Using immobilization as a quick diagnostic indicator for resistance to phosphine

Authors: ATHANASSIOU, CHRISTOS - University Of Thessaly; KAVALLIERATOS, NICKOLAS - Agricultural University Of Athens; Brabec, Daniel - Dan; AGRAFIOTI, PARAKEVI - University Of Thessaly; SAKKA, MARIA - University Of Thessaly; Campbell, James - Jim

Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2019
Publication Date: 6/16/2019
Citation: Athanassiou, C.G., Kavallieratos, N.G., Brabec, D.L., Agrafioti, P., Sakka, M., Campbell, J.F. 2019. Using immobilization as a quick diagnostic indicator for resistance to phosphine. Journal of Stored Products Research. 82:17-26. https://doi.org/10.1016/j.jspr.2019.01.004.
DOI: https://doi.org/10.1016/j.jspr.2019.01.004

Interpretive Summary: Treatment of grain and other materials with phosphine, a fumigant gas, is widely used for the control of insect pests, but there are increasing reports of insects with resistance to phosphine. There are protocols to detect phosphine resistance, but most are labor and time intensive and require specialized equipment and expertise. Rapid methods to detect resistance levels that can be used in the field before a treatment are needed. In this study, a quick diagnostic test for resistance to phosphine in stored-product beetle species was used to evaluate initial responses to phosphine by different populations of thirteen species, obtained from USA, Greece, Australia, Germany and Spain. This rapid test approach is based on exposure of insects to high concentrations of phosphine (1000 and 3000 ppm) for short exposure periods and measurement of time until all individuals are immobilized as a measure of resistance level in a population. For the majority of the species and populations obtained from laboratory colonies, which are most likely susceptible to phosphine, the time required for immobilization ranged between 8 and 14 min at 3000 ppm of phosphine. In contrast, for some of the field populations, which have likely been exposed to phosphine, immobilization did not reach 100% even after 300 min of exposure to 3000 ppm phosphine. Based on the results of the present study, this quick test, using 3000 ppm, can be effective at identifying phosphine resistance and critical threshold times for each of the tested species were generated.

Technical Abstract: In the present study, we evaluated a quick diagnostic test for resistance to phosphine in stored-product beetle species. We collected different populations of thirteen species, obtained from different laboratories and areas throughout the world, i.e., USA, Greece, Australia, Germany and Spain. There were also tested populations that have been sampled from different facilities (field populations). We used the Detia Degesch Phosphine Tolerance Test Kit (DDPTTK), which is based on the exposure of the insects on a high concentration of phosphine for shorter exposure periods. The tested concentrations to phosphine were 1000 and 3000 ppm. Briefly, 20 adults of the tested populations were placed in a 100 ml plastic syringe. The observations were taken every two minutes and the exposed adults were classified as either walking normally or not walking normally (immobilization). In light of our findings, the time to reach immobilization of all adults was notably increased at 3000 ppm in comparison with 1000 ppm. For the majority of the species and laboratory populations tested, at 3000 ppm, the time required for immobilization ranged between 8 and 14 min. In contrast, for some of the field populations immobilization did not reach 100% even after 300 min of exposure, at either 1000 or 3000 ppm. Based on the results of the present study, we recommend that the DDPTTK can be operated at 3000 ppm, and we provide the critical threshold times per species for the characterization of tolerance/resistance.