none An "H"-type olfactometer was designed and built to test the response of bark be etle (Dendroctonus frontalis parasites to various beetle and tree host odors. The design has several advantages over other types of olfactometers. Strong air currents are not utilized, parasites have free movement in the test chamber, and a concentration gradient of test compound is maintained. Parasites tested in the olfactometer demonstrated strong positive responses to air drawn over logs infested with bark beetle larvae and varied responses to tree host odors. Techniques; Parasites diseases and disorders; Host parasite relationships Coeloides pissodis (Braconidae ); Chalcidoidea; Behavioural techniques; Olfactometer design & function in attractant & host preference studies; Host preference; Coleopteran pheromone component attraction, olfactometer design, evaluation