GALL WASP (HYMENOPTERA, CYNIPIDAE) MORTALITY IN A SPRING TALLGRASS PRAIRIE FIRE

The life history of the cynipid gall wasp, Antistrophus silphii Gillette, leaves it vulnerable to mortality in spring fires in the habitat of its host plant, Silphium integrifolium var. laeve Torrey and Gray. This article examines the mortality of gall wasp larvae during a prescribed burn at the Konza Prairie Research Natural Area in the tallgrass prairie of northeast Kansas. The three goals of the study were to determine (1) if A. silphii galls are most frequently found on the tallest S. integrifolium shoots, (2) if there is a relationship between growing season gall height and overwinter lodging, and (3) if gall wasps can survive fire at the heights at which they are found after overwinter lodging. A 1988 survey found that galls were relatively rare on short shoots (<100 cm), were most abundant on middle-length shoots (100-140 cm), and occurred at random on long shoots (>140 cm), suggesting that gall wasps avoided short shoots but that gall placement did not maximize gall height. A 1992 survey found that growing season gall height was not related to overwinter lodging of galled shoots, indicating that any gall wasp shoot selection patterns affecting later gall height were disrupted by winter lodging. Gall wasps placed at post-overwinter lodging heights were unable to survive an experimental fire, but a few gall wasps survived when placed above the range of naturally-occurring gall heights. A. silphii and other species with similar life histories must re-establish after fire by immigration, with subsequent population levels affected by indirect effects of fire on host-plant quality.