Insecticide resistance status of Myzus persicae in Greece: long-term surveys and new diagnostics for resistance mechanisms

Synthesis, biological evaluation and molecular docking of novel nereistoxin derivatives containing phosphonates as insecticidal/AChE inhibitory agents

In continuation of our program aimed at the discovery and development of natural product-based insecticidal agents, a series of novel nereistoxin derivatives containing phosphonate were synthesized and characterized by 31P, 1H, 13C NMR and HRMS. The bioactivities of the derivatives were evaluated for the acetylcholinesterase (AChE) inhibition potency and insecticidal activity. The AChE inhibitory effects of the derivatives were investigated using the in vitro Ellman method. Half of the compounds exhibited excellent inhibition of AChE. All the compounds were assessed for insecticidal activities against Mythimna separate (Walker) and Rhopalosiphum padi in vivo. Some derivatives displayed promising insecticidal activity against Rhopalosiphum padi. Compounds 5b and 6a displayed the highest activity against R. padi, showing LC50 values of 17.14 and 18.28 μg mL-1, respectively, close to that of commercial insecticide flunicotamid (LC50 = 17.13 μg mL-1). Compound 9g also showed notable insecticidal activity, with an LC50 value of 23.98 μg mL-1. Additionally, the binding modes of the active compounds 5b, 6a and 9g with AChE were analyzed in-depth though molecular docking and the intrinsic reasons for the differences in the strength of the compound's activities were elucidated. In summary, our findings demonstrate the potential of these nereistoxin derivatives as promising candidates for the development of novel pesticides.

First monitoring of resistance and corresponding mechanisms in the green peach aphid, Myzus persicae (Sulzer), to registered and unregistered insecticides in Saudi Arabia

Insecticides are widely used as the primary management strategy for controlling Myzus persicae, the devastating pest ravaging various vegetables, fruits, crops, and ornamentals. This study examined the susceptibility of M. persicae field populations to bifenthrin, fosthiazate, acetamiprid, spirotetramat, afidopyropen, and flonicamid while exploring the possible metabolic mechanisms of resistance. The study findings revealed that M. persicae field populations exhibited susceptible-to-moderate resistance to bifenthrin (resistance ratio (RR) = 0.94-19.65) and acetamiprid (RR = 1.73-12.91), low-to-moderate resistance to fosthiazate (RR = 3.67-17.00), and susceptible-to-low resistance to spirotetramat (RR = 0.70-6.68). However, all M. persicae field populations were susceptible to afidopyropen (RR = 0.44-2.25) and flonicamid (RR = 0.40-2.08). As determined by the biochemical assays, carboxylesterases were involved in the resistance cases to bifenthrin and fosthiazate, whereas cytochrome P450 monooxygenases were implicated in the resistance cases to acetamiprid. However, glutathione S-transferases were not implicated in the documented resistance of M. persicae field populations. Overall, the susceptibility of M. persicae field populations to flonicamid and afidopyropen-two unregistered insecticides in Saudi Arabia-suggests their potential as promising chemicals that can expand the various alternatives available for controlling this devastating pest. Although the detected moderate levels of resistance to bifenthrin, fosthiazate, and acetamiprid indicate a shift in the selection pressure of insecticides for M. persicae due to Saudi regulations, which have resulted in eventual obsolescence of conventional insecticides in favor of novel insecticides. Finally, rotational use of aforementioned insecticides can help in managing insecticide resistance in M. persicae.

Resistance Mechanisms of Sitobion miscanthi (Hemiptera: Aphididae) to Malathion Revealed by Synergist Assay

A resistant strain (MRS) of Sitobion miscanthi was cultured by continuous selection with malathion for over 40 generations. The MRS exhibited 32.7-fold resistance to malathion compared to the susceptible strain (MSS) and 13.5-fold, 2.9-fold and 4.8-fold cross-resistance for omethoate, methomyl and beta-cypermethrin, respectively. However, no cross-resistance was found to imidacloprid in this resistant strain. The realized heritability for malathion resistance was 0.02. Inhibitors of esterase activity, both triphenyl phosphate (TPP) and S,S,S,-tributyl phosphorotrithioate (DEF) as synergists, exhibited significant synergism to malathion in the MRS strain, with 11.77-fold and 5.12-fold synergistic ratios, respectively, while piperonyl butoxide (PBO) and diethyl maleate (DEM) showed no significant synergism in the MRS strain. The biochemical assay indicated that carboxylesterase activity was higher in MRS than in MSS. These results suggest that the increase in esterase activity might play an important role in S. miscanthi resistance to malathion. Imidacloprid could be used as an alternative for malathion in the management of wheat aphid resistance.

Target site mutations underlying insecticide resistance in Tunisian populations of Myzus persicae (Sulzer) on peach orchards and potato crops

BACKGROUND

The massive use of synthetic insecticides strongly affects the level of insecticide resistance in populations of Myzus persicae worldwide. The selection of target site insensitivity-mutations is particularly worrying in areas where agro-industrial crops are vulnerable to the attacks of aphids that vector viruses, as in the case of Tunisia. Knowledge of the resistance mechanisms evolved locally in this aphid pest is a prerequisite to improving and retaining the sustainability of integrated pest management strategies.

RESULTS

Target site mutations were surveyed in several populations of M. persicae collected from peach and potato crops between 2011 and 2017 in three Tunisian regions using real-time allele-specific PCR. The L1014F mutation (kdr locus) was found at a moderate frequency mostly in the heterozygous state and the homozygous resistant genotype was very uncommon. The M918T mutation (super-kdr locus) was present in a few heterozygous individuals, whereas the M918L mutation was detected for the first time in Tunisia and extreme North Africa. This latter mutation was shown to be widespread and well-established in Tunisia mainly as homozygous individuals, and was more abundant on peach than on potato crops. The S431F mutation (MACE) was found in a few heterozygous individuals. No individuals carrying the R81T mutation linked to neonicotinoid resistance were detected.

CONCLUSION

This study points out a critical situation for the efficacy of pyrethroid insecticides to control M. persicae populations in Tunisia. It also confirms the rapid spread of the M918L mutation which has been detected in many different areas of the Mediterranean basin. © 2022 Society of Chemical Industry.

Neonicotinoid’s resistance monitoring, diagnostic mechanisms and cytochrome P450 expression in green peach aphid [Myzus persicae (Sulzer) (Hemiptera: Aphididae)]

Green peach aphid [Myzus persicae (Sulzer) (Hemiptera: Aphididae)] is a significant pest with a known history of insecticide resistance. Neonicotinoids could manage this pest; however, their frequent use led to the evolution of resistance in field populations of M. persicae. Toxicity data for neonicotinoid insecticides synergized with pipernyl butoxide (PBO) in a field population (FP) were collected and compared to a laboratory susceptible clone (SC) of aphids. The enhanced expression of metabolic resistance-related cytochrome P450 gene CYP6CY3 and an arginine-threonine substitution were detected in FP, causing a single point mutation (R81T) at β1 subunit of nicotinic acetylcholine receptor (nAChR) within D loop. High level of resistance to imidacloprid was developed in FP with 101-fold resistance ratio and moderate resistance level (10.9-fold) to acetamiprid. The results of PBO synergized bioassay suggested that cytochrome P450 enzymes were involved in the resistance to neonicotinoids. The mRNA transcriptional level of CYP6CY3 gene was significantly higher (3.74 fold) in FP compared to SC. The R81T mutation associated with neonicotinoid resistance had 26% resistant allele frequency in FP. Both P450 enzymes and R81T mutation of nAChR were found in field-evolved neonicotinoid resistance. It is concluded that field-evolved resistance in green peach aphid could be managed by using appropriate synergists such as PBO.

Flupyradifurone resistance in Myzus persicae populations from peach and tobacco in Greece

BACKGROUND

Myzus persicae has evolved resistance to various insecticides in Greece. Here we examine the effectiveness of the insecticide flupyradifurone against aphid clones collected from tobacco and peach in Greece during 2017-2020. Furthermore, we monitored the frequency of the neonicotinoid resistance mutation R81T in the sampled clones, and the association between the responses to flupyradifurone and acetamiprid.

RESULTS

Of 43 clones tested with flupyradifurone, 6.977%, 60.465% and 32.558% showed low (10-14), moderate (19-89) and high (104-1914) resistance factor (RF) values, respectively. Resistance was higher in clones from peach than from tobacco with 42.308% and 17.647% of clones (respectively) failing into the high RF category (median RF values 67.5 and 36.4 for clones from peach and tobacco, respectively). Acetamiprid resistance was detected in clones collected in 2019-2020, in line with our previous study in Greece. The analysis of the whole dataset (54 clones collected during 2017-2020) revealed that all tobacco clones had RF < 7.5, whereas 55.263%, 18.421% and 26.316% of the peach clones exhibited low (<12), moderate (20-48) and high (100-145) RF values, respectively. A significant but moderate association between flupyradifurone and acetamiprid responses was detected (r = 0.513, P < 0.001). The R81T mutation was detected in aphids from peach (5.6% and 32.6% as homozygotes and heterozygotes, respectively) and in one aphid specimen (heterozygote) from tobacco. R81T was partially associated with the resistance to both insecticides, but many highly resistant clones did not possess the mutation, indicating the possible operation of one or more alternative underlying resistance mechanisms.

CONCLUSIONS

The use of flupyradifurone and acetamiprid in IPM/IRM should be based on further ongoing susceptibility monitoring. © 2021 Society of Chemical Industry.

Changes in the genetic composition of Myzus persicae nicotianae populations in Chile and frequency of insecticide resistance mutations

Myzus persicae is a cosmopolitan aphid that is highly polyphagous and an important agricultural pest. The subspecies M. persicae nicotianae has been described for highly specialized phenotypes adapted to tobacco (Nicotiana tabacum). In Chile, the population of M. persicae nicotianae was originally composed of a single red genotype that did not possess insecticide resistance mutations. However, in the last decade, variation in the colour of tobacco aphids has been observed in the field. To determine whether this variation stems from the presence of new genotypes, sampling was carried out across the entire distribution of tobacco cultivation regions in Chile. The aphids collected were genotyped, and the frequency of kdr (L1014F), super-kdr (M918T), modification of acetylcholinesterase (MACE) and nicotinic acetylcholine receptor β subunit (nAChRβ) mutations associated with insecticide resistance was determined. A total of 16 new genotypes of M. persicae nicotianae were detected in Chile: four of them possessed the MACE mutation, and none of them possessed the kdr, super-kdr or nAChRβ mutation. The previously described red genotype was not detected in any of the sampled fields over two seasons. These results raise questions about the mechanisms underlying changes in the genetic structure of M. persicae nicotianae populations in Chile. Future research aimed at addressing these questions could provide new insight into aphid evolution and agricultural practices.

Toxicity, Sublethal and Low Dose Effects of Imidacloprid and Deltamethrin on the Aphidophagous Predator Ceratomegilla undecimnotata (Coleoptera: Coccinellidae)

Simple Summary

Chemical insecticides are used to control agricultural pests all over the world. However, extensive use of chemical insecticides can be harmful to human health and negatively impact the environment and biological control agents. We studied the toxicity and sublethal effects of imidacloprid and deltamethrin on the aphidophagous coccinellid predator Ceratomegilla undecimnotata (Coleoptera: Coccinellidae). We evaluated one low (LD₃₀) and one sublethal dose (LD₁₀) for both insecticides. Lethal and sublethal effects of both insecticides negatively affected survival, development, reproduction, and longevity, and reduced the intrinsic (r) and finite (λ) rate of increase and the net reproduction rate (R₀) of treated populations compared to the control. Our findings indicate that the use of imidacloprid and deltamethrin in combination with C. undecimnotata in the context of IPM should be taken with caution due to the toxic effects of the chemicals in the biocontrol agent under laboratory conditions.

Abstract

Ceratomegilla undecimnotata (Coleoptera: Coccinellidae) is a common aphidophagous coccinellid predator used in biological control against aphid pests. Knowing toxicity, lethal, and sublethal effects of insecticides on natural enemies is essential in order to incorporate them into Integrated Pest Management (IPM). In the present study, the lethal and sublethal effects of imidacloprid and deltamethrin were evaluated on the fourth instar larvae of C. undecimnotata and subsequently on the full life cycle. Our results strongly suggest that sublethal and low doses of imidacloprid and deltamethrin at LD₁₀ and LD₃₀ affected fourth instar larvae duration time, adult preoviposition period, total preoviposition period, and fecundity. Moreover, the intrinsic (r) and finite (λ) rate of increase and the net reproduction rate (R₀) significantly decreased in populations treated with imidacloprid compared to the control population. The data clearly suggest that imidacloprid and deltamethrin have a negative influence on population growth parameters of C. undecimnotata at sublethal and low doses and, therefore, these insecticides should be used with caution within the context of IPM.

UDP-Glycosyltransferases from the UGT344 Family Are Involved in Sulfoxaflor Resistance in Aphis gossypii Glover

Simple Summary

The cotton aphid, Aphis gossypii Glover, is a notorious pest in cotton and cucurbit fields. The control of A. gossypii has typically relied on the application of chemical insecticides. Sulfoxaflor is the first commercially available sulfoximine insecticide, which exhibits great efficacy against sap-feeding insect pests and has been applied as an alternative insecticide for controlling of A. gossypii in China. Consequently, A. gossypii quickly developed resistance to this insecticide. Hence, in this study, to clarify the potential detoxifying roles of UGTs (one of the phase II detoxification enzymes) in resistance of A. gossypii against sulfoxaflor, the synergistic effects of two synergists (sulfinpyrazone and 5-nitrouracil) against sulfoxaflor were investigated using the susceptible and laboratory-established sulfoxaflor resistant strain (SulR), and the expression levels of 15 UGT genes were determined by qRT-PCR. Furthermore, the involvement of highly upregulated UGTs in sulfoxaflor-resistant strain was functionally tested by RNA interference (RNAi). Our results suggest that overexpression of UGTs contributes to sulfoxaflor resistance in A. gossypii, which should be useful for understanding sulfoxaflor resistance mechanisms.

Abstract

UDP-glycosyltransferases (UGTs) are major phase II detoxification enzymes that catalyze the transfer of glycosyl residues from activated nucleotide sugars to acceptor hydrophobic molecules and play very important roles in the biotransformation of various endogenous and exogenous compounds. Our previous studies demonstrated that UGTs participated in the detoxification of insecticides in Aphis gossypii. However, the potential roles of UGTs in A. gossypii resistance to sulfoxaflor are still unclear. In this study, two inhibitors of UGT enzymes, sulfinpyrazone and 5-nitrouracil, significantly increased the toxicity of sulfoxaflor to a resistant strain of A. gossypii, whereas there were no synergistic effects in the susceptible strain. Based on the transcriptome sequencing results, the expression levels of 15 UGTs were analyzed by quantitative real-time PCR, and we found that seven UGT genes were highly over-expressed in a sulfoxaflor-resistant strain compared to the susceptible strain, including UGT344B4, UGT344C5, UGT344A11, UGT344A14, and UGT344L2. Further suppressing the expression of UGT344B4, UGT344C5, and UGT344A11 by RNA interference significantly increased the sensitivity of resistant aphids to sulfoxaflor, indicating that the overexpression of UGT genes is potentially associated with sulfoxaflor resistance. These results could provide valuable information for further understanding the mechanisms of insecticide resistance.

Field evolved resistance to pyrethroids, neonicotinoids, organophosphates and macrolides in Rhopalosiphum padi (Linnaeus) and Sitobion avenae (Fabricius) from China

Rhopalosiphum padi (Linnaeus) and Sitobion avenae (Fabricius) are the predominant pests coexisting on wheat plants. In this study, the susceptibilities of 29 R. padi and 30 S. avenae populations from 15 provinces in China to pyrethroids (beta-cypermethrin and bifenthrin), neonicotinoids (imidacloprid and thiamethoxam), organophosphates (omethoate and chlorpyrifos) and macrolides (avermectin) were determined during 2018-2019. The median lethal insecticide concentrations (LC₅₀) indicated that R. padi was more sensitive than S. avenae to most of the insecticides. Monitor results showed that most wheat aphid populations were moderately resistant to pyrethroids. Two R. padi populations were highly resistant to beta-cypermethrin with 127.3-fold and 442.8-fold resistance ratio (RR), and two were highly resistant to bifenthrin (RR of 293.9 and 320.6, respectively). One S. avenae population was highly resistant to beta-cypermethrin (RR of 136.8) and one was highly resistant to bifenthrin (RR of 313.4). All populations of two wheat aphids exhibited low to moderate resistance to neonicotinoids (RR < 100). But over half populations were sensitive or exhibited low resistance to organophosphates and macrolides. The pair-wise correlation coefficients for the insecticide LC₅₀ revealed a positive correlation between beta-cypermethrin and bifenthrin resistance, as well as between the resistance to bifenthrin and omethoate for the two-aphid species. Similarly, significant correlations were detected between the resistance to beta-cypermethrin and avermectin for R. padi. These results may be relevant for developing effective insecticide management strategies that prevent or delay the development of resistance among wheat aphids.

An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 3: alternatives to systemic insecticides

Over-reliance on pesticides for pest control is inflicting serious damage to the environmental services that underpin agricultural productivity. The widespread use of systemic insecticides, neonicotinoids, and the phenylpyrazole fipronil in particular is assessed here in terms of their actual use in pest management, effects on crop yields, and the development of pest resistance to these compounds in many crops after two decades of usage. Resistance can only be overcome in the longterm by implementing methods that are not exclusively based on synthetic pesticides. A diverse range of pest management tactics is already available, all of which can achieve efficient pest control below the economic injury level while maintaining the productivity of the crops. A novel insurance method against crop failure is shown here as an example of alternative methods that can protect farmer's crops and their livelihoods without having to use insecticides. Finally, some concluding remarks about the need for a new framework for a truly sustainable agriculture that relies mainly on natural ecosystem services instead of chemicals are included; this reinforcing the previous WIA conclusions (van der Sluijs et al. Environ Sci Pollut Res 22:148-154, 2015).

Long-term studies on the evolution of resistance of Myzus persicae (Hemiptera: Aphididae) to insecticides in Greece

The aphid Myzus persicae s.l. (Hemiptera: Aphididae) is an important pest of many crops worldwide with a complex life cycle, intensely controlled by chemical pesticides, and has developed resistance to almost all used insecticides. In Greece, the aphid exhibits high genetic variation and adaptability and it is a classic example of evolution in the making. We have been studying M. persicae for over 20 years, on different host plants and varying geographical areas, analyzing its bio-ecology and the ability to develop resistance to insecticides. In this review, we present new and historical data on the effectiveness of insecticides from seven chemical groups used to control the aphid in Greece and the incidence of seven resistance mechanisms, including the new fast-spreading R81T point mutation of the postsynaptic nicotinic acetylcholine receptor. Thousands of samples were tested by biological, biochemical and molecular assays. The aphid populations were found to have developed and maintain resistance at medium to high levels to organophosphates, carbamates, pyrethroids and neonicotinoids for decades. In the latter group, a marked increase is recorded during an ~10-year period. The data analyzed and the extensive bibliography, advocate the difficulty to control the aphid making the design and application of IPM/IRM programs a challenge. We discuss principles and recommendations for the management of resistance, including the use of compounds such as flonicamid, spirotetramat, flupyradifurone and sulfoxaflor. We emphasize that resistance is a dynamic phenomenon, changing in time and space, requiring, therefore, continuous monitoring.

Structuration of multilocus genotypes associated with insecticide resistance of the peach potato aphid, Myzus persicae (Sulzer), in potato fields in southern Belgium

BACKGROUND

The peach potato aphid, Myzus persicae, has developed resistance to many insecticides. In Belgium, M. persicae is one of the most common aphids in potato fields and one of the most effective virus vectors. We monitored resistance mutations to pyrethroids, carbamates and neonicotinoids and related these results to microsatellite genotyping to provide information to support the choice of management tactics.

RESULTS

Most of the 254 aphids tested (97.6%) displayed at least one mutation conferring resistance to pyrethroids (L1014F, M918L and M918T) and 36.2% additionally carried the modified acetylcholinesterase (MACE) carbamates resistance making them resistant to two insecticide action modes. Ten mutation combinations were detected, two of which were frequent and a strong linkage was found between MACE and M918L mutations. The R81T mutation conferring resistance to neonicotinoids was not detected. Microsatellites highlighted a moderate genetic diversity [69 multilocus genotypes (MLG) detected], severe deviations from Hardy-Weinberg expectations, a highly significant excess of heterozygotes and linkage disequilibrium between all pairs of loci. A structuration of MLGs in association with the mutation combinations was observed. Genetic differentiation was mainly not significant between sampling locations and most MLGs were geographically widespread. These results suggest the likely coexistence of parthenogenesis (obligatory or facultative) and sexual reproduction, and the existence of 'old' parthenogenetic overwintering asexual lineages.

CONCLUSION

The results of this monitoring at a regional scale provide useful information on insecticide resistance, genetic diversity and reproductive modes, and highlight the need to reduce the insecticide selection pressure and to implement mitigating techniques.

Temperature-Dependent Demographic Characteristics and Control Potential of Aphelinus asychis Reared from Sitobion avenae as a Biological Control Agent for Myzus persicae on Chili Peppers

Aphelinus asychis, a polyphagous parasitoid, has been widely used as an efficient biological control agent against the aphid Myzus persicae. Aiming to evaluate the influence of temperature on the biological characteristics and control potential of A. asychis for M. persicae, we compared the life table parameters and control potential of A. asychis, which included the developmental time, longevity, fecundity, intrinsic rate of increase (r), and finite killing rate (θ). The results showed that increasing the temperature significantly decreased the developmental time and longevity of A. asychis. The r at 24 (0.2360 d⁻¹) and 28 °C (0.2441 d⁻¹) were significantly greater than those at 20 (0.1848 d⁻¹) and 32 °C (0.1676 d⁻¹). The θ at 24 (0.4495), 28 (0.5414), and 32 °C (0.4312) were also significantly greater than that at 20 °C (0.3140). The relationship between population fitness (r and θ) and temperature followed a unary quadratic function (R² > 0.95). The temperatures for the expected maximum intrinsic rate of increase (r_max) and the maximum finite killing rate (θ_max) were 25.7 and 27.4 °C, respectively. In conclusion, A. asychis could develop and produce progenies within the temperature range of 20–32 °C, and its control efficiency for M. persicae at 24, 28, and 32 °C was greater than that at 20 °C. The most suitable temperature range for controlling M. persicae with A. asychis in the field might be between 25.7 and 27.4 °C.

Differential metabolism of neonicotinoids by Myzus persicae CYP6CY3 stably expressed in Drosophila S2 cells

The peach-potato aphid, Myzus persicae, is a serious crop pest that has developed imidacloprid resistance, mainly through overexpression of CYP6CY3. Here, we established a metabolic assay using Drosophila S2 cells that stably expressed CYP6CY3. We found that CYP6CY3 showed metabolic activity against imidacloprid, as well as acetamiprid, clothianidin, and thiacloprid, but had no activity against dinotefuran. Our study suggested that stable gene expression in Drosophila S2 cells is useful for examining which insecticide is metabolized by P450 monooxygenases.

Geographical Distribution of Ectropis grisescens (Lepidoptera: Geometridae) and Ectropis obliqua in China and Description of an Efficient Identification Method

Ectropis grisescens Warren 1894 (Lepidopotera: Geometridae) and Ectropis obliqua Prout 1915 (Lepidopotera: Geometridae) are the most destructive chewing pests in China's tea plantations. Ectropis grisescens sex pheromone lures and E. obliqua nucleopolyhedrosis virus (EoNPV) are two species-specific and effective bio-control technologies to control these pests. Because these two species are morphologically similar, tea growers are unable to discriminate them by visual inspection. Hence, determining whether to use E. grisescens sex pheromone lures or EoNPV is difficult without knowledge on the geographical distribution of these two Ectropis species in China. In this study, we developed an efficient identification method, which is considerably cheaper and faster than sequencing the cytochrome c oxidase I gene. Overall, 2,588 E. grisescens and E. obliqua samples, collected from 13 provinces and municipalities in China covering the major regions where these pests have been reported, were identified. All insect samples from southern Jiangsu Province were identified as E. obliqua. Both Ectropis species were mix-distributed at the Anhui-Zhejiang Province border areas, whereas E. grisescens was mostly collected from the other sampling sites. Thus, E. obliqua might be mainly distributed at the junction of Jiangsu, Anhui, and Zhejiang Provinces. In contrast, E. grisescens has a considerably wide distribution area and is the main lepidopteran pest in the tea plantations of China. Our results contribute to improve the management of E. grisescens and E. obliqua populations and provide new insights for further studies on these two species.

Temporal and spatial distribution of insecticide-resistance mutations in the green peach aphid Myzus persicae (Hemiptera: Aphididae) on primary and secondary host plants in central Chile

BACKGROUND

The aphid Myzus persicae develops insensitivity to almost all classes of insecticides through target site mutations. The aim of this study was to assess the temporal and spatial distribution of resistant aphids that grow on peach trees and weeds, and establish the role of the secondary hosts as a reservoir of resistant genotypes.

RESULTS

The frequency of genotypes (RR, RS, and SS) was affected by the host plant, mainly for knock-down resistance (kdr) and modified acetylcholinesterase (MACE) mutations (P < 0.05). A higher frequency of RS and RR was observed in aphids found on peach trees than on weeds. The frequency of the R allele was significantly higher (P < 0.01) than expected in autumn and on weeds for the kdr and MACE mutations, while the frequency of the S allele was high in all seasons for all insecticide-resistance mutations (P < 0.01). The most abundant multilocus genotype was characterized as being RS for the kdr mutation and SS for both super-kdr and MACE.

CONCLUSION

This study provides farm-scale evidence that weeds are not an important reservoir of the R allele, but they are for the S allele. Hence, the presence of heterozygous genotypes on peach trees is most likely attributable to weeds. © 2017 Society of Chemical Industry.

Monitoring insecticide resistance and diagnostics of resistance mechanisms in the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae) in China

Myzus persicae (Sulzer) is one of the most serious agricultural pests in China, and management strategies mainly rely on insecticidal treatment. To evaluate the resistance of field populations of M. persicae to seven insecticides, we assessed the susceptibility of 11 field populations collected from eight provinces in China using leaf-dip bioassays. Toxicity assays showed that M. persicae field populations have developed several levels of resistance to each tested insecticide. For pyrethroids, the field populations have developed a high level of resistance to β-cypermethrin and cypermethrin, while the resistance to bifenthrin is still low. The resistance ratios of field populations to imidacloprid ranged from 1.48 to 52.36, and eight populations have developed moderate to high resistance. Resistance to acetamiprid is low, and only two populations have a moderate level of resistance. Most of the field populations of M. persicae developed moderate to high resistance to methomyl and omethoate. To investigate potential resistance mechanisms, we analyzed the enzyme activity of carboxylesterases, the type of amplified esterase genes, as well as the kdr (L1014F) mutation. All of the field populations exhibited a higher esterase activity compared to the laboratory susceptible strain. An amplified FE4, as well as the L1014F mutation, were also found in all of our experimental field populations. These results provide valuable insight into the current status of insecticide resistance and will prove to be a valuable resource in designing appropriate resistance management strategies for M. persicae in China.

Evolution of imidacloprid resistance in Myzus persicae in Greece and susceptibility data for spirotetramat

BACKGROUND

Myzus persicae s.l. is a major crop pest globally and has evolved resistance to a range of insecticide classes making it increasingly difficult to control in some areas. Here we compare bioassay monitoring data for two important compounds, imidacloprid and spirotetramat, on field samples/clones collected in Greece.

RESULTS

A total of 122 aphid samples/clones from central and northern Greece were examined in dose-response bioassays with imidacloprid. There was an overall increase in the level of resistance (resistance factor = 15-40) within tobacco-collected samples from 78.7% in 2007 to 86.7% in 2015. The corresponding frequencies for peach samples were 13.3% and 6.7%. These results were confounded however by the first identification of the R81T target mutation in Greece during 2015 (4.3% as heterozygotes in peach) and 2016 (21.3% as heterozygotes in peach). No resistance to spirotetramat was found at the 60 clones collected in 2015.

CONCLUSION

Resistance to imidacloprid is continuing to increase within Greek M. persicae s.l. populations and the situation is likely to deteriorate further with the recent identification of the R81T resistance mutation. Resistance to spirotetramat has not been found and is therefore a good alternative to neonicotinoids for resistance management. © 2017 Society of Chemical Industry.

Susceptibility of Australian Myzus persicae (Hemiptera: Aphididae) to Three Recently Registered Insecticides: Spirotetramat, Cyantraniliprole, and Sulfoxaflor

The green peach aphid, Myzus persicae (Sulzer), is a significant agricultural pest that has developed resistance to a large number of insecticides globally. Within Australia, resistance has previously been confirmed for multiple chemical groups, including pyrethroids, carbamates, organophosphates, and neonicotinoids. In this study, we use leaf-dip and topical bioassays to investigate susceptibility and potential cross-resistance of 12 field-collected populations of Australian M. persicae to three recently registered insecticides: sulfoxaflor, spirotetramat, and cyantraniliprole. Despite all 12 populations carrying known resistance mechanisms to carbamates, organophosphates, and pyrethroids, and two populations also exhibiting low-level metabolic resistance to neonicotinoids, we found little evidence of variation in susceptibility to sulfoxafor, spirotetramat, or cyantraniliprole. This provides further evidence that cross-resistance to spirotetramat, cyantraniliprole, and sulfoxaflor in M. persicae is not conferred by the commonly occurring resistance mechanisms MACE, super-kdr, amplification of the E4 esterase gene, or enhanced expression and copy number of the P450 gene, CYP6CY3. Importantly, this study also established toxicity baseline data that will be important for future monitoring of insecticide responses of M. persicae from both broadacre and horticultural crops.

Qualitative Sybr Green real-time detection of single nucleotide polymorphisms responsible for target-site resistance in insect pests: the example of Myzus persicae and Musca domestica

Chemical insecticides have been widely used to control insect pests, leading to the selection of resistant populations. To date, several single nucleotide polymorphisms (SNPs) have already been associated with insecticide resistance, causing reduced sensitivity to many classes of products. Monitoring and detection of target-site resistance is currently one of the most important factors for insect pest management strategies. Several methods are available for this purpose: automated and high-throughput techniques (i.e. TaqMan or pyrosequencing) are very costly; cheaper alternatives (i.e. RFLP or PASA-PCRs) are time-consuming and limited by the necessity of a final visualization step. This work presents a new approach (QSGG, Qualitative Sybr Green Genotyping) which combines the specificity of PASA-PCR with the rapidity of real-time PCR analysis. The specific real-time detection of Cq values of wild-type or mutant alleles (amplified used allele-specific primers) allows the calculation of ΔCqW-M values and the consequent identification of the genotypes of unknown samples, on the basis of ranges previously defined with reference clones. The methodology is applied here to characterize mutations described in Myzus persicae and Musca domestica and we demonstrate it represents a valid, rapid and cost-effective technique that can be adopted for monitoring target-site resistance in field populations of these and other insect species.

Transgenic Expression of a Viral Cystatin Gene CpBV-CST1 in Tobacco Confers Insect Resistance

A viral gene, CpBV-CST1, was identified from a polydnavirus Cotesia plutellae bracovirus (CpBV). Its protein product was significantly toxic to lepidopteran insects. This study generated a transgenic tobacco plant expressing CpBV-CST1 Expression of transgene CpBV-CST1 was confirmed in T1 generation (second generation after transgenesis) in both mRNA and protein levels. Young larvae of Spodoptera exigua (Hübner) suffered high mortalities after feeding on transgenic tobacco. All 10 T1 transgenic tobacco plants had no significant variation in speed-to-kill. In order to further explore insect resistance of these transgenic tobaccos, bioassays were performed by assessing antixenosis and antibiosis. S. exigua larvae significantly avoided T1 plants in a choice test. Larvae fed with T1 plant exhibited significant decrease in protease activity in the midgut due to consuming CpBV-CST1 protein produced by the transgenic plant. Furthermore, the transgenic tobacco exhibited similar insect resistance to other tobacco-infesting insects, including a leaf-feeding insect, Helicoverpa assulta, and a sap-feeding insect, Myzus persicae These results demonstrate that a viral cystatin gene can be used to develop insect-resistant transgenic plant, suggesting a prospective possibility of expanding the current transgenic approach to high-valued crops.

Computational Insights into the Different Resistance Mechanism of Imidacloprid versus Dinotefuran in Bemisia tabaci

Insecticide resistance is a critical problem for pest control and management. For Bemisia tabaci, striking high metabolic resistance (generally conferred by CYP6CM1) was observed for imidacloprid (IMI) and most other neonicotinoid members. However, dinotefuran (DIN) displayed very low resistance factors, which indicated distinct metabolic properties. Here, molecular modeling methods were applied to explore the different resistance features of IMI versus DIN within the Q type of CYP6CM1. It was found that Arg225 played crucial roles in the binding of IMI-CYP6CM1vQ with a cation-π interaction and two stable H-bonds; however, such interactions were all absent in the DIN-CYP6CM1vQ system. The stable binding of IMI with CYP6CM1vQ would facilitate the following metabolic reaction, while the weak binding of DIN might disable its potential metabolism, which should be an important factor for their distinct resistance levels. The findings might facilitate future design of the antiresistance neonicotinoid molecules.