Emergence of overwintered larvae of eye-spotted bud moth, Spilonota ocellana (Lepidoptera: Tortricidae) in relation to temperature and apple tree phenology at Summerland, British Columbia

摘要

We recorded daily appearance of overwintered larvae of eye-spotted bud moth (ESBM), Spilonota ocellana (Denis & Schiffermuller) in spring 1992, 1994, and 1996 in an un-sprayed apple orchard at Summerland, British Columbia, to relate larval emergence to degree-day (DD) accumulation and apple phenology. In all years the first larva was found between mid-March and early April, and none appeared after late April. Median emergence of larvae occurred when Mclntosh apple trees were at early, tight-cluster stage of fruit-bud development. Larval head capsule measurements showed that ESBM usually overwinter as fifth and sixth instars, with a small proportion (< = 6%) as fourth-instar larvae. In the laboratory we monitored emergence of non-diapausing overwintered larvae from apple branches incubated at 8.8, 9.4, 12.9, 15.0, 18.0, and 20.9 °C. A least-squares linear regression described emergence over this temperature range relatively accurately (r~2 = 0.57, P < 0.05) and a base temperature for emergence (T_b= 1.0 deg C ± 0.6) was extrapolated from this regression. Regression analysis indicated median emergence should require 154.6 ± 6.7 DD above 1 deg C (DD_(1 deg C)). Using daily air-temperature maxima and minima and 1 March to start accumulating DD_(1deg C ), the error between predicted and observed days to median emergence in the field was -6.7 ± 3.1 d; the regression model predicted early in every case. Using observed larval appearance on apples (1992, 1994, & 1996) and an iterative process, we determined that a combination of 6 deg C as the T_b and 1 January as a date to start accumulating DD_(6 deg C), minimized the coefficient of variation for the three-year mean DD_(6 deg C) accumulations (82.7 ± 3.5 DD_(6 deg C)) required for 50% of the larvae to appear in the field. While this latter DD index described observed emergence of larvae accurately, and its use may help improve management of ESBM, it should be validated using independent data before growers use it routinely.