OBSERVATIONS ON GERRIS INCOGNITUS AND GERRIS GILLETTEI (HETEROPTERA: GERRIDAE) Joan R. Callahan Department of Biological Sciences, University of Arizona, Tucson, Arizona 85721 ABSTRACT — Information is presented on identifying characteristics, size, sex ratio, wing polymorphism, migratory behavior, diving behavior, habitat, and life cycle of Gerris incognitus Drake and Hottes and G. gillettei Lethierry and Severin. The ecological importance of water striders in general is discussed. Relatively little work has been done on the ecology and behavior of most North American water striders. Only Gerris remigis Say, the most common species, has received much attention (Torre-Bueno 1917, Essenberg 1915, Riley 1920, Murphey 1971a, 1971b). The pur-pose of this paper is to provide information on 2 of the most ne-glected gerrid species, G. incognitus Drake & Hottes and G. gillettei Lethierry & Severin, chosen because of their abundance in the study area. Location and Methods This study was conducted between April 23 and June 5, 1972, at Jewel Lake and 3 adjacent ponds, all located in Tilden Regional Park, Contra Costa County, California. Collecting was limited to the adults, as no key is available for identification of nymphs of these 2 species. A 4 in. X 6 in. short-handled dipnet proved most satis-factory for obtaining specimens, and on Jewel Lake it was used from an inflatable plastic raft. Screening was impractical due to the dense growth of pondweed and filamentous algae in the habitat of both species. Results 1. Identification Gerris incognitus and G. gillettei are similar in appearance and their identity has often been confused (Drake and Harris 1928). The females are particularly difficult to separate, as are those of several members of the genus (Sprague 1967). Under low magnifi-cation, males are easily distinguished by the presence, in incognitus, of long silvery hairs on either side of the ventral surface of the first genital segment (Usinger 1956). Other characteristics are given in some keys (Kuitert 1942) but were found to be less useful for identification. Identification of females was achieved by the laborious process of obtaining copulating pairs, identifying the males, and using the 15
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