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Figure 4.4 Rates of water loss (open columns) and metabolic water production (filled columns) in resting (a) and hovering (b) flies of four Drosophila species. Values for water loss during flight are net rates calculated by subtracting resting values (means ± SD).

Source: Lehmann et al. (2000).

the opening area of their spiracles according to metabolic needs (Lehmann 2001).

The combination of a nectar diet and high metabolic water production leads to water excess in large flying bees, and respiratory water loss, although extremely high, may not be enough to dissipate the water burden. The first direct measurements of water loss in flight were made on large carpenter bees Xylocopa capitata (Hymenoptera, Anthophoridae) during both tethered and free flight. At moderate temperatures bees in free flight evaporated 27 mg (Nicolson and Louw 1982).

Male X. nigrocincta evaporate nectar at the nest entrance in order to reduce their water load prior to territorial patrolling (Wittmann and Scholz 1989). Bumblebees in free flight produce water by metabolism faster than they can lose it by evaporation and must excrete urine to prevent water loading (Bertsch 1984; Nichol 2000). Evaporative

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