TEMPERATURE-DEPENDENT DEVELOPMENT AND PREDICTION OF HATCH OF OVERWINTERED EGGS OF THE FRUITTREE LEAFROLLER, ARCHIPS ARGYROSPILUS (WALKER) (LEPIDOPTERA: TORTRICIDAE)

Thermal responses and temperature-dependent development of laboratory- and field-overwintered eggs of the fruittree leafroller, Archips argyrospilus (Walker), were described using data from constant-temperature laboratory experiments. The time required for completion of hatch of overwintering eggs declined throughout winter until the end of January, after which increasing exposure to natural or artificial cold conditions had minimal effect on median hatching time. There was little year to year variation in response to cold treatments, and thus it was concluded that diapause is terminated by 1 February. Time to hatch decreased with increasing temperature. Distributions of hatch times were near normal, with mean and median development times similar at any given temperature. Development time (days ± SD) at a mean temperature of 20 °C was similar under constant (10.7 ± 1.1) and fluctuating (9.1 ± 1.4) temperature regimes. A nonlinear, six-parameter, biophysical model, fitted (r2 = 0.99) to median hatching rates at 11 temperatures (0.5–30 °C) indicated development was nonlinear below 10 °C, increased linearly between 10 and 25 °C, was maximal at 27.5 °C, and decreased above 27.5 °C. The lower developmental threshold (± SE), estimated to be 4.95 ± 0.54 °C by linear regression (r2 = 0.98) and the x-intercept method, was used to construct a degree-day (DD) model for predicting egg hatch. Median egg development required 154 DD above 4.95 °C. Observed median egg hatch in two different field sites and years was within ± 3 days of the predicted date, using max–min air temperatures, a base temperature of 5 °C, and a starting date of 1 February for accumulating DD. This model should prove useful for scheduling management actions against fruittree leafroller on apples and pears.