Investigating the influence of heavy metals on aster leafhopper fitness and associated symbiotic bacteria

Aster leafhopper (ALH; Macrosteles quadrilineatus) is the vector of the bacterial plant pathogen, Aster Yellows phytoplasma (AYp; Candidatus Phytoplasma asteris). Successful transmission of insect-vectored pathogens requires conditions conducive to both pathogen and vector fitness. Recent studies have elucidated inadvertent negative effects of heavy metal containing fungicides on insects, however this phenomenon has not been investigated thoroughly in plant pathogen vectors. To better understand whether heavy metal inputs regularly applied to AYp-susceptible crops affect the insect, ALH development rates and survivorship were evaluated under copper and untreated conditions on oats (A. sativa) in a controlled environment. Estimates of nymphal development stage and survivorship were monitored until adulthood and indicated subtle effects on developmental and survival rates. ALH populations and AYp disease incidence was also measured in the field, but showed no significant field-level differences. Furthermore, recent studies have demonstrated the importance of bacterial symbionts on insect fitness and pathogen transmission. The ALH is known to have two obligate symbionts, Sulcia and Nasuia, that provide essential amino acids not obtained from the vector’s diet. Developmental effects we observe in the ALH in response to copper hydroxide may be due to the antimicrobial nature of these heavy metal containing compounds. To test this hypothesis, qPCR was used to measure the prevalence and relative abundance of known ALH symbionts and provided evidence of differences in abundance between treatment.