SEASONAL-CHANGES IN ABUNDANCE AND GONOTROPHIC AGE OF HOST-SEEKING TABANIDAE (DIPTERA) FROM A SUB-ARCTIC LABRADOR PEATLAND

Canopy and Malaise traps continuously sampled host-seeking female taba nids throughout the 1990 and 1991 night seasons at Iron Arm Fen in sub arctic Labrador. A total of 19,426 tabanids representing 3 genera and 18 species was collected. Subsamples of each daily catch were dissecte d to determine gonotrophic age. Horse flies (mainly Hybomitra spp.) ac counted for 96% of all tabanids; the remainder were deer flies (Chryso ps spp) Hybomitra arpadi (Szilady) and Hy bomitra aequetincta (Becker) were the dominant species, comprising 60.6 and 24.8% of collections, respectively. They were also among the Ist 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 Iro n Arm Fen. Seasonal changes in the gonotrophic age structure of host-s eeking 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 Ir on Arm Fen, Hybomitra lurida (Fallen) and Hybomitra zo nalis (Kirby) were facultatively autogenous, whereas Hybomitra pechuma ni (Teskey & Thomas), Hybomitra hearlei (Philip), Hybomitra frontalis (Walker), Hybomitra astuta (Osten Sacken), Chrysops zinzalus (Philip), and Chrysops nigripes Zetterstedt were obligately autogenous during t heir 1st ovarian cycle.