Biology and development of Chaetophthalmus dorsalis (Malloch) (Diptera: Tachinidae) parasitising Helicoverpa armigera (Hübner) and H. punctigera Wallengren (Lepidoptera: Noctuidae) larvae in the laboratory

Chaetophthalmus dorsalis is a common larval parasitoid of several economically important species of Noctuidae in Australia but little is known about its biology. This paper describes aspects of the behaviour and development of C. dorsalis parasitising Helicoverpa armigera and H. punctigera larvae in the laboratory. At 25°C, C. dorsalis laid a mean of 577 ovolarviparous eggs, 8–9 days after emergence. Parasitoids were able to complete development when newly emerged planidia were placed on all host instars except first instars. Planidia manually placed on the dorsum of the first thoracic segment of host larvae showed no preference to penetrate segments immediately behind the head capsule where they could not be removed by the host. Planidia were significantly faster at penetrating the cuticle of early- (second to fourth) instar compared with late- (fifth and sixth) instar larvae, and late-instar H. punctigera larvae compared with equivalent instars of H. armigera. Parasitoid larval development was significantly faster when planidia were placed on late-instar H. punctigera larvae than on early-instar larvae but puparium development and puparium weight were not affected by host age. Parasitised Helicoverpa larvae gained weight at the same rate as unparasitised larvae until 2–3 days before the exit of C. dorsalis larvae when they entered a premature prepupal phase. Developmental thresholds and day-degree requirements for C. dorsalis were calculated and compared with H. armigera. A new host record for C. dorsalis reared from Neocleptria punctifera (Noctuidae) larvae is given.