Inhibited development in Ostertagia ostertagi infections – a diapause phenomenon in a nematode

摘要: Experiments are described which show that in a recently isolated field strain of the cattle nematode, Ostertagia ostertagi, primary stimulus to induction inhibited development at early fourth larval stage (EL4) host is chilling infective larvae (L3). Thus exposure L3 temperature 4 °C for 8 weeks prior their oral administration calves resulted mean 66% established worm burden becoming EL4 stage. This provides an explanation seasonal occurrence Britain stages O. ostertagi during cold climate late autumn and winter.If were exposed prolonged period (> 19 weeks), infection calves, then prevalence amongst worms declined. After 33 population consisted almost entirely adults only 2% stages. suggested selective mortality inhibition prone was taking place explained why under natural grazing conditions not available on pasture spring.The duration infected with chilled consistently between 16 18 maturation majority occurred spontaneously after such irrespective season. equivalent normal winter when unsuitable free living prevail.The by environmental chilling, fixed within spontaneous characteristic true diapause.