Oscinella pusilla Meigen and Oscinella frit Linnaeus - Frit Fly
Systematic position.Class Insecta, order Diptera, family Chloropidae, genus Oscinella.
Biological group.This is an oligophagous pest of grain crops.
Morphology and biology.The body of the adult O. pusilla is black and 1.5 to 2 mm long. Halteres, abdominal sternites, fore-tibiae and mid-tibiae are yellow; hind tibiae have dark band. Femora are black. Antennae have four segments, positioned parallel to each other. White or cream cylindrical eggs reach 0.7 mm long. Adult larvae are white-yellow, having a cylindrical form. Its body is pointed anteriorly, being rounded posteriorly. Two fleshy rounded tubercles with spiracles are located on anal segment. One row of big spicules and one row of small ones are marked on the cuticle of each segment. Abdomen is yellow ventrally and legs are black with yellow tarsi. Antennae are divergent. Female is considerably bigger than male. Eggs and larva of O. frit are similar to those of O. pusilla. Over-wintering takes place during the middle and older larva instars in stems of winter crops and wild cereal grasses. Pupation is observed in spring at air temperature 12°C, lasting 10-14 days. Emergence of flies of first generation occurs during early to mid May (depending on zone), lasting until the end of June at the minimum temperature of about 16°C. Maximum flight is observed at the end of June (in the zone of high damage), when plants have 1-3 leaves. Additional feeding on pollen and nectar is necessary for the insects on wild plants. Oviposition begins 9-13 days after emergence. Males perish after coupling. Females lay eggs on young growth of spring crops. Eggs are laid one by one or in groups (1-15 eggs) on coleoptile, leaf plate, behind sheath of first leaf, on ground. Fecundity reaches 25-30 eggs. Embryonic development lasts 4-10 days. Larvae of younger instars penetrate into stem core, crawling toward tillering node, forming brown canal. The larvae of older instars feed on tissues of growing-points. Pests of first generation are very dangerous, damaging the main shoot or stems of primary tillers. The larval period lasts 13-20 days. Only one larva lives in one stem. Before pupation it gnaws out the stem to the epidermis. Pupation takes place in the place of feeding. Emergence of flies of the second generation is observed in July. Females lay eggs on stems of underdeveloped plants, on ears of spring crops, on wild cereal grasses. Larvae of second generation are less harmful, because they only damage the stems of secondary tillers and ears. Flies of third generation emerge from the end of July until September. Eggs are laid in August on dropped grain of spring crops, on young growth of winter crops, on wild grasses. Life span is 22-46 days.
Distribution.The insects are widespread in West Europe, North America; they are also observed in Asia. Within the territory of the Former Soviet Union the species occurs very widely up to 62 degrees north. Both species are found in all areas, but have different population densities. High harmful activity of O. pusilla is reported in forest-steppe and steppe zones. High harmful activity of O. frit is observed in forest and forest-steppe zones of Russia and Ukraine. Southern border goes along line Balta - Poltava - Voronezh - Saratov - Samara.
Ecology.Wintering larvae are cold-resistant. Lower temperature thresholds for the species development is 10-12°C, upper threshold is 35°C (average daily air temperatures). An accumulation of degree days of 54-63° is necessary for the maturing of gametes. The insects usually develop in 2-3, sometimes 5 generations (in Middle Asia). O. frit prefers moderate temperatures (16-22°C) and sufficient humidity (70-80%). O. pusilla normally endures high temperatures (25-30°C) and insufficient humidity (40-60°C). Most important predators are Triaspis obsaerellus Nees., Bracon longillus Wesm., Ganaspis sp., Trichomalus statutus Forst., Spalangia fuscipes Nees., Halticoptera circulus Walk., Ophonus rufipes Deg., Broscus cephalotes L., Pterostichus cupreus L., Pt. punctulatus Sch., Carabus convexus F.
Economic significance.The pest causes the greatest damage to wheat, barley, oats, rye, even to maize and wild cereal grasses Agropyrum repens P.B., Phleum pratense L., Agrostis gigantea Roth, A. vulgaris L., Agrostis sp., Poa annua L., P. pratensis L., P. compressa L., Festuca rubra L., F. elatior L., Bromus sterilis L., Dactylis glomerata L. O. pusilla prefers barley and wheat; O. frit selects oats. Control measures include deep (20-25 cm) under-winter plowing, using ploughs with coulters, packing of ground by rollers before sowing, early and dense sowing, eradication of weeds, insecticide treatments of young growth of spring crops.
Reference citations:Agapova E.G. 1967. Oscinella frit L. and Oscinella pusilla Meig. (Diptera, Chloropidae) and criteria of their identification. PhD Thesis. Leningrad: VIZR. 17 p. (In Russian)
Aleksandrov Yu.P., Fedosov N.A. 1969. On development of frit fly. Zashchita rastenii 10: 39-41. (In Russian)
Andreeva N.V. 1926. Biological cycle of frit fly (Oscinella frit L.). In: Bogdanov-Kat'kov N.N., ed. Bulletin of office of entomo-phytopathological congresses. V. 3(4-5). Leningrad: VIZR. 367-78 p. (In Russian)
Dubrovskaya N.A., Strelkova E.A. 1970. Biology and harmfulness of frit fly in the north-eastern part of Byelorussia. In: Dubrovskaya N.A., ed. Proceedings of Byelorussian Agricultural Academy. V. 65. Gorki: Byelorussian Agricultural Academy. 97- 104 p. (In Russian)
Ilyukhin M.A. 1963. Frit fly on corn in conditions of Orel Region. Transactions of Orel Pedag. Inst. 18(1): 87-92. (In Russian)
Reinov A.I. 1929. Materials on Oscinella frit L. in conditions of Omsk Region. Proceedings of Siberian Plant Protection Station (Tomsk): 85-91. (In Russian)
Selivanova S.N. 1951. Ecological features of frit fly. Zoologicheskii zhurnal 30(6): 540-544. (In Russian)
Vasina A.N. 1929. Inhabitation of Oscinella frit L. on wild grasses. Zashchita rastenii ot vreditelei 6(1-2): 63-70. (In Russian)
Zhukovskii A.V. 1932. Reasons for population of spring crops by frit fly (Oscinella frit L.). In: Bek M.M., ed. Proceedings of VIZR. V. 8(5-6). Leningrad: VIZR. 514-529 p. (In Russian)