Role of Nonpreference in the Resistance of Cabbage Varieties to the Onion Thrips (Thysanoptera: Thripidae)

Abstract

Preference of Thrips tabaci , Lindeman adults for four varieties of cabbage was tested in the field by putting uninfested potted plants next to plots of wheat, oats, or alfalfa as thrips were moving out of these crops, and in the laboratory by placing thrips adults in circular plastic boxesand allowing them to choose among leaf disks from the heads of the same four varieties. In the field tests, more T. tabaci adults accumulated on heads of varieties previously identified as susceptible (‘Market Prize’ and ‘Supergreen,’ means of 28.4 and 16.2 thrips per head, respectively, over five tests) compared with those identified as resistant (‘Titanic 90’ and ‘Falcon’ means of 5.5 and 2.9, respectively). This difference was consistent for all three crops used as source plots and for all stages of cabbage development once the developing heads reached a fresh weight of 10 g. For the frame (outer) leaves of the cabbage plant, ‘Falcon’ was generally preferred over the other varieties, although the numbers of thrips colonizing frame leaves of all varieties decreased to nearly zero late in the season. In the laboratory tests, no differences in preference among leaf disks from the heads of the four varieties were observed.