Accumulation and turnover of 2-tridecanone in Tetranychus urticae and its consequences for resistance of wild and cultivated tomatoes

In this study we assessed the dynamic changes of 2-tridecanone in a herbivo rous mite (Tetranychus urticae) on tomato (Lycopersicon esculentum, cv. 'Mo neymaker'), a plant with methyl ketones in the tetracellular tips of the gl andular trichomes (Type VI). We showed that spider mites accumulate 2-tride canone when foraging on cultivated tomato. Thus, the rate of mite-trichome contact multiplied by the amount of toxin per trichome tip exceeded the rel ative rate of toxin turnover multiplied by the amount of toxin per mite. Th e relative rate of toxin turnover was estimated to be 1.1 per day on cucumb er, a plant without this toxin. The amount per trichome tip varied from 0.3 3 ng for middle-leaf trichomes to 1.26 ng for main-stem trichomes. Hence, t o achieve a static level of 2-tridecanone equal to 8-17 ng per mite - repre senting the level we found in mites on middle leaves - the rate of mite-tri chome contact should be 26-57 per day. Because methyl ketone apparently acc umulates in the spider mites on tomato, the rate of mite-trichome contact i s probably higher than that. We expect the accumulation of ketones to occur especially on the stems of cultivated tomato, since this is the area most densely occupied with glandular hairs and because here the hairs have highe r levels of the methyl ketones. Using dose-response relationships assessed earlier (Chatzivasileiadis and S abelis, 1997, 1998), we estimated that the number of mite-trichome contacts causing 50% mortality per day is equal to 88 on a tomato stem, whereas it equals 70 for another strain of spider mites collected from cucumber. On wi ld tomato, L. hirsutum f. glabratum (PI 134417), just one to two contacts w ould suffice to cause 50% mortality per day. We suggest that methyl ketones from glandular hairs on tomato are an important mortality factor for spide r mites on wild tomato and probably also on cultivated tomato .