Immersion survival differs among three Diabrotica species

Soil dwelling invertebrates including insects and their larvae are subjected to severe oxygen limitations when the soil becomes saturated or covered by water. Differential survival of this stress may in part explain ecological range of a species and could lead to cultural control methods for economically important species. We tested immersion survival for larvae of three species of Diabrotica (viz., D. balteata LeConte, D. undecimpunctata undecimpunctata Mannerheim, and D. virgifera virgifera LeConte). Groups of larvae were submersed in conditioned, hypoxic (dissolved oxygen < 0.3 ppm) tap water, held at 10, 15, 20, or 25 °C, and periodically removed and assayed for survivorship. We found that time to 50% mortality (LT50) differed significantly between species. Third instar D. u. undecimpunctata were most sensitive to immersion at 25 °C (LT50 = 9 h), D. balteata were intermediate (LT50 = 15 h) and D. v. virgifera larvae were least sensitive (LT50 = 23 h). Second instar D. v. virgifera were significantly more tolerant of immersion than the other species (LT50 = 56 h versus 15 h for D. u. undecimpunctata and 11 h for D. balteata). Mortality during immersion corresponds with the build up of lactic acid. Survivorship for all species increased with decreasing temperature. The use of flooding in rootworm management is briefly discussed.