Variation in trichome density and resistance against a specialist insect herbivore in natural populations of Arabidopsis thaliana

1. The annual herb Arabidopsis thaliana is a prime model organism of plant molecular genetics, and is currently used to explore the molecular basis of resistance to herbivores. However, both the magnitude and the causes of variation in resistance among natural populations of A. thaliana are poorly known. The hypotheses (a) that resistance to a specialist herbivore, the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is positively related to the density of leaf trichomes, and (b) that oviposition preference by female moths is positively correlated to larval performance on different populations and maternal lines of the host plant were examined. 2. Variation in leaf trichome density and resistance to P. xylostella within and among six natural populations of A. thaliana in Sweden was quantified. Resistance was quantified by examining the number of eggs laid on plants exposed to ovipositing female moths and by monitoring larval development on plants of different origin. 3. Trichome density varied significantly among populations; for 4-week-old plants (exposed to ovipositing moths), it also varied significantly among maternal families within populations. The rate of oviposition varied significantly both among populations and among families within populations. This variation could partly be explained by a negative relationship between trichome density and egg number, and a positive relationship between plant size and egg number. Time to pupation, pupal mass, and time to adult eclosion did not vary among populations or maternal lines of the host plant, and offspring performance was not related to P. xylostella oviposition preference. The results indicate that A. thaliana populations may respond to selection for increased resistance to P. xylostella, and suggest that trichome production contributes to resistance against this specialist herbivore.