The effect of temperature on the photoperiodic ‘counters’ for female morph and sex determination in two clones of the black bean aphid, Aphis fabae

Abstract Experiments were performed on two clones of the black bean aphid, Aphis fabae Scopoli – one from Aberdeen, Scotland (57°N), the other from Cambridge, England (52°N) − to determine the number of long‐ or short‐night cycles required for 50% induction of winged versus wingless females on the one hand and males versus females on the other (i.e. required day number, RDN), at three temperatures, 12.5, 15 and 17.5°C. In the case of female morph determination, the RDN for long‐night cycles was temperature compensated, whereas that for short‐night cycles was highly temperature dependent. For sex determination, the RDN for long‐night cycles was again temperature compensated, whereas, due to the mechanism of sex determination, male production was close to 100% in our protocol, even with a maximal number of short‐night cycles, and the RDN could therefore not be assessed. Model‐generated response curves, using the recently developed ‘double circadian oscillator model’ for photoperiodic time measurement in insects and mites, closely resembled the observations. It could also be shown that differences observed between response curves of female morph and sex determination in the Scottish clone were due, according to the model, to differences in their photoperiodic ‘counters’, rather than to differences in their clocks.