The foliar chemical profile of criollo avocado, Persea americana var. drymifolia (Lauraceae), and its relationship with the incidence of a gall-forming insect, Trioza anceps (Triozidae)

Abstract

Abstract The role of phytochemical diversity in plant defense was studied using the specialist herbivore Trioza anceps Tuthill (avocado gall-forming insect), and the volatile fraction of the foliar chemicals of its host, the creole avocado (Persea americana var. drymifolia (Schect. & Cham.) Blake). Two hypotheses were tested: a) plant defense is determined by phytochemical diversity, and b) plant defense is determined by single compounds or specific blends of compounds. Simple and multiple regressions and a size and shape analysis (which considers the compounds relative and absolute concentrations within the leaf blend) were used to test these hypotheses. Simple regressions of gall incidence and chemical diversity and the tree origin elevation and latitude were very weak. The linear multiple regression to explain gall incidence with 33 foliar compounds and geographical data produced a model with low predictive power (R2 = 0.13). The size and shape analysis showed intraspecific variation in leaf chemical profiles among five tree groups, classified by the number of galls per 10 cm2 of leaf. Discriminant analysis separated clearly the tree groups’ chemical profiles through specific compounds. These results suggest that the gall incidence is associated with specific chemical profiles, rather than to high or low foliar phytochemical diversity.