D3281: Love triangle? Brassica napus, Aster yellows, and Aster leafhoppers (Hemiptera: Cicadellidae)

Pathogens, including fungi and bacteria, viruses, and mollicutes, often attack plants in agricultural systems. Aster Yellows phytoplasma (AYp) is a mollicute that infects many hosts, many of which are essential to agriculture. Once a plant senses a stressor, such as a phytoplasma, many plants will produce secondary metabolites, which can alter the plant’s physiological state. Previous work has established that these compounds’ presence can alter the feeding behaviour of herbivorous insect species. Past studies have shown that phytoplasmas can manipulate their insect vectors' host choice by decreasing vector attraction to infected plants, consequently aiding in the pathogens' spread. Research into the pathosystem involving AYp, its insect vectors, and the host plants is needed to understand to what degree AYp-infected plants can influence insect behaviour and disease dynamics. This study used uninfected and infected Brassica napus plants in no-choice and two-choice bioassays to evaluate the effects of AYp infection, at two timeframes, on vector settling behaviour and development. This study reports that AYp-uninfected aster leafhoppers preferentially settled on AYp-infected B. napus plants at the early stages of AY infection, compared to AYp-uninfected B. napus plants. However, there was no settling preference during the later stage of AY infection. AYp-uninfected B. napus had significantly higher reproductive success for aster leafhoppers than AYp-infected B. napus. Increasing AYp titre was positively correlated with time post-infection and visual symptomology severity. This project helps to shed additional light on Aster Yellows phytoplasma epidemiology and its relationship with aster leafhoppers.