Influence of host-plant sex and habitat on survivorship of insect galls within the geographical range of the host-plant



This study evaluated the influence of host-plant sex and habitat on the
abundance and survivorship of the galling Psyllidae, Neopelma baccharidis Burckhardt
1987 (Homoptera) on several populations of the host-plant Baccharis
dracunculifolia De Candole (Asteraceae) within its geographical range in Brazil.
Three questions were addressed: (i) what is the effect of host-plant sex and the
habitat occupied by Baccharis dracunculifolia on the abundance of galls induced
by Neopelma baccharidis? Plant sex did not affect the abundance of galls per
plant while host-plant habitat had a significant effect. Twice as many galls were
found on plants in xeric habitats as on plants in mesic habitats; (ii) what is the
influence of host-plant sex and habitat on the survivorship rates of Neopelma
baccharidis? Populations occurring in mesic habitats suffered 3 times greater
mortality than populations in xeric habitats; (iii) does the richness and abundance
of inquilines of Neopelma baccharidis galls vary between habitats? Habitat
type did not influence the pattern of inquiline richness. The abundance of
inquilines was also very similar between xeric (51%) and mesic habitats (49%).
This study suggests that host-plant sex did not affect the abundance of the psyllid
galls on B. dracunculifolia, while the habitat occupied by the host-plant had a
strong influence on gall abundance, with more galls occurring in xeric habitats
than in mesic habitats. Otherwise, no effect of habitat was found on gall
inquilines. The mechanism generating the pattern of gall abundance was the differential
mortality of galls between habitat types.
KEY WORDS: habitat effects, herbivory, insect galls, plant sex, richness, survivorship.

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