The influence of moonlight and weather on catches of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in light and pheromone traps

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Abstract
Records of hourly trap catches of Helicoverpa armigera (Hübner) in a light trap and two pheromone traps in Andhra Pradesh, India, were used to assess the influence of moonlight and weather on trap performance. The environmental factors that were considered were mean hourly temperature, relative humidity, wind speed and maximum hourly percentage moon illuminance. The mean number of adults caught per hour reached a peak at 03.00 h in the light trap and at 02.00 h in one of the pheromone traps. The environmental factors were not sufficiently severe to produce any marked activity thresholds, although zero catches were recorded in the light and pheromone traps on occasions when the mean hourly temperature was 11°C. Despite there being obvious relationships between hourly light and pheromone trap catches with temperature, relative humidity and wind speed, it was not possible to determine whether these were causally related or merely coincidental relationships. Some of the observed relationships could not be explained in terms of known physiological or behavioural characteristics of the insect. It was evident that the light trap performance was influenced by the level of moon illuminance because this affected both the timing and size of the peak catch.