Between 2022 and 2023, researchers collected 35 field populations of B. tabaci from 18 major agricultural regions spanning the country, from the tropical vegetable fields of Sanya on Hainan Island to the northern plains of Inner Mongolia. The sampling covered crops as varied as eggplant, tomato, cucumber, chili pepper, sweet potato, and winter melon. Each population was subjected to laboratory bioassays against nine widely used insecticides representing six chemical classes: the biological pesticide abamectin, the neonicotinoids thiamethoxam and imidacloprid, the chloronicotinyl compound thiacloprid, the pyrethroids bifenthrin and deltamethrin, the ketoenol spirotetramat, the diamide cyantraniliprole, and the insect growth regulator pyriproxyfen. Crucially, the team tested adults, eggs, and nymphs separately, recognizing that susceptibility can differ dramatically across the whitefly’s life stages.

The methodology was rigorous and standardized. For adult bioassays, treated cotton leaf discs were placed on agar in small tubes, each receiving 40 to 50 field-collected adults, with mortality scored after 48 hours. Egg assays involved dipping leaves bearing freshly laid eggs into serial insecticide dilutions and counting unhatched embryos seven days later, while nymph assays used root-dipped cotton seedlings infested with synchronized second-instar nymphs, evaluated after two weeks. All results were compared against a laboratory-susceptible reference strain, originally collected in 2008 and never exposed to pesticides, allowing the calculation of resistance factors, the ratio of the field population’s lethal concentration to that of the susceptible baseline. Resistance was classified on a five-tier scale ranging from susceptible to very high, with resistance factors above 100 marking the most alarming category.

The good news first: abamectin remains a rare bright spot. Across 27 tested populations, adults were either fully susceptible or showed only low resistance, and several regions, including Sanya, Jinan, Hangzhou, Beijing, and Yuncheng, actually became more sensitive to the compound in 2023 than in 2022. This suggests that, when used appropriately, abamectin continues to deliver effective field control in China, a finding consistent with earlier nationwide monitoring from 2015 to 2021. In an era when many once-reliable insecticides are failing, the durability of this biological pesticide stands out.

The neonicotinoids tell a very different story. Resistance to imidacloprid ranged from a modest 1.79-fold to a staggering 255-fold in a Sanya population, with very high resistance also recorded in Yuncheng. Thiamethoxam resistance reached high levels in three populations, peaking at 71-fold, and thiacloprid resistance climbed to 140-fold in Sanya. Year-over-year comparisons revealed troubling upward trends in several regions, particularly in central and southern China, where median resistance factors for neonicotinoids exceeded 50. The authors attribute this escalation to prolonged and intensive use of these compounds, and note that cross-resistance mediated by metabolic detoxification enzymes, particularly cytochrome P450s and esterases, likely accelerates the problem. Continued reliance on neonicotinoids, they warn, risks eroding their long-term efficacy entirely.

Pyrethroid resistance presented a more mixed picture. Bifenthrin resistance remained low to moderate nationwide, peaking at around 16-fold, but deltamethrin resistance spanned an extraordinary range, from 2-fold to nearly 105-fold, with the highest value recorded in Yunnan’s Yuanmou region. Southwest China emerged as a pyrethroid hotspot, with median resistance factors exceeding 40. The researchers also compared molecular genotyping data with the bioassay phenotypes and found a crucial nuance: resistance-associated mutations alone do not fully determine phenotypic resistance. Some mutations appeared even in susceptible reference insects, indicating that genetic background, mutation frequency, and metabolic mechanisms all interact to shape real-world resistance. Molecular diagnostics, the authors conclude, must always be interpreted alongside bioassay data.

The newer chemistries, often promoted as solutions to resistance problems, showed their own warning signs. Egg-stage bioassays revealed consistently high resistance to spirotetramat, with resistance factors exceeding 300 in multiple populations and peaking at 357-fold in Suzhou, Anhui. Cyantraniliprole resistance was generally moderate, but a few populations displayed extreme values, with Hangzhou eggs showing a resistance factor above 4,000, and Tianjin above 2,000. Among nymphs, spirotetramat resistance reached 204-fold in Yueyang, while cyantraniliprole resistance peaked at 721-fold in Beijing in 2022, though it declined sharply the following year. Pyriproxyfen, an insect growth regulator used against whitefly nymphs since 1989, showed consistently high resistance across most monitored regions, with values up to 195-fold. The authors suggest that in some areas pyriproxyfen may no longer be suitable for whitefly control at all, a striking verdict for a compound with decades of market history.

Beneath the chemical story lies an evolutionary one. Genotyping of the ace1 acetylcholinesterase gene and the voltage-gated sodium channel gene revealed that resistance-associated alleles are already widespread. At the F331W locus, 15 of 18 populations were homozygous resistant, a legacy of more than 60 years of organophosphate exposure. The pyrethroid-linked mutations L925I and T929V were also common, often appearing as heterozygotes or mixed genotypes that signal ongoing selection and gene flow among populations. Equally significant was the species composition: of the 35 populations sampled, 31 were exclusively the Mediterranean (MED) cryptic species, with only four mixed MEAM1-MED populations, all from Sanya. MED, known for its superior insecticide tolerance and more efficient virus transmission, has essentially completed its displacement of MEAM1 across China, likely because it survives better under intensive neonicotinoid and pyriproxyfen spraying.

The virus dimension amplifies the concern. TYLCV, transmitted exclusively by B. tabaci, was detected in 10 of 11 tomato-derived populations, with infection rates exceeding 95 percent in nearly all of them. The virus also appeared in chili, cucumber, watermelon, and hami melon samples, though at more variable rates. Previous research has shown that TYLCV infection actually enhances MED survival and reproduction while shortening development time, creating a feedback loop in which the most insecticide-resistant vector is also the most efficient virus spreader. This dual threat, resistant insects and rampant virus, is precisely the scenario that integrated pest management programs are designed to prevent, and the study’s authors argue it demands coordinated action.

The path forward, the researchers emphasize, is resistance-informed and region-specific management. Because resistance profiles differ sharply across China’s cropping systems and climates, a one-size-fits-all spraying schedule is doomed to fail. Instead, they recommend rotating insecticides with distinct modes of action, selecting compounds according to the susceptibility of specific life stages, using molecular monitoring as an early-warning system for emerging resistance alleles, and pairing chemical control with virus suppression tactics such as removing infected plants, managing weed hosts, and reducing vector populations early in the crop cycle. Although the survey focused on China, the patterns it documents, rapid susceptibility shifts, strong regional selection pressures, immature-stage resistance, MED dominance, and widespread virus transmission, mirror challenges reported from Spain and Israel to Australia and Pakistan. Continuous surveillance, cross-regional data sharing, and adaptive management, the authors conclude, will be essential to curb further resistance escalation and protect agricultural productivity far beyond China’s borders.

Subject of Research: Nationwide monitoring of insecticide resistance, cryptic species composition, and TYLCV prevalence in Bemisia tabaci across China

Article Title: Nationwide spatiotemporal monitoring of insecticide resistance in Bemisia tabaci in China (2022–2023)

Article References: Yang, J., Li, Q., Zhang, Y., Ji, Y., Du, H., Guo, Z., Xie, W., Wang, S., Wu, Q., Zhang, Y., & Yang, X. (2026). Nationwide spatiotemporal monitoring of insecticide resistance in Bemisia tabaci in China (2022–2023). Journal of Agriculture and Food Research, 31, Article 103339. https://doi.org/10.1016/j.jafr.2026.103339

Image Credits: AI Generated

DOI: 10.1016/j.jafr.2026.103339

Keywords: Bemisia tabaci, insecticide resistance, whitefly, neonicotinoids, TYLCV, MED cryptic species, pyriproxyfen, spirotetramat, cyantraniliprole, resistance monitoring, integrated pest management, China

The research team, based at Zhejiang University, Nanjing Agricultural University and the International Center for Tropical Agriculture in Colombia, worked with the Middle East Asia Minor 1 (MEAM1) cryptic species of Bemisia tabaci, the highly efficient invasive vector of TYLCV. In their experimental setup, newly emerged whiteflies were first given a six-hour acquisition access period on TYLCV-infected tomato plants and then exposed to a range of temperatures for just one hour. Quantitative PCR measurements of viral DNA revealed a striking pattern: the amount of TYLCV in the insects climbed steadily as temperatures rose, peaking at 38 degrees Celsius. At 40 and 42 degrees, viral loads remained above the 27-degree control level but fell significantly below the 38-degree peak, suggesting that moderate heat stress is most favorable for virus accumulation while extreme heat may trigger additional countermeasures in the insect.

To understand what was happening inside the whiteflies during that critical one-hour window, the researchers turned to transcriptome sequencing. Whiteflies held at 38 degrees for one hour were compared with controls kept at the normal rearing temperature of 27 degrees. The analysis identified 62 upregulated and 25 downregulated genes, and the enriched pathways pointed squarely at the cellular stress machinery: protein processing in the endoplasmic reticulum, the longevity regulating pathway, the spliceosome and endocytosis. The differentially expressed genes in these pathways were dominated by heat shock proteins, the molecular chaperones that protect cells from thermal damage, along with lethal (2) essential for life-like proteins. The team also flagged several transcription-related genes whose altered expression could plausibly influence viral gene transcription and protein synthesis within the vector.

That last observation proved to be the key to the whole study. Heat shock protein transcription is controlled by heat shock factor, or HSF, a transcription factor that becomes activated under elevated temperatures, trimerizes and binds conserved heat shock elements in the promoters of its target genes. In the whitefly genome, the researchers identified the full-length open reading frame of BtHSF, a 2,283-base-pair gene encoding a 760-amino-acid protein of roughly 84.1 kilodaltons with a conserved HSF DNA-binding domain at residues 14 to 144. Importantly, BtHSF is expressed in the midgut and primary salivary glands, the two tissues that form the critical barriers TYLCV must cross for plant-to-plant transmission, and in which the virus has previously been shown to replicate.

The pivotal discovery came when the team used the TYLCV intergenic region as bait to screen a whitefly cDNA library in a yeast one-hybrid system. Among the proteins that bound this viral DNA sequence was HSF itself. Yeast carrying the HSF prey plasmid grew on selective medium, while control transformants did not, confirming a specific protein-DNA interaction. The researchers then scanned the viral intergenic region using the JASPAR database and identified a putative HSF binding motif, TTTTTGAA, located in the complementary sense of the region. When they mutated this motif to GCAATTGC, the activating effect of BtHSF on the viral sequence was abolished, demonstrating that the interaction depends on this specific heat shock element embedded in the viral genome.

Dual-luciferase reporter assays in Drosophila S2 cells quantified just how powerful this effect is. When BtHSF was overexpressed alongside a reporter construct driven by the wild-type TYLCV intergenic region, luciferase activity rose more than eightfold compared with the empty-vector control. The mutated intergenic region lost this responsiveness entirely. In other words, the whitefly stress-response transcription factor does not merely bind the viral genome as a passive passenger; it actively drives transcription of the viral genes downstream of the intergenic region, which encodes the instructions for replication-associated proteins and the coat protein that defines the virion.

The causal chain from temperature to viral load was then tested directly. First, the team confirmed that BtHSF controls heat shock protein expression in whiteflies: silencing BtHSF with orally delivered double-stranded RNA significantly reduced transcript levels of BtHSF itself and of most heat shock proteins tested, including several HSP70 and HSP19 family members. Conversely, heat stress above 34 degrees caused at least a 47-fold increase in heat shock protein expression, with levels rising progressively as treatment temperature increased, mirroring the pattern of virus accumulation. The researchers also found that TYLCV infection itself upregulates BtHSF expression, hinting that the virus may exploit the stress response even under normal conditions.

The decisive experiment came from knocking down BtHSF in viruliferous whiteflies. After a 48-hour feeding on dsRNA, BtHSF expression dropped by 36 percent, and the consequences for the virus were dramatic. Quantitative PCR showed significantly reduced TYLCV DNA abundance, western blotting revealed a marked decrease in viral coat protein, and immunofluorescence staining of dissected tissues showed that the proportion of virus-positive midguts fell from 75 percent to 52 percent, while virus-positive primary salivary glands dropped from 66 percent to 46 percent. Because the salivary glands are the final gateway through which the virus exits the insect and enters a new plant, this reduction in tissue-level infection directly implicates HSF in the transmission cycle, not merely in viral persistence within the vector.

What makes this mechanism especially noteworthy is its apparent conservation across biological systems. The authors point out that heat shock factor 1 has been implicated in the replication of several animal viruses: it supports dengue virus and vaccinia virus replication in their hosts, binds the long terminal repeat promoter of HIV-1, and activates the BamHI-Q promoter of Epstein-Barr virus to promote viral transcription. The finding that a plant DNA virus co-opts the same stress-activated transcription factor in its insect vector suggests that HSF-mediated promotion of viral replication may be a general feature of virus-host and virus-vector interactions, spanning organisms as distant as whiteflies and humans. The team also notes that other heat-responsive transcription factors identified in their RNA-seq data, such as ATF3, ZBED1 and DRGX, may modulate virus accumulation indirectly, though their roles remain to be tested.

The study also leaves open questions that will shape future work. Viral loads declined above 38 degrees, which the authors attribute to possible strengthening of vector immunity or the physiological costs of massive heat shock protein production at extreme temperatures. And while the MEAM1 whitefly was the focus here, the MED species, which has an even broader distribution in China, carries an HSF with an identical DNA-binding domain, making it likely, though unproven, that the same mechanism operates there. For agriculture, the implications are sobering: as heat waves intensify and expand, the molecular switch identified in this study could help explain why vector-borne plant viruses surge in warm seasons and warm regions. Understanding that HSF sits at the junction of insect stress physiology and viral propagation offers a potential target for interventions aimed at breaking the temperature-virus-vector link, whether through breeding, vector control or antiviral strategies that disrupt the transcription factor’s grip on the viral genome.

Subject of Research: How heat stress activates heat shock factor to promote tomato yellow leaf curl virus accumulation in its whitefly vector

Article Title: Heat stress promotes the accumulation of tomato yellow leaf curl virus in its insect vector by activating heat shock factor

Article References: Heat stress promotes the accumulation of tomato yellow leaf curl virus in its insect vector by activating heat shock factor. (n.d.). https://doi.org/10.1007/s44297-024-00039-8

Image Credits: AI Generated

DOI: 10.1007/s44297-024-00039-8

Keywords: tomato yellow leaf curl virus, TYLCV, Bemisia tabaci, whitefly, heat stress, heat shock factor, heat shock proteins, vector competence, plant virus, begomovirus, transcription factor, climate change