Gall-Insect Community on Big Sagebrush Varies With Plant Size but not Plant Age

Identity and Seasonal Abundance of Beneficial Arthropods Associated with Big Sagebrush (Artemisia tridentata) in Central Washington State, USA

Big sagebrush (Artemisia tridentata) characterizes and dominates the sagebrush steppe, the largest temperate semi-desert ecosystem in North America. The beneficial arthropod fauna hosted by A. tridentata is poorly known but could be of importance to nearby agriculture seeking to exploit biologically-based pest management. Over four years, we identified and assessed the seasonal abundance of beneficial arthropods (predators, parasitoids, pollinators) associated with A. tridentata during spring to autumn in the Yakima Valley of central Washington using sticky traps. During 2011–2014, 207 sticky traps were placed on non-blooming and blooming A. tridentata plants for a total of 966 trapping days. Overall, across all seasons, we trapped 259.7 beneficial arthropods per trap and 92% of these were parasitoid wasps. Significantly greater numbers of beneficial arthropods were associated with blooming A. tridentata during autumn (410/trap) than non-blooming plants in the spring (181.3/trap) or summer (85.1/trap). Parasitoid wasps and predatory true bugs were most abundant during the autumn, but ladybeetles, lacewings, spiders, bees, and predatory thrips were most common during spring. The association of high numbers of predators, parasitoids, and pollinators with A. tridentata during blooming and non-blooming periods indicates that this plant is an important reservoir of beneficial arthropods in the sagebrush steppe of central Washington. Consequently, biologically-based pest management programs in central Washington may benefit from careful management and retention of A. tridentata plants on crop borders.

Tripartite symbiosis of plant-weevil-bacteria is a widespread phenomenon in the Negev Desert

The weevil Conorhynchus palumbus develops in a mud chamber affixed to the roots of the summer annual plant Salsola inermis in the Negev Desert of Israel. The weevil carries nitrogen fixing bacteria, and evidence suggests that plants with weevils utilize the fixed nitrogen. To characterize the distribution, abundance and significance of this unique interaction, we surveyed Salsola plants in 16 sites throughout the Negev Desert. We excavated ~100 plants from each site, recorded the presence of weevils in their roots, and characterized the soil properties in each site. Weevil mud chambers were present in all of the sampled sites and their abundance was positively correlated with soil nitrogen content and with plant size, and negatively correlated with soil grain-size. Intriguingly, we found two additional weevil species–Menecleonus virgatus and Maximus mimosae–residing in mud chambers on Salsola roots, and found one additional Salsola species–S. incanescens–accommodating weevils. Nitrogen fixing bacteria were found in weevil larvae of the two additional species and at multiple sites. Overall, our findings suggest that potentially beneficial associations between weevils and plants may be more common than previously acknowledged, and may play an important role in this desert ecosystem.