EARLY-SEASON DEFOLIATION OF SORB US AUCUPARIA (L.) ANDACER PLATANOIDES (L.) CAN INDUCE DEFENSE MECHANISMSAGAINST THE SPIDER MITE TETRANYCHUS URTICAE (KOCH)

摘要

Artificial defoliation is oftenused in studies of induced defense reactions ofplants to damage by arthropods. However, littleis known about the role of various external fac-tors that may determine the nature of inducibledefenses. Here we tested whether light level un-der which plants grow could affect the naturalinvasion of two-spotted spider mite (Tetranychusurticae Koch) with a broad range of host plants.For this study we used two host species that differwidely in shade tolerance: shade-adapted Norwaymaple (Acer platanoides L.) and sun-adapted Eu-ropean mountain ash (Sorbus aucuparia L.). Thepurpose of this study was to explore mite inva-sion and to test whether prior simulated defo-liation, light conditions and host species differ-ences in secondary defense metabolites (solublephenolics) play a role in the pattern of invasion.One-year-old maple and ash seedlings growing inpots were placed into two shade houses that pro-duced a treatment with 5% light transmittance,and the second group of seedlings was placed infull sunlight. The experiment was carried out in alocation chronically affected by spider mite pres-ence. The defoliation was performed in mid-Mayby manual removal of 0 (control), 25, 50, 75 and100% of leaves. Natural two-spotted spider miteinvasion took place in mid-July and was observedonly on seedlings growing in the shade. Miteswere found on leaves of almost all seedlings. How-ever, the intensity of feeding damage to leaves wasrelated to the level of earlier defoliation. Control and slightly to moderately (25-50%) defoliatedseedlings of both species were most affected byspider mites. Mite feeding behavior was directlylinked to changes in concentration of leaf carbonand phenolic compounds. Carbon content waspositively correlated with the percent of seedlingsdamaged by spider mites in both tree species (R~2>0.80; P <0.05). The highest concentration of phe-nolic compounds was observed in leaves of seed-lings subjected to 50 and 75% defoliation. Our results indicated that two-spotted spidermites preferred plants grown in a shade environ-ment and within these plants favored leaves whichare high in carbon and low in phenolic com-pounds. Both plant species were able to surviveearly season leaf damage inflicted by spider mites.Inducible phenolic compounds were among de-fensive secondary metabolites contributing tolow spider mite success in plants recovering fromartificial spring defoliation.