HOST-PLANT PREFERENCE OF AN INSECT HERBIVORE MEDIATED BY UV-B AND CO2IN RELATION TO PLANT SECONDARY METABOLITES

Leaves of European silver birch (Betula pendula Roth) seedlings subjec ted both to ambient and increased levels of CO2 concentration (350 and 700 ppm) with no UV-B and supplementary UV-B radiation were offend to winter moth (Operophtera brumata L.) larvae in laboratory choice expe riments. According to chemical analysis of the leaves, the high CO2 co ncentration decreased the levels of phenolic acids and two flavonoids. The UV-B treatment increased the content of flavonoids. Winter moth l arvae consumed most of the leaves of birch seedlings which had been ex posed to UV-B radiation in both CO2 environments. Therefore, the effec t of the main leaf flavonoids, myricitrin and quercitrin, on the feedi ng of winter moth larvae was tested by an artificial diet choice exper iment. The addition of the two main flavonoid glycosides into artifici al diet had no stimulatory effect on larval feeding. Consequently, inc reases in flavonoid content may not be directly responsible for the la rval preference for UV-B exposed leaves. (C) 1998 Elsevier Science Ltd . All rights reserved.