The Distribution of Shoot-fly Larvae (Diptera, Acalypterae) within Pasture Grasses and Cereals in England

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Abstract
During the winter months, when larval populations of shoot flies (Diptera, Acalypterae) are relatively static, pure clumps of grasses in southern England were sampled. The tillers were dissected and the shoot-fly larvae removed and identified to determine what species were present and how and in what numbers they were distributed within the species of grasses. Concurrently, a permanent pasture was sampled in which the grasses were closely intermixed, and it was found in the two cases that the same host preferences of the insects were broadly maintained. Those preferences are due to the selectivity of the ovipositing female rather than the dietary requirements of the larvae, which are facultative parasites of most grasses and cereals.A Table is given of the relative abundance of the larvae of 17 species in 16 different grasses and indicates the degree of host specificity of each insect. For example, Oscinella frit (L.), the frit fly of oats, is found in 11 of the common grasses but not in Dactylis glomerata whereas O. albiseta, (Mg.) is found only in this grass.Horizontal migration of larvae from tiller to tiller can take place; vertical migration may also take place from ploughed-in grasses to cereals sown above. It is shown that migration is mainly limited to autumn and spring when soil temperatures are above the thermal threshold of activity of the larvae.