On critical night lengths and temperature compensation in the photoperiodic response of two geographical clones of the black bean aphid, Aphis fabae

Photoperiodic response curves were determined for two clones of the black b ean aphid, Aphis fabae Scopoli, at three temperatures, 12.5, 15 and 17.5 de greesC. Critical night lengths for the induction of winged females in an En glish clone (52 degrees N) were 10.5, 11 and 11.5 h, respectively, and 10, 10.5 and 11 h in a Scottish clone (57 degrees N). Critical night lengths fo r male induction were 10.5, 11 and 11 h at 12.5, 15 and 17.5 degreesC in th e English clone, and 10, 10.5 and 10.5 h, respectively, in the Scottish clo ne. High incidences of winged females and males were observed at all scotop hases longer than the critical night length in both clones. In addition, in the English clone, the incidences of winged female and male producers in c ontinuous darkness were 0% at 15 and 17.5 degreesC, and 6% at 12.5 degreesC . In the Scottish clone, however, continuous darkness resulted in high inci dences of both winged female and male producers at 12.5 and 15 degreesC, bu t 0% winged female producers and 6% male producers at 17.5 degreesC. In sco tophases shorter than the critical night length, including continuous light , no males or winged females were observed in either clone under the non-cr owded rearing conditions used. The results are discussed in terms of the 'd ouble circadian oscillator model' for photoperiodic induction.