Two-spotted spider mites (Tetranychus urticae) perform better on soybean plants grown in saline conditions

Many environmental factors, including soil characteristics, are critically important for plants, herbivorous arthropods, and their interactions. Soil salinity negatively impacts plants, leading to reduced productivity and it is an increasing problem in the agricultural fields of North Dakota. Despite increasing evidence that salinity reduces plant quality, little is known about how salinity may influence herbivorous pests on these plants. This study investigated how soil salinity impacted two-spotted spider mites on soybean plants. We conducted two greenhouse experiments using soybeans grown in soil with manipulated levels of salinity (4 levels ranging from 0.3-4 EC 1:1). In the first experiment, two-spotted spider mite fecundity was measured for three days in clip cages. In the second experiment, population growth was measured after seven days on whole soybean plants. Two-spotted spider mite fecundity and population growth were greater on soybeans grown in soils with higher salinity compared to plants grown in less saline soils. These short term studies, which are representative of fields with low-moderate saline soil, suggest that negative effects of soil salinity on crop plants may be further compounded by increases in pest pressure. Our research indicates that environmental stressors can directly influence crop production while indirectly influencing plants by modifying their herbivorous pests.