Prevalence of four species of egg parasitoids attacking tabanid eggs in Manitoba, Canada

Egg masses of the horse fly, Hybomitra nitidifrons nuda (McDunnough), and the deer fly, Chrysops aestuans Wulp (Diptera: Tabanidae), were collected during the summers of 1996-2000 from five different locations in southern Manitoba. On average, hymenopterous egg parasitoids were reared from more than 90% of collected egg masses. Telenomus hybomitrae Iranpour and Galloway and (or) Telenomus utilis Iranpour and Galloway (Hymenoptera: Platygastridae: Telenominae) emerged from multilayered egg masses of H. n. nuda. However, Trichogramma semblidis (Aurivillius) (Hymenoptera: Trichogrammatidae) and (or) Telenomus chrysopsis Iranpour and Galloway were reared from single-layered egg masses of C. aestuans. In H. n. nuda egg masses, more than 33% of individual eggs were parasitized and more than ail additional 35% were apparently damaged by the two telenomine parasitoids. In C. aestuans egg masses, approximately 40% of individual eggs were parasitized and 18% produced neither parasitoids nor larvae.