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UBC Theses and Dissertations

A comparative study of two seed bugs, Geocoris bullatus (Say) and G. discopterus Stål (Hemiptera: Lygaeidae) in the Yukon Robinson, Jennifer J.


Geocoris bullatus (Say 1831), (Henriptera: Lygaeidae) has been collected and studied across North America but the present work is the first detailed study of western North American G. discopterus Stål 1874. In fact, it has been claimed that G. discopterus is solely a species of the east. As the two species are taxonomically difficult to separate, when they were apparently discovered together at several localities in the southwestern Yukon, a detailed investigation of their systematics and distribution seemed necessary. Species status of Yukon G. bullatus and G. discopterus was established morphologically using standard taxonomic characters. Biological species status was confirmed through breeding experiments. The life cycles of Yukon G. bullatus and G. discopterus were studied and significant differences were discovered in the generation time and phenology. G. discopterus is univoltine and usually overwinters in the adult stage, while G. bullatus is bivoltine and overwinters in the egg stage. Fat body dissections revealed adult G. discopterus fat body size increased toward the end of summer. No such trend was recognized in adult G. bullatus. Total fatty acid levels were assayed for each species, and adult G. discopterus were found to contain higher quantities than G. bullatus, perhaps correlating with the overwintering strategy in G. discopterus An investigation of the habitats occupied by each species was performed through an in depth vegetation analysis. G. discopterus was found to prefer xeric sites situated on south-facing slopes and outwash plains while G. bullatus occupied disturbed mesic roadsides and wastelands. Habitat preference differences coupled with phenological differences may account for the apparent sympatry of these two Geocoris species at some Yukon localities. Comparison of the xeric habitat of G. discopterus to known glacial relict sites in the interiors of Alaska, Yukon and Siberia reveal striking similarities. Late Pleistocene pollen cores also compare favorably with these G. discopterus habitats. In view of this and the disjunct North American distribution of G. discopterus, this species is hypothesized to be a relict species from the late Pleistocene ice age.

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