Meeting Abstract

P2.115  Wednesday, Jan. 5  The underground chambers of Manduca sexta – Curse of the oxygen or treasure troves? FöRSTER, Thomas D.*; SPRAGUE, Jonathan C.; WOODS, H. Arthur; University of Montana, Missoula; University of Montana, Missoula; University of Montana, Missoula thomas.foerster@mso.umt.edu

Late larval stage tobacco hornworms (Manduca sexta) build underground chambers for pupation. The benefits of the chamber are unknown but may include minimizing water loss, providing shelter for the larval-pupal molt, and avoiding predators and parasites. Chamber construction, however, may come at the cost of potentially reduced oxygen availability, especially in wet soil. Using a finite element model approach we modeled the oxygen distribution in the soil. Most of the model parameters were estimated in the field or using lab experiments on field-collected chambers. The functional influence of increased soil water content on the apparent diffusion coefficients was modeled from the literature (Moldrup et al., 2000, Soil Sci. Soc. Amer. Journ. 64, 94-100) and fitted to our own measurements in desert soil. In dry desert soil, mean chamber oxygen partial pressure was 19 kPa, only slightly below the ambient partial pressure at the soil surface. However, the picture changed if soil water content was increased. Due to reduced diffusivity in the soil, oxygen partial pressure in the chamber dropped to 15 kPa, but still above the critical oxygen partial pressure. The model predictions indicate that increased soil water content alone does not reduce oxygen availability enough to become a limiting factor during pupal development.