Abstract
Nymphal development of the small brown planthopper, Laodelphax striatellus, is delayed by short day photoperiod. The incidence of 'delayed development (DD)' individuals under 12L-12D at 25°C was compared among unselected parents, offspring of DD-type parents, and of 'non-delayed development (ND)'-type parents. The incidence of DD in the offspring of DD-type parents was 33.7%, and that of ND-type parents was 5%. The former was slightly higher and the latter was significantly lower than the incidence, 24.7%, of DD in the unselected parents. Both the incidence of DD and the incidence of macroptery in females increased with an increase in nymphal density. Moreover, the line which has been selected for macroptery for 15 generations showed a higher incidence of DD than the line selected for brachyptery.
