We tested two hypotheses that investigated the pattern of attack by a gall-inducing insect on its host plant Astronium fraxinifolium (Anacardiaceae) in two contrasting habitats: cerrado (a savannic formation that indicates harsh conditions) and gallery forest (indicating moist conditions): (i) that galling female preference and larval performance are higher in xeric than mesic habitats; (ii) that vigorous modules are more attacked by the galling female insects where their larvae achieve higher performance independent of the habitat. The attack preference by the female galling did not differ between habitats. However, the larval performance was higher in the xeric habitat (cerrado) (76%) compared to the mesic habitat (gallery forest) (24%), partially supporting the first hypothesis. In general, bottom-up and top-down forces controlling the gall-inducing insect were higher in the mesic habitat. Shoot size of A. fraxinifolium did not influence the selection by the females for oviposition in any of the habitats. But, larger shoots provided better larval performance only in xeric habitats. In this way, galling performance is strongly habitat dependent and long-term differences in mortality rates between mesic and xeric habitats may have led to greater performance and success in dry environments.
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Vol. 122 • No. 1