Calendar and degree-day requirements for emergence of adult wheat midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae) in Saskatchewan, Canada

Abstract

Insect/host plant phenologies are particularly important in the management of wheat midge in western Canada. Emergence of adult wheat midge, Sitodiplosis mosellana (Géhin), was evaluated at 19 sites in Saskatchewan in 1991–2000. Emergence was assessed in relation to calendar days and accumulated degree-days above five base air temperatures. Three sites that received less than 20 mm rainfall in May were deleted from the analysis because emergence was erratic and delayed. Males emerged 2–3 days before females. Calendar dates for 10%, 50% and 90% emergence of both sexes were July 11 ± 5.9 days, July 18 ± 5.4 days and July 25 ± 5.9 days, respectively. Deviations between observed and expected emergence dates at most sites related to degree-day accumulations between March 1 and July 31. Emergence was 2–8 days earlier than expected at sites with the highest degree-day accumulation and 4–10 days later than expected at sites with the lowest accumulation. Degree-day requirements for emergence declined as the base air temperature increased. In most instances, accumulated degree-days above 5 °C provided the most accurate estimates of emergence. With a 5 °C base temperature, accumulated degree-days (DD) for 10%, 50% and 90% emergence of both sexes averaged 693 DD ± 2.8 days, 784 DD ± 2.5 days and 874 DD ± 3.2 days, respectively. Deviations between observed and expected emergence dates at most sites related to precipitation in May and June. Emergence was 1–7 days earlier than expected at sites receiving 20–30 mm rain in May. Conversely, emergence was 2–8 days later than expected at sites receiving more than 145 mm rain in May and June. Adult emergence was re-assessed in 2008. Dates for 10%, 50% and 90% emergence of both sexes differed from expected values by one day or less. Accumulated degree-days above 5 °C for 10%, 50% and 90% emergence differed from expected values by 8–35 DD. The merits of using calendar dates and degree-days to predict emergence of adult wheat midge are discussed.