Thrips tabaci Lind. is a global pest and also represents a serious threat to onion production in Poland. In 2 years (2015–2016) of field studies, 8 onion cultivars were evaluated to characterize the resistance to onion thrips and to determine if any biochemical and anatomical features of onion plants are associated with antixenotic and/or antibiotic mechanisms of resistance. Additionally, the influence of mechanical injury on the content of several biochemical compounds in onion leaves was made. The resistance to thrips colonization during the migration period, abundance, and thrips damage throughout the whole vegetation season was determined. We identified two cultivars, Tęcza and Wenta, resistant to thrips colonization and abundance, and one cultivar Wenta resistant to thrips damage. A positive correlation between concentrations of the reducing sugars and thrips abundance and conversely negative relationships between the total phenolic content and thrips damage was confirmed in both years. We suspect that a thinner epidermal layer, a smaller area of epidermal and mesophilic cells, and a lower diameter of vascular bundles may favor the resistance of onion cultivars to thrips. Thrips foraging resulted in a decrease in the content of soluble sugars, sucrose, and plant pigments in the leaves of all onion varieties.

Thrips tabaci Lindeman is a global pest and also represents a serious threat to onion production in Poland. In 2 years (2015–2016) of field studies, 8 onion cultivars were evaluated to characterize their susceptibility to onion thrips and to determine if leaf colour is associated with thrips preference. The actual count and the proportional abundance of adult thrips collected from onion leaves during plant colonization by insects were both used to express the preference of thrips for different onion cultivars. At the same time, the colour measurements were analysed by considering the CIELAB (CIE 1976 L*a*b*) and CIE L*C*h* colour spaces. There were distinct differences in the susceptibility of onion cultivars to colonization by onion thrips. Leaf colour coordinate values were correlated with attractiveness to thrips; typically, higher lightness (L*), yellowness (b*), chroma (C*), hue (h*), and lower redness (a*) attracted more thrips. We concluded that the vivid, intense green-yellowish leaf colour of susceptible varieties might have been the cause of the thrips preference observed. We also identified useful genotypes, Tęcza and Wenta, for host plant resistance to thrips and suggest a link between colour and antixenotic resistance. The resistant cultivars had darker, green-grey-yellowish leaves.

We determined the abundance, species composition, sex ratio and seasonal dynamics of thrips on one cultivar of Welsh onion ( Allium fistulosum ) and eight cultivars of onion ( Allium cepa ) in South Poland within three vegetation seasons (2014–2016). Nine species of Thysanoptera were identified on A. cepa and A. fistulosum . Irrespective of the onion cultivar, Thrips tabaci was the dominant species (64.4% of all collected thrips specimens), while Frankliniella intonsa also occurred in high numbers (28.3%). Conversely, Welsh onion was most often inhabited by F. intonsa (62.7%), although T. tabaci was also numerous (28.3%). The predatory Aeolothrips intermedius accounted for 4.5% on A. cepa and 2.9% on A. fistulosum . In the most numerous species, T. tabaci, F. intonsa and A. intermedius populations were formed mainly by females. The cultivar most colonised by thrips was Kroll of A. fistulosum. The tested cultivars of A. cepa demonstrated varying degrees of attractiveness to thrips in the subsequent years. The relationship between populations of T. tabaci , F. intonsa and A. intermedius changed in the subsequent months of the growing season. In June, mainly T. tabaci and F . intonsa occurred on onion plants, while from July, the percentage shares of F. intonsa and the predatory A. intermedius in the thrips population on many onion cultivars increased. The level of attractiveness of A. cepa related to onion thrips, which is reported as a main pest of onion, varies depending on the year and cultivar.