SENSITIVE STAGES IN THE PHOTOPERIODIC DETERMINATION OF WING FORMS ANDREPRODUCTION IN THE WATER STRIDER, AQUARIUS-PALUDUM (FABRICIUS)

The present work was performed to clarify the photosensitive stage for wing-form determination and reproduction in Aquarius paludum. Only 40 -60% of the adults were long winged when they were reared under 12 hr light-12 hr dark (12L-12D) during the first two instars and under 15.5 L-8.5D during the rest of nymphal stage. However, all became long-wing ed, when they were exposed to 12L-12D until the end of the third insta r. The exposure to 15.5L-8.5D till the end of the third instar induced short-winged adults of less than 15%, but long days until the fourth instar promoted about 40%. The exposure to long days either during the third, fourth or fifth instar promoted brachyptery, whereas all becam e long-winged when they were reared under long days either during the first or second instar. The exposure during the fifth instar induced m aturing oocytes. The results indicate that the photosensitive stage fo r brachyptery occurs from the third to the beginning of the fifth inst ar, whereas that for oocyte maturation occurs during the fifth instar. Such a difference may refute the supposition of the oogenesis-flight syndrome that the two factors are tightly linked.