Periodicity of Diel Activity of Graminella nigrifrons (Homoptera: Cicadellidae) and Implications for Leafhopper Dispersal

Activity periodicity of Graminella nigrifrons (Forbes) virgin adults on maize seedlings was studied in the laboratory. Light intensity was manipulated to examine its effect on vertical distribution and interplant movement of virgin males and females of different ages. Vertical distribution of G. nigrifrons depended upon light intensity and photoperiod, and varied according to sex and age of leafhoppers. Most males and females stayed within the plant canopy during the photophase. Approximately 60% of the males left the plant canopy after light was reduced to simulate dusk, but most females began this upward vertical movement before dusk. No free-running cycles of vertical movement of females were observed under constant light or darkness, suggesting that movement periodicity is not circadian. Fewer young than older males and females flew above the plant canopy during dusk and scotophase; this suggests that newly eclosed adults may undergo a teneral period before engaging in dispersal flights. Within the canopy, males moved between plants more rapidly than females, and this movement decreased markedly during dusk and scotophase. Implications of activity periodicity for dispersal of G. nigrifrons and spread of maize chlorotic dwarf waikavirus are discussed.