Resistance Monitoring for Eight Insecticides on the Sweetpotato Whitefly (Hemiptera: Aleyrodidae) in China

Knockdown of one cytochrome P450 gene CYP6DW4 increases the susceptibility of Bemisia tabaci to dimpropyridaz, a novel pyridazine pyrazolecarboxamide insecticide

Bemisia tabaci is a formidable insect pest worldwide, and it exhibits significant resistance to various insecticides. Dimpropyridaz is a novel pyridazine pyrazolecarboxamide insecticide used against sucking insect pests, but there is little information regarding its metabolic detoxification in arthropods or cross-resistance with other insecticides. In this study, we found that dimpropyridaz shows no cross-resistance with three other popular insecticides, namely abamectin, cyantraniliprole, and flupyradifurone. After treatment of B. tabaci adults with a high dose of dimpropyridaz, higher cytochrome P450 monooxygenase (P450) activity was detected in the survivors, and the expression of the P450 gene CYP6DW4 was highly induced. Cloning and characterization of the full-length amino acid sequence of CYP6DW4 indicated that it contains conserved domains typical of P450 genes, phylogenetic analysis revealed that it was closely related to a B. tabaci protein, CYP6DW3, known to be involved in detoxification of imidacloprid. Silencing of CYP6DW4 by feeding insects with dsRNA significantly increased the susceptibility of B. tabaci to dimpropyridaz. In addition, homology modeling and molecular docking analyses showed the stable binding of dimpropyridaz to CYP6DW4, with binding free energy of -6.65 kcal/mol. Our findings indicate that CYP6DW4 plays an important role in detoxification of dimpropyridaz and possibly promotes development of resistance in B. tabaci.

Dynamic monitoring of the insecticide resistance status of Bemisia tabaci across China from 2019-2021

BACKGROUND

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a major agricultural insect pest that causes severe economic losses worldwide. Several insecticides have been applied to effectively control this key pest. However, owing to the indiscriminate use of chemical insecticides, B. tabaci has developed resistance against these chemical compounds over the past several years.

RESULTS

From 2019 to 2021, 23 field samples of B. tabaci were collected across China. Twenty species were identified as the Mediterranean 'Q' type (MED) and three were identified as MED/ Middle East-Asia Minor 1 mixtures. Subsequently, resistance of the selected populations to different insecticides was evaluated. The results showed that 13 populations developed low levels of resistance to abamectin. An overall upward trend in B. tabaci resistance toward spirotetramat, cyantraniliprole and pyriproxyfen was observed. In addition, resistance to thiamethoxam remained low-to-moderate in the 23 field populations.

CONCLUSION

These findings suggest that the overall resistance of the field-collected B. tabaci populations has shown an upward trend over the years in China. We believe our study can provide basic data to support integrated pest management and insecticide resistance management of field B. tabaci in China. © 2023 Society of Chemical Industry.

Cytochrome P450 CYP6DB3 was involved in thiamethoxam and imidacloprid resistance in Bemisia tabaci Q (Hemiptera: Aleyrodidae)

High level resistance for a variety of insecticides has emerged in Bemisia tabaci, a globally notorious insect. Neonicotinoid insecticides have been applied widely to control B. tabaci. Whether a differentially expressed gene CYP6DB3 discovered from transcriptome data of B. tabaci is involved in the resistance to neonicotinoid insecticides remains unclear. In the study, CYP6DB3 expression was significantly up-regulated in both thiamethoxam- and imidacloprid-resistant strains relative to the susceptive strains. We also found that CYP6DB3 expression was up-regulated after B. tabaci adults were exposed to thiamethoxam and imidacloprid. Moreover, knocking down CYP6DB3 expression via feeding corresponding dsRNA significantly reduced CYP6DB3 mRNA levels by 34.1%. Silencing CYP6DB3 expression increased the sensitivity of B. tabaci Q adults against both thiamethoxam and imidacloprid. Overexpression of CYP6DB3 gene reduced the toxicity of imidacloprid and thiamethoxam to transgenic D. melanogaster. In addition, metabolic studies showed that CYP6DB3 can metabolize 24.41% imidacloprid in vitro. Collectively, these results strongly support that CYP6DB3 plays an important role in the resistance of B. tabaci Q to imidacloprid and thiamethoxam. This work will facilitate a deeper insight into the part of cytochrome P450s in the evolution of insecticide resistance and provide a theoretical basis for the development of new integrated pest resistance management.

Insecticide Resistance and Its Management in Two Invasive Cryptic Species of Bemisia tabaci in China

The sweet potato whitefly Bemisia tabaci is a major agricultural pest with a wide host range throughout the world. The species designation for B. tabaci includes numerous distinct cryptic species or biotypes. Two invasive B. tabaci biotypes, MEAM1 (B) and MED (Q), were found in China at the end of the 20th century and at the beginning of the 21st century. MEAM1 (B) and MED (Q) show higher pesticide resistance levels than native strains, and the levels of resistance vary with changes in insecticide selection pressure. Recent studies have revealed metabolic resistance mechanisms and target site mutations in invasive B. tabaci strains that render them resistant to a range of insecticides and have uncovered the frequency of these resistance-related mutations in B. tabaci populations in China. Novel pest control agents, such as RNA-based pesticides and nano-pesticides, have achieved effective control effects in the laboratory and are expected to be applied for field control of B. tabaci in the future. In this review, we discuss the mechanisms of resistance developed by these invasive B. tabaci populations since their invasion into China. We also provide suggestions for ecologically sound and efficient B. tabaci control.

Resistance to dinotefuran in Bemisia tabaci in China: status and characteristics

BACKGROUND

Bemisia tabaci (Gennadius) is a serious agricultural pest worldwide. Neonicotinoids are the most important new class of synthetic insecticides used in the management of B. tabaci. However, B. tabaci populations have developed resistance to various active ingredients in neonicotinoids following long-term and widespread application.

RESULTS

Dinotefuran exhibited high toxicity against most B. tabaci field populations. One population (Din-R) with a high level of resistance to dinotefuran (255.6-fold) was first identified in the field. The Din-R population exhibited medium to high levels of resistance to all the tested neonicotinoid insecticides and a high level of resistance to spinetoram. Genetic inheritance analysis revealed that resistance to dinotefuran was incompletely recessive and polygenic. The synergist piperonyl butoxide significantly increased the toxicity of dinotefuran to Din-R. P450 activity in the Din-R population was 2.19-fold higher than in the susceptible population. RNA-sequencing analysis showed that 12 P450 genes were significantly upregulated in the Din-R population, of which CYP6DW5, CYP6JM1 and CYP306A1 were found to exhibit more than 3.00-fold higher expression in Din-R when using a reverse transcription quantitative real-time polymerase chain reaction. Expression of eight P450 genes was obviously induced by dinotefuran, and CYP6DW5 showed the highest expression level. After knockdown of CYP6DW5 in Din-R, the toxicity of dinotefuran increased significantly.

CONCLUSION

P450 had a crucial role in dinotefuran resistance in B. tabaci, and CYP6DW5 was involved in the resistance. These results provide important information for the management of resistance in B. tabaci and improve our understanding of the resistance mechanism of dinotefuran. © 2022 Society of Chemical Industry.

Differential insecticide resistance in Bemisia tabaci (Hemiptera: Aleyrodidae) field populations in the Punjab Province of Pakistan

The cotton whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) has a propensity for developing high-level resistance to insecticides. Management of B. tabaci in cotton grown in Pakistan depends on insecticide use, resistance monitoring has become essential to minimize the development of resistance. In this study, resistance was monitored in adult whiteflies collected from cotton fields in the Bahawalpur, Faisalabad, Lodhran, Multan, and Vehari districts of the Punjab Province, Pakistan during 2017, 2018, and 2019. Resistance monitoring was carried out for two insect growth regulators (pyriproxyfen and buprofezin) four neonicotinoids acetamiprid, imidacloprid, thiamethoxam, thiacloprid, and the historically used pyrethroid, bifenthrin and organophosphate, chlorpyrifos. Results based on resistance ratio (RR) showed that moderate to high level of resistance against noenicitinoids insecticides have been observed in all four districts while whiteflies exhibited very low to low resistance to pyriproxyfen and buprofezin. The RRs for acetamiprid, imidacloprid, thiamethoxam, thiacloprid varied from 7.60 to 50.99, 19.32 to 65.72, 17.18 to 54.65 and 6.49-47.49-fold, respectively. Bifenthrin and chlorpyrifos showed very low toxicity against whiteflies in all districts except Faisalabad, with RRs of 12.28-50.56-fold and 7.94-26.24-fold, respectively. The results will facilitate 'smart' selection and guide rates of insecticide applications for whitefly management in cotton for effective whitefly management while also delaying the development of resistance.

Heat-shock protein 70-a hub gene-underwent adaptive evolution involved in whitefly-wild tomato interaction

BACKGROUND

The whitefly Bemisia tabaci causes severe damage to cultivated tomato plants, but actively avoids the wild tomato Solanum habrochaites. Moreover, the mortality of whitefly increases significantly after feeding with the wild tomato. However, additional experiments are warranted to more carefully elucidate the specific molecular elements underlying the interaction between whitefly and wild tomato.

RESULTS

Our results showed that S. habrochaites significantly increases the mortality of whitefly adults and decreases both their fertility and fecundity. In addition, the expression of stress-response genes in whitefly after exposure to S. habrochaites was analyzed using RNA sequencing. Weighted gene co-expression network analysis was conducted to identify the hub genes to determine their potential associations with the mortality of whitefly. These results suggested that the expression of heat-shock protein (HSP), multicopper oxidase, and 2-Oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline (OHCU) decarboxylase genes were induced in whitefly. To validate the gene associations with whitefly mortality, a high-throughput in vivo model system and RNAi-based gene silencing were used. The results revealed that the RNAi-mediated depletion of the HSP gene, which belongs to the HSP70 subfamily, increased the mortality of whitefly. Furthermore, the selection pressure analysis showed that a total of five amino acid sites of positive selection were identified, three of which were located in the nucleotide-binding domain and the other two in the substrate-binding domain.

CONCLUSIONS

This is the first report on the potential implication of HSPs in whitefly-wild plant interactions. This study could more precisely identify the molecular mechanisms of whitefly in response to wild tomatoes. © 2022 Society of Chemical Industry.

The Toxicity, Sublethal Effects, and Biochemical Mechanism of β-Asarone, a Potential Plant-Derived Insecticide, against Bemisia tabaci

Bemisia tabaci is a threat to agriculture worldwide because of its potential to cause devastating damage to various crops. β-asarone is a bioactive pesticidal chemical originating from Acorus calamus (or “Sweet Flag”) plants, and it displays significant lethal effects against insect pests. In this study, we established a baseline of susceptibility to β-asarone from China and patterns of cross-resistance to other popular insecticides. We found that all the 12 field-collected B. tabaci populations exhibited high susceptibility to β-asarone, and there was no cross-resistance detected for other tested insecticides. We subsequently evaluated the sublethal effects of β-asarone on physiology and biochemistry via LC₂₅ treatment (4.7 mg/L). LC₂₅ of β-asarone resulted in prolonged developmental duration and decreased survival rates in B. tabaci nymphs, pseudopupae, and adults. Significant reductions in oviposition duration, fecundity, and hatchability were also observed. Additionally, the metabolic enzyme activity and expression profiles of selected cytochrome P450 monooxygenase (P450) genes following the LC₂₅ treatment of β-asarone suggest that enhanced detoxification via P450s could be involved in the observed sublethal effects. These findings demonstrate the strong toxicity and significant sublethal effects of β-asarone on B. tabaci and suggest that the induced overexpression of P450 genes could be associated with the response to β-asarone.

Comparative study of neonicotinoid insecticides (NNIs) and NNI-Related substances (r-NNIs) in foodstuffs and indoor dust

Comparative studies of neonicotinoid insecticides (NNIs) and NNI-related substances (r-NNIs) in foodstuffs and indoor dust are rare. Herein, we investigated the feature fragmentations of nine NNIs in high-energy collision dissociation cells via high-resolution orbitrap mass spectrometry and observed that NNIs can consistently generate several feature fragments (e.g., C6H5NCl+, C4H3NSCl+, and C6H5NF3+). Consequently, NNIs and r-NNIs were comprehensively (targeted, suspect, and feature fragment-dependent) detected in 107 foodstuff and 49 indoor dust samples collected from Nanjing City (eastern China). We fully or tentatively identified 9 target NNIs and 5 r-NNIs in these samples. NNIs and r-NNIs were detected in 93.5% of the analyzed foodstuff samples, and high concentrations were detected in vegetables (mean: 409 ng/g wet weight [ww]) and fruits (127 ng/g ww). Regarding indoor dust, imidacloprid and acetamiprid exhibited extremely high detection frequencies and contamination levels, and the highest mean concentrations of NNIs and r-NNIs were detected in dormitory samples. Based on the NNI and r-NNI concentrations in the analyzed samples, the mean estimated daily intake values for Chinese adults and children via dietary intake and dust ingestion were 2080-8190 ng/kg bw/day and 378-2680 pg/kg bw/day, respectively.

Metabolic Resistance in Abamectin-Resistant Bemisia tabaci Mediterranean from Northern China

Abamectin, produced by the soil-dwelling actinomycete Streptomyces avermitilis, belongs to the macrocyclic lactones class of pesticides, has nematocidal, acaricidal, and insecticidal activity, and is highly effective when used against targeted species. Bemisia tabaci, the tobacco whitefly, is a highly destructive insect to agricultural production worldwide, and various insecticide-resistant strains have been identified in China. Here, we monitored levels of resistance to abamectin in twelve field-collected B. tabaci populations from northern China, and confirmed that, compared with the lab reference strain, six field populations exhibited strong abamectin resistance, while the other six exhibited low-to-medium resistance. Among these, the Xinzheng (XZ) population displayed about a 40-fold increased resistance to abamectin, and experienced significant cross-resistance to chlorpyrifos and imidacloprid. The abamectin resistance of XZ was found to be autosomal and incompletely dominant. Metabolic enzyme and synergism tests were conducted, and two metabolic enzymes, glutathione S-transferase and P450 monooxygenase, were found to be conducive to the field-developed abamectin resistance of the XZ population. The above results provide valuable information that can be used in identifying new pest control strategies and delaying the evolution of resistance to abamectin in field populations of whiteflies.

Area-wide insecticide resistance and endosymbiont incidence in the whitefly Bemisia tabaci MEAM1 (B biotype): A Neotropical context

Agriculture insecticides are used against insect pest species, but are able to change community structure in contaminated habitats, and also the genetic pool of exposed individuals. In fact, the latter effect is a relevant tool to in situ biomonitoring of pollutant contamination and impact, besides its practical economic and management concerns. This takes place because the emergence of individuals with resistance to insecticides is particularly frequent among insect pest species and usually enhances insecticide overuse and crop losses. Pest insects of global prominence such as whiteflies are a focus of attention due to problems with insecticide resistance and association with endosymbionts, as the case of the invasive putative species Bemisia tabaci MEAM1. The scenario is particularly complex in the Neotropics, where insecticide use is ubiquitous, but whose spatial scale of occurrence is usually neglected. Here we explored the spatial-dependence of both phenomena in MEAM1 whiteflies recording resistance to two widely used insecticides, lambda-cyhalothrin and spiromesifen, and endosymbiont co-occurrence. Resistance to both insecticides was frequent exhibiting low to moderate frequency of lambda-cyhalothrin resistance and moderate to high frequency of spiromesifen resistance. Among the prevailing whitefly endosymbionts, Wolbachia, Cardinium and Arsenophonus were markedly absent. In contrast, Hamiltonella and Rickettsia prevailed and their incidence was correlated. Furthermore, Rickettsia endosymbionts were particularly associated with lambda-cyhalothrin susceptibility. These traits were spatially dependent with significant variation taking place within an area of about 700 Km². Such findings reinforce the notion of endosymbiont-associated resistance to insecticides, and also of their local incidence allowing spatial mapping and locally-targeted mitigation.

Knockdown of UGT352A5 decreases the thiamethoxam resistance in Bemisia tabaci (Hemiptera: Gennadius)

Uridine diphosphate (UDP)-glycosyltransferases (UGTs), which are major phase II detoxification enzymes, have been implicated in the glycosylation of lipophilic endobiotics and xenobiotics and thus potentially lead to the evolution of insecticide resistance. In this study, we identified and cloned two putative UGT genes from transcriptome data which are named UGT352A4 and UGT352A5. As demonstrated by qRT-PCR, two UGT genes were over-expressed in the thiamethoxam-resistant (THQR) strain relative to the susceptible (THQS) strain. Moreover, the induction experiment revealed that the expression of the UGT352A5 gene was significantly increased following exposure to thiamethoxam in the THQR strain. Furthermore, the expression of both UGT352A4 and UGT352A5 was downregulated after RNA interference, whereas only the silencing of UGT352A5 resulted in a noticeable increase in the mortality of THQR adults. Our results represent the first line of evidence showing that UGT352A5 might be responsible for conferring thiamethoxam resistance in B. tabaci. The results will be shed new insights for obtaining a better understanding of the role of UGTs in the evolution of insecticide resistance and developing new insect resistance management tactics within the sustainable integrated pest management framework.

Annual analysis of field-evolved insecticide resistance in Bemisia tabaci across China

BACKGROUND

Over recent decades, many efficacious insecticides have been applied for control of Bemisia tabaci, one of the most notorious insect pests worldwide. Field-evolved insecticide resistance in B. tabaci has developed globally, but remains poorly understood in China.

RESULTS

In this study, a total of 30 field samples of the whitefly Bemisia tabaci from eight provinces of China were collected in 2015 to 2018. Twenty-four of the populations were identified as Mediterranean, 'Q' type (MED), three were Middle East-Asia Minor 1, 'B' type (MEAM1), and three were mixtures of MED/ MEAM1. After identifying whether they belong to MED or MEAM1, the selected individuals were used in bioassays assessing insecticide resistance to abamectin, thiamethoxam, spirotetramat, cyantraniliprole, and pyriproxyfen. Our results showed that all populations in the eight regions had little or no resistance to abamectin; abamectin resistance was highest in the Hunan (Changsha) and Hubei (Wuhan) regions and was lowest in the island region of Hainan (Sanya). The resistance of B. tabaci to spirotetramat, cyantraniliprole, and pyriproxyfen increased each year. The resistance to thiamethoxam remained low because of the high LC₅₀ value for the laboratory strain.

CONCLUSION

These findings suggest that a rotation system using efficacious B. tabaci insecticides with differing mode of actions ought to be implemented for sustainable control to reduce the potential of resistance development. This study provides important data to support the integrated pest management and insecticide resistance management of B. tabaci in China. © 2021 Society of Chemical Industry.

Amplicon sequencing detects mutations associated with pyrethroid resistance in Bemisia tabaci (Hemiptera: Aleyrodidae)

BACKGROUND

Bemisia tabaci (Gennadius) is a major damaging agricultural pest that exhibits high resistance to pyrethroid insecticides. L925I (TTA to ATA) and T929V (ACT to GTT) mutations in the para-type voltage-gated sodium channel (VGSC) are associated with resistance of B. tabaci to pyrethroids. Amplicon sequencing is a reliable and highly efficient method to detect the frequency of mutations linked with insecticide resistance.

RESULTS

Similar frequencies of L925I and T929V mutations were obtained by amplicon sequencing and Sanger sequencing (L925I: 0.3548 vs 0.3619; T929V: 0.6140 vs 0.6381) with overlap of 95% confidence interval in the SX population of B. tabaci. In five populations of B. tabaci from China, the maximum and minimum frequencies of the two mutations were found in the LN (L925I: 0.1126; T929V: 0.8834) and JS (L925I: 0.8776; T929V: 0.1166) populations by amplicon sequencing. However, there was no significant difference in frequencies between the L925I and T929V mutations. The sum frequency of L925I and T929V exceeded 0.9688 in all populations. In addition, a combining mutation, L925 + T929V (L925I and T929V located in same allele), was found in five populations by amplicon sequencing even though its highest frequency was only 0.0157.

CONCLUSION

We established an efficient approach for detecting frequency of mutation by amplicon sequencing. The frequencies of L925I and T929V in VGSC associated with pyrethroid resistance were detected in this study, which could provide foundational data for resistance management of B. tabaci. © 2021 Society of Chemical Industry.

Genome-Wide Identification and Analysis of Chitinase-Like Gene Family in Bemisia tabaci (Hemiptera: Aleyrodidae)

Chitinases are of great importance in chitin degradation and remodeling in insects. However, the genome-wide distribution of chitinase-like gene family in Bemsia tabaci, a destructive pest worldwide, is still elusive. With the help of bioinformatics, we annotated 14 genes that encode putative chitinase-like proteins, including ten chitinases (Cht), three imaginal disk growth factors (IDGF), and one endo-β-N-acetylglucosaminidase (ENGase) in the genome of the whitefly, B. tabaci. These genes were phylogenetically grouped into eight clades, among which 13 genes were classified in the glycoside hydrolase family 18 groups and one in the ENGase group. Afterwards, developmental expression analysis suggested that BtCht10, BtCht5, and BtCht7 were highly expressed in nymphal stages and exhibit similar expression patterns, implying their underlying role in nymph ecdysis. Notably, nymphs exhibited a lower rate of survival when challenged by dsRNA targeting these three genes via a nanomaterial-promoted RNAi method. In addition, silencing of BtCht10 significantly resulted in a longer duration of development compared to control nymphs. These results indicate a key role of BtCht10, BtCht5, and BtCht7 in B. tabaci nymph molting. Our research depicts the differences of chitinase-like family genes in structure and function and identified potential targets for RNAi-based whitefly management.

Evaluating Acylsugars-Mediated Resistance in Tomato against Bemisia tabaci and Transmission of Tomato Yellow Leaf Curl Virus

The sweetpotato whitefly, Bemisia tabaci, is a major pest of cultivated tomato. Whitefly feeding-related injuries and transmission of viruses including tomato yellow leaf curl virus (TYLCV) cause serious losses. Management strategy includes planting resistant cultivars/hybrids. However, TYLCV resistance is incomplete and whiteflies on TYLCV-resistant cultivars/hybrids are managed by insecticides. Acylsugars'-mediated resistance against whiteflies has been introgressed from wild solanums into cultivated tomato. This study evaluated acylsugar-producing tomato lines with quantitative trait loci (QTL) containing introgressions from Solanum pennellii LA716, known to alter acylsugars' levels or chemistry. Evaluated acylsugar-producing lines were the benchmark line CU071026, QTL6/CU071026-a CU071026 sister line with QTL6, and three other CU071026 sister lines with varying QTLs-FA2/CU71026, FA7/CU071026, and FA2/FA7/CU071026. Non-acylsugar tomato hybrid Florida 47 (FL47) was also evaluated. Acylsugars' amounts in FA7/CU071026 and FA2/FA7/CU071026 were 1.4 to 2.2 times greater than in other acylsugar-producing lines. Short chain fatty acid, i-C5, was dominant in all acylsugar-producing lines. Long chain fatty acids, n-C10 and n-C12, were more abundant in FA7/CU071026 and FA2/FA7/CU071026 than in other acylsugar-producing lines. Whiteflies preferentially settled on non-acylsugar hybrid FL47 leaves over three out of five acylsugar-producing lines, and whiteflies settled 5 to 85 times more on abaxial than adaxial leaf surface of FL47 than on acylsugar-producing lines. Whiteflies' survival was 1.5 to 1.9 times lower on acylsugar-producing lines than in FL47. Nevertheless, whiteflies' developmental time was up to 12.5% shorter on acylsugar-producing lines than on FL47. TYLCV infection following whitefly-mediated transmission to acylsugar-producing lines was 1.4 to 2.8 times lower than FL47, and TYLCV acquisition by whiteflies from acylsugar-producing lines was up to 77% lower than from FL47. However, TYLCV accumulation in acylsugar-producing lines following infection and TYLCV loads in whiteflies upon acquisition from acylsugar-producing lines were not different from FL47. Combining TYLCV resistance with acylsugars'-mediated whitefly resistance in cultivated tomato could substantially benefit whiteflies and TYLCV management.

Cross-resistance and biochemical mechanism of resistance to cyantraniliprole in a near-isogenic line of whitefly Bemisia tabaci Mediterranean (Q biotype)

Bemisia tabaci, sweetpotato whitefly, is one notorious insect pest on a series of crops worldwide, and many populations show high resistance to various insecticides. The cyantraniliprole-resistant strain of B. tabaci SX-R (138.4-fold) was obtained by selections with an outdoor-collected cyantraniliprole resistant population. By crossing and repeated backcrossing to a susceptible MED-S strain, the trait of cyantraniliprole resistance from SX-R was moved into MED-S to establish one near-isogenic line (CYAN-R). MED-S and CYAN-R were utilized to build patterns of cross-resistance, CYAN-R strain exhibited 63.317-fold resistance to cyantraniliprole, but no cross-resistance to several other successfully commercialized chemical agents. After that significant inhibition of cyantraniliprole resistance by piperonyl butoxide (PBO) and increased cytochrome P450 (3.4-fold) were observed in CYAN-R strain, indicating putative involvement of P450 in detoxification. Furthermore, five published detoxification-related P450 genes in B. tabaci, CYP4C64, CYP6CM1, CYP6CX1, CYP6CX4, and CYP6DZ7 were selected and expression levels of them were measured for exploring mechanisms of cyantraniliprole resistance. Compare with MED-S, no significant overexpression of the five P450 genes was observed in the CYAN-R strain. Above results could be conductive to study on mechanism of cyantraniliprole resistance and will be very helpful for the management of whitefly.

Monitoring insecticide resistance and diagnostics of resistance mechanisms in Bemisia tabaci Mediterranean (Q biotype) in China

Bemisia tabaci is one of notorious agricultural insect pests in China, and the strategies of management largely depend on application of insecticides. In order to assess levels of resistance in field populations of B. tabaci to six insecticides including abamectin, cyantraniliprole, pymetrozine, imidacloprid, chlorpyrifos and bifenthrin, we monitored the susceptibility to all tested insecticides in five field populations across China and the results indicated that field populations of B. tabaci have developed various levels of resistance to each chemical agent. Furthermore, para-type voltage gated sodium channel mutations (L925I and T929V) and acetylcholinesterase ace1 mutation (F331W) were confirmed, and expression levels of CYP6CM1, CYP4C64, GSTd7 and ABCG3 were detected for investigating mechanisms of imidacloprid resistance in the five field-collected populations. The results showed that, in all tested populations, frequencies of F331W were 100%, and the frequencies of the L925I and T929V were in the range of 28.5 to 47.0% and 11.0 to 53.5%, respectively. Moreover, CYP6CM1 and CYP4C64 were significantly overexpressed in two tested populations, respectively, and GSTd7 was significantly overexpressed in one population. No overexpression of ABCG3 was observed in all the populations. Above results provided valuable insight into the current status of insecticide resistance and could be contributed to design strategies of management for B. tabaci.

Development and Fitness of the Parasitoid, Encarsia formosa (Hymenoptera: Aphelinidae), on the B and Q of the Sweetpotato Whitefly (Hemiptera: Aleyrodidae)

Encarsia formosa Gahan is an important endoparasitoid of the whitefly, Bemisia tabaci Gennadius. In the present study, we compared the fitness and population parameters of E. formosa when parasitizing the two most invasive and destructive whitefly species in China, the B and Q of B. tabaci. We also studied whether natal host influenced on parasitism and host-feeding capacities of E. formosa on B. tabaci B versus Q. Age-stage life table analysis indicated that E. formosa developmental duration was shorter, fecundity was higher, and longevity was greater on B. tabaci B than on Q. The life table parameters, including the intrinsic rate of increase (r), finite rate of increase (λ), net reproduction rate (R0), and the mean generation time (T), indicated that the fitness of E. formosa on B. tabaci B is higher than B. tabaci Q. We also found that the host species used to rear E. formosa affected the parasitoid's subsequent parasitism and host feeding on B. tabaci B and Q. When E. formosa were reared on B. tabaci B, its subsequent parasitism rate on third-instar nymphs was significantly higher on B. tabaci B than on Q. These results will be useful for managing the biological control of B. tabaci in the field.

Toxicity of seven insecticides to different developmental stages of the whitefly Bemisia tabaci MED (Hemiptera: Aleyrodidae) in multiple field populations of China

Chemical control is important in the management of the tobacco whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). Susceptibility of B. tabaci to insecticides may vary among different developmental stages and geographical populations. In this study, we examined toxicity of seven commonly-used insecticides to B. tabaci MED in four field populations from China. Avermectin has high level of toxicity to all stages of B. tabaci MED in all four populations. Cyantraniliprole and sulfoxaflor have high toxicity to adults. Spirotetramat, cyantraniliprole and flonicamid have high toxicity to nymphs but not adults. Acetamiprid, cyantraniliprole and sulfoxaflor have high toxicity to eggs. However, the relative toxicity of B. tabaci MED to these chemicals varied across different populations, with little consistency in population differences across developmental stages. Our findings together with some instances where LC₉₅ values were higher than field recommended dosages indicate field-evolved resistance to insecticides (such as thiamethoxam and sulfoxaflor) and stage-specific mechanisms that will influence effective control of B. tabaci MED by insecticides.

Photochemistry of Solid Films of the Neonicotinoid Nitenpyram

The environmental fates of nitenpyram (NPM), a widely used neonicotinoid insecticide, are not well-known. A thin solid film of NPM deposited on a germanium attenuated total reflectance (ATR) crystal was exposed to radiation from a low-pressure mercury lamp at 254 nm, or from broadband low pressure mercury photolysis lamps centered at 350 or 313 nm. The loss during photolysis was followed in time using FTIR. The photolysis quantum yields (ϕ), defined as the number of NPM molecules lost per photon absorbed, were determined to be (9.4 ± 1.5) × 10^-4 at 350 nm, (1.0 ± 0.3) × 10^-3 at 313 nm, and (1.2 ± 0.4) × 10^-2 at 254 nm (±2σ). Imines, one with a carbonyl group, were detected as surface-bound products and gaseous N₂O was generated in low (11%) yield. The UV-vis absorption spectra of NPM in water was different from that in acetonitrile, dichloromethane, and methanol, or in a thin solid film. The photolytic lifetime of solid NPM at a solar zenith angle at 35° is calculated to be 36 min, while that for NPM in water is 269 min, assuming that the quantum yield is the same as in the solid. Thus, there may be a significant sensitivity to the medium for photolytic degradation and the lifetime of NPM in the environment.

Lethal and Sublethal Effects of Clothianidin on the Development and Reproduction of Bemisia tabaci (Hemiptera: Aleyrodidae) MED and MEAM1

The Bemisia tabaci (Gennadius) cryptic species complex includes important crop pests, and among them, the cryptic species Mediterranean (MED) and Middle East-Asia Minor 1 (MEAM1) cause substantial crop losses in China. The second-generation neonicotinoid clothianidin acts as an agonist of the nicotinic acetylcholine receptor in the insect nervous system and has both stomach and contact activity. In this study, the toxicity of clothianidin and five other insecticides to MED and MEAM1 was examined. The sublethal effects of clothianidin on the development and reproduction of MED and MEAM1 were also investigated. Among the six insecticides tested, clothianidin showed toxicities to both MED and MEAM1 adults with LC50 values of 5.23 and 5.18 mg/liter, respectively. The sublethal effects of clothianidin were assessed by treating MED and MEAM1 adults with the LC25 of 1.58 and 1.13 mg/liter, respectively. The LC25 treatments accelerated the development of the F1 generation but reduced survival and fecundity of both species. Our results indicate that clothianidin could be useful for the management of B. tabaci MED and MEAM1.

RNA interference of glutamate-gated chloride channel decreases abamectin susceptibility in Bemisia tabaci

The Bemisia tabaci (Gennadius) cryptic species complex comprises very destructive insect pests of agricultural crops worldwide and has been found to be resistant to various insecticides in China. Abamectin is one of the most widely used insecticides for insect pest control and the glutamate-gated chloride channel (GluCl) in insects was presumed to be the main target site of abamectin. In this study, a 1353bp full-length cDNA encoding GluCl (named BtGluCl, GenBank ID: MF673854) was cloned and characterized from B. tabaci. BtGluCl encodes 450 amino acids, which shares 71-81% identity with other insect GluCl isoforms. Spatial and temporal expression revealed BtGluCl was highly expressed in the 4th nymphal instar and adult head, and the least expressed in the 1st nymphal instar and adult leg. Dietary ingestion of dsBtGluCl significantly reduced the mRNA level of BtGluCl in the treated adults by 62.9% and greatly decreased abamectin-induced mortality. Thus, our results could be conducive to further understanding the mechanisms of resistance to abamectin in arthropods.