Comparing bioassay and diagnostic molecular marker for phosphine resistance in Turkish populations of Rhyzopertha dominica (F., 1792) (Coleoptera: Bostrichidae)

Phosphine gas is the major pesticide applied to stored cereal grains against insects across the world and has been used in Turkiye since the 1950s. Increasing resistance to this fumigant is a problem in stored grain pests worldwide. This study determined the phosphine resistance ratios of the lesser grain borer, Rhyzopertha dominica (F., 1792) (Coleoptera: Bostrichidae) in 18 populations from 12 provinces of Turkiye between 2013 and 2017. Discriminating dose studies showed 3 of 15 populations comprise phosphine-resistant specimens. Dose-response bioassays established that resistance ratios were between 96 and 533-fold. The current molecular resistance marker, which detects the amino acid mutation P49S in the DLD (dihydrolipoamide dehydrogenase) gene, were assayed in phosphine-resistant populations. The R allele occurred at a high frequency (83.7%) in 15 highly resistant populations and was absent in three susceptible populations. For 324 individuals from the resistant populations the average proportion of homozygous resistant, heterozygous resistant and homozygous susceptible alleles were 62.0, 18.9 and 19.1%, respectively. The genetic marker detection results were comparable to bioassay results in relation to the resistance status of Turkish populations of R. dominca. So, genetic testing for phosphine resistance will simplify resistance management in Turkiye.