Publications about phosphine resistance

Abstract

Development of resistance in major grain insect pest species to the key fumi-gant phosphine (hydrogen phosphide) across the globe has put the viability and sustainability of phosphine in jeopardy. The resistance problem has been aggravated over the past two decades, due mostly to the lack of suitable al- ternatives matching to the major attributes of phosphine, including its low price, ease of application, proven effectiveness against a broad pest spectrum, compatibility with most storage conditions, and international acceptance as a residue-free treatment. In this review, we critically analyze the published literature in the area of phosphine resistance with special emphasis on the methods available for detection of resistance, the genetic basis of resistance development, key management strategies, and research gaps that need to be addressed.

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Abstract

The use of phosphine has been effective against a wide range of stored-product pests in different types of commodities and facilities. However, its continuous and improper use has led to resistance development in -several major insect species. Although phosphine resistance has been reported from many countries across the globe, reports from Europe have been very limited. In the present study, we determined phosphine resistance in insect populations that had been collected from a range of storages across Greece, using two different diagnostic protocols. Apart from the traditional Food and Agriculture Organization (FAO) protocol, a field test kit (known as the Detia Degesch Tolerance Test Kit, DDTTPK) was utilized, for “same day” determination of the resistance status of field collected insects. In total, 53 populations belonging to Rhyzopertha dominica, Sitophilus oryzae, Sitophilus granarius, Cryptolestes fer- rugineus, Tribolium confusum, Tribolium castaneum and Oryzaephilus surinamensis were tested. For the majority of the species and populations tested, both FAO and DDPTTK provided similar results, for the susceptibility to phosphine and thus, the quick test could be used with success for an initial same day screening of phosphine resistance. Among the tested species, the populations recorded with the most frequent survival at the FAO testing dose of phosphine was that of R. dominica. The dissimilar evaluation and characterization of resistance to phosphine between diagnostic protocols is particularly important, as it poses risks in the over or underestimation of the resistance status of a given population. Our data indicate that the DDPTTK could be used to determine resistance to phosphine in the field, before the initiation of fumigations to disinfest stored commodities.

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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 in different counties, 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 2 min and the exposed adults were classified as either walking normally or being immobilized (knocked down), i.e., not walking normally. In light of our findings, the time to reach knockdown of all adults was notably reduced 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 knockdown ranged between 8 and 14 min. In contrast, for some of the field populations, knockdown 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.

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Abstract

A key component in the management of resistance to fumigant phosphine in stored products pests is their early detection and implementation of control strategies. Currently, resistance testing involves exposing adults to a specific discriminating concentration over a fixed time period (20–48 h). Although it is widely adopted, this test takes significant time for assay preparation (up to 4 wk) as well as diagnosis (1–2 wk). To address these lacunae, we have established a ‘quick knockdown test’ using a key grain insect pest, rice weevil, Sitophilus oryzae (L.). Susceptible, weakly and strongly phosphine-resistant reference strains were exposed to a threshold concentra- tion of phosphine over short exposure periods (min to h). The time to knockdown (KT) responses to phosphine were characterized at 2 (1,440 ppm) and 5 mg/liter (3,600 ppm). The time to 99.9% KT (KT99.9) at 2 mg/liter was 12.52 min for the susceptible adults, compared with 167.9 and 1,510 min in the case of weakly and strongly resistant phenotypes, respectively. As anticipated, increasing the concentration of phosphine to 5 mg/liter halved the KT99.9 (81.57 min) to separate weakly and strongly resistant populations than it was required at 2 mg/liter. We validated the KT99.9 value for the 5 mg/liter against field-derived populations of S. oryzae. The results were aligned with the existing Food and Agriculture Organization approach, confirming that the proposed ‘quick test’ is a reliable tool to rapidly diagnose resistance in this species.

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