Cross-resistance between cyenopyrafen and pyridaben in the twospotted spider mite Tetranychus urticae (Acari: Tetranychidae)

Monitoring detoxification enzyme levels and resistance of Tetranychus urticae against some METI-group chemicals in Türkiye cotton fields

Acaricides used against Tetranychus urticae Koch, 1836 (Acari: Tetranychidae) in cotton fields cause control failure over time. To determine the resistance status of T. urticae populations to tebufenpyrad and bifenazate, different populations collected from Aydın (AYD), Adana (ADA), Şanlıurfa (SAN), and Diyarbakır (DIY) provinces of Türkiye, between 2019 and 2020, were subjected to diagnostic dose bioassays. Firstly, the spider mites were eliminated with a discriminating dose. Afterwards, LC50 and LC90 of the remaining populations were determined and the ten highest resistant populations were selected. The highest phenotypic resistance to bifenazate was observed in AYD4 and DIY2 (LC50 57.14 mg L- 1 with 85.01-fold and LC50 30.15 mg L- 1with 44.86-fold, respectively), while the lowest phenotypic resistance was found in SAN6 (LC50 1.5 mg L- 1; 2.28-fold). Considering the phenotypic resistance to tebufenpyrad, the highest resistance was found in AYD4 population (LC50 96.81 mg L- 1; 12.92-fold), while the lowest - in DIY28 population (LC50 21.23 mg L- 1; 2.83-fold). In pharmacokinetic studies, the ADA16 population was compared with the sensitive German Susceptible Strain population and it was determined that carboxylesterase activity was statistically higher (1.46 ± 0.04 nmol/min/mg protein enzyme activation 2.70-fold). The highest activation of glutathione S-transferase was detected in ADA16 (1.49 ± 0.01 nmol/min/mg protein; 2.32-fold). No mutations were found in PSST (METI 1), the point mutation site for tebufenpyrad, and Cytb (METI 3), the point mutation site for bifenazate. In terms of phenotypic resistance, bifenazate was found to be moderately resistant in two populations (85.01 and 44.86-fold), while tebufenpyrad was moderately resistant in one population (12.92-fold). This study showed that both acaricides are still effective against T. urticae populations.

Novel Acaricidal Silico-Containing Pyrazolyl Acrylonitrile Derivatives Identified through Rational Carbon-Silicon Bioisosteric Replacement Strategy

The identification of novel pyrazolyl acrylonitrile acaricides with improved properties is of great value for the control of phytophagous mites. A series of innovative silicon-containing pyrazolyl acrylonitriles were rationally designed by applying a bioisosteric carbon-silicon replacement strategy and prepared based on novel synthetic methodology. As a result of our research, we discovered compound A25 which possesses outstanding acaricidal activity. With an LC50 value of 0.062 mg/L, compound A25 was found to be 2.3-fold and 1.9-fold more potent than the commercial acaricides cyenopyrafen and cyetpyrafen, respectively. Enzymatic inhibitory assay indicated that the active principle M1 of compound A25 possesses an IC50 value of 2.32 μM against Tetranychus cinnabarinus SDH, which was about twofold superior compared to the active metabolites of cyenopyrafen (IC50 = 4.72 μM). Molecular docking study showed that the active metabolites 2 and 3 and their corresponding silicon counterparts form H-bonds and cation-π interaction with the residues of Trp165, Tyr433, and Arg279.

Rhizoaspergillin A and Rhizoaspergillinol A, including a Unique Orsellinic Acid-Ribose-Pyridazinone-N-Oxide Hybrid, from the Mangrove Endophytic Fungus Aspergillus sp. A1E3

Two new compounds, named rhizoaspergillin A (1) and rhizoaspergillinol A (2), were isolated from the mangrove endophytic fungus Aspergillus sp. A1E3, associated with the fruit of Rhizophora mucronata, together with averufanin (3). The planar structures and absolute configurations of rhizoaspergillinol A (2) and averufanin (3) were established by extensive NMR investigations and quantum-chemical electronic circular dichroism (ECD) calculations. Most notably, the constitution and absolute configuration of rhizoaspergillin A (1) were unambiguously determined by single-crystal X-ray diffraction analysis of its tri-pivaloyl derivative 4, conducted with Cu Kα radiation, whereas those of averufanin (3) were first clarified by quantum-chemical ECD calculations. Rhizoaspergillin A is the first orsellinic acid-ribose-pyridazinone-N-oxide hybrid containing a unique β-oxo-2,3-dihydropyridazine 1-oxide moiety, whereas rhizoaspergillinol A (2) and averufanin (3) are sterigmatocystin and anthraquinone derivatives, respectively. From the perspective of biosynthesis, rhizoaspergillin A (1) could be originated from the combined assembly of three building blocks, viz., orsellinic acid, β-D-ribofuranose, and L-glutamine. It is an unprecedented alkaloid-N-oxide involving biosynthetic pathways of polyketides, pentose, and amino acids. In addition, rhizoaspergillinol A (2) exhibited potent antiproliferative activity against four cancer cell lines. It could dose-dependently induce G2/M phase arrest in HepG2 cells.

The complex II resistance mutation H258Y in succinate dehydrogenase subunit B causes fitness penalties associated with mitochondrial respiratory deficiency

BACKGROUND

The acaricides cyflumetofen, cyenopyrafen and pyflubumide inhibit the mitochondrial electron transport chain at complex II [succinate dehydrogenase (SDH) complex]. A target site mutation H258Y was recently discovered in a resistant strain of the spider mite pest Tetranychus urticae. H258Y causes strong cross-resistance between cyenopyrafen and pyflubumide, but not cyflumetofen. In fungal pests, fitness costs associated with substitutions at the corresponding H258 position that confer resistance to fungicidal SDH inhibitors have not been uncovered. Here, we used H258 and Y258 near-isogenic lines of T. urticae to quantify potential pleiotropic fitness effects on mite physiology.

RESULTS

The H258Y mutation was not associated with consistent significant changes of single generation life history traits and fertility life table parameters. In contrast, proportional Sanger sequencing and droplet digital polymerase chain reaction showed that the frequency of the resistant Y258 allele decreased when replicated 50:50 Y258:H258 experimentally evolving populations were maintained in an acaricide-free environment for approximately 12 generations. Using in vitro assays with mitochondrial extracts from resistant (Y258) and susceptible (H258) lines, we identified a significantly reduced SDH activity (48% lower activity) and a slightly enhanced combined complex I and III activity (18% higher activity) in the Y258 lines.

CONCLUSION

Our findings suggest that the H258Y mutation is associated with a high fitness cost in the spider mite T. urticae. Importantly, while it is the most common approach, it is clear that only comparing life history traits and life table fecundity does not allow to reliably estimate fitness costs of target site mutations in natural pest populations. © 2023 Society of Chemical Industry.

Mechanisms underlying the impact and interaction of temperature and UV-B on the hatching of spider mite and phytoseiid mite eggs

BACKGROUND

A spider mite control method using night-time ultraviolet (UV)-B irradiation was recently developed for strawberry greenhouses (UV method). The control effect of this UV method is negatively affected by increasing temperature. Tetranychus urticae eggs are more resistant to a single dose of UV-B irradiation than Neoseiulus californicus eggs. By contrast, N. californicus can better survive nightly UV-B irradiation with the UV method compared with T. urticae. To elucidate the mechanism underlying these phenomena, we explored the hypotheses that higher temperature promotes photoenzymatic repair (PER) and that mortality is determined by UV-B susceptibility in the embryonic stage exposed to UV-B.

RESULTS

PER efficacy was not promoted by increasing temperature. The lowest hatchability (around zero) of T. urticae eggs after a single dose of UV-B irradiation (0.288 and 0.432 kJ m^-2 ) without photoreactivation was seen in the morphogenesis stages between "cleavage ended" and "eye points became colored". Based on these results, we developed a linear function of daily UV-B irradiance and deviation of cumulative irradiance during vulnerable embryonic developmental phases from 50% lethal dose (LD₅₀ ) after a single dose of UV-B irradiation. The difference between T. urticae and N. californicus and changes in UV-B vulnerability due to temperature could be explained by this simple relationship.

CONCLUSION

Slower development in T. urticae than N. californicus in nature and developmental delay under low temperatures increase the ovicidal effects of the UV method. This shows the advantage of the simultaneous use of the UV method and biological control, contributing to the development of integrated pest management. © 2022 Society of Chemical Industry.

The H92R substitution in PSST is a reliable diagnostic biomarker for predicting resistance to mitochondrial electron transport inhibitors of complex I in European populations of Tetranychus urticae

BACKGROUND

Mitochondrial Electron Transport Inhibitors of complex I (METI-I), such as tebufenpyrad and fenpyroximate, are acaricides that have been used extensively to control Tetranychus urticae Koch (Acari: Tetranychidae) for more than 20 years. Because of the ability of this spider mite to rapidly develop acaricide resistance, field (cross-) resistance monitoring and elucidation of resistance mechanisms are extremely important for resistance management (RM). In the present study, 42 European T. urticae field populations were screened for tebufenpyrad and fenpyroximate resistance, and the correlation between resistance and the H92R substitution in PSST was investigated.

RESULTS

According to the calculated lethal concentration values that kill 90% of the population (LC₉₀ ), tebufenpyrad and fenpyroximate would fail to control many of the collected populations at recommended field rates. Six populations exhibited high to very high resistance levels (200- to over 1950-fold) to both METI-Is. Analysis based on the LC₅₀ values displayed a clear correlation between tebufenpyrad and fenpyroximate resistance, further supporting cross-resistance, which is of great operational importance in acaricide RM. The previously uncovered METI-I target-site mutation H92R in the PSST homologue of complex I (NADH:ubiquinone oxidoreductase) was found with high allele frequencies in populations resistant to tebufenpyrad and fenpyroximate. Synergist assays showed this mutation is not the only factor involved in METI-I resistance and additive or synergistic effects of multiple mechanisms most likely determine the phenotypic strength.

CONCLUSIONS

The predictive value of resistance by H92R is very high in European populations and offers great potential to be used as a molecular diagnostic marker for METI-I resistance. © 2022 Society of Chemical Industry.

Combination of target site mutation and associated CYPs confers high-level resistance to pyridaben in Tetranychus urticae

Pyridaben is a mitochondrial electron transport complex I inhibitor. The H110R mutation in the PSST subunit has been reported as a major factor in pyridaben resistance in the two-spotted spider mite, Tetranychus urticae. However, backcross experiments revealed that the mutant PSST alone conferred only moderate resistance. In contrast, inhibition of cytochrome P450 (CYP) markedly reduces resistance levels in a number of highly resistant strains. It was reported previously that maternal factors contributed to the inheritance of pyridaben resistance in the egg stage, but the underlying mechanisms have yet to be elucidated. Here, we studied the combined effects of the PSST H110R mutation and candidate CYPs, as metabolic resistance factors, on pyridaben resistance in T. urticae. We found that the maternal effects of inheritance of resistance in the egg stage were associated with CYP activity. Analysis of differential gene expression by RNA-seq identified CYP392A3 as a candidate causal factor for the high resistance level. Congenic strains, where the alleles of both PSST and CYP392A3 were derived from a resistant strain (RR_i; i = 1 or 2) and a susceptible strain (SS_i) in a common susceptible genetic background, were constructed by marker-assisted backcrossing. RR_i showed upregulation of CYP392A3 and high resistance levels (LC₅₀ > 10,000 mg L^-1), while SS_i had LC₅₀ < 10 mg L^-1. To disentangle the individual effects of PSST and CYP392A3 alleles, we also attempted to uncouple these genes in RR_i. We conclude that given the variation in LC₅₀ values and expression levels of CYP392A3 in the congenic and uncoupled strains, it is likely that the high pyridaben resistance levels are due to a synergistic or cumulative effect of the combination of mutant PSST and associated CYPs, including CYP392A3, but other yet to be discovered factors cannot be excluded.

Co-occurrence of subunit B and C mutations in respiratory complex II confers high resistance levels to pyflubumide and cyenopyrafen in the two-spotted spider mite Tetranychus urticae (Acari: Tetranychidae)

BACKGROUND

Pyflubumide and cyenopyrafen are respiratory complex II (complex II) inhibitors. Previous quantitative trait locus analyses suggested associations of I260V and S56L in complex II subunit B (B-I260V) and subunit C (C-S56L) with pyflubumide and cyenopyrafen resistance, respectively, in Tetranychus urticae. However, although resistant strains had been selected separately by these acaricides, all strains were homozygous for both B-I260V and C-S56L. Hence, the effects of each mutation on resistance development remain unclear.

RESULTS

We established strains homozygous for B-I260V with C-S56 (B-I260V_I260V/C-S56_S56) and for C-S56L with B-I260 (B-I260_I260/C-S56L_S56L). High resistance levels (LC₅₀  > 1000 mg L^-1 ) to pyflubumide and cyenopyrafen was not conferred by B-I260V or C-S56L alone. Next, we prepared intermixed strains by crossing B-I260V_I260V/C-S56_S56 and B-I260_I260/C-S56L_S56L. Selection of the intermixed strains by either acaricide caused very high resistance levels (LC₅₀  ≥ 10 000 mg L^-1 ) to both acaricides and fixed both mutations. Allele-selected recoupling of the mutations without acaricide selection also conferred very high resistance levels to both acaricides in the intermixed strains. Unlike these, B-I260V or C-S56L alone conferred very high and high resistance levels to cyflumetofen, respectively.

CONCLUSION

We conclude that the effect of individual mutations characteristically varies among complex II inhibitors. Moreover, very high resistance levels to pyflubumide and cyenopyrafen is conferred by the co-occurrence of B-I260V and C-S56L mutations, which alone have limited effects on resistance level.

Susceptibility to Acaricides and the Frequencies of Point Mutations in Etoxazole- and Pyridaben-Resistant Strains and Field Populations of the Two-Spotted Spider Mite, Tetranychus urticae (Acari: Tetranychidae)

The two-spotted spider mite Tetranychus urticae Koch is a major agricultural pest worldwide and is known to rapidly develop resistance to pesticides. In the present study, we explored a field strain that was collected in 2000 and 2003 and has been exhibiting resistance to etoxazole and pyridaben over the last 16 years. The resistance ratios of the etoxazole- and pyridaben-resistant strains (ER and PR) to etoxazole or pyridaben were more than 5,000,000- and 4109.6-fold higher than that of the susceptible strain, respectively. All field-collected populations showed resistance to etoxazole and pyridaben. The ER and PR strains showed cross-resistance to several acaricides. Both I1017F and H92R point mutations were detected in 7 out of 8 field groups. Spirodiclofen and spiromesifen resulted in more than 77.5% mortality in the 8 field groups. In addition, the genotype frequency of the I1017F point mutation was 100.0% in the ER strain, and that of the H92R point mutation was 97.0% in the PR strain. All of the field populations were found to have a high frequency of I1017F. These results suggest that the observation of resistance patterns will help in designing a sustainable IPM program for T. urticae.

Fenpyroximate resistance in Iranian populations of the European red mite Panonychus ulmi (Acari: Tetranychidae)

The European red mite, Panonychus ulmi (Koch), is one of the most important apple orchard pests worldwide. Fenpyroximate, a mitochondrial electron transport inhibitor of complex I (METI-I), is a commonly used acaricide to control this pest. In this study, we determined fenpyroximate resistance levels for 11 P. ulmi populations from Iran and a spirodiclofen-resistant strain from Germany (PSR-TK). The LC₅₀ values ranged between 121.8 and 5713.9 mg a.i. L^-1 and the highest resistance ratio (RR) was 47-fold for the Padena population. PBO, TPP and DEM synergist ratios (SRs) were the highest for the PSR-TK (SR = 6.7), Shahin Dej (SR = 6.1) and Semirom3 (SR = 3.6) populations, respectively. In vitro enzyme activity measurements also showed that there was a higher glutathione S-transferases (GSTs) activity in the PSR-TK and Shahin Dej population compared to the most susceptible populations, whereas the esterase and P450 monooxygenase activity were not significantly higher in the resistant populations. Last, we screened all populations for the presence of two mutations previously associated with METI-I resistance in spider mites but none of these mutations could be detected. To conclude, moderate to high levels of fenpyroximate resistance were observed in P. ulmi populations from Iran, with increased detoxification most likely underlying fenpyroximate resistance.

Resistance to pyridaben in Canadian greenhouse populations of two-spotted spider mites, Tetranychus urticae (Koch)

Two-spotted spider mite (TSSM) Tetranychus urticae (Koch) is an important agricultural pest that causes considerable yield losses to over 150 field and greenhouse crops. Mitochondrial electron transport inhibitors (METI) acaricides are commonly used to control mite species in commercial Canadian greenhouses. Development of resistance to METIs in TSSM populations have been reported worldwide, but not until recently in Canada. The objectives of this study were to: 1) monitor the acaricide-susceptibility in greenhouse TSSM populations, and 2) investigate the resistance to pyridaben, a METI acaricide, in greenhouse resistant and pyridaben-selected (SRS) mite strains. The increased mortality to the pyridaben sub-lethal concentration (LC₃₀) when SRS mites were exposed to piperonyl butoxide (PBO), a general cytochrome P450 monooxygenase inhibitor, and higher P450 activity compared to the greenhouse strain (RS) mites, indicated that P450s may be at least partially responsible for the resistance. The molecular mechanisms of target site insensitivity-mediated resistance in the pyridaben resistant strain of TSSM were investigated by comparing the DNA sequence of NADH dehydrogenase subunits TYKY and PSST, NADH-ubiquinone oxidoreductase chain 1 and 5 (ND1, ND5) and the NADH-ubiquinone oxidoreductase subunit 49 kDa from SRS to the reference strain (SS) and RS. Despite a number of nucleotide substitutions, none correlated with the pyridaben resistance. Understanding the underlying mechanisms of TSSM adaptation to acaricides is an essential part of resistance management strategy in any IPM program. The findings of this study will encourage growers to apply acaricides with different modes of action to reduce the rate at which acaricide resistance will occur in greenhouse TSSM populations.

QTL mapping using microsatellite linkage reveals target-site mutations associated with high levels of resistance against three mitochondrial complex II inhibitors in Tetranychus urticae

The acaricides cyflumetofen, cyenopyrafen, and pyflubumide act as inhibitors of the mitochondrial electron transport system at complex II (succinate dehydrogenase; SDH), a new mode of action in arthropods. The development and mechanisms of low-level resistance against cyenopyrafen and cyflumetofen have been previously reported in Tetranychus urticae. In the present study, we investigated high levels of resistance against three SDH inhibitors in T. urticae field populations and clarify the genetic basis of resistance using quantitative trait locus (QTL) analysis. First, we constructed a microsatellite linkage map comprising 64 markers assembled into three linkage groups (LGs) with total length of 683.8 cM and average marker spacing of 11.03 cM. We then used the linkage map to perform QTL mapping, and identified significant QTLs contributing to resistance to cyflumetofen (one QTL on LG1), cyenopyrafen (one QTL on LG3), and pyflubumide (two QTLs on LG1 and LG3). The QTL peaks on LG1 for cyflumetofen and pyflubumide overlapped and included the SdhB locus. For cyenopyrafen resistance, the QTLs on LG3 included the SdhC locus. For cyflumetofen resistance, we found an I260T mutation in SdhB. For pyflubumide and cyenopyrafen resistance, we detected I260V and S56L substitutions in SdhB and SdhC, respectively, by direct sequencing. Both I260 in SdhB and S56 in SdhC were present in highly conserved regions of the ubiquinone binding site formed at the interface among SdhB, SdhC, and SdhD. Mutations at these positions have been implicated in resistance against fungicides that act as Sdh inhibitors in various pathogens. Therefore, we consider these mutations to be target-site resistance mutations for these acaricidal SDH inhibitors.

Emergence of fipronil resistant Rhipicephalus microplus populations in Indian states

The intensive usage of chemical acaricides for the control of the cattle tick Rhipicephalus microplus has resulted in the development and establishment of multi-acaricide resistant populations. Fipronil, a phenylpyrazole insecticide, is currently marketed in India for the management of this important veterinary tick species. Here, we tested Indian isolates of R. microplus which have developed multi-acaricide resistance, for their susceptibility to fipronil. Twenty-five field isolates from five agro-climatic zones of the country were collected and tested by adult immersion test (AIT) and larval packet test (LPT). Sixteen isolates with resistance factor (RF) in the range of 1.56-10.9 were detected using LPT, whereas only 11 isolates with RF ranging from 1.05 to 4.1 were detected using AIT. A significant variation of RF between both tests was found, which raises doubt about the suitability of larva-based assays in screening of fipronil resistance. The data indicated possible cross-resistance between groups of acaricides in fipronil-resistant tick populations.

Molecular and genetic analysis of resistance to METI-I acaricides in Iranian populations of the citrus red mite Panonychus citri

The citrus red mite, Panonychus citri, is a major pest on citrus all around the world. Mitochondrial Electron Transport Inhibitors of complex I (METI-I) acaricides such as fenpyroximate have been used extensively to control P. citri populations, which resulted in multiple reports of METI-I resistant populations in the field. In this study, biochemical and molecular mechanisms of fenpyroximate resistance were investigated in P. citri. Seven populations were collected from Northern provinces of Iran. Resistance ratios were determined and reached up to 75-fold in comparison to a fenpyroximate susceptible population. Cross-resistance to two additional METI-I acaricides, pyridaben and tebufenpyrad, was detected. PBO synergism experiments, in vivo enzyme assays and gene expression analysis suggest a minor involvement of cytochrome P450 monooxygenases in fenpyroximate resistance, which is in contrast with many reported cases for the closely related Tetranychus urticae. Next, we determined the frequency of a well-known mutation in the target-site of METI-Is, the PSST subunit, associated with METI-I resistance. Indeed, the H92R substitution was detected in a highly fenpyroximate resistant P. citri population. Additionally, a new amino acid substitution at a conserved site in the PSST subunit was detected, A94V, with higher allele frequencies in a moderately resistant population. Marker-assisted back-crossing in a susceptible background confirmed the potential involvement of the newly discovered A94V mutation in fenpyroximate resistance. However, introduction of the A94V mutation in the PSST homologue of D. melanogaster using CRISPR-Cas9 did not result in fenpyroximate resistant flies. In addition, differences in binding curves between METI-Is and complex I measured directly, in isolated transgenic and wildtype mitochondria preparations, could not be found.

The cytochrome P450 CYP389C16 contributes to the cross-resistance between cyflumetofen and pyridaben in Tetranychus cinnabarinus (Boisduval)

BACKGROUND

Acaricide resistance is a serious problem in spider mites. Cyflumetofen is a new complex II inhibitor, whereas pyridaben acts at complex I and has been used for decades. Although cross-resistance between cyflumetofen and pyridaben has been observed in Tetranychus cinnabarinus, the specific mechanisms at play have not yet been investigated.

RESULTS

Investigation into the cross-resistance mechanisms identified five P450s, among which CYP389C16 was evaluated as the most likely candidate conferring cross-resistance. Knockdown of CYP389C16 expression via RNA interference diminished the level of cross-resistance in the cyflumetofen-resistant strain. In addition, recombinant CYP389C16 (40 pmol) effectively metabolized 25.0 ± 0.7% of cyflumetofen, 39.7 ± 1.0% of pyridaben, and 69.3 ± 3.3% of AB-1 (active de-esterified metabolite of cyflumetofen) within 2 h. In addition, hydroxylation metabolite of AB-1 was identified by HPLC-MS/MS.

CONCLUSIONS

The study reveals that overexpressed CYP389C16 is involved in the cross-resistance between cyflumetofen and pyridaben in T. cinnabarinus. © 2019 Society of Chemical Industry.

Field-evolved resistance and cross-resistance of the two-spotted spider mite, Tetranychus urticae, to bifenazate, cyenopyrafen and SYP-9625

The acaricide bifenazate acts as complex III inhibitor whereas cyenopyrafen and SYP-9625 act as complex II inhibitors. All these acaricides are commonly used to control two-spotted spider mite (TSSM), Tetranychus urticae Koch. We examined field-evolved and laboratory-selected resistance of TSSM to these three acaricides and determined cross-resistance among them. Six field populations of TSSM showed low levels of resistance to bifenazate with resistance ratios ranging from 2.20 to 10.65 compared to a susceptible strain. SYP-9625, structurally similar to cyenopyrafen, showed slightly higher activity to TSSMs but significant cross-resistance in both field populations and a laboratory-selected strain by SYP-9625. However, low levels of resistance to these two chemicals were found in field populations even when used for short time periods. Cross-resistance was not found between bifenazate and Complex II inhibitors, cyenopyrafen and SYP-9625, in both field populations and the laboratory-selected strain. Field-evolved resistance of TSSM to the tested acaricides is still low and should be delayed by the implementation of resistance management practices. Cross-resistance between cyenopyrafen and SYP-9625 is obvious, so they should not be used together in resistance management strategies based on mode of action rotation.

Resistant inheritance and cross-resistance of cyflumetofen in Tetranychus cinnabarinus (Boisduval)

As a new acaricide, cyflumetofen can effectively control Tetranychus, Panonychus, as well as other phytophagous mites. But its risk and the way of genetic and resistant inheritance in mites are not clear. In this study, two cyflumetofen-resistant strains (CyR and YN-CyR) were selected for 104 and 12 generations, and developed 104.7-fold and 25.6-fold resistance, respectively. Three crossing groups (CyR_80 × SS, CyR_104 × SS, YN-CyR × SS) were conducted to explore the resistant inheritance of cyflumetofen in T. cinnabarinus changed along with resistant level or not. The results of reciprocal crosses and backcrosses revealed that the incomplete recessive and multiple genes trait involved in two resistant strains. The different stage of resistance also has a same genetic trait. A cross-resistance study revealed that there was no cross-resistance between cyflumetofen and other four acaricides including avermectin, fenpropathrin, propargite and bifenazate respectively, but the cross-resistance to pyridaben reached a high level with 63.8-fold, which indicates an underlying mechanism that can both mediate cyflumetofen- and pyridaben-resistance in T. cinnabarinus.

Does Long-Term Feeding on Alternative Prey Affect the Biological Performance of Neoseiulus barkeri (Acari: Phytoseiidae) on the Target Spider Mites?

The predatory mite Neoseiulus barkeri (Hughes) is a good biological control agent for many small sucking pests. We aimed to determine whether rearing long term on alternative prey versus target prey species affected the performance of N. barkeri. Therefore, we investigated the prey preference, life tables, and population parameters of N. barkeri between alternative prey Tyrophagus putrescentiae (Schrank) and three species of spider mites, Tetranychus urticae Koch, Panonychus citri (McGregor), and Eotetranychus kankitus Ehara. We found that N. barkeri preferred the tetranychid mites to the alternative prey. Between the tetranychid mites, the predator consumed more P. citri and E. kankitus than T. urticae. When reared on T. urticae, the total developmental time and longevity of N. barkeri were the longest, whereas the intrinsic rate of increase was the lowest, indicating that the biotic fitness of predatory mite preyed on target of T. urticae was higher than on alternative prey of T. putrescentiae. However, total developmental time, longevity, and fecundity did not differ between N. barkeri reared on T. putrescentiae and P. citri, although these parameters were higher than those for mites reared on E. kankitus, indicating that the predatory mite reared on T. putrescentiae may not be affected to control P. citri, and that coexistence of P. citri and E. kankitus may enhance the control efficiency of N. barkeri. Altogether, our results demonstrated that long-term feeding on the alternative prey T. putrescentiae did not affect the performance of the predatory mite N. barkeri on various target spider mites.

Combination of restriction endonuclease digestion with the ΔΔCt method in real-time PCR to monitor etoxazole resistance allele frequency in the two-spotted spider mite

Monitoring resistance allele frequency at the early stage of resistance development is important for the successful acaricide resistance management. Etoxazole is a mite growth inhibitor to which resistance is conferred by an amino acid substitution in the chitin synthase 1 (CHS1; I1017F) in T. urticae. If the susceptible allele can be specifically digested by restriction endonuclease, the ΔΔCt method using real-time PCR for genomic DNA (RED-ΔΔCt method) may be available for monitoring the resistance allele frequency. We tested whether the etoxazole resistance allele frequency in a pooled sample was accurately measured by the RED-ΔΔCt method and validated whether the resistance variant frequency was correlated with etoxazole resistance phenotype in a bioassay. Finally, we performed a pilot test using field populations. Strong linearity of the measures by the RED-ΔΔCt method with practical resistance allele frequencies; resistance allele frequency in the range between 0.5% to at least 0.75% was strictly represented. The strong linear relationship between hatchability of haploid male eggs after the etoxazole treatments (phenotype) and resistance allele frequencies in their mothers provided direct evidence that I1017F is a primary resistance factor to etoxazole in the strains used for experiments. The pilot test revealed a significant correlation between egg hatchability (including both diploid female eggs and haploid male eggs) and estimators in field populations. Consequently, we concluded that the RED-ΔΔCt method is a powerful tool for monitoring a resistance allele in a pooled sample.

A mutation in the PSST homologue of complex I (NADH:ubiquinone oxidoreductase) from Tetranychus urticae is associated with resistance to METI acaricides

The acaricidal compounds pyridaben, tebufenpyrad and fenpyroximate are frequently used in the control of phytophagous mites such as Tetranychus urticae, and are referred to as Mitochondrial Electron Transport Inhibitors, acting at the quinone binding pocket of complex I (METI-I acaricides). Because of their very frequent use, resistance evolved fast more than 20 years ago, and is currently wide-spread. Increased activity of P450 monooxygenases has been often associated with resistance, but target-site based resistance mechanisms were never reported. Here, we report the discovery of a mutation (H92R) in the PSST homologue of complex I in METI-I resistant T. urticae strains. The position of the mutation was studied using the high-resolution crystal structure of Thermus thermophilus, and was located in a stretch of amino acids previously photo-affinity labeled by fenpyroximate. Selection experiments with a strain segregating for the mutant allele, together with marker-assisted back-crossing of the mutation in a susceptible background, confirmed the involvement of the mutation in METI-I resistance. Additionally, an independent genetic mapping approach; QTL analysis identified the genomic region of pyridaben resistance, which included the PSST gene. Last, we used CRISPR-Cas9 genome editing tools to introduce the mutation in the Drosophila PSST homologue.

Synthesis, Acaricidal Activity, and Structure-Activity Relationships of Pyrazolyl Acrylonitrile Derivatives

A series of novel pyrazolyl acrylonitrile derivatives was designed, targeting Tetranychus cinnabarinus, and synthesized. Their structures were identified by combination of ¹H NMR, ¹³C NMR, and MS spectra. The structures of compounds 18 and 19 were further confirmed by X-ray diffraction. Extensive greenhouse bioassays indicated that compound 19 exhibits excellent acaricidal activity against all developmental stages of T. cinnabarinus, which is better than the commercialized compounds cyenopyrafen and spirodiclofen. It was shown that the acute toxicity of compounds 19 to mammals is quite low. The structure-activity relationships are also discussed.

Molecular analysis of cyenopyrafen resistance in the two-spotted spider mite Tetranychus urticae

BACKGROUND

Cyenopyrafen is a recently developed acaricide with a new mode of action as a complex II inhibitor. However, it was recently shown that cross-resistance to cyenopyrafen can occur in resistant field strains of Tetranychus urticae, which might be linked to the previous use of classical METI acaricides. Here, we selected for cyenopyrafen resistance and studied the molecular mechanisms that underlie resistance.

RESULTS

Selection for cyenopyrafen resistance confers cross-resistance to the complex II inhibitor cyflumetofen, but also to pyridaben, a frequently used complex I inhibitor. Cyenopyrafen resistance is highly synergised by piperonyl butoxide, and a 15-fold higher P450 activity was detected in the resistant strain. Target-site resistance was not detected. Genome-wide gene expression data, followed by a meta-analysis of previously obtained gene expression data, revealed the overexpression specifically of CYP392A11 and CYP392A12.

CONCLUSIONS

Cyenopyrafen resistance is strongly linked to the overexpression of two P450s, which probably explains the observed cross-resistance. This information is highly valuable, as the novel complex II inhibitors cyenopyrafen and cyflumetofen are in the process of worldwide registration. The role of both CYP392A11 and CYP392A12 should be further supported by functional expression, but they are very promising candidates as molecular diagnostic markers for monitoring cyenopyrafen susceptibility in the field.

Functional characterization of the Tetranychus urticae CYP392A11, a cytochrome P450 that hydroxylates the METI acaricides cyenopyrafen and fenpyroximate

Cyenopyrafen is a Mitochondrial Electron Transport Inhibitor (METI) acaricide with a novel mode of action at complex II, which has been recently developed for the control of the spider mite Tetranychus urticae, a pest of eminent importance globally. However, some populations of T. urticae are cross-resistant to this molecule, and cyenopyrafen resistance can be readily selected in the lab. The cytochrome P450s genes CYP392A11 and CYP392A12 have been strongly associated with the phenotype. We expressed the CYP392A11 and the CYP392A12 genes with T. urticae cytochrome P450 reductase (CPR) in Escherichia coli. CYP392A12 was expressed predominately as an inactive form, witnessed by a peak at P420, despite optimization efforts on expression conditions. However, expression of CYP392A11 produced a functional enzyme, with high activity and preference for the substrates Luciferin-ME EGE and ethoxycoumarin. CYP392A11 catalyses the conversion of cyenopyrafen to a hydroxylated analogue (kcat = 2.37 pmol/min/pmol P450), as well as the hydroxylation of fenpyroximate (kcat = 1.85 pmol/min/pmol P450). In addition, transgenic expression of CYP392A11 in Drosophila melanogaster, in conjunction with TuCPR, confers significant levels of fenpyroximate resistance. The overexpression of CYP392A11 in multi-resistant T. urticae strains, not previously exposed to cyenopyrafen, which had been indicated by microarray studies, was confirmed by qPCR, and it was correlated with significant levels of cyenopyrafen and fenpyroximate cross-resistance. The implications of our findings for insecticide resistance management strategies are discussed.

The economic importance of acaricides in the control of phytophagous mites and an update on recent acaricide mode of action research

Acaricides are one of the cornerstones of an efficient control program for phytophagous mites. An analysis of the global acaricide market reveals that spider mites such as Tetranychus urticae, Panonychus citri and Panonychus ulmi are by far the most economically important species, representing more than 80% of the market. Other relevant mite groups are false spider mites (mainly Brevipalpus), rust and gall mites and tarsonemid mites. Acaricides are most frequently used in vegetables and fruits (74% of the market), including grape vines and citrus. However, their use is increasing in major crops where spider mites are becoming more important, such as soybean, cotton and corn. As revealed by a detailed case study of the Japanese market, major shifts in acaricide use are partially driven by resistance development and the commercial availability of compounds with novel mode of action. The importance of the latter cannot be underestimated, although some compounds are successfully used for more than 30 years. A review of recent developments in mode of action research is presented, as such knowledge is important for devising resistance management programs. This includes spirocyclic keto-enols as inhibitors of acetyl-CoA carboxylase, the carbazate bifenazate as a mitochondrial complex III inhibitor, a novel class of complex II inhibitors, and the mite growth inhibitors hexythiazox, clofentezine and etoxazole that interact with chitin synthase I.

Alternaria toxin-induced resistance in rose plants against rose aphid (Macrosiphum rosivorum): effect of tenuazonic acid

Many different types of toxins are produced by the fungus, Alternaria alternata (Fr.) Keissler. Little is known, however, regarding the influence of these toxins on insects. In this study, we investigated the toxin-induced inhibitory effects of the toxin produced by A. alternata on the rose aphid, Macrosiphum rosivorum, when the toxin was applied to leaves of the rose, Rosa chinensis. The results demonstrated that the purified crude toxin was non-harmful to rose plants and rose aphids, but had an intensive inhibitory effect on the multiplication of aphids. The inhibitory index against rose aphids reached 87.99% when rose plants were sprayed with the toxin solution at a low concentration. Further results from bioassays with aphids and high performance liquid chromatography (HPLC) analyses demonstrated that tenuazonic acid (TeA) was one of the most important resistance-related active components in the crude toxin. The content of TeA was 0.1199% in the crude toxin under the HPLC method. Similar to the crude toxin, the inhibitory index of pure TeA reached 83.60% 15 d after the rose plants were sprayed with pure TeA solution at the lower concentration of 0.060 μg/ml, while the contents of residual TeA on the surface and in the inner portion of the rose plants were only 0.04 and 0.00 ng/g fresh weight of TeA-treated rose twigs, respectively, 7 d after the treatment. Our results show that TeA, an active component in the A. alternata toxin, can induce the indirect plant-mediated responses in rose plants to intensively enhance the plant's resistances against rose aphids, and the results are very helpful to understand the plant-mediated interaction between fungi and insects on their shared host plants.