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Abstract

Brachyptera seticornis egg masses incubated at constant temperatures between 4 and 18°C. They were examined weekly until the start of embryonal development, and more frequently thereafter. During the hatching period, the number of hatchlings was determined every day. In a sample kept at 10.8°C, length and width of the eggs were recorded every 7 - 14 days until embryonal development began, and then every 2 - 4 days thereafter. Developmental stages were drawn and photographed. They were in essence similar to the development of Kamimuria tibialis (KISHIMOTO & ANDO 1985). The mean number of eggs per batch was 717 (95 % C.L. = ± 67, n = 24). Mean hatching rates were 60 - 100 %. The length (L) of the hatching period was positively correlated with mean incubation time (I) (to 50 % hatch): L = 0.487 x I - 56.1 (r² = 0.59, p <0.0001, n = 52). After oviposition the eggs first spent 2 - 3 months in dormancy. This was followed by embryonal development (d), which was strongly correlated with incubation temperature (T): d = 135.4 x T^-0.37 (r² = 0.76, p <0.0001, n = 52). The duration of dormancy (D) increased slightly with temperature. It seems to be dependent on the date of oviposition. Eggs which were laid at a later date showed a shorter duration of dormancy. Differing lenghts of photoperiod (7.25 and 14 h, respectively) had no significant influence on hatching rate, length of dormancy or embryonal development. At 10.8°C, eggs absorbed water and swelled during the first 1 or 2 days but showed no change in size during dormancy, until embryonal development started. Then the eggs began to expand, and continued to do so until hatching. Changes in their volume could be described by a sigmoid curve, the turning point of which coincidedwith blastokinesis. Mean egg volumes increased from 5.01 x 10⁶ µm³ (95 % C.L. ± 0.34 x 10⁶µm³) to 7.87 x 10⁶ µm³ (95 % C.L. ± 0.39 x 10⁶ µm³). These data will be published later elsewhere.