Emergence of flies from overwintering populations of cabbage root fly pupae |
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Authors: | S FINCH ROSEMARY H COLLIER |
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Institution: | (née KAY) National Vegetable Research Station, Wellesbourne, Warwick |
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Abstract: | ABSTRACT. - 1 Once pupal diapause had been terminated, over-wintering cabbage root fly (Delia radicum (L.)) pupae from Wellesbourne required a further 14 days at 20°C for most of the flies to emerge.
- 2 There were considerable variations in the rates of fly emergence from thirteen populations of cabbage root fly pupae collected between latitudes 50° 42′ and 54° 59′ in England and Wales. These thirteen populations could be grouped into early-, intermediate- and late-emerging types. In the early-emerging type, flies emerged within 14 days at 20°C whereas in the late-emerging type emergence was protracted and was completed only after 100 days at 20°C in one population from Halsall, Lancashire. In the intermediateemerging type, approximately two-thirds of the flies emerged within 14 days at 20° C, the remainder taking considerably longer.
- 3 The intermediate-emerging types could be just mixtures of the early- and late-emerging types.
- 4 Subjecting pupae to diapause-breaking temperatures (4°C) for up to 1 year failed to shorten the time to subsequent fly emergence in any of the populations.
- 5 Populations of early, intermediate- and late-emerging fies could be selected from a parental population, heterogeneous with respect to emergence, within one generation.
- 6 The type of emergence that occurred in a locality was not correlated with latitude.
- 7 Any models developed for forecasting the most appropriate time to apply insecticide in a locality will have to include information about the emergence pattern of the fly population in that locality.
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Keywords: | Delia radicum cabbage root fly diapause overwintering different populations emergence patterns |
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