Synchronous crepuscular flight of female Asian gypsy moths: Relationships of light intensity and ambient and body temperatures

Female gypsy moths (Lymantria dispar) of Asian heritage studied in central Siberia Germany exhibit a highly synchronous flight at dust, after light in tensity falls to about 2 lux. This critical light intensity sets the time o f flight behaviors independent of ambient temperature. Flight follows sever al minutes of preflight wing fanning during which females in Germany and th ose from a laboratory colony (derived from Siberian stock) raised their tho racic temperatures to 32-33 degrees C at ambient temperatures of 19-22 degr ees C. Thoracic temperature of females in free flight exceeded the air temp erature (19-22 degrees C) by approximately 11-13 degrees C. The duration of wing fanning was strongly dependent on ambient temperature. In Germany, wh ere ambient temperatures at dust ranged between 21 and 25 degrees, females wing fanned for only 2.1 +/- 0.2 (SE) min; in the much colder temperatures prevalent at dusk in Bellyk, central Siberia (11-13 degrees C), females spe nt 11.2 +/- 0.6 min in preflight wing fanning. The majority (less than or e qual to 80%) of mated and even virgin females initiated flight during the e vening of the day they eclosed. However, in Bellyk, a small proportion (12% ) of females wing fanned for an extended time but then stopped, whereas oth ers (9%) never wing fanned and, therefore, did not take flight. Females als o were capable of flight when disturbed during the daylight hours in German y where the maximal temperature was high (27-30 degrees C), but not in Sibe ria, where temperatures peaked at only 17-19 degrees C. However, Siberian f emales were able to propel themselves off the tree on which they were perch ed by executing several vigourous wing flicks when approached by the predac eous tettigoniid, Tettigonia caudata.