Effectiveness of hot water treatments against the eggs of Scaphoideus titanus Ball

Abstract: The leafhopper Scaphoideus titanus (Hemiptera: Cicadellidae) is the principal vectorof flavescence dorée, a severe grapevine disease spreading in Europe. The project PROPSCAPHunited four European research institutes in order to improve risk management schemes againstthe spread of flavescence dorée's vector on propagation material. Amongst others, the impact ofthe standard hot water treatment against the disease on the development of the S. titanus eggs wasstudied. In autumn 2008, one-year-old and two-year-old cuttings were collected in S. titanusinfested vineyards in France, Italy and Switzerland and sent to our institute. After storage in acold chamber until March 2009, half of the cuttings were exposed for 45 minutes to a hot watertreatment at 50°C. Thereafter, treated and untreated cuttings were placed in cages and thehatching of S. titanus nymphs was assessed. At least 10-times more nymphs hatched from twoyear-old cuttings than from the one-year- old cuttings. This confirmed the ability of S. titanus tolay eggs on propagation material. However, hot water treatments significantly reduced thenumber of hatched nymphs, e.g. the exposure to hot water killed about 80% of deposited eggs. Inconclusion, hot water treatments do not only have a major impact on flavescence dorée, they alsokill most of its vector's eggs. Thus, the hot water treatment of rootstocks and scions beforegrafting is strongly recommended in order to reduce the risk of S. titanus' propagation. Beforecommercialisation grafts should be hot-water treated once again, since the chemical protection ofrootlings is not always 100% effective in the nursery fields. All these measures together willensure the propagation of plant material free of flavescence dorée and they will minimise the riskof disease’s and vector's spread.