Seasonal changes in abundance and gonotrophic age of host-seeking Tabanidae (Diptera) from a subarctic Labrador peatland.

Canopy and Malaise traps continuously sampled host-seeking female tabanids throughout the 1990 and 1991 flight seasons at Iron Arm Fen in subarctic Labrador. A total of 19,426 tabanids representing 3 genera and 18 species was collected. Subsamples of each daily catch were dissected to determine gonotrophic age. Horse flies (mainly Hybomitra spp.) accounted for 96% of all tabanids; the remainder were deer flies (Chrysops spp.). Hybomitra arpadi (Szilady) and Hybomitra aequetincta (Becker) were the dominant species, comprising 60.6 and 24.8% of collections, respectively. They were also among the 1st species to emerge (in early July) and persisted for the entire flight season (until mid-August). Seasonal abundance for each species varied between the 2 yr of study. Both H. arpadi and H. aequetincta were obligately anautogenous at Iron Arm Fen. Seasonal changes in the gonotrophic age structure of host-seeking females of these species indicated a mid-July emergence peak in 1990 and an early July peak in 1991. Among the other tabanid species collected at Iron Arm Fen, Hybomitra lurida (Fallen) and Hybomitra zonalis (Kirby) were facultatively autogenous, whereas Hybomitra pechumani (Teskey & Thomas), Hybomitra hearlei (Philip), Hybomitra frontalis (Walker), Hybomitra astuta (Osten Sacken), Chrysops zinzalus (Philip), and Chrysops nigripes Zetterstedt were obligately autogenous during their 1st ovarian cycle.