Reproductive Potential and Population Growth of the Worm <i>Enchytraeus buchholzi</i> (Clitellata: Enchytraeidae) Under Laboratory Conditions as Well as Regression Models

The worm <i>Enchytraeus buchholzi</i> is a new pest injuring American ginseng <i>Panax quinquefolium</i>. To explore its reproductive potential and then estimate its population dynamics, the authors conducted two related experiments: (1) measuring individual fecundity in its lifetime by rearing each of the parent adults alone in a wet sandy dish at 18 and 21 °C indoors; (2) testing population growth by rearing each of the parent adults together with its offspring for a time longer than two generations at 21 °C. In Experiment I, five dependent variables, namely daily mean cocoons (<i>DMC</i>), cumulative cocoons (<i>CC</i>), eggs per cocoon (<i>EPC</i>), daily mean eggs (<i>DME</i>) and cumulative eggs (<i>CE</i>), were extracted, with each of them subject to a stepwise regression analysis on rearing time (<i>T</i>) and its power series as independent variables. Equaling to the net reproductive rate (<i>R</i>₀), the generational adult equivalent (<i>GAE</i>) was calculated via a conversion of F₁ generational eggs into adult equivalents (<i>AE</i>). In Experiment II, both an exponential and a logistic function were applied to construct regression equations. The results indicated that (1) a parent adult of <i>E. buchholzi</i> was able to live for a period as long as 10 and 13 full generations at the two temperatures tested and lay 84.8 and 110.6 cocoons containing 545 and 714 eggs, respectively; (2) <i>DMC</i> reached its maximum between 7 and 9 days of rearing and then declined slowly along a straight regression line; (3) <i>CC</i> rose steadily along a quadratic curve; (4) both <i>EPC</i> and <i>DME</i> varied following a cubic curve; (5) <i>CE</i> increased steadily along a cubic curve; (6) the new polynomial models suitably reflected the numerical growth trends of cocoons and eggs in the F₁ generation in a broad sense, while corresponding derivative equations quantified both the daily reproductive potential and resistance of the worm, thus revealed its daily reproductive capacity; (7) <i>R</i>₀ was 41.2 <i>AE</i> at 21 °C and 42.5 <i>AE</i> at 18 °C when a population of <i>E. buchholzi</i> lived in a niche with unlimited ambient resources; (8) this kind of temporal population generated by individual reproduction had fully demonstrated its significant, generational reproductive potential; and (9), through living in such a limited area as the wet sandy dish, bypassing an exponential growth process, the laboratory population grew up along a logistic curve from the F₁ to F₃ generations. The statistical relationships help to comprehend the individual reproduction of <i>E. buchholzi</i>, understand deeply the logical sequence and the difference between individual and population reproductions, predict population dynamics of the worm, and provide its integrated pest management with a solid basis. The experimental study has expanded theories on bionomics and population ecology, opening up a new area for research work in related fields.