Plant phloem-based defence (PBD) against phloem-feeding insects is characteristic of the sieve occlusion by phloem lectins and β-1,3-glucan callose, both of which are produced under regulation by ethylene and MYB transcription factors. Wheat PBD requires β-1,3-glucan synthase-like proteins GSL2, GSL10, and GSL12, and may also require insect-resistant mannose-binding lectins Hfr-1 and Wci-1, which can accumulate in the phloem upon aphid feeding. This study elucidates whether any of the 73 MYB genes identified previously in the common wheat Triticum aestivum genome plays a role in wheat PBD activation with regard to the GSLs and lectins. Wheat MYB genes TaMYB19, TaMYB29, and TaMYB44 are highly activated in response to infestation of English grain aphid, and their silencing facilitates aphid feeding on wheat phloem and represses wheat PBD responses. Repressed PBD is shown to decrease aphid-induced callose deposition in wheat leaf epidermis and decrease aphid-induced expression of genes GSL2, GSL10, GSL12, Hfr-1, and Wci-1 in wheat leaf tissues. Based on single gene silencing effects, TaMYB19, TaMYB29, and TaMYB44 contribute 55–82% of PBD responses. However, the contributions of TaMYB genes to PBD are eliminated by ethylene signalling inhibitors, while simultaneous silencing of the three TaMYB genes cancels the tested PBD responses. Therefore, TaMYB19, TaMYB29, and TaMYB44 are co-regulators of wheat PBD and execute this function through crosstalk with the ethylene signalling pathway.

Cytochrome P450 monooxygenases (P450s) and UDP-glycosyltransferases (UGTs) are involved in the evolution of insecticide resistance. Leptinotarsa decemlineata (Say), the Colorado potato beetle (CPB), is a notorious insect that has developed resistance to various insecticides including neonicotinoids. This study investigated whether the differentially expressed P450 genes CYP9Z140 and CYP9AY1 and UGT gene UGT321AP1, found in our transcriptome results, conferred resistance to thiamethoxam in L. decemlineata. Resistance monitoring showed that the sampled field populations of L. decemlineata adults collected from Urumqi City and Qapqal, Jimsar, and Mulei Counties of Xinjiang in 2021–2023 developed low levels of resistance to thiamethoxam with resistance ratios ranging from 6.66- to 9.52-fold. Expression analyses indicated that CYP9Z140, CYP9AY1, and UGT321AP1 were significantly upregulated in thiamethoxam-resistant populations compared with susceptible populations. The expression of all three genes also increased significantly after thiamethoxam treatment compared with the control. Spatiotemporal expression patterns showed that the highest expression of CYP9Z140 and CYP9AY1 occurred in pupae and the midgut, whereas UGT321AP1 was highly expressed in adults and Malpighian tubules. Knocking down all three genes individually or simultaneously using RNA interference increased the sensitivity of adult L. decemlineata to thiamethoxam. These results suggest that overexpression of CYP9Z140, CYP9AY1, and UGT321AP1 contributes to the development of thiamethoxam resistance in L. decemlineata and provides a scientific basis for improving new resistance management of CPB.