Temperature influences walking speed and walking activity of Trichogramma brassicae (Hym., Trichogrammatidae)

Walking speeds and walking activities (walking time divided by total time) of Trichogramma brassicae were determined at 12, 16, 20 and 25 degreesC. Walking speed was measured during a 5-min period, and walking activity over a 4-day period. Both walking speed and walking activity were strongly influenced by temperature. Walking speed increased linearly with the temperature and was twice as high at 20 as at 12 degreesC. At 25 degreesC, walking activity was high during the whole day, at 20 and 16 degreesC it decreased during the afternoon, whereas at 12 degreesC the wasps became most active only at noon or later. At low temperatures, there was a strong individual variation in walking activity. At 25 degreesC, T. brassicae was active most of the time, so the area searched per time unit can only increase at temperatures above 25 degreesC if walking speed increases. At temperatures below 20 degreesC, searching was more restricted by low walking activity than by low walking speed. Even disregarding other effects of temperature, the reduction in walking speed and walking activity at suboptimal temperatures means that T. brassicae can only search half of the area at 20 degreesC. and only one-seventh at 15 degreesC that it can search at 25 degreesC.