FLIGHT BEHAVIOR OF BEMISIA-TABACI IN A VERTICAL FLIGHT CHAMBER - EFFECT OF TIME OF DAY, SEX, AGE AND HOST QUALITY

The free-flight behaviour of Bemisia tabaci (Gennadius) (Homoptera: Al eyrodidae), the sweet potato whitefly, was investigated in a vertical flight chamber. A mercury-vapour lamp presented from above induced a p hototactic flight response. Although flight propensity was comparable from 06.00 to 19.00 hours, flight duration was maximum between 06.00 a nd 10.00 hours. Males flew longer than females and their mean flight d uration remained constant throughout the day. Females flew longer from 06.00 to 13.00 hours than from 13.00 to 19.00 hours. Both sexes were capable of sustaining flight for more than 2 h, although less than 5% of those tested did so. Flight activity also was influenced by age and by host quality. The propensity to take off, proportion exhibiting ph ototactic orientation and flight duration varied with the age of the w hitefly. Host quality influenced the timing of flight behaviour. White flies reared on senescing plants exhibited greater take-off rates and initiated longer phototactic flights up to 4 days following adult eclo sion when compared to individuals reared on vegetative plants. Thereaf ter, individuals reared on vegetative plants exhibited greater respons e levels. Whiteflies reared on vegetative plants weighed more and surv ived longer than did individuals reared on senescing plants. Whiteflie s that responded to the overhead light initially exhibited a strong ph otokinetic and phototactic response. Over the course of the flight, th ese responses declined and flight instability increased, as indicated by an overall decrease in the mean rate of climb, accompanied by an in crease in the variability of this parameter and an increase in horizon tal displacement. Although males and females displayed similar flight characteristics, females exhibited a greater rate of climb than did ma les, and for both sexes, individuals that flew longer than 25 min had a greater rate of climb than did individuals that flew for less than 2 5 min.