The Effects of Salinity on the Herbivorous Crop Pest Tetranychus urticae (Trombidiformes: Tetranychidae) on Soybean and Corn.

Many environmental factors, including soil characteristics, are critical for plants, herbivorous arthropods, and their interactions. Despite increasing evidence that soil salinity drastically impacts plants, little is known about how salinity affects the herbivorous arthropod pests feeding on those plants. We investigated how soil salinity affects the twospotted spider mite (Tetranychus urticae Koch) feeding on corn (Zea mays L.) and soybean (Glycine max L.). We performed two greenhouse studies, one focusing on the impact of salinity on individual mite fecundity over a period of 3 d and the other focusing on population growth of T. urticae over 7 d. Both experiments were performed across varying salinity levels; electrical conductivity values ranged from 0.84 to 8.07 dS m-1. We also performed the 3-d fecundity experiment in the field, across naturally varying saline conditions. Overall, the twospotted spider mite performed better as salinity increased; both fecundity and population growth tended to have a positive linear correlation with salinity. These studies suggest that salinity can be important for herbivores, just as it is for plants. Moreover, the negative effects of soil salinity on crop plants in agroecosystems may be further compounded by a greater risk of pest problems. Salinity may be another important environmental stressor that can directly influence crop production while also indirectly influencing herbivorous pests.