Variations in life history parameters and their influence on rate of population increase of different pathogenic isolates of the pine wood nematode, Bursaphelenchus xylophilus

Abstract Two virulent isolates and two avirulent isolates of Bursaphelenchus xylophilus and one isolate of B. mucronatus were used to investigate the relationships between life history parameters, rate of population increase and virulence. The results showed that on fungal cultures of Botrytis cinerea, virulent B. xylophilus completed one generation much faster than did avirulent B. xylophilus and B. mucronatus. There was a tendency that virulent B. xylophilus isolates laid more eggs during the egg laying period than did avirulent populations. Shorter generation time and higher fecundity resulted in a higher rate of population increase. Generation time and fecundity were primary factors determining rate of population increase. Difference in rate of population increase is closely related to variation of virulence: virulent B. xylophilus increased population size at the fastest rate, avirulent B. xylophilus was slower, and B. mucronatus was slowest. It is assumed that similar variations in life history parameters and rate of population increase are also expressed in pine trees and help to explain variation of virulence in the field.