DAILY PATTERNS OF ACTIVITY OF FEMALES OF THE ORANGE WHEAT BLOSSOM MIDGE, SITODIPLOSIS-MOSELLANA (GEHIN) (DIPTERA, CECIDOMYIIDAE)

The daily patterns of activity of females of the orange wheat blossom midge, Sitodiplosis mosellana (Gehin), were observed in controlled lab oratory conditions and in field conditions in eastern Saskatchewan in mid-July 1986 and 1987. In the field, during the daytime, females rest ed on stems of wheat plants within 30 cm of the ground and, at approxi mately 2000 hours CST, flew up to wheat heads. Most oviposition took p lace between 2000 and 2145 hours (or 75 min before, to 30 min after, s unset). Toward the end of the oviposition period, females were frequen tly seen drinking dew from wheat heads. On some evenings, females migr ated down from the heads following oviposition, but on more than half of the evenings they remained on the heads until early morning. Howeve r, they never moved down to the low level they occupied during the day until the next morning, when the migration was usually complete by 09 00-1000 hours. Light intensity appeared to regulate the vertical migra tion of females. Cloudy conditions may allow an earlier onset of ovipo sition. Flight was limited to air temperatures above 14-15-degrees-C a nd oviposition to temperatures above 10-11-degrees-C. Wind speeds of 1 0 km per h or more and rain occasionally limited activity. In the labo ratory. oviposition activity occurred almost exclusively during the sc otophase, mainly in the first 2 h. Mean total fecundity was 83.6 +/- 1 0.9 (+/- SE) eggs, and mean longevity was 6.6 +/- 0.6 days. No oviposi tion took place on the 1 st night, and the greatest mean daily fecundi ty occurred on the 3rd night.