Field Efficacy of Brief Exposure of Adults of Six Storage Pests to Nitrogen-Controlled Atmospheres

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