Insecticide Resistance in Drosophila melanogaster (Diptera: Drosophilidae) is Associated with Field Control Failure of Sour Rot Disease in a New York Vineyard.

Sour rot is a complex disease of grapes caused by an interaction of yeast, acetic acid bacteria, and Drosophila spp. Application of insecticides (most commonly zeta-cypermethrin) targeting Drosophila has previously provided substantial control of sour rot in wine grapes of New York vineyards. In harvest season of 2018, a control failure of sour rot and high populations of Drosophila, mostly Drosophila melanogaster, were observed in a vineyard in the Finger Lakes region, NY, despite repeated applications of zeta-cypermethrin (Mustang Maxx). To determine if resistance was responsible for the control failure, we quantified the toxicity of zeta-cypermethrin and the four other insecticides registered for Drosophila control in NY vineyards. Diagnostic concentrations (susceptible strain LC95, 4 × LC95, and 16 × LC95) were used to evaluate percentage survival of the field flies relative to the susceptible Canton-S strain. Resistance to zeta-cypermethrin, acetamiprid, and malathion, but not to spinosad and spinetoram, was observed in the field-collected flies. This study provides evidence that insecticide resistance of Drosophila is associated with control failure of sour rot in some vineyards, and directly influencing grape production. The implications of these results to insecticide resistance monitoring and management are discussed.

Unraveling the Etiology of North American Grapevine Yellows (NAGY): Novel NAGY Phytoplasma Sequevars Related to 'Candidatus Phytoplasma pruni'.

North American grapevine yellows (NAGY) disease has sometimes been attributed to infection of Vitis vinifera L. by Prunus X-disease phytoplasma ('Candidatus Phytoplasma pruni') but this attribution may not be fully adequate. In this study, phytoplasma strains related to 'Ca. Phytoplasma pruni' were found in NAGY-diseased grapevines in Maryland, Pennsylvania, Virginia, Ohio, Missouri, and New York State. Based on restriction fragment length polymorphism analysis of 16S ribosomal RNA gene (16S rDNA) sequences, the strains (termed NAGYIII strains) were classified in group 16SrIII (X-disease group) but they contained a recognition site for the restriction endonuclease MseI that is not present in the 16S rDNA of 'Ca. Phytoplasma pruni'. The 16S rDNA of the strains differed by three or four nucleotides from that of 'Ca. Phytoplasma pruni', indicating that they belonged to two novel 16S rDNA sequevars, designated NAGYIIIα and NAGYIIIß. Both sequevars differed from 'Ca. Phytoplasma pruni' by a single base in each of three regions corresponding to species-unique (signature) sequences described for 'Ca. Phytoplasma pruni'. Phylogenetic analyses of 16S rRNA genes and SecY proteins, and single-nucleotide polymorphism analyses of secY and ribosomal protein genes, further distinguished the two grapevine sequevar lineages from one another and from 'Ca. Phytoplasma pruni'. The NAGYIIIα and NAGYIIIß sequevars also differed from 'Ca. Phytoplasma pruni' in regions of the folded SecY protein that are predicted to be near or exposed at the outer surface of the phytoplasma membrane. No evidence indicated that diseased grapevines contained any phytoplasma strain conforming to 'Ca. Phytoplasma pruni' sensu stricto. Because the NAGYIII sequevars have not been reported in X-disease, a question is raised as to whether NAGYIII and Prunus X-disease are caused by different phytoplasma genotypes.