Regional population differences of the brown planthopper (Nilaparvata lugens Stål) in Cambodia using genotyping-by-sequencing.

The brown planthopper Nilaparvata lugens Stål (BPH) can be found year-round in tropical region and causes severe damage to rice. Although there has been documented BPH damage to rice crops in the past decade in Cambodia, the extent of this epidemic is poorly understood. Here, we examined the time variation of BPH population in the abundance of morphotypes in 13 main rice-producing provinces (86 sites) by aspirator method and in the Takeo Province (five sites) by yellow sticky trap method. At least three generations were observed during the 3-month collection period in the rainy growing season. Regarding the occurrence of BPH morphotypes, in July the macropterous adults were restricted to south Cambodia and in August all morphotypes, adults (macropterous and brachypterous) and nymphs, appeared in all sampling sites. To explain the difference of regional distribution, the genetic differentiation was analyzed in south and northwest Cambodia (three sites) by using single nucleotide polymorphisms (SNP) analysis via genotyping-by-sequencing (GBS) using next-generation sequencing. The 2455 SNPs obtained by GBS clarified the three sub-populations and they corresponded to the expected dissemination patterns. These results provide a clue to understand the differentiation and epidemic of BPH in Cambodia.

Current status of insecticide susceptibility in the brown planthopper in Cambodia.

Little information exists about pesticide availability and its effect on pest control in rural regions of developing countries. The availability of different insecticidal ingredients in rural areas of Cambodia was determined by inspecting labels on products used by farmers and in retail shops. A large number of products available in markets and used by farmers contained abamectin, emamectin benzoate, cypermethrin, and chlorpyrifos. The effects on the brown planthopper (BPH; Nilaparvata lugens (Stål)) were investigated by comparing the susceptibility of three BPH populations in Cambodia to twelve active ingredients in 2015. All populations showed high susceptibility to abamectin and cypermethrin; however, regional differences in susceptibility were observed for the other ingredients. The implication was that farmers selected the most effective products based on sellers' opinions. It is important to monitor insecticide use and BPH susceptibility in each region of Cambodia in order to minimize the risk of high BPH population densities.