Abstract
Although near-isogenic lines (NILs) can standardize genetic backgrounds among individuals, it has never been applied in parthenogenetically reproduced animals. Here, through multiple rounds of backcrossing and spinosad screening, we generated spinosad resistant NILs in the western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), with a haplo-diploid reproduction system. The resultant F. occidentalis NIL-R strain maintained a resistance ratio over 30,000-fold, which was comparable to its parental resistant strain, Spin-R. More importantly, F. occidentalis NIL-R shared 98.90% genetic similarity with its susceptible parental strain Ivf03. By developing this toolset, we are able to segregate individual resistance and facilitate the mechanistic study of insecticide resistances in phloem-feeding arthropods, a group of devastating pest species reproducing sexually as well as asexually.
Highlights
Near-isogenic lines (NILs) are strains which genetic makeups are identical except for few specific locations or genetic loci (Muehlbauer et al, 1988; Young et al, 1988)
In comparison to the backcrossed inbred lines (BILs) used in amphigenetic insects, one major difference was that we obtained resistant males (e.g., F1P1) by parthenogenesis and insecticide screening, while in backcross inbred lines (BILs), self-crossing, insecticide screening and one additional step of males selecting are used to generate resistant males (Zhu et al, 2015)
The other difference was the step of BC8 females backcrossing with resistant males from BC7P1, but not self-crossing used in amphigenetic insects
Summary
Near-isogenic lines (NILs) are strains which genetic makeups are identical except for few specific locations or genetic loci (Muehlbauer et al, 1988; Young et al, 1988). Classic NILs construction methods, such as backcross inbred lines (BILs) and recombinant inbred lines (RILs), are applicable exclusively to amphigenetic insects, including fruit fly, beet armyworm, diamondback moth, and silkworm (Pierce and Lucchesi, 1981; Mu et al, 2004; Yuan et al, 2010; Zhu et al, 2015). A genetic linkage experiment has demonstrated that spinosad resistance in F. occidentalis was controlled by a single autosomal recessive gene and was not influenced by maternal effects (Bielza et al, 2007a). An orthogonal experiment was designed to optimize the ISSR-PCR reaction system in F. occidentalis to obtain as many polymorphic bands as possible to achieve an accurate measurement of near-isogenicity Both strains were kept separately but under the same conditions, i.e., 27 ± 1◦C and 50% relative humidity.
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