MIGRATION AND THE EFFECT OF 3 ENVIRONMENTAL-FACTORS ON THE PRE-REPRODUCTIVE PERIOD OF THE COTTON-BOLLWORM MOTH, HELICOVERPA-ARMIGERA

Migration by noctuid moths generally occurs while the adults are sexua lly immature, and so the pre-reproductive period provides an indicatio n of the time available for migratory flight. Helicoverpa armigera (Hb .) (Lepidoptera: Noctuidae) is considered to be a facultative migrant, emigrating in response to a deterioration in local environmental cond itions for adult survival and larval development; hence the effects of temperature, vapour-pressure deficit and the availability of sugar so lution on the duration of the pre-reproductive period are investigated . Temperatures below 28-degrees-C lengthened female pre-reproductive p eriods but, contrary to the findings of Isley (1935) for Helicoverpa z ea (Boddie), temperatures above 28-degrees-C shortened them. Females m aintained at a vapour-pressure deficit of 23.7 +/- 0.5 mmHg (c. 12% r. h.) and 6.45 +/- 0.15 mmHg (c. 76% r.h.) did not have significantly di fferent pre-reproductive period distributions. The availability of 10% w/v sugar solution (provided ad libitum) had a marked effect on both the survival and the pre-reproductive period of both sexes. Moths give n water for four nights followed by sugar solution thereafter, took si gnificantly longer to reach reproductive maturity than those given sug ar solution from emergence. Survival to reproductive maturity of moths given water only throughout their lives was poor (c. 20%). The signif icance of these findings to the migratory behaviour of H.armigera is d iscussed.