Weeds and arthropod pest management: two-spotted spider mite (Tetranychus urticae) fecundity on four weed species

The presence and abundance of weed assemblages within or near agricultural fields can support undesirable herbivorous insect populations.  Weeds often provide insects with shelter and alternate food resources, and thus can facilitate pest population growth and dispersal to crop plants. Our goal was to determine the potential of several common weed species to support populations of a polyphagous arthropod pest, namely the two spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). For this study, we investigated spider mite reproduction on a highly accepted crop plant (soybean, Fabaceae), and four different weed families that are widely distributed in both agricultural and natural systems: common lambsquarters (Chenopodiaceae), Eastern black nightshade (Solanaceae), redroot pigweed (Amaranthaceae), and wild mustard (Brassicaceae). Three adult female spider mites were added to each plant, confined using a clip cage, and the number of surviving adults, immatures, and eggs were quantified after one week. Our results suggest wild mustard and common lambsquarters were highly suitable as host plants, with pest densities equal to or exceeding that on soybean. However, no spider mites survived on eastern black nightshade or redroot pigweed. This is contrary to results from similar studies, and may be related to differences in plant characteristics or adaptations of different spider mite strains, areas which we plan to investigate further. This study suggests certain weeds can support high spider mite populations, and therefore weed management should be considered in concert with arthropod pest management.