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Taxonomy of Tetranychus ludeni (Acari: Tetranychidae) in New Zealand and its ecology on Sechium edule

A taxonomic survey or spider mites in New Zealand showed that many specimens previously determined to be Tetranychus cinnabarinus are in fact T. ludeni. This species is found on many host plants and 10 new host plant records are reported in this paper. Field observations in Auckland showed that Phytoseiulus persimilis (Acari: Phytosciidac) was the main natural enemy of T. ludeni on Sechium edule, and a species of Stethorus (Coleoptera: Coccinellidae) was the minor predator of this spider mite. T. ludeni densities per leaf on the upper surface of S. edule were 5-8 times as many as on the lower surfaces. This pattern is different from this species on other host plants and other species of Tetranychus, which are mostly found on the lower leaf surface. Since laboratory tests showed that T. ludeni produced similar numbers of eggs on either leaf surface, the preference by T. ludeni for upper surface is hypothesised to be caused by other factors, among which is the distribution of the predatory mite P. persimilis, which was mostly found on the lower leaf surface. The disparity in the within-leaf distribution between the predator and prey provided the prey a certain degree of refuge and reduced the searching efficiency of the predator, which is considered to be the main reason for the less effective biocontrol of T. ludeni on this plant. Laboratory studies on confined leaf discs supplied with relatively high densities of prey showed that P. persimilis performed similarly well on T. ludeni and T. urticae, both in terms of rates of predation and oviposition. Therefore, the hypothesis that the biological control of T. ludeni by P. persimilis is less effective because T. ludeni may not be a very suitable prey of, or very nutritious to, P. persimilis is not supported.