Population dynamics of two-spotted spider mites in multiple year strawberry crops in Canterbury

The population dynamics and dispersion characteristics of two-spotted spider mite (Tetranychus urticae Koch) in strawberry plants (cv. Red Gauntlet) were examined. Several indices of dispersion were compared; Green’s coefficient of dispersion was simple to use and gave reproducible results over several seasons. Mite dispersion was strongly contagious at the start and end of the season, November and March, respectively, but only weakly contagious between these months. Most mites were found on the large mature leaflets located at the side of the plant; hence, leaflets in this category were suitable sample units. Fewer mites were found on strawberry plants more than one season old. Development of induced resistance by the plant in response to previous mite feeding may be responsible for this phenomenon rather than the influence of natural enemies.