The response of Tabanid species to CO₂-baited insect flight traps in northern California (Diptera : Tabanidae).

Details are given of catches of Tabanids in Malaise-type traps [cf. RAE/B 54, p. 191] baited with carbon dioxide [cf. 61, 443] and operated in northern California from 6th April to 26th June 1966. Females of 18 species were taken; Silvius notatus (Big.), Tabanus similis Macq., T. kesseli Philip and Apatolestes comastes Will. made up 78% of the total. Wind direction and the percentage canopy cover surrounding traps had little effect on the numbers at various sites. The ratio of Tabanids caught in traps baited with carbon dioxide to those in unbaited traps was 57:1. The temperature range at which all species sought hosts was 23.9-32.2 deg C. Normal host-seeking times for most species were markedly altered on hot days (days with daily maximum temperatures above 32.2 deg C). Of the 18 species trapped, 11 also fed on tame deer (Odocoileus hemionus columbianus) at temperatures between 21.1 and 37.8 deg C. Species of Chrysops fed on the face and ears, Silvius most commonly on the rear legs, Hybomitra on the face and Tabanus on the neck, back and rarely the face. The ratio of Symphoromyia to Tabanids feeding on deer was about 40:1.