SEASONAL POPULATIONS OF THE DIAMONDBACK MOTH, PLUTELLA XYLOSTELLA (LEPIDOPTERA: PLUTELLIDAE) IN RELATION TO DAY-DEGREE ACCUMULATION

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Abstract
The life history of Plutella xylostella (L.) was studied in plantings of Brussels sprouts at Cambridge, Ontario in 1977 and 1978. Adults were monitored by using sticky traps constructed of bristol board; eggs, larvae, and pupae were monitored by sampling plants. In both years in the spring, some of the first eggs were found before adults were caught in the traps. The trap collections indicated four periods of adult flight each year. During the last period of flight in 1977 eggs were laid; however, the fifth generation was not completed. Day-degree analyses of the populations indicated that 293 day-degrees (C) above a threshold temperature (7.3°C) were required to complete one generation. Using day-degree accumulations it was possible to predict accurately the periods when various stages of the pest were dominant even though there was considerable overlap of various stages in the field.