Evaluation of dosimeter tubes for monitoring phosphine fumigations

Within integrated pest management options, fumigation of stored products is one method to help control post-harvest insect infestations in our food and agricultural products. Fumigant gas concentration monitoring is important to confirm that the treatment was adequate to achieve the desired insect control, but monitoring can be relatively expensive and labor intensive. This study evaluated how accurately dosimeter tubes could monitor phosphine fumigation treatments. The dosimeter tube is designed to continuously react with phosphine gas during the fumigation period and yields a measurement in terms of concentration * time product or CT, which can be interpreted as cumulative exposure. Two models of dosimeter tubes were evaluated (high range and low range). The reference method for these trials were wireless phosphine monitoring sensors, which recorded gas concentrations at hourly intervals during an exposure, and from this a CT product was also calculated. Model LPG-1, high-range dosimeter tube, measured within ? 25% of the phosphine monitoring sensors for CT dosages less the 70,000 ppm*hr. Model LPG-2, low-range tube, tended to significantly over-estimate phosphine CT dosage by 50%e10 0% of the phosphine monitoring sensor references. Secondly, bioassays of fumigant efficacy were performed using susceptible and resistant adult Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), lesser grain borers, and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), red flour beetle, for estimating insect control at the varied fumigation CT treatments. For the susceptible strains, CT dosages-5000 ppm*hr controlled both species. However, the insect control varied from 60% to 100% for resistant adults at CT dosages of-20,000 ppm*hr. The dosimeter tubes function in these ranges of dosages where each insect species are controlled and the dosimeter tube model LPG-1 provides reasonable estimates of the fumigation dosage for a given treatment level. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study evaluated the accuracy of dosimeter tubes in monitoring phosphine fumigation treatments. The high-range dosimeter tube measured within ? 25% of the phosphine monitoring sensors for CT dosages less than 70,000 ppm*hr, while the low-range tube tended to over-estimate phosphine CT dosage by 50%-100%. For susceptible strains, CT dosages of 5000 ppm*hr controlled both species, but the insect control varied for resistant adults at CT dosages of -20,000 ppm*hr. The dosimeter tubes function well within these ranges, with model LPG-1 providing reasonable estimates of the fumigation dosage.