A model of egg production by Heterodera schachtii (Nematoda: Heteroderidae)

Abstract

Egg production by the sugarbeet cyst nematode, Heterodera schachtii, infecting sugarbeet, Beta vulgaris, was assessed at temperatures of 13, 18, 24, and 30 °C in constant-temperature tanks. The minimum-threshold temperature for degree-day accumulation relative to egg production was identified as 8 °C. The relationship between cumulative degree-days (DD) (base 8 °C) and egg production was examined. Egg production began between 160 and 270 DD after hatch and reached a maximum between 390 and 480 DD. Observed egg production (Y) across all temperatures was described as a logistic function of degree-days: Y = 202/(1 + 23726 e−0.034 DD) (r2 = 0.84; P < 0.05). The model depicts initiation of egg production at 140 DD, a maximum average egg production of 202 eggs per female reached at approximately 410 DD, and a maximum rate of egg production of 1.7 eggs/DD reached at approximately 290 DD. The accuracy of the model was limited because observed cumulative egg production was confounded by egg hatch. Accordingly, the cumulative egg production data were adjusted for egg hatch. The adjusted cumulative egg production (Y) was described as a logistic function of cumulative degree-days: Y = 420/(1 + 3319 e−0.023 DD) (r2 = 0.98; P < 0.05). The function depicts egg production initiated at approximately 120 DD. Average maximum egg production is 420 eggs per female occurring at approximately 680 DD, with a maximum egg-production rate of 2.4 eggs/DD occurring at approximately 350 DD.