GALL MORPHOLOGY AND COMMUNITY COMPOSITION IN ASPHONDYLIA-FLOCOSSA (CECIDOMYIIDAE) GALLS ON ATRIPLEX-POLYCARPA (CHENOPODIACEAE)

Asphondylia flocossa Hawkins (Diptera: Cecidomyiidae) and its associat ed community of natural enemies were sampled in galls on Atriplex poly carpa (Torrey) Watson (Chenopodiacedae) at 3 locations north of Phoeni x, AZ, between October 1994 and March 1995. Galls collected in the aut umn had dramatically smaller diameters and shorter trichomes than gall s collected in the spring. Asphondylia flocossa were more likely to em erge from larger than average galls with a thick trichome layer in bot h the autumn and winter samples. The different species of natural enem ies each emerged from galls with different characteristics. There was significant variation among taxa of natural enemies for both gall diam eter and trichome depth in both the spring and autumn samples. The com munity of natural enemies also varied significantly among populations and more markedly between seasons. Both Asphondylia flocossa and Riley a tegularis Gahan (Hymenoptera: Eurytomidae) were much more abundant i n spring samples than in autumn samples. Ln contrast, Torymus cappilac eus (Huber) (Hymenoptera: Torymidae) and an undescribed species of Gal eopsomyia (Hymenoptera: Eulophidae) were abundant in the autumn sample s but almost non-existent in the spring samples. The first 2 species t ended to emerge from relatively large galls while the latter 2 species tended to emerge from small galls. Torymus; umbilicatus (Gahan) (Hyme noptera: Torymidae) was the only parasitoid abundant in samples from b oth seasons. This species emerged from galls with the widest range of diameters and trichome depths of any species, both within and between seasons. The feeding biology of the individual species coupled with se asonal and temporal covariation in gall morphology makes natural enemy control of gall size unlikely. The data is consistent with the hypoth esis that gall morphology influences insect community composition.