Influence of Variety on Abundance and Within-Plant Distribution of Onion Thrips (Thysanoptera: Thripidae) on Cabbage

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Abstract
Numbers of onion thrips, Thrips tabaci Lindeman, were significantly lower in August and early September in the heads of two resistant cabbage varieties (‘Titanic 90’ and ‘Falcon’) than in two susceptible varieties (‘Market Prize’ and ‘Supergreen’). Numbers of onion thrips on the frame or outer leaves were significantly higher on resistant than susceptible varieties in September. These differences remained when thrips numbers were adjusted using the head and frame dry weight as covariates to remove any effect of differences in head or frame size among varieties. After adjustment, the populations on susceptible heads ranged from 2.8 to 11.5 times as high as populations on resistant heads from 17 August to 14 September in 1983 and 1984. The resistant varieties ‘Falcon’ and ‘Titanic 90’ had as many thrips per plant as suceptible varieties, but fewer thrips infested the head of resistant varieties and caused less cosmetic damage to the marketable product.