Megalurothrips usitatus is a major pest of cowpea in tropical regions, where frequent insecticide use has promoted the development of resistance. In this study, field populations of M. usitatus were collected from five major cowpea-producing areas in Hainan from 2023 to 2025, and their susceptibility to five commonly used insecticides was evaluated using a modified leaf-tube residual film method. Resistance levels varied among regions and insecticides, with southern populations generally showing higher LC₅₀ values than central and northern populations. The tested neonicotinoid insecticide, acetamiprid, showed the highest resistance levels. By 2025, the resistance ratios of the Ledong, Sanya, and Lingshui populations to acetamiprid reached 298.48-, 139.60-, and 130.25-fold, respectively. Spinosyn resistance also increased rapidly, particularly in southern Hainan. The resistance ratio to spinetoram reached 110.78-fold in the Ledong population, while resistance to spinosad reached 37.06-fold in the Lingshui population. However, the absolute LC₅₀ values of spinosad and spinetoram remained relatively low compared with those of acetamiprid and chlorfenapyr, indicating that these two spinosyn insecticides retained relatively high bioassay activity in laboratory bioassays. A significant positive correlation was detected between the LC₅₀ values of spinosad and spinetoram across field populations (r = 0.8972, p < 0.0001), suggesting cross-resistance within the spinosyn class. These results indicate that resistance management for M. usitatus in Hainan should prioritize reducing the use of high-resistance-risk insecticides, avoiding consecutive applications of spinosyns, and designing region-specific rotation programs based on local resistance monitoring.

Background: The bean flower thrips, Megalurothrips usitatus, is a destructive agricultural pest with increasing resistance to pyrethroid insecticides. Most mechanistic studies emphasize mutations in the pore-forming voltage-gated sodium channels α-subunit, whereas the contribution of insect-specific sodium-channel auxiliary subunits remains unclear. Methods: We used dsRNA feeding, pyrethroid bioassays, RNA sequencing, and RT-qPCR validation to evaluate the role of temperature-induced paralytic E (TipE) in M. usitatus. Results: The optimized RNAi condition was 400 μg/mL of dsTipE for 48 h, which reduced TipE expression by 32.55%. TipE knockdown increased adult mortality after exposure to λ-cyhalothrin and permethrin, indicating increased pyrethroid-associated susceptibility under laboratory conditions. Transcriptome sequencing identified 205 differentially expressed genes, with enrichment in metabolism-related pathways. RT-qPCR confirmed reduced expression of CYP307a1, an ecdysteroid-biosynthesis-related P450 gene, and SCD, a lipid-metabolism gene, while Na_v α-subunit transcript abundance did not change significantly. Conclusions: These results identify TipE as an auxiliary-subunit factor associated with pyrethroid susceptibility in M. usitatus and provide a transcriptome-based working model linking sodium-channel auxiliary regulation with endocrine- and lipid-metabolism-related responses. This study expands the candidate space for pyrethroid resistance research beyond Na_v α-subunit mutations, although the causal roles of CYP307a1 and SCD require further validation.

The extended application of pesticides has intensified the resistance problem in Liriomyza trifolii within Hainan Province. This study aimed to elucidate the underlying mechanisms contributing to the elevated resistance observed in this pest by employing whole-genome resequencing (WGS) technology. Through the analysis and comparison of WGS data focusing on Voltage-gated sodium channels (VGSC) from diverse regions and sensitive strains of L. trifolii in Hainan Province. A total of six nonsynonymous single nu-cleotide polymorphisms (nsSNPs) and thirty-one synonymous single nucleotide poly-morphisms (sSNPs) were detected in the five field populations MY, TS, DA, TY, and JY. Among the six nsSNPs, three (PyR1: M918T, L1014F, and PyR2: T933I) have been con-firmed as linked to pyrethroids resistance, while one (D IVS6: V1845I) was associated with resistance to indoxacarb. Moreover, the frequency of these four mutations generally in-creases with decreasing latitude. Additionally, under sustained pesticide selection pres-sure, L. trifolii exhibits an evolutionary pattern characterized by a dN/dS ratio (nsSNP/sSNP = 6/31 ≈ 0.19) of less than 1. Among the 31 sSNPs that held an absolute quantitative advantage, the highest occurrence frequency reached 94.44 % (G2033: JY), and this sSNP occurred in all populations. In contrast, among a limited number of 6 nsSNPs, the highest occurrence frequency attained 100% (L1014F: all populations). This study sub-stantiates that the elevated resistance observed in L. trifolii within Hainan Province can be ascribed to the presence of four nsSNPs-M922T, T933I, L1018F, and V1845I in their VGSC. Furthermore, the emergence of cross-resistance between pyrethroids and indoxacarb has been identified. This research offers a novel theoretical foundation for future investigations into the resistance mechanisms of L. trifolii.

The extended application of pesticides has intensified the resistance problem in Liriomyza trifolii within Hainan Province. This study aimed to elucidate the underlying mechanisms contributing to the elevated resistance observed in this pest by employing Whole-Genome Re-sequencing (WGR) technology. Through the analysis and comparison of WGR data focusing on voltage-gated sodium channel (VGSC) from diverse regions and LT-S of L. trifolii in Hainan Province, we identified a total of six nonsynonymous single nucleotide polymorphisms (nsSNPs) and thirty-one synonymous single nucleotide polymorphisms (sSNPs) in five wild populations MY, TS, DA, TY, and JY. Among the six nsSNPs, three (PyR1: M918T, L1014F, and PyR2: T933I) have been confirmed as linked to pyrethroid resistance, while one (D IVS6: V1845I) was associated with resistance to indoxacarb. Moreover, the frequency of these four mutations generally increases with decreasing latitude. Additionally, under sustained pesticide selection pressure, L. trifolii exhibits an evolutionary pattern characterized by a dN/dS ratio (nsSNP/sSNP = 6/31 ≈ 0.19) of less than 1. Among the 31 sSNPs that held an absolute quantitative advantage, the highest occurrence frequency reached 94.44% (G2033: JY), and this sSNP occurred in all populations. In contrast, among a limited number of 6 nsSNPs, the highest occurrence frequency attained 100% (L1014F: all populations). This study substantiates that the elevated resistance observed in L. trifolii within Hainan Province can be ascribed to the presence of four nsSNPs-M922T, T933I, L1018F, and V1845I in their VGSC. Furthermore, the emergence of cross-resistance between pyrethroids and indoxacarb has been identified. This research offers a novel theoretical foundation for future investigations into the resistance mechanisms of L. trifolii.