Stage-specific Population Development and Fecundity of Paratrichodorus minor

Abstract

A conceptual model of the life cycle of Paratrichodorus minor consisting of the egg stage, four juvenile stages, and the adult stage was proposed. Development of an individual from one stage to the next was described by a probability distribution defined by the mean length of time spent in the stage and the standard deviation associated with the mean duration. Experiments were conducted to estimate stage durations, stage-specific survivorships, and a fecundity rate for females. Eggs hatched on agar plates at a mean time of 53.3 ± 7.3 degree-days using a basal threshold of 10 C (DD[sub1][sub0]) with a range of 40-64 DD[sub1][sub0] after deposition. Forty-five percent of the eggs observed ultimately hatched. Of the eggs that died, 44% died before the nematode form could be observed in the egg and 56% died after movement had been observed. First generation population peaks following inoculation with first-stage juveniles occurred at 28 DD[sub1][sub0] for second-stage juveniles, 67 DD[sub1][sub0] for third-stage juveniles, 109 DD[sub1][sub0] for fourth-stage juveniles, and 143 DD[sub1][sub0] for adults. Adult males are rare and were never observed in these studies. The fecundity rate was 0.784 eggs/(female-DD[sub1][sub0][sup-]¹), but the maximum length of the egg-laying period was not determined. The minimum egg-laying period was 73-113 DD[sub1][sub0], and minimum egg production was 57-86 eggs per female. The preovipositional period for adult females was estimated to be 79 DD[sub1][sub0]. In the presence of a host, total population numbers increased, but in the absence of a host, the population declined to 33 % of the initial level after 300 DD[sub1][sub0]. Key words: Paratrichodor'us minor, population dynamics, fecundity.