Most insects are thought to fly by creating a leading-edge vortex that remains attached to the wing as it translates through a stroke. In the species examined so far, stroke amplitude is large, and most of the aerodynamic force is produced halfway through a stroke when translation velocities are highest. Here we demonstrate that honeybees use an alternative strategy, hovering with relatively low stroke amplitude (Ϸ90°) and high wingbeat frequency (Ϸ230 Hz). When measured on a dynamically scaled robot, the kinematics of honeybee wings generate prominent force peaks during the beginning, middle, and end of each stroke, indicating the importance of additional unsteady mechanisms at stroke reversal. When challenged to fly in low-density heliox, bees responded by maintaining nearly constant wingbeat frequency while increasing stroke amplitude by nearly 50%. We examined the aerodynamic consequences of this change in wing motion by using artificial kinematic patterns in which amplitude was systematically increased in 5°increments. To separate the aerodynamic effects of stroke velocity from those due to amplitude, we performed this analysis under both constant frequency and constant velocity conditions. The results indicate that unsteady forces during stroke reversal make a large contribution to net upward force during hovering but play a diminished role as the animal increases stroke amplitude and flight power. We suggest that the peculiar kinematics of bees may reflect either a specialization for increasing load capacity or a physiological limitation of their flight muscles.bee flight ͉ flight in heliox ͉ stroke amplitude ͉ unsteady mechanisms ͉ wingbeat kinematics I n 1934, August Magnan and André Sainte-Lague (1) concluded from a simple mathematical analysis that the flight of bees was ''impossible.'' Since this time, bees have symbolized both the inadequacy of aerodynamic theory as applied to animals and the hubris with which theoreticians analyze the natural world. Although the assumptions used by Magnan and SainteLague have since proven erroneous (2), conventional fixed-wing aerodynamic theory is indeed insufficient to explain the flapping flight of bees and other small insects. In particular, the performance of insect wings, when tested under steady conditions in wind tunnels, is too low to account for the forces required to sustain flight (3). However, a number of more recent studies have demonstrated that wings perform much better when started from rest or rotated continuously around their base (4-6) due to the formation of a leading-edge vortex (LEV). Instead of shedding to initiate stall, the LEV remains attached throughout each stroke, presumably because of the transport of vorticity by span-wise flow (7-9). Whereas the delayed stall forces are greatest at midstroke, flapping wings generate additional forces during stroke reversals. These forces, which result from the rapid rotation of the wing, added mass effects, and the influence of the wake shed from previous strokes, are very sensitive to the precise p...

We exposed adult male Drosophila melanogaster to cold, desiccation or starvation, and examined expression of several genes during exposure and recovery. Frost was expressed during recovery from cold, and was up-regulated during desiccation. Desiccation and starvation (but not cold) elicited increased expression of the senescence-related gene smp-30. Desat2 decreased during recovery from desiccation, but not in response to starvation or cold. Hsp70 expression increased after 1 h of recovery from cold exposure, but was unchanged in response to desiccation or starvation stress, and Hsp23 levels did not respond to any of the stressors. We conclude that D. melanogaster's responses to cold and desiccation are quite different and that care must be taken to separate exposure and recovery when studying responses to environmental stress.

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SUMMARYWe use a factorial experimental design to test whether rearing at colder temperatures shifts the lower thermal envelope for flight of Drosophila melanogaster Meigen to colder temperatures. D. melanogaster that developed in colder temperatures (15°C) had a significant flight advantage in cold air compared to flies that developed in warmer temperatures (28°C). At 14°C, cold-reared flies failed to perform a take-off flight ~47% of the time whereas warm-reared flies failed ~94% of the time. At 18°C, cold-and warmreared flies performed equally well. We also compared several traits in cold-and warm-developing flies to determine if colddeveloping flies had better flight performance at cold temperatures due to changes in body mass, wing length, wing loading, relative flight muscle mass or wing-beat frequency. The improved ability to fly at low temperatures was associated with a dramatic increase in wing area and an increase in wing length (after controlling for wing area). Flies that developed at 15°C had ~25% more wing area than similarly sized flies that developed at 28°C. Cold-reared flies had slower wing-beat frequencies than similarly sized flies from warmer developmental environments, whereas other traits did not vary with developmental temperature. These results demonstrate that developmental plasticity in wing dimensions contributes to the improved flight performance of D. melanogaster at cold temperatures, and ultimately, may help D. melanogaster live in a wide range of thermal environments.