*USDA-Agricultural Research Service, 1500 N. Central Avenue, Sidney, MT 59270, USA; Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Republic of Panama; Department of Integrative Biology, University of California, 3060 Valley Life Sciences Building #3140, Berkeley, CA 94720, USA.
Integr Comp Biol. 2008 Jul;48(1):119-33. doi: 10.1093/icb/icn011. Epub 2008 Mar 25.
Directed aerial displacement requires that a volant organism's airspeed exceeds ambient wind speed. For biologically relevant altitudes, wind speed increases exponentially with increased height above the ground. Thus, dispersal of most insects is influenced by atmospheric conditions. However, insects that fly close to the Earth's surface displace within the flight boundary layer where insect airspeeds are relatively high. Over the past 17 years, we have studied boundary-layer insects by following individuals as they migrate across the Caribbean Sea and the Panama Canal. Although most migrants evade either drought or cold, nymphalid and pierid butterflies migrate across Panama near the onset of the rainy season. Dragonflies of the genus Pantala migrate in October concurrently with frontal weather systems. Migrating the furthest and thereby being the most difficult to study, the diurnal moth Urania fulgens migrates between Central and South America. Migratory butterflies and dragonflies are capable of directed movement towards a preferred compass direction in variable winds, whereas the moths drift with winds over water. Butterflies orient using both global and local cues. Consistent with optimal migration theory, butterflies and dragonflies adjust their flight speeds in ways that maximize migratory distance traveled per unit fuel, whereas the moths do not. Moreover, only butterflies adjust their flight speed in relation to endogenous fat reserves. It is likely that these insects use optic flow to gauge their speed and drift, and thus must migrate where sufficient detail in the Earth's surface is visible to them. The abilities of butterflies and dragonflies to adjust their airspeed over water indicate sophisticated control and guidance systems pertaining to migration.
定向空中迁徙要求飞行生物的空速超过环境风速。对于具有生物学意义的高度，风速随离地面高度的增加呈指数级增长。因此，大多数昆虫的扩散受大气条件的影响。然而，靠近地球表面飞行的昆虫在飞行边界层内移动，在该层中昆虫的空速相对较高。在过去的 17 年中，我们通过跟踪个体穿越加勒比海和巴拿马运河的迁徙，研究了边界层昆虫。尽管大多数迁徙昆虫逃避干旱或寒冷，但灰蝶科和凤蝶科的蝴蝶在雨季开始时迁徙穿越巴拿马。琵蝽属的蜻蜓在 10 月与锋面天气系统同时迁徙。迁徙距离最远，因此最难研究的日行性蛾 Urania fulgens 在中美洲和南美洲之间迁徙。迁徙的蝴蝶和蜻蜓能够在多变的风中朝着首选的罗盘方向进行定向运动，而飞蛾则随风在水面上漂移。蝴蝶使用全球和局部线索进行定向。与最优迁徙理论一致，蝴蝶和蜻蜓调整飞行速度的方式是最大化每单位燃料的迁徙距离，而飞蛾则不这样做。此外，只有蝴蝶根据内源性脂肪储备调整飞行速度。这些昆虫可能使用光流来衡量它们的速度和漂移，因此它们必须在对它们可见的足够详细的地球表面上进行迁徙。蝴蝶和蜻蜓在水面上调整空速的能力表明它们具有复杂的迁徙控制和制导系统。
