Characterization of Resistance, Evaluation of the Attractiveness of Plant Odors, and Effect of Leaf Color on Different Onion Cultivars to Onion Thrips (Thysanoptera: Thripidae)

Abstract

Onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), is a worldwide pest of onion, Allium cepa L. In field studies on onion resistance conducted in 2007 and 2008 using 49 cultivars, 11 showed low leaf damage by T. tabaci. In laboratory studies, the 11 cultivars, along with two susceptible checks and four additional cultivars, were evaluated to characterize resistance to T. tabaci and to determine if color and/or light reflectance were associated with resistance to T tabaci. No-choice tests were performed with adults and the numbers of eggs and larvae were counted on each cultivar after three and 10 d, respectively. In choice tests in which all cultivars were planted together in a circle in a single pot, 100 adults were released and the number of adults on each plant was evaluated 24 h later. The behavioral response of walking T. tabaci adults to plant odors was studied in a glass Y-tube olfactometer. The reflectance spectrum of leaves was measured using a UV-VIS spectrophotometer. Results indicate that resistant cultivars showed an intermediate-high antibiotic effect to T. tabaci and all of them showed a very strong antixenotic effect. There were no significant preferences in the response of walking T. tabaci adults to plant odors. The two susceptible cultivars had the highest values of leaf reflectance for the first (275-375 nm) and second (310-410 nm) theoretical photopigment-system of T. tabaci, and these values were significantly different from most resistant cultivars. These results suggest a strong response of T. tabaci to onion cultivars with higher reflectance in the ultraviolet range (270-400 nm). Overall, these results appear promising in helping to identify categories of resistance to T. tabaci in onions that can be used in breeding programs.

Antixenotic Resistance of Cabbage to Onion Thrips (Thysanoptera: Thripidae). I. Light Reflectance

“…This study on cabbage and previous work on onions (Diaz-Montano et al 2012) suggest that breeding for plant color, or at least light reßectance that inßuences T. tabaci behavior, should be an important part of an overall breeding strategy for host plant resistance to this difÞcult pest. However, these studies also suggest that further work is needed to link the characteristics of light reßectance in cabbage, and other crops, to the physiological perception of light in T. tabaci.…”

“…Accordingly, the average reßectance was computed in the range of sensitivity of the (5) Þrst, 275Ð375 nm (R av1 ), (6) second, 275Ð 400 nm (R av2 ), and (7) third, 400 Ð 650 nm (R av3 ) theoretical photoreceptor systems of T. tabaci. No blue receptor was hypothesized for T. tabaci, as was done in a previous study (Diaz-Montano et al 2012), because its existence was not supported by the available electrophysiological data from F. occidentalis (Matteson et al 1992). All reßectance spectrometry variables were computed for head leaves (i.e., Head_R av ) and old leaves (i.e., Old_R av ), as well as their contrast (Contr_R av ): computed value of the head leaf divided by that of the old leaf of the same cabbage plant.…”

“…Although visual systems are usually optimized for contrast detection, absolute levels of light can also inßuence behaviors. Finally, at least one other study has shown an effect of visual cues on thrips choice behavior; in a free-choice antixenosis experiment, T. tabaci abundance and the brightness of onion leaves were signiÞcantly correlated, especially in the UV range of light (Diaz-Montano et al 2012). In this study, the correlations were similar to what we found in cabbage in 2009, that is, the most resistant cabbage varieties had the lowest reßec-tance in the UV range, whereas the most susceptible ones had the highest on their old leaves.…”

Iris yellow spot virus (Tospovirus: Bunyaviridae): from obscurity to research priority

“…He found a limited number of instances in which selection was able to reduce virus damage. The effect of onion foliage colour on thrips feeding behaviour has been well documented: yellow-greencoloured foliage is less attractive than blue-green-coloured foliage to thrips (Diaz-Montano et al, 2012;Jones et al, 1934;Molenaar, 1984). Although foliage colour depends on nutritional level, these foliage types can be distinguished by different amounts of epicuticular waxes on leaf surfaces.…”

“…Results from numerous groups have indicated that thrips populations are often lower on onions with less epicuticular wax when compared with waxier types (Diaz-Montano et al, 2012;Jones et al, 1934;Molenaar, 1984). This may be advantageous to growers by reducing the frequencies of insecticide sprays over the growing season.…”