Evaluation of dosimeter tubes for monitoring phosphine fumigations

Authors: Brabec, Daniel - Dan; Morrison, William - Rob; Campbell, James - Jim; Arthur, Franklin; Bruce, Alexander; Yeater, Kathleen

Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2021
Publication Date: 3/1/2021
Citation: Brabec, D.L., Morrison III, W.R., Campbell, J.F., Arthur, F.H., Bruce, A.I., Yeater, K.M. 2021. Evaluation of dosimeter tubes for monitoring phosphine fumigations. Journal of Stored Products Research. 91. Article 101762. https://doi.org/10.1016/j.jspr.2021.101762.
DOI: https://doi.org/10.1016/j.jspr.2021.101762

Interpretive Summary: Fumigation of stored products with phosphine is one method to help control post-harvest insect infestations in agricultural products. To evaluate the effectiveness of a fumigation treatment, gas concentration and time of exposure needs to be measured. A variety of methods are available for fumigation monitoring, but they tend to be either labor and time intensive to get detailed information or require expensive instrumentation. A new dosimeter tube system is commercially available that measures the cumulative gas concentration over time (CT) and is relatively inexpensive and easy to use, but little information on their accuracy is available. Our tests showed that the high-range dosimeter tubes gave similar results to those from electronic fumigation monitoring instruments, but the low range tubes were found to give significantly higher readings. Mortality of susceptible and phosphine-resistant lesser grain borers and red flour beetles were also evaluated to determine reference CT values that would provide insect control. For the susceptible strains, CT dosages ~5000 ppm*hr controlled both species. However, insect mortality varied from 60%-100% for resistant adults at CT dosages of ~20,000 ppm*hr. The dosimeter tubes appeared to provide reasonable estimates of the fumigation dosage for most treatment levels at a much lower cost, although they did not provide real time measurements that could be used to adjust treatment duration or allow for the addition of additional fumigant if needed. These devices would also allow monitoring of CT in situations where other types of monitoring are not feasible, such as during transportation.

Technical Abstract: 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. Phosphine 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%-100% 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%-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.