Resistance to 2-tridecanone in Tetranychus urticae: Effects of induced resistance, cross-resistance and heritability

Earlier studies of resistance to the tomato toxin 2-tridecanone revealedsimilar levels of resistance among tomato and cucumber strains ofTetranychus urticae, whereas we anticipated the tomatostrains to have a higher resistance. Between-strain differences, however, maybeconcealed by toxin accumulation and/or cross-resistance. Mites do accumulate2-tridecanone to a considerable extent, but we have shown before that thiscannot explain the lack of difference in resistance. In this paper, we provideevidence against cross-resistance: selection for resistance to a homologouscompound from cucumber, 2-nonanone, did not confer resistance to 2-tridecanone.Observed increases in resistance levels over generations may be due toinductionor selection. To study induction, adult females from a cucumber strain and atomato strain were exposed to a sublethal dose of 2-tridecanone. One day afterexposure, the cucumber strain gained in resistance to 2-tridecanone (c.8-fold),whereas the tomato strain showed a decrease in resistance. These changes inresistance disappeared within three days after exposure, the time the mitesneedto dispose themselves of the toxin. The results support earlier findings thatresistance is induced in the cucumber strain, but not in the tomato strain. Toassess the heritability of resistance to 2-tridecanone, offspring was obtainedfrom individual females, and both the mothers and their offspring were testedfor resistance. For the cucumber strain, offspring from susceptible orresistantmothers did not differ in resistance. For the tomato strain, however, offspringfrom resistant mothers were significantly more resistant to the toxin thanoffspring from susceptible mothers. This result provides unambiguous evidencethat resistance to 2-tridecanone can be selected for.