EFFECTS OF EARLY-SEASON DEFOLIATION OF ANTHYLLIS CYTISOIDES (A MEDITERRANEAN BROWSE SPECIES) ON FURTHER HERBIVORE ATTACK

To determine if defoliation of a woody plant affects foraging by foliv orous insects, we examined the infection rate (number of leaves damage d per total number of leaves sampled on marked stems) of Anthyllis cyt isoides under three experimental treatments: 10, 50 and 90% plant defo liation. Observations were made for three age classes, established by trunk base perimeter (equal to or lower than 11 cm, between 11 and 20 cm, larger than 20 cm). Plants respond positively to artificial defoli ation by increasing total vegetative length of the stem and total infl orescence length. This response is most evident in young individuals. Response to herbivory was measured as overall infection rate and also as infection rate by different feeding guilds-chewing, mining, or suck ing insects. We found that increased defoliation elicited increased re sistance of leaves to insect attack. This was particularly evident in young plants. Different insect guilds respond in different ways. Attac k by chewing insects declines with defoliation for all plant age class es; only sucking insects which feed on the oldest plants reduce feedin g rate with plant defoliation. Finally, mining insects present the opp osite trend in young and senescent plants. (C) 1996 Academic Press Lim ited