MAJOR FACTORS IN SURVIVAL OF THE IMMATURE STAGES OF HYLEMYA BRASSICAE (DIPTERA: ANTHOMYIIDAE) ON CABBAGE

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Abstract
Studies on the population dynamics of the cabbage maggot, Hylemya brassicae (Bouché), on cabbage were carried out at two locations in Ontario from 1967 to 1970. Analysis of life-table data for nine generations showed that extensive mortalities occurred during the following age intervals: (1) egg stage; (2) between hatching and the second moult; (3) third-instar larvae; (4) pupal stage. Density dependent mortality occurred only during the latter period. The analysis of age interval survivals and graphical key factor analysis showed that "misadventure" of the larvae between hatching and the second moult was the key factor. The overall mortality process from egg to adult eclosion was density dependent, revealing the importance of pupal parasitism as a stabilizing factor. A predictive model based on density relationships was found to explain 62% of the variance in generation survival. The remainder of the variance is unexplained and may be due to sampling error and/or the influence of factors not measured.