Soil and Moisture Effects on the Dynamics of Early Instar Clover Root Curculio (Coleoptera: Curculionidae) and Biomass of Alfalfa Root Nodules

Abstract

Movement and survival of early instar clover root curculio, Sitona hispidulus (F.), and the development of root nodules in alfalfa, Medicago sativa L., were examined in relation to soil texture and moisture. Early instars were subjected to three soil textures (loamy sand, loam, and silty-clay loam) and two moisture potential regimes approximating very moist and slightly moist conditions, respectively. Survival of early instars was significantly higher in the slightly moist silty-clay loam (61%) and lowest in the slightly moist loamy sand (23%). These results suggest that cracks 1.0 mm or larger in the silty-clay loam increased access of the first instars to alfalfa root nodules. Production of root nodules was significantly greater in the loamy sand, yet clover root curculio survival in this soil type was lower, indicating that this soil deterred first instar access to critical nodule resources. We tested the ability of first instars to penetrate soils of three different textures and five moisture levels. First instars penetrated moist and slightly moist silty-clay loam and coarse sand significantly better than severely moist and saturated treatments, and also better than loamy sand at any moisture level. This was due to the presence of large cracks and/or pores in the drier silty-clay loam and coarse sand. This information will be useful for identifying soil conditions in alfalfa fields that influence the pest potential of this insect and hence assist in developing more effective integrated pest management strategies.