Emerald ash borer flight estimates revised
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Using computer-monitored fl ight mills, we found that tethered emerald ash borer (Agrilus planipennis) adults can fl y up to the equivalent of 2.8 km/day at speeds greater than 1.5 m/ sec (3.5 mph), with mated females fl ying twice as far as unmated females (P < 0.0001), suggesting that gravid females are programmed to make dispersal fl ights. This is supported by the absence of a correlation (R 2 = 0.0005) between distance fl own and female size (Figure 1). Females “fl own” for 8 hours per day and then allowed to rest, feed, and drink for 16 hours continued to make long fl ights for up to fi ve days: the maximum distance fl own was 9.84 km in four days, with 50 percent of beetles fl ying over 4 km per day and 10 percent fl ying over 7 km per day. It is diffi cult and can be misleading to draw conclusions about free fl ight from fl ight mill data. There are at least four potential sources of error in the assumption that fl ight mill speed = true fl ight speed of the insect in free fl ight: - Inertial drag of the armature (work expended turning the armature) - Torsional drag of the magnet (dynamo effect) - Inconvenience of being attached to the armature (glued at the pronotum) - Lift provided by the armature (all fl ight effort results in forward motion). Thus, it is not clear whether true fl ight speed is greater or less than the speed recorded on a fl ight mill. Flight mill data are best interpreted relatively, as we did when comparing fl ight by males, unmated females, and mated females. In order to be able to draw conclusions about fl ight in the wild, fl ight mills must be calibrated: there are very few instances in which this has been possible.