MIGRATORY SYNDROME IN THE WATER STRIDER AQUARIUS-PALUDUM (HETEROPTERA, GERRIDAE) REARED IN HIGH VERSUS LOW NYMPHAL DENSITIES

The effect of crowding in nymphal stage on the induction of developmen t of macropterous adults with high flight ability was studied in the l aboratory in the water strider Aquarius paludum. High density induced a higher proportion of macropterous morphs than low density. No brachy pterous adults developed flight muscles in either experimental density . When kept under high density, about 80% of adults kept indirect flig ht muscles for 25-30 days after adult emergence, whereas only about 50 % or 60% of females and males, respectively, retained theirs when grow n under low density. The remaining adults histolysed indirect flight m uscles in both groups. Development during the fourth and fifth instars only under high density may induce a higher proportion of macropterou s adults than those under low density.