Light and Temperature Thresholds for Take-Off by Aphids

Migratory flights by aphids can begin only when weather, especially light and temperature, permits take-off. For example light and temperature thresholds for take-off restrict the flight of Aphisfabae leaving its host plant within the daylight hours (Johnson & Taylor 1957). Once airborne, the temperature thresholds for continued flight differ considerably from those for take-off (Cockbain 1961; Taylor 1963). Some species of aphid, notably Schizaphis graminum, have been repeatedly recorded as migrating long distances. Because of the time taken for such migration, aphids must fly for more than one period of daylight and several species, including S. graminum, have been sampled at 2000 ft (609 m) over Kansas during the night (Berry & Taylor 1968). Hence either flight must continue, or take-off occur, during the night when light and temperature are most likely to be limiting (Taylor 1965). There is little evidence about continued flight at very low light intensities (Halgren & Taylor 1968); we here consider whether nocturnal take-off can contribute to overnight flights. We measured light and temperature thresholds for take-off by several species of aphid, including Aphisfabae and Schizaphis graminum, to seek specific limiting values that may permit, or prevent, nocturnal take-off as a prelude to long distance migration. The experiments showed also that some alatae were unwilling to take flight a second time, no matter how short the first flight had been and that some did not take off, as expected, at the end of the teneral period (Taylor 1957). This complicates the presentation of the temperature thresholds and has led to a revision of the former view of migrant aphids discussed elsewhere (Shaw 1968a, b).