Population Dynamics and Secondary Production by Ranatra montezuma (Heteroptera:Nepidae)

Abstract

The thermally stable (21 ± 4°C) aquatic environment of Montezuma Well, Arizona, influenced the voltinism and secondary production of Ranatra montezuma. In contrast to other species of Nepidae, R. montezuma is multivoltine, producing three asynchronous cohorts from mid-February to mid-November. Mean density of spring, summer, and fall cohorts of R. montezuma (5 instars and adults) was 39, 65, and 27 animals/m², respectively. R. montezuma overwinters in the adult stage, despite the warm, near-thermally constant environment. The total duration of instar development for R. montezuma reared in the laboratory was 75 d at 21°C and 46 d at 26°C. Annual production of R. montezuma was estimated over a two-year period with the size-frequency method. The two-year average estimated annual production of R. montezuma was 0.97 g dry wt m^-2 yr^-1. Two-year average annual biomass was 0.072 g/m², the two-year average annual P/B̄ ratio was 13.4, and the two-year average cohort P/B̄ was 3.63. The summer cohort contributed at least 50 percent of the total annual production of R. montezuma.