Document: DIL-3-52-20

Galls as habitats: The inquiline communities of insect galls.

SANVER, D.* and B.A.HAWKINS

University of California at Irvine, Irvine, CA 92697 USA ¹

Abstract:
The ability to form galls is widespread among insects. Inquilines are herbivorous or omnivorous organisms that do not directly feed on the galling insect, but rather, use the gall tissue as a habitat or food resource. These organisms, which are often important components of galler communities, have been largely ignored in studies that focus on insect gall makers and their natural enemies. We compiled data from the primary literature on inquilines of insect-induced galls for 114 galler systems (defined as one gall maker species on one host plant) in order to determine whether the inquiline diversity in a particular gall community correlates with any ecological, physiological or taxonomic characteristics of galls. We measured inquiline species richness as the number of inquiline species/number of natural enemy species for each system in order to attain a measure of relative diversity that was free of sampling bias across different systems. The resulting taxonomic list of known inquilines spans 48 families and 97 genera of insects and fungi. The biological relationships between inquilines and gallers are similarly diverse and include secondary gallers that build a gall either in or on the existing gall, parasitic inquilines that parasitize the galler in addition to feeding on the gall tissue, and fungal pathogens that invade the host plant through the gall. We conducted quantitative analyses on the following independent variables: host plant architecture (tree, shrub or herbaceous plant), latitude, gall size, gall type (leaf, stem, bud, or flower) and gall maker taxon. Inquiline diversity was significantly correlated only with host plant architecture and latitude; galls on trees supported the richest inquiline communities, and inquiline diversity was highest in the temperate zone. However, the relative paucity of inquiline data in the literature is reflected in our results; therefore, it is premature to reach any strong conclusions. Our goal is to emphasize the need to include these organisms in all studies of galls in order to attain a more accurate assessment of inquilines and their effect on galler communities.

Keywords: galls, inquilines, diversity

This abstract is being presented at: 3:30 PM in session:
HERBIVORE EFFECTS ON PLANTS