Canadian Forest Service Publications

The effect of photoperiod on the calling behaviour of virgin females of the true armyworm, Pseudaletiae unipuncta (Haw.) (Lepidoptera: Noctuidae) 1986. Delisle, J.; McNeil, J.N. J. Insect Physiol. 32(3): 199-206.

Year: 1986

Issued by: Laurentian Forestry Centre

Catalog ID: 14459

Language: English

Availability: PDF (request by e-mail)

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The effect of photoperiod on the calling behaviour of Pseudaletia unipuncta virgin females was examined under five different photoperiodic regimes at 25°C, 65% r.h. The age at which females called for the first time following emergence varied with photoperiod; generally calling was later under long-scotophase conditions. However under a 6 h scotophase there was also a delay in calling and >63% of the females tested never called. There was a considerable variability in the daily calling patterns between the different photoperiods, and the mean onset time of calling was not constant with either "light on" or "light off". There was however a constancy of the mean onset time of calling relative to the mid-point of both the photo- and scotophase at all photoperiods tested, indicating that females could measure the absolute duration of either the photo- or scotophase. Transferring females from one photoperiodic condition to another once calling had been initiated, determined that it was the "lights off" signal that _P. unipuncta females used to phase set the clock governing circadian calling behaviour.

Females subjected to a decrease of 4 or 6 h in the length of the scotophase following the initiation of calling required several days to adjust to the new photoperiodic regime and a high proportion of females did not call during the night following the transfer. A 4 or 6 h increase in the scotophase did not inhibit calling on the night following the transfer but females still required several days to adjust completely. However, females experiencing a 2 h increase or decrease in the duration of the scotophase were able to maintain normal calling behaviour. The results of these experiments are discussed in relation to the seasonal biology of the true armyworm and the hypothesis that this is a migrant species.