Field efficacy of brief exposure of adults of six storage pests to nitrogen-controlled atmospheres

Abstract

The efficacy of a brief exposure (1, 7, and 10 days) to a nitrogen-controlled atmosphere (N-CA) for major storage<br />pests in a field validation study in the Czech Republic is reported. The main goal was to estimate how quickly the<br />mobile adult stages of six species of storage beetles (Oryzaephilus surinamensis, Cryptolestes ferrugineus, Tribolium<br />confusum, Tribolium castaneum, Sitophilus granarius, and Sitophilus oryzae) are killed after introduction of the<br />infested commodity to prevent their further spread to the surrounding storage bins. The trials were conducted in a<br />metal bin containing 25 t of seeds using the system of continual top-down nitrogen filling to replace the oxygen. The<br />composition of N-CA in the silo was measured continually. The target N-CA concentration (i.e., ≤ 1% O<sub>2</sub> and 99% N<sub>2</sub>)<br />was reached at the bottom of the silo after 12 h of the purging phase of nitrogen silo filling. A one-day exposure to<br />N-CA corresponds to top-down filling, which initially gives higher concentrations of N2 in the upper than in the lower<br />part of the silo: low efficacy was reached at the silo bottom (0–33.3%), while higher efficacy (16.7–100%) was reached<br />at the top of the silo bin. The mortality variation at both locations was species dependent: the most sensitive was O.<br />surinamensis, and the least sensitive were S. granarius and S. oryzae. Seven days of N-CA exposure led to 100% mortality<br />of all tested species except for S. granarius (96.7% mortality at the bottom), while 10 days of N-CA exposure led<br />to 100% mortality of all adults located at both the bottom and the top of the silo. This experiment showed that one<br />day of exposure to N-CA caused significant mortality to reduce the spread of insects from the top of the silo but not<br />from the silo bottom, and 10 days of exposure completely prevent the adult mobile pest stages of all tested species<br />from spreading from the treated silo and causing cross-infestation in the storage facility.