Development of Eucelatoria bryani and Eucelatoria rubentis (Diptera: Tachinidae) in Different Instars of Helicoverpa zea (Lepidoptera: Noctuidae)

Abstract

Development of the tachinids Eucelatoria bryani Sabrosky and E. rubentis (Coquillett) in the last 2 larval instars of the host corn earworm, Helicoverpa zea (Boddie), was examined. Developmental differences exist between parasitoid species, and within a species, depending on host instar at the time of parasitization. Development was fastest for E. bryani reared in hosts parasitized as 5th instars and was slowest for E. rubentis reared from hosts parasitized as 4th instars. These 2 closely related species also differ in their physiological relationship with H. zea . Second and 3rd instars of E. rubentis become enclosed in a thickened gelatinous sheath, probably of host origin. Such a sheath does not form around larvae of E. bryani . Size of E. bryani was not affected by host instar at the time of parasitization. Host instar at the time of parasitization did not affect the size of E. rubentis females, but E. rubentis males were significantly larger from hosts parasitized as 5th instars. Although both species deposited larger clutches of eggs in older hosts, clutch size was greater in both host-instars for E. bryani than for E. rubentis . Its greater clutch size and lack of size variation in its progeny reared from different host classes indicate that E. bryani is more efficient in using H. zea as a host resource. Given its faster larval development, E. bryani should be a superior larval competitor when both species parasitize H. zea . Interspecific differences may result from E. bryani being more of a specialist parasitoid whereas E. rubentis is more polyphagous.