Occurrence of target-site resistance to neonicotinoids in the aphid Myzus persicae in Tunisia, and its status on different host plants

Myzus persicae resistance to neonicotinoids-unravelling the contribution of different mechanisms to phenotype

BACKGROUND

Deciphering the mechanisms underlying insecticide resistance is key to devising appropriate strategies against this economically important trait. Myzus persicae, the green peach-potato aphid, is a major pest that has evolved resistance to many insecticide classes, including neonicotinoids. M. persicae resistance to neonicotinoids has previously been shown to result from two main mechanisms: metabolic resistance resulting from P450 overexpression and a targetsite mutation, R81T. However, their respective contribution to resistant phenotypes remains unclear.

RESULTS

By combining extensive insecticide bioassays with and without addition of the synergist PBO, and gene copy number and expression quantification of two key P450 enzymes (CYP6CY3 and CYP6CY4) in a 23 clone collection, we, (i) confirmed that metabolic resistance is correlated with P450 expression level, up to a threshold, (ii) demonstrated that the R81T mutation, in the homozygous state and in combination with P450 overexpression, leads to high levels of resistance to neonicotinoids, and, (iii) showed that there is a synergistic interaction between the P450 and R81T mechanisms, and that this interaction has the strongest impact on the strength of resistance phenotypes. However, even though the R81T mutation has a great effect on the resistance phenotype, different R81T genotypes can exhibit variation in the level of resistance, explained only partially by P450 overexpression.

CONCLUSION

To comprehend resistance phenotypes, it is important to take into account every mechanism at play, as well as the way these mechanisms interact. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Pyrethroid and carbamate resistance in Czech populations of Myzus persicae (Sulzer) from oilseed rape

BACKGROUND

Failures in controlling Myzus persicae by pyrethroids and carbamates have been observed in Czechia since 2018. Eleven populations collected from Czech oilseed rape fields during 2018-2021 were tested for susceptibility to 11 insecticides. The presence of a single nucleotide polymorphism (SNP) leading to knockdown resistance in M. persicae populations was screened using allelic discriminating quantitative real-time polymerase chain reaction (qPCR). The presence of mutations related with the resistance of M. persicae to pyrethroids and carbamates was detected by sequencing paratype voltage-gated sodium channel and acetylcholinesterase 2 genes, respectively.

RESULTS

Resistance to alpha-cypermethrin and pirimicarb was detected in most of the tested populations. The L1014F mutation was detected in 44.5% of M. persicae individuals surviving the field-recommended dose of alpha-cypermethrin. Sequencing of partial para gene for paratype voltage-gated sodium channel detected five different SNPs leading to four amino acid substitutions (kdr L1014F; s-kdr M918L; s-kdr M918T; and L932F). No pyrethroid-sensitive genotype was detected. The S431F amino acid substitution conferring resistance to carbamates was detected in 11 of 20 individuals with different pyrethroid-resistance genotypes.

CONCLUSION

Resistance of M. persicae to both pyrethroids and carbamates was detected in nine of 11 populations. High resistance of M. persicae was correlated with mutations of the sodium channel. Sulfoxaflor, flonicamid, and spirotetramat are proposed as effective compounds to control pyrethroid- and carbamate-resistant populations of M. persicae. © 2023 Society of Chemical Industry.

The current status, challenges, and future perspectives for managing diseases of brassicas

The Brassica genus comprises the greatest diversity of agriculturally important crops. Several species from this genus are grown as vegetable and oil crops for food, animal feed and industrial purposes. In particular, B. oleracea has been extensively bred to give rise to several familiar vegetables (cabbage, broccoli, cauliflower, kale and Brussels Sprouts, etc.) that are grouped under seven major cultivars. In 2020, 96.4 million tonnes of vegetable brassicas were produced globally with a 10.6% increase over the past decade. Yet, like other crops, the production of brassicas is challenged by diseases among which, black rot, clubroot, downy mildew and turnip yellows virus have been identified by growers as the most damaging to UK production. In some cases, yield losses can reach 90% depending upon the geographic location of cultivation. This review aims to provide an overview of the key diseases of brassicas and their management practices, with respect to the biology and lifecycle of the causal pathogens. In addition, the existing controls on the market as well as those that are currently in the research and development phases were critically reviewed. There is not one specific control method that is effective against all the diseases. Generally, cultural practices prevent disease rather than reduce or eliminate disease. Chemical controls are limited, have broad-spectrum activity, are damaging to the environment and are rapidly becoming ineffective due to the evolution of resistance mechanisms by the pathogens. It is therefore important to develop integrated pest management (IPM) strategies that are tailored to geographic locations. Several knowledge gaps have been identified and listed in this review along with the future recommendations to control these four major diseases of brassicas. As such, this review paper will act as a guide to sustainably tackle pre-harvest diseases in Brassica crops to reduce food loss.

P450-mediated resistance in Myzus persicae (Sulzer) (Hemiptera: Aphididae) reduces the efficacy of neonicotinoid seed treatments in Brassica napus

BACKGROUND

The prophylactic use of seeds treated with neonicotinoid insecticides remains an important means of controlling aphid pests in canola (Brassica napus) crops in many countries. Yet, one of the most economically important aphid species worldwide, the peach potato aphid (Myzus persicae), has evolved mechanisms which confer resistance to neonicotinoids, including amplification of the cytochrome P450 gene, CYP6CY3. While CYP6CY3 amplification has been associated with low-level resistance to several neonicotinoids in laboratory acute toxicity bioassays, its impact on insecticide efficacy in the field remains unresolved. In this study, we investigated the impact of CYP6CY3 amplification on the ability of M. persicae to survive neonicotinoid exposure under laboratory and semi-field conditions.

RESULTS

Three M. persicae clones, possessing different copy numbers of CYP6CY3, were shown to respond differently when exposed to the neonicotinoids, imidacloprid and thiamethoxam, in laboratory bioassays. Two clones, EastNaernup209 and Osborne171, displayed low levels of resistance (3-20-fold), which is consistent with previous studies. However, in a large-scale semi-field trial, both clones showed a surprising ability to survive and reproduce on B. napus seedlings grown from commercial rates of neonicotinoid-treated seed. In contrast, an insecticide-susceptible clone, of wild-type CYP6CY3 copy number, was unable to survive on seedlings treated in the same manner.

CONCLUSION

Our findings suggest that amplification of CYP6CY3 in M. persicae clones substantially impairs the efficacy of neonicotinoid seed treatments when applied to B. napus. These findings highlight the potentially important real-world implications of resistances typically considered to be 'low level' as defined through laboratory bioassays. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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.

Spatial Variation in Australian Neonicotinoid Usage and Priorities for Resistance Monitoring

Australia is the third largest exporting country of cereals and a leader in other major commodity crops, yet little data exist on pesticide usage patterns in agriculture. This knowledge gap limits the management of off-target chemical impacts, such as the evolution of pesticide resistance. Here, for the first time, we quantify spatial patterns in neonicotinoid applications in Australia by coalescing land use data with sales and market research data contributed by agrichemical and agribusiness companies. An example application to resistance management is explored through the development of recommendations for the cosmopolitan crop pest, Myzus persicae (Sulzer) (Hemiptera: Aphididae), utilizing spatial statistical models. This novel dataset identified Australian neonicotinoid usage patterns, with most neonicotinoid products in Australia applied as cereal, canola, cotton and legume seed treatments and soil applications in sugarcane. Importantly, there were strong regional differences in pesticide applications, which will require regionally specific strategies to manage off-target impacts. Indeed, the estimated spatial grid of neonicotinoid usage demonstrated a statistically significant influence on the distribution of M. persicae neonicotinoid resistance, indicating off-target impacts are unevenly distributed in space. Future research on neonicotinoid usage will be supported by the spatial grids generated and made available through this study. Overall, neonicotinoid pesticides are widely relied upon throughout Australia's plant production systems but will face increasing pressure from resistance evolution, emerging research on off-target impacts, and stricter regulatory pressures.

Molecular innovations underlying resistance to nicotine and neonicotinoids in the aphid Myzus persicae

The green peach aphid, Myzus persicae, is a globally distributed highly damaging crop pest. This species has demonstrated an exceptional ability to evolve resistance to both synthetic insecticides used for control, and natural insecticides produced by certain plants as a chemical defense against insect attack. Here we review work characterizing the evolution of resistance in M. persicae to the natural insecticide nicotine and the structurally related class of synthetic neonicotinoid insecticides. We outline how research on this topic has provided insights into long-standing questions of both evolutionary and applied importance. These include questions pertaining to the origins of novel traits, the number and nature of mutational events or 'adaptive steps' underlying the evolution of new phenotypes, and whether host plant adaptations can be co-opted to confer resistance to synthetic insecticides. Finally, research on the molecular mechanisms underlying insecticide resistance in M. persicae has generated several outstanding questions on the genetic architecture of resistance to both natural and synthetic xenobiotics, and we conclude by identifying key knowledge gaps for future research. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Case Study Using Recommended Reference Genes Actin and 18S for Reverse-Transcription Quantitative Real-Time PCR Analysis in Myzus persicae

Myzus persicae is a globally important pest with the ability to adjust to a wide range of environmental situations, and many molecular technologies have been developed and applied to understand the biology and/or control this pest insect directly. Reverse-transcription quantitative real-time PCR (RT-qPCR) is a primary molecular technology that is used to quantify gene expression. Choosing a stable reference gene is significantly important for precisely clarifying the expression level of the target gene. Actin and 18S have been recommended as stable compounds for real-time RT-qPCR in M. persicae under the tested biotic and abiotic conditions. In this study, we checked the stability of Actin and 18S by analyzing the relative expression levels of the cytochrome 450 monooxygenase family member genes CYP6CY3 and CYP6-1, carboxylesterase gene E4 and vacuolar protein sorting gene VPS11 via RT-qPCR under various conditions. The expression levels of these four target genes were normalized using both Actin and 18S individually and the combination of these two genes. Our results confirmed that Actin and 18S can be used as reference genes to normalize the expression of target genes under insecticide treatment and starvation in M. persicae. However, at the developmental stages of M. persicae, the expression of the four tested target genes was normalized stably by Actin but not 18S, with the latter presenting a problematic change with the developmental stages. Thus, the stability of reference genes in response to diverse biotic and abiotic factors should be evaluated before each RT-qPCR experiment.

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.

Spatiotemporal Dynamics and Natural Mortality Factors of Myzus persicae (Sulzer) (Hemiptera: Aphididae) in Bell Pepper Crops

Pest populations are mostly regulated by climate, intra- and interspecific competition, natural enemies, and host plant quality. Myzus persicae (Sulzer) (Hemiptera: Aphididae) is a widely adapted aphid in the agroecosystems and is one of the main bell pepper pests. In the present study, we determined the spatial and temporal dynamics and the regulatory factors of M. persicae populations in bell pepper crops. The number of aphids and their natural enemies were evaluated during 2 years in four commercial bell pepper fields. Myzus persicae density data were related to temperature, rainfall, and natural enemies by multiple regression analysis and were then submitted to geostatistical analysis. The density of M. persicae was higher during the plant's reproductive growth stage. Rainfall, Chrysoperla spp., and Toxomerus spp. regulate M. persicae populations. Initial infestations of this pest occur along the edges of the fields and subsequently spread towards the center. This information is useful for integrated management programs aimed at anticipating periods of higher abundance of M. persicae and identifying arthropods to be prioritized in biological control.

Neonicotinoids removal by associated binary, tertiary and quaternary advanced oxidation processes: Synergistic effects, kinetics and mineralization

The degradation of four representative neonicotinoids, namely Thiamethoxam, Imidacloprid, Acetamiprid and Thiacloprid, was carried out by the sequential association of different advanced oxidation processes, including Ozonation, Electro-chemical Oxidation, Ultrasound, Ultraviolet radiation, and their different possible associations. There are no published papers in the literature on the removal of this type of insecticides through these associated oxidation processes. Single oxidation processes did not achieve total pollutants removal in less than 3 h (only UV radiation treatment obtain a total removal of Thiamethoxan in 150 min, but with mineralization below 15% TOC). For double sequential processes, Electro-oxidation-Ozone treatment obtains a total removal of Imidacloprid in 120 min and an increase of mineralization to 50% TOC. Three or four sequential processes are recommended to improve degradation and mineralization rates in a significant way, Electro-oxidation-Ozone-UV treatment obtains a total removal of Thiamethoxan in 80 min with mineralization over 75% TOC. These results confirm important synergistic effects which were quantified. The global trend indicates that Thiamethoxam is the most oxidizable neonicotinoid, whereas Acetamiprid is the most recalcitrant compound. The degradation rate of each neonicotinoid followed pseudo-first-order kinetics and the different oxidation pathways were also quantified from a kinetic point of view.

Relative Toxicity and Residual Activity of Nanocapsules and Commercial Formulations of Pirimicarb and Pymetrozine Against Myzus persicae (Hemiptera: Aphididae)

The green peach aphid, Myzus persicae (Sulzer), is one of the most common pest species that has the potential to transmit more than 100 plant viruses. Controlling this pest is difficult because it has become resistant to a wide range of insecticides. Nanoformulation has the capacity to reduce the pesticide load in agriculture and thus reduce the risks on human health and the environment. In this study, nanocapsules of pirimicarb and pymetrozine were prepared using nanostructured lipid carriers. The size, morphology, and encapsulation efficiency of nanocapsules were investigated using dynamic light scattering, scanning electron microscopy, and UV-VIS spectrophotometer. Zeta potential studies revealed stability of the nanocapsules of both insecticides. The encapsulation efficiencies were 85 and 81% for pirimicarb and pymetrozine, respectively. The nanocapsules were spherical with sizes of 35.38 and 35.12 nm for pirimicarb and pymetrozine, respectively. The LC50 values for the wettable powder (WP) and nanocapsule of pirimicarb after 48 h were 216.2 and 73.2 mg ai/l; for pymetrozine after 96 h, the values were 40.6 and 14.8 mg ai/l, respectively. Durations of residual activity for WP and nanocapsule formulations of pirimicarb were 7 and 15 d, respectively. The residual activity periods for WP and nanocapsule formulations of pymetrozine were 9 and 17 d, respectively. The results revealed that nanoencapsulation can improve performance allowing for reduced doses and increased duration of insecticidal activity for both of the insecticides tested.

Cabbage stem flea beetle's (Psylliodes chrysocephala L.) susceptibility to pyrethroids and tolerance to thiacloprid in the Czech Republic

The cabbage stem flea beetle (CSFB), Psylliodes chrysocephala (Coleoptera: Chrysomelidae), has recently become a major pest species in winter oilseed rape in the Czech Republic. The susceptibility of CSFB populations from two localities to six pyrethroids, two neonicotinoids, one organophosphate and one oxadiazine was evaluated in 2015–2018 in glass vial experiments. The susceptibility of CSFB to thiacloprid and thiamethoxam was evaluated in feeding experiment in 2017 and 2018. High susceptibility of CSFB populations to lambda-cyhalothrin, cypermethrin, esfenvalerate, tau-fluvalinate, etofenprox, deltamethrin, chlorpyrifos, indoxacarb and acetamiprid was observed in the glass vial experiments. The LC50 and LC90 data obtained for pyrethroids in these experiments in 2015 represent baseline for CSFB resistance monitoring to pyrethroids in the Czech Republic. High tolerance of CSFB to thiacloprid of CSFB was demonstrated in glass vial and the feeding experiment, too.

Neonicotinoids: molecular mechanisms of action, insights into resistance and impact on pollinators

Neonicotinoids are insecticides that target insect nicotinic acetylcholine receptors (nAChRs), exhibiting high selective toxicity to insects over vertebrates and good systemic activity in crop plants. For these reasons, neonicotinoids currently make up ∼30% of insecticide sales worldwide. However, due to their adverse impact on pollinators such as honey bees and bumble bees, neonicotinoids are being banned from the EU, and other countries may follow. It is therefore crucial to understand the mechanism underlying neonicotinoid actions on pollinators as well as on the nAChRs of pests, with a view to understanding their selectivity. Here we review the molecular mechanisms of neonicotinoid actions at an atomic level, through structural and resistance mechanism studies and propose relevant research topics for further studies on the future of pest management.

Evaluation of Insecticides induced hormesis on the demographic parameters of Myzus persicae and expression changes of metabolic resistance detoxification genes

Insecticide induced-hormesis is a bi-phasic phenomenon generally characterized by low-dose induction and high-dose inhibition. It has been linked to insect pest outbreaks and insecticide resistance, which have importance in the integrated pest management (IPM). In this paper, hormesis effects of four insecticides on demographic parameters and expression of genes associated with metabolic resistance were evaluated in a field collected population of the green peach aphid, Myzus persicae Sulzer. The bioassay results showed that imidacloprid was more toxic than acetamiprid, deltamethrin and lambda-cyhalothrin. After exposure to sublethal doses of acetamiprid and imidacloprid for four generations, significant prolonged nymphal duration and increased fecundity were observed. Subsequently, mean generation time (T) and gross reproductive rate (GRR) was significantly increased. Moreover, expression of CYP6CY3 gene associated with resistance to neonicotinoids was increased significantly compared to the control. For pyrethriods, across generation exposure to sublethal doses of lambda cyhalothrin and deltamethrin prolonged the immature development duration. However, the expression of E4 gene in M. persicase was decreased by deltamethrin exposure but increased by lambda cyhalothrin. Based on results, demographic fitness parameters were effected by hormetic dose and accompanied with detoxifying genes alteration, hence, which would be evaluated in developing optimized insect pest management strategies.

Neonicotinoid insecticides mode of action on insect nicotinic acetylcholine receptors using binding studies

Nicotinic acetylcholine receptors (nAChRs) are the main target of neonicotinoid insecticides, which are widely used in crop protection against insect pests. Electrophysiological and molecular approaches have demonstrated the presence of several nAChR subtypes with different affinities for neonicotinoid insecticides. However, the precise mode of action of neonicotinoids on insect nAChRs remains to be elucidated. Radioligand binding studies with [³H]-α-bungarotoxin and [³H]-imidacloprid have proved instructive in understanding ligand binding interactions between insect nAChRs and neonicotinoid insecticides. The precise binding site interactions have been established using membranes from whole body and specific tissues. In this review, we discuss findings concerning the number of nAChR binding sites against neonicotinoid insecticides from radioligand binding studies on native tissues. We summarize the data available in the literature and compare the binding properties of the most commonly used neonicotinoid insecticides in several insect species. Finally, we demonstrate that neonicotinoid-nAChR binding sites are also linked to biological samples used and insect species.