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The presence of large populations of pine voles in apple orchards suggests that in the field reproduction of these pests has few constraints. Yet, evidence collected from our colony at Union College indicates that in the laboratory reproduction is not at random but instead is socially restrained and predictable. Unless these findings are artifacts of laboratory life, they may help explain some of the data collected in the field. Horsfall (1963) trapped voles every month of the year from an orchard near Cloverdale, VA. Since he found pregnant females in all collections, he concluded that reproduction occurred throughout the year with a peak in the summer months. On the other hand, Valentine and Kirkpatrick(1970) found pregnant females in only seven months of the year in orchards near Danville, VA. The conflict in data has not been resolved and may be a result of social factors that could not be determined in the field. In the laboratory, we found that reproduction in pine voles is influenced by a variety of social conditions.