SummaryFumigation with phosphine gas is the primary method of controlling stored grain pests. In Turkey, phosphine has been used extensively since the 1950's. Even though high levels of phosphine resistance have been detected in several key stored products pests across the world, it has never been studied in Turkey despite this long history of phosphine use. High-level phosphine resistance has been detected and genetically characterised previously in the rust red flour beetle, Tribolium castaneum in other countries. Since this pest is also a common problem in stored grain environment in Turkey, the current study was undertaken for the first time, to investigate the distribution and strength of phosphine resistance in T.castaneum. Four strains of T. castaneum were tested through bioassays for determining the weak and strong phosphine resistance phenotypes on the basis of the response of adults to discriminating phosphine concentrations of 0.03 mg/L and 0.25 mg/L, for 20 hour exposures respectively. Phenotype testing showed all strains exhibited some level of phosphine resistance with a maximum level of 196 fold. Sequencing and genetic testing of seven field-collected strains showed that all of them carried a strong resistance allele in at the rph2 locus similar to the one previously reported. Our results show that strong resistance to phosphine is common in Turkish strains of T. castaneum.
Keywords:Wheat, phosphine resistance, Tribolium castaneum, molecular diagnostic, dihydrolipoamide dehydrogenase, dld
ÖzetDepolanmış hububattaki zararlılarla mücadeledeki ana yöntem fosfin gazı ile fumigasyondur. Fosfin gazı Türkiye'de 1950'li yıllardan beri yoğun olarak kullanılmaktadır. Fosfinin uzun yıllardan beri depolanmış hububatta kullanımına ve dünyada da pek çok ülkede yüksek seviyelerde fosfin direncinin belirlenmiş olmasına rağmen Türkiye'de bugüne kadar bu konuda herhangi bir çalışma yapılmamıştır. Yüksek seviyelerde fosfin direnci, un biti Tribolium castaneum'da belirlenerek direnç yapısı genetik olarak tanımlanmıştır. Bu zararlı Türkiye'de depolanmış buğdayda yaygın bir zararlı konumunda olduğundan, bu ilk çalışma fosfin direncinin T. castaneum'daki durumunu ve ülkedeki dağılımını ortaya koymak üzere yürütülmüştür. Dört popülasyon, zayıf ve kuvvetli direnç için sırasıyla ayırıcı fosfin konsantrasyonları olan 0.03mg/L ve 0.25mg/L dozları ile 20 saat süreyle uygulama temeline dayanan bioassaylerle test edilmişlerdir. Bu testlerde popülasyonların tümünde direnç olduğu ve direnç oranının 196 kata kadar ulaştığı belirlenmiştir. Yapılan genetik çalışmalar ve sekans, tüm popülasyonların kuvvetli direnç allellerine sahip olduklarını ve bu popülasyonların daha önce literatürde rapor edilenlere benzer olarak rph2 lokusundaki direnç allelini taşıdıklarını göstermiştir. Çalışma sonuçlarımız, T. castaneum'un Türkiye popülasyonlarında fosfine karşı güçlü bir direncin yaygın olduğunu göstermektedir.
Typically, in bag-stack or silo fumigations the concentration of phosphine is not constant, and yet most of what is known about phosphine efficacy against grain insects comes frorn studies with fixed concentrations. Indeed, where changing concentration experiments have been performed, researchers have been unable to explain observed efficacy on the basis of data frorn fixed concentrations. The ability to predict insect mortality in relation to changing phosphine concentrations would facilitate the development of effective fumigation protocols. In this paper, we explore the prospects for making such predictions. After reviewing published and new results, we conclude that the commonly used concentration x time (Ct) product is y e l iable for this purpose. New results, for a strongly resistant strain of Rhyzopertha dominica frorn Australia, suggest that the relationship Cnt = kmay be useful for predicting mortality of this type of insect in changing concentrations. However, in the case of a strain of Sitophilus oryzae with a type of resistance common in Australian S. oryzae, the relationship C t = k proved to be less reliable.
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