Calling behaviour in M. convecta females under different temperature and photoperiodic conditions

The effects of temperature and photoperiod on calling behaviour in females of the Australian common armyworm, Mythimna convecta (Walker) (Lepidoptera: Noctuidae), were studied in the laboratory. Age at first calling was greater at 15 and 20 degree C compared with 25 degree C, but there were no significant differences between 25 and 30 degree C. Females kept at 10 degree C did not call, but if transferred at 10 days to 20 degree C they called after a period similar to the pre-calling period at constant 20 degree C. Onset time of calling was earlier at 15 and 20 degree C compared with 25 and 30 degree C, but there were no significant differences in calling duration. At 20 degree C, age at first calling was increased by shorter daylength (12 h and 14 h, compared with 16 h), and there was an interaction between daylength and moth age affecting the duration of calling. Onset times advanced with longer daylength, but peak calling was later in relation to the length of the scotophase. These results are discussed in connection with migration in M. convecta. Evidence for a circadian rhythm of calling was found in females entrained for 3 nd 8 days after emergence under reverse-cycle conditions and then transferred to constant darkness. However, after 56 h and 80 h respectively of darkness, calling became de-synchronized. Subsequently, it appeared to re-synchronize to a different clock, which approximately correlated with the normal photoperiods the moths had experienced during larval development.