Mortality Factors in a Population of Neodiprion sertifer (Hymenoptera: Diprionidae)

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Abstract
The effects of a nuclear polyhedrosis virus and other mortality factors on a population of Neodiprion sertifer were studied during a 4-yr period. The population remained at intermediate density levels with only small variations between years. Sawfly densities varied between 9670 and 46030 eggs ha-1. Parasitoids caused between 19% and 34% mortality of the eggs and between 8% and 30% mortality of the larvae; parasitism rates showed no significant relationship with host density. The virus disease caused between 2% and 23% mortality. There was a significant negative correlation between this mortality in cocoons showed a significant positive correlation with population size. It was concluded that virus epizootic to develop. The most frequently observed causes of high mortality during N. sertifer outbreaks in southern Sweden were egg parasitism and cocoon predation. Life-table analysis of data from the study area suggests that this population could have been regulated by small mammal predation.

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