Susceptibility of Philippine populations of diamondback moth, Plutella xylostella Linn. (Lepidoptera:Plutellidae) to flubendiamide with special reference to genotyping and resistance dynamics

Flubendiamide belongs to a novel class of insecticide that selectively targets the ryanodine receptor (RyR) of the insect such as Plutella xylostella (Lepidoptera: Plutellidae), commonly known as diamondback moth (DBM). This insect is considered as a notorious global described that the P. xylostella Sudlon strain resistance to flubendiamide is due to target-site flubendiamide to Plutella xylostella populations, collected from cabbage plantations with previously reported flubendiamide resistance (Sudlon, Cebu) and the three other selected locations (Majayjay, Calauan and Baguias), were studied using the leaf dip assay method, and then subjected to prosequencing analysis. Done-response of those local DBM populations indicated that two years after the first recorded flubendiamide resistance in Sudlon, Cebu strain (LC sub 50 = 270.6; 2.5+-0.35SD) high levels of resistance were still evident, not just in Sudlon but also in populations from other three (Majayjay, Calauan, Buguais) selected geographical locations. The reported resistance from the four selected locations ranged from 6,000 to 10,000 fold higher compared to the sensitive strain. In addition, the resistance ratio observed from Sudlon strain collected in 2014 was 12 times higher than Sudlon strain collected in 2012 (Traczca et al., 2012) which has a value of 12,885.71 ppm and 1,000 fold, respectively. Genotyping by pyrosequencing method, attest the presence of previously described G4946E RyR mutation connotes to high level resistance to diamide insecticides in a diamondback moth population samples. Pyrosequencing analysis showed that of the four local DBM strains collected, only the Calauan, Laguna strain showed the same genotype and genotypic frequency as with the previously studied Philippine strain, Sudlon Cebu with 100% homozygous GAA resistant allele which resulted to glycine to glutamic acid substitution. The other DBM populations Baguias, Benguet and Majayjay, Laguna showed different G4946E genotypic percentage and genotype. As observed, the assay successfully detected the polymorphism of the triplet at the coding position 4946E in genomic DNA among different locations of DBM strains in the Philippines. Also although they were collected from the country and the location had almost the same climatic conditions not all of them acquired similar genotype to confirm the existence of diamide cross-resistance. It was also observed that DBM resistance to flubendiamide exists in four locations in the Philippines. Even though Buguias, Benguet acquired only 33% homozygous resistant allele, still the resistance ratio observed can be considered very high (6000 fold higher) compared with susceptible strain. This implies that mutation at very low frequency have little or no impact on the resistance of this strains to diamides in bioassays. However, it indicates that mutation occurred in the populations and will eventually spread to adjacent areas as observed by the spread of initially reported in Cebu and after two years, now in different places such as Laguna and to the tip of the Luzon, Buguias, Benguet. The evolution of insecticides resistance in field-collected diamondback moth was analyzed by using regression analysis based on a non-linear model to understand the resistance dynamics to flubendiamide insecticide among of field populations of DBM from Sudlon, Cebu and Buguinas, Benguet populations among 2011 to 2015. The dynamics of the considered high-level resistance population (Sudlon, Cebu) could be modelled by polynomial-cubic equation. The Sudlon strain hand evolved a high level of resistance to flubendiamide when detected in 2012, and elevated up to 14000 fold in 2013 then decreased in 2015. However, still significantly high value dictates insecticide resistance to Flubendiamide. For the slightly resistant population (Baquias, Benguet), its dynamics could be modeled by polynomial-linear. The dynamics of the resistance development to be flubendiamide among DBM selected populations were driven mainly by the selection based on the application history of flubendiamide in study areas which resulted to the change in resistance response of the insects by the change of genetic frequency.