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The effects of temperature and photoperiod on calling behaviour in females of the Australian common armyworm, 'Myrhimnu convecta' (Walker) (Lepidoptera: Noctuidae), were studied in the laboratory. Age at first calling was greater at 15 and 20°C compared with 25°C, but there were no significant differences between 25 and 30°C. Females kept at 10°C did not call, but if transferred at 10 days to 20°C they called after a period similar to the pre-calling period at constant 20°C. Onset time of calling was earlier at 15 and 20°C compared with 25 and 30°C, but there were no significant differences in calling duration. At 20°C, age at first calling was increased by shorter daylength (12h and 14h, compared with 16h), 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 and 8 days after emergence under reverse-cycle conditions and then transferred to constant darkness. However, after 56h and 80h 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. |
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