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Summary: Ant mutualists alter the composition and attack rate of
the parasitoid community for the gall wasp Disholcaspis
eldoradensis (Cynipidae)
B R I A N D . I N O U Y E and A N U R A G A . A G R A W A L Center for Population Biology,
University of California, Davis, U.S.A.
Abstract. 1. The strength or density dependence of pairwise species interactions
can depend on the presence or absence of other species, especially potential
mutualists.
2. The gall wasp Disholcaspis eldoradensis induces plant galls that secrete a sweet
honeydew from their top surfaces while the wasp larvae are active. These galls are
actively tended by Argentine ants, which collect the honeydew and drive off
parasitoids attempting to attack the gall wasp.
3. When ants were excluded, the total rate of parasitism by seven species of
parasitoids increased by 36%, and the rate of gall-wasp emergence decreased by
54%.
4. The total percentage parasitism was affected by gall density when ants were
excluded but not when ants were unmanipulated, suggesting a change in
parasitoid functional responses due to ant tending.
5. In addition, excluding ants significantly altered the proportions of different
parasitoid species that emerged from galls; one parasitoid species increased from
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