Studies on Paratylenchus nanus. II. Population changes around apple roots

Abstract

The numbers of fourth-stage larvae, males, and females of Paratylenchus nanus in soil around apple roots have been examined and found to be partially correlated with seasonal changes in the trees. Bulking subsamples did not give sufficient information, and so trends were determined from individual samples. Numbers of females were assessed: (a) per soil sample; (b) per weight of apple roots in each soil sample. In soil, all stages showed a decline in numbers in winter and summer and an increase in spring (Sept.). At other times numbers remained stationary except for a decrease in larval numbers in October and an increase in numbers of females between November and January. Males always exceeded females in number and larvae always exceeded adults, but the proportion of females in the adult population increased from 27% in winter to 41% in summer. Numbers of females – the only parasitic stage recovered – per gram of apple root decreased in winter, increased in spring, and decreased again in summer.

Survival of the different stages under an adverse environment suggested that high temperatures in summer and low temperatures with high moisture levels in winter were partly responsible for the decreases in number at these times.