Seasonal abundance and distribution of Tetranychus urticae (Acari: Tetranychidae), the two spotted spider mite, on cotton in Australia and implications for management

Abstract

AbstractThe two spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), is a pest of cotton in Australia yet has received little attention. To develop sampling strategies for pest management the seasonal abundance and intra-crop distribution of T. urticae on cotton was studied. T. urticae colonized cotton crops at seedling emergence in October. Populations declined through November/December then increased progressively thereafter, at varying times and rates. Higher initial infestation levels were correlated with earlier, potentially more damaging, mite outbreaks. Survival of T. urticae through November/December appears crucial in determining the extent to which this potential is realized. Nodes 3 to 5 below the terminal were most heavily infested and should be used as the sampling unit for mites. The within plant distribution of T. urticae was unaffected by cotton variety or insecticide applications. T. urticae was more abundant on the edges of fields than in the interior early in the season (October and November) indicating colonization from an external source. The edge effect diminished with time, suggesting a lack of continuous colonization. The only exceptions to this pattern occurred when T. urticae migrated from senescent maize crops into the nearby cotton crops in early January. A simple sampling technique, based on the presence or absence of mites on leaves was developed for pest management purposes.