Bemisia tabaci exhibited their longest flights between 3 and 5 days following adult eclosion. They rarely engaged in flight when they were < 4 hr old and were only capable of short-duration flights after day 7. This difference in flight capacity appears to be associated with changes in the flight musculature and mitochondria. Myofibrils and mitochondria accounted for approximately 50% and 33% of the area within the flight muscles, respectively. These two elements, however, varied with the age and sex of the whitefly. The percentage of the total area occupied by myofibrils was lower in 9-day-old males relative to females and all other age categories. Sarcomere length decreased in older whiteflies, regardless of the sex. Myofibril diameter did not vary with the age of the whitefly, but the diameter of female whitefly myofibrils was greater than the diameter of male whitefly myofibrils. The number of myosin filaments within a myofibril unit increased with age, peaking at 5 days of age for females and 7 days of age for males. In all age groups, females had more myosin filaments than were found in males. Changes in mitochondria and levels of glycogen were related to the observed differences in flight activity. The area occupied by mitochondria was small in < 4-h-old and 9-day-old whiteflies, and mitochondrial cristae were undeveloped in newly emerged whiteflies. In 7- and 9-day-old whiteflies the cristae began to separate, leaving visible spaces within the mitochondria. Glycogen granules were abundant in the flight musculature of newly emerged (< 4-hr-old), 1-day-old and 3-day-old whiteflies, but by 5 days of age only 25% of whiteflies contained glycogen granules. Seven- and 9-day-old whiteflies contained no visible glycogen. An examination of the flight muscle of whiteflies after flights of varying duration (up to 60 min) revealed no relationships between flight duration and the number of mitochondria or the percentage of the total area occupied by mitochondria. There was, however, a positive relationship between flight duration and the percentage of total area occupied by myofibrils. © 1995 Wiley-Liss, Inc.
