none Liriomyza bryoniae; HYMENOPTERAN-PARASITES; Dacnusa sibirica; Host searching behaviour, use of marking pheromone; PLANT-HOSTS; Lycopersicum esculentum (tomato); Hymenopteran parasite host searching behaviour Dacnusa sibirica; PHEROMONES-; Marking, use in dipteran host searching; DIPTERAN-HOSTS; Liriomyza bryoniae; Host searching behaviour, use of marking pheromone. We studied the rules used by the female parasitoid, Dacnusa sibirica Telenga (Hymenoptera: Braconidae), for deciding when to leave a tomato leaflet on which she is searching for larvae of the leafminer, Liriomyza bryoniae Kalt. (Diptera: Agromyzidae). Females would deposit a marking pheromone on the leaflet and would leave the leaflet when the amount of the pheromone accumulated to the threshold L, which is proportional to the amount of search effort on the leaflet. L appears to increase with host density since it rises after every encounter with a host (or mine). D. sibirica would employ an area-concentrated search, which is advantageous in foraging for hosts showing a clumped distribution.