Biopores from mole crickets (Scapteriscus spp.) increase soil hydraulic conductivity and infiltration rates

Abstract

Soil organisms can seasonally and temporally influence many factors of soil formation and structure. Burrowing insects create biopores resulting in preferential flow through the soil profile. Most insect species have one or more life stages in soil, however, social insects are the primary taxa studied in context of soil function and structures. Soil-inhabiting southern mole cricket, Scapteriscus borellii Giglio-Tos and tawny mole cricket, Scapteriscus vicinus Scudder (Orthoptera: Gryllotalpidae), create subterranean tunnels and likely alter soil infiltration and hydraulic conductivity. X-ray CT scans were used to generate three-dimensional images of tunnel characteristics of Scapteriscus mole cricket in different soils and for various life stages. One mole cricket was introduced to a polyvinyl chloride (PVC) cylindrical arena filled with soil and allowed to construct their tunnels for 7 days under controlled conditions in the greenhouse. X-ray CT scans produced high resolution, three-dimensional renderings of tunnel architecture. Greenhouse trials also compared the hydraulic conductivity of saturated soil (Ksat) infested with mole crickets to soil columns with earthworms. Additionally, infiltration and runoff rates were compared under field conditions in bermudagrass (Cynodon dactylon(L.)×Cynodon transvaalensis (Burtt-Davy)) in the presence and absence of mole crickets. Both species produce tunnels generally ≥2.5 times their body in width. Southern mole cricket tunnels produce twice as many tunnels branches near the surface compared to lower in the soil profile. Immature and adult mole crickets produce tunnels that are similarly constructed yet adults displace about three times the amount of soil during immatures. Mole crickets construct tunnels 64.1cm long with 208.8cm3 volume in loamy soils, which is about double the length and volume of tunnels in clay soils. The Ksat was similar when mole crickets or earthworms were present, but both were greater relative to arenas with no soil invertebrates. Under field conditions, plots in bermudagrass where mole crickets were active had 41% reduction in runoff and a 12% greater infiltration relative to un-infested turfgrass. Biopores created by mole crickets in turfgrass and pastures create preferential flow through soil that may increase the movement of water and solutes from the soil to groundwater. This work highlights the interconnections between biodiversity in soils and soil function, and the importance of expanding studies on soil invertebrates beyond the few candidate taxa already studied.