PERIODICITY OF DIEL ACTIVITY OF GRAMINELLA-NIGRIFRONS (HOMOPTERA, CICADELLIDAE) AND IMPLICATIONS FOR LEAFHOPPER DISPERSAL

Activity periodicity of Graminella nigrifrons (Forbes) virgin adults o n maize seedlings was studied in the laboratory. Light intensity was m anipulated to examine its effect on vertical distribution and interpla nt movement of virgin males and females of different ages. Vertical di stribution of G. nigrifrons depended upon light intensity and photoper iod, and varied according to sex and age of leafhoppers. Most males an d females stayed within the plant canopy during the photophase. Approx imately 60% of the males left the plant canopy after light was reduced to simulate dusk, but most females began this upward vertical movemen t before dusk. No free-running cycles of vertical movement of females were observed under constant light or darkness, suggesting that moveme nt periodicity is not circadian. Fewer young than older males and fema les flew above the plant canopy during dusk and scotophase; this sugge sts that newly eclosed adults may undergo a teneral period before enga ging in dispersal flights. Within the canopy, males moved between plan ts more rapidly than females, and this movement decreased markedly dur ing dusk and scotophase. Implications of activity periodicity for disp ersal of G. nigrifrons and spread of maize chlorotic dwarf waikavirus are discussed.