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THE LIFE HISTORY AND BIONOMICS OF A BRITISH PHYTOPHAGOUS CHALCIDOID OF THE GENUS HARMOLITA (ISOSOMA )
Author(s) -
JAMES E. C.
Publication year - 1927
Publication title -
annals of applied biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 80
eISSN - 1744-7348
pISSN - 0003-4746
DOI - 10.1111/j.1744-7348.1927.tb07009.x
Subject(s) - biology , ovipositor , instar , inflorescence , genus , bionomics , larva , botany , cecidomyiidae , zoology , repens , pupa , hymenoptera
Summary. This paper is a contribution to our very scanty knowledge of the British Harmolita , a phytophagous genus of the superfamily Chalcidoidea (Hymenoptera). Many species of this genus are pests on cereals and cultivated grasses; one species, Harmlita tritici , is the notorious joint‐worm of America and Russia, whilst species attacking many other cereals and grasses have been recorded in Europe and America. An account is here given for the first time of the life history and biology of a British species of Harmolita , namely Harmolita graminicola , which is a gall former on couch grass ( Triticum repens ). The larva of another undetermined species of Harmolita , also gallicolous on Triticum repens is figured and briefly described. The adult of Harmolita graminicola begins to emerge in the last week of June and continues to appear during the first week of July. When the inflorescence has appeared through the sheathing leaves the female fly will not lay eggs on them. One egg is deposited on each culm just beneath the rudimentary inflorescence, the ovipositor of the fly piercing the sheathing leaves in order to reach the desired position. The Harmolitae of both species were bred in captivity and the length of the period of incubation of the egg was found to be between three and four weeks. Experiments were conducted to ascertain whether parthenogenesis occurred in this species. The results were negative although perhaps not numerous enough to be conclusive. The larva possesses four instars and moults three times whilst feeding, another moult occurring at pupation. The larval instars can be differentiated most exactly by the state of development of the sub‐apical tooth on the mandible. The sub‐apical tooth is absent from the mandibles of the first instar; only incipiently developed in the second instar; better developed in the third and fully formed in the fourth instar. The larva becomes full fed in October and hibernation takes place in the larval stage. Pupation begins to occur near the end of April but the great majority pupate in the middle of May. There is a short semi‐pupal stage of from 12 to 24 hours duration immediately before the pupal moult takes place. The pupal stage lasts about 40 days and there is only one generation each year. The larva of Bracon erythrostictus (Lyle) was found to be parasitic on Harmolita in the latter's larval stages; no other insect parasites were found. Both Harmolita graminicola (Gir) and the undetermined species refused to breed on wheat or any other plants of the Triticum genus although many attempts were made to induce them to do so.