release of volatiles from flowers on infected plants relative to healthy plants. In contrast, ZYMV infection suppressed volatile emissions from flowers but did not change those from foliage, relative to healthy plants. Field and laboratory studies show that beetle vectors show a preference for the leaves of wilting E. tracheiphila infected plants and flowers of healthy plants. ZYMV-induced suppression of floral volatiles explains why beetles that carry E. tracheiphila tend to avoid ZYMV infected plants.

This study shows that plant pathogens can interact indirectly through changes to host plant phenotype and subsequent effects on vector behavior, and demonstrates the importance of considering all co-occurring pathogens in a system when studying transmission biology and epidemiology.