Revista Chilena de Historia Natural 78 (3): 393-399, 2005
RESEARCH ARTICLE
Galler-induced reduction of shoot growth and fruit production in the shrub Colliguaja
integerrima (Euphorbiaceae)
We evaluated experimentally the effect of a gall-maker insect on vegetative and
reproductive traits of the shrub Colliguaja integerrima (Euphorbiaceae). We performed two experiments: (1) a chemical
(insecticide) exclusion to prevent gall formation, and (2) a mechanical removal of new galls at the early stage to prevent gall growth. In
the study area, galled shrubs were common (77 %). Because the pattern of insect attack may influence plant fitness, the distribution of
egg clusters deposited by the galler and the number of galls among shrubs were also evaluated. Fruit production was inversely
associated with the number of galls, but did not correlate with shrub height, shrub cover, and number of shoots. Ungalled shoots were
longer than galled shoots after 12 months initiated the experiment. Chemical exclusion produced a delayed positive effect on plant
reproduction. Fruit production was higher in experimental than control branches after 24 months. Mechanical removal of galls
increased fruit production in comparison to control branches in the next reproductive season. These results indicate that the galler
reduces shoot growth, and has a delayed detrimental impact on fruit production of C. integerrima. Because the chance of
finding new galls was higher on the previously infected shrubs, it is possible that reinfection processes account for the cumulative
negative effects of the bud-galling insect on plant fitness.
Key words:
bud-galling insect,
central Chile, Mediterranean ecosystem
