Ovipositional Behaviour of the Parasitoid Fly, Exorista japonica (Diptera: Tachinidae), in the Laboratory: Diel Periodicity and Egg Distribution on a Host

Abstract

Ovipositional behaviour, diel periodicity of oviposition and egg distribution on the host of the parasitoid fly, Exorista japonica were studied in the laboratory. The hosts provided were larvae of Mythimna separata. The rate of adult fly emergence, and the number of eggs destroyed by hosts were also examined when one egg per host was laid on different body segments of a host. When provided with two hosts every 4 h from 22:00 on day 4 for 4 consecutive days, females laid more eggs in the morning and the rate of oviposition reduced with the passage of time towards evening; no eggs were laid during the period of darkness. The mean number of mature eggs, determined by dissection, showed a similar tendency to oviposition with a peak just after the end of the dark period and a subsequent decrease, although the decline was not statistically significant. When hosts were provided for the flies at 08:00 and 20:00 for 60 min each, no significant difference was found between the number of ovipositions at each time. Therefore, there is the possibility that the diel periodicity of oviposition of E. japonica was influenced by the number of mature eggs, which accumulated mainly during the night. The eggs laid on a host were concentrated on the head and thoracic segments when 1, 2 or 3 eggs were laid per host. When one egg per host was laid on different body segments, the rate of adult emergence followed a U-shaped curve, being lower on the 6th and 7th abdominal segments, which may have been mainly due to the host's ability to remove or destroy eggs laid on its body. These results suggested that E. japonica females selectively oviposit on certain parts of the host's body, an adaptation to the defence behaviour of the host.