The bionomics of the free-living larvae and the transmission of Dictyocaulus filaria between lambs in North-East England

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Abstract
The bionomics of the free-living larvae of Dictyocaulus filaria on pasture, and the transmission of infection between lambs, were studied during different seasons of the year m North-East England.The rate of development of first-stage larvae to the third stage took 4–9 days in late spring and summer, 1½–4 weeks in autumn and 5½–7 weeks in winter. The proportion of first-stage larvae developing to the third stage ranged from 10–28% in autumn and winter, and 2–25% in spring and summer. The rate of mortality of the third-stage larvae was approximately logarithmic in nature, although the survival time was shorter in spring and summer than in autumn and winter. Third-stage larvae were able to survive from autumn until the spring of the following year in sufficient numbers to perpetuate transmission but not to cause clinical disease.