Effect of temperature on host plant‐specific leaf‐ and root‐feeding performances: a comparison of grape phylloxera biotypes C and G

Abstract Grape phylloxera, Daktulosphaira vitifoliae (Fitch) (Hemiptera: Phylloxeridae), is a destructive pest for global viticulture. With the grafting of the susceptible cultivated grapevine (Vitis vinifera L., Vitaceae) on top of tolerant Vitis spp. rootstock, root infestation no longer causes vine death. These tolerant rootstock vines are hybrids of American species that are often highly susceptible to leaf infestation. Though leaf infestation is normally rarely seen on V. vinifera, some commercial vineyards have been showing high intensities of leaf galls for many years. In this study, two possible factors are investigated to explain these anomalies: (1) intra‐specific differences in phylloxera host plant specialization, and (2) improved environmental settings for infestation due to temperature increase. To study the former, a phylloxera biotyping assay was conducted after whole‐plant (both root and leaf) infestations, and for the latter, a temperature increase simulation was performed with potted plants in climate chambers. Both assays also contained a phylloxera control biotype C, obtained from an American rootstock hybrid (Vitis berlandieri Planch. × Vitis riparia Michx.). The biotyping assay showed that field‐sampled populations from V. vinifera leaf galls had innate advantages to infest the leaves of this host plant species compared to those of the American rootstock hybrid. This is therefore the first study to categorize a phylloxera population as biotype G, using controlled experimental conditions with biological pest control. At moderate temperatures (22 °C), infestation was similar as in the biotyping assay, but at higher temperatures (27 °C), biotype G seems to lose its comparative advantage to infest V. vinifera leaves. Specifically, at higher temperatures, insect performance in terms of leaf gall intensity, development, and egg‐laying of both biotype G and C is improved on American rootstock hybrids and worsened on V. vinifera compared to infestations at moderate temperatures. We discuss possible explanations for these findings and how these experimental results may be extrapolated to field settings.