ON THE LIFE‐HISTORIES AND ECONOMIC STATUS OF CERTAIN CYNIPID PARASITES OF DIPTEROUS LARVAE, WITH DESCRIPTIONS OF SOME NEW LARVAL FORMS

Abstract

Summary. Cothonaspis rapae (Westd.) was found to be an effective parasite of the Cabbage Root Maggot (Hylemyia brassicae Bouche) in the Cambridge district. Twenty‐five per cent. of the total of host maggots and puparia examined were found to be parasitised by this cynipid. The average duration of a life cycle of C. rapae is 92 days and the length of the larval stage is about 55 days. There are two generations in the season; the first appears in May and the second in August and September.The winter is passed in the larval stage. Hypermetamorphosis occurs in the life cycle, the primary larva being eucoiliform with three long pairs of thoracic processes, a long cauda, and suctorial mouth parts. The full grown larva is a typical mandibulate hymenopterous grub without cauda or appendages of any kind. The life‐histories of Figites anthomyiarum Bouché, Kleidotoma marshalli (Marshall) and an undetermined Kleidotoma are described.They are all effective parasites during the early larval stages of carrion feeding Diptera such as the Calliphora erythrocephala, Sarcophaga carnaria, Lucilia sericata, etc. The writer estimates that saprophagous maggots are reduced in numbers by 30 per cent. owing to parasitisation by various Cynipid parasites during the early larval stages. These three parasites have each two broods per season. The duration of the Figitids' life cycle is about 60 days, but that of both Kleidotomids takes from 10 to 20 days longer. There does not appear to be any definite period of emergence, but one generation overlaps another. The primary larva of F. anthomyiarum is a modified eucoiliform. No primary larva of a figitine species has been hitherto described. The primary larvae of the two Kleidotomids are eucoiliform but with short thoracic processes. These types of primary larvae are each succeeded by an entirely new type of endoparasitic larva which bears pronounced affinities to the polypod embryonic stage. The writer has termed this type of larva the polypodeiform larva. The polypodeiform larva of both F. anthomyiarum and Kleidotoma marshalli are figured and described.The early stage forms of parasitic Cynipid larvae are reviewed and compared. Several experiments were conducted to test whether Cynipids parasitising saprophagous maggots would oviposit in phytophagous maggots and vice versa. Under suitable conditions F. anthomyiarum was induced to oviposit in the maggots of H. brassicae (phytophagous) but the eggs did not develop. C. rapae, however, could not be induced to oviposit in saprophagous Anthomyid larvae.