Short-term and transgenerational effects of the neonicotinoid nitenpyram on susceptibility to insecticides in two whitefly species

Morphological and Phylogenetic Analyses Reveal Three New Species of Entomopathogenic Fungi Belonging to Clavicipitaceae (Hypocreales, Ascomycota)

This study aims to report three new species of Conoideocrella and Moelleriella from Yunnan Province, Southwestern China. Species of Conoideocrella and Moelleriella parasitize scale insects (Coccidae and Lecaniidae, Hemiptera) and whiteflies (Aleyrodidae, Hemiptera). Based on the phylogenetic analyses of the three-gene nrLSU, tef-1α, and rpb1, it showed one new record species (Conoideocrella tenuis) and one new species (Conoideocrella fenshuilingensis sp. nov.) in the genus Conoideocrella, and two new species, i.e., Moelleriella longzhuensis sp. nov. and Moelleriella jinuoana sp. nov. in the genus Moelleriella. The three new species were each clustered into separate clades that distinguished themselves from one another. All of them were distinguishable from their allied species based on their morphology. Morphological descriptions, illustrations, and comparisons of the allied taxa of the four species are provided in the present paper. In addition, calculations of intraspecific and interspecific genetic distances were performed for Moelleriella and Conoideocrella.

Transgenerational sublethal pyrethroid exposure gives rise to insecticide resistance in a pest insect

The evolution of insecticide resistance has been attributed to strong directional selection by lethal concentrations of insecticides, but there is growing evidence that sublethal doses may also modify resistance through the hormetic effects. Hormesis is a beneficial effect caused by exposure to low doses. However, the role of parental (transgenerational) effects on hormesis, and through that on insecticide resistance, is still unclear. We investigated the effects of several sublethal pyrethroid insecticide (Decis) doses on survival, body mass, and reproduction within four generations (F0, F1, F2, and F3) of the Colorado potato beetle (Leptinotarsa decemlineata). We found that insecticide exposure had mostly linear adverse within-generation effects: decreased larva-to-adult survival, adult body mass, and egg hatching. However, transgenerational exposure led to hormetic effects: increased larva-to-adult survival and pre-diapause adult body mass. Moreover, transgenerational effects were even more positive for offspring exposed to insecticides, leading to decreased larva-to-adult survival, increased body mass, and egg hatching. Our results show that despite mostly negative within-generation effects, transgenerational sublethal exposure to insecticide can cause unwanted positive hormetic effects in their offspring, making them to resist or tolerate the insecticides better, even though the underlying mechanisms are still unclear.

Effect of Paclobutrazol Application on Enhancing the Efficacy of Nitenpyram against the Brown Planthopper, Nilaparvata lugens

The brown planthopper (BPH), Nilaparvata lugens, is one of the most destructive rice pests in Asia. It has already developed a high level of resistance to many commonly used insecticides including nitenpyram (NIT), which is a main synthetic insecticide that is used to control BPH with a much shorter persistence compared to other neonicotinoid insecticides. Recently, we found that an exogenous supplement of paclobutrazol (PZ) could significantly enhance the efficacy of NIT against BPH, and the molecular mechanism underlying this synergistic effect was explored. The results showed that the addition of a range of 150-300 mg/L PZ increased the toxicity of NIT against BPH with the highest mortalities of 78.0-87.0% on the 16th day after treatments, and PZ could also significantly prolong the persistence of the NIT efficacies. Further investigation suggested that PZ directly increased the content of flavonoids and H2O2 in rice and increased the activity of polyphenol oxidase, which might be involved in the constitutive defense of rice in advance. Additionally, there was an interaction between PZ and BPH infestation, indicating that PZ might activate the host defense responses. Therefore, PZ increased the efficacy of NIT against the brown planthoppers by enhancing the constitutive and inducible defense responses of rice. Our study showed for the first time that PZ could contribute to improving the control effects of insecticides via inducing the defense responses in rice plants against BPH, which provided an important theoretical basis for developing novel pest management strategies in the field.

Sublethal Effects of Neonicotinoid Insecticides on the Development, Body Weight and Economic Characteristics of Silkworm

Silkworm Bombyx mori (L.) (Lepidoptera: Bombycidae) is a critical insect for silk producers, but the inappropriate application of insecticides negatively affects the physiology and behavior of silkworms. This study found that the effects of neonicotinoid insecticides applied using two spraying methods on the growth and development of silkworms were different: the median lethal concentration (LC₅₀) values of two pesticides applied using the leaf-dipping method were 0.33 and 0.83 mg L^-1 and those of two pesticides applied using the quantitative spraying method were 0.91 and 1.23 mg kg^-1. The concentration of pesticides on the mulberry leaves did not decrease after their application using the quantitative spraying method, and a uniform spraying density was observed after the mulberry leaves were air-dried (no liquid) under realistic conditions. We then treated silkworms with the quantitative spraying method and leaf-dipping method. The treatment of silkworm larvae with imidacloprid and thiamethoxam at sublethal concentrations significantly prolonged the development time and significantly decreased the weight and pupation rate, as well as economic indicators of enamel layers and sputum production. Thiamethoxam treatment significantly increased the activities of carboxylesterase (CarE) and glutathione-S-transferase (GST). The activity of CarE and GST increased, decreased, and then increased, and the highest activity was detected on the 10th and 12th days. Thiamethoxam exposure significantly elevated the transcription levels of CarE-11, GSTe3 and GSTz2 and induced DNA damage in hemocytes. This study confirmed that the quantitative spray method is more stable than the leaf-dipping method. Moreover, imidacloprid and thiamethoxam treatment affected the economy and indexes of silkworms and induced changes in detoxification enzymes and DNA damage in silkworms. These results provide a basis for understanding the mechanism of the sublethal effects of insecticides on silkworms.

Effects of imidacloprid-induced hormesis on the development and reproduction of the rose-grain aphid Metopolophium dirhodum (Hemiptera: Aphididae)

Field populations of insect pests are affected by sub-lethal doses of insecticides, leading to hormesis. Imidacloprid is a neonicotinoid insecticide widely used to control various sucking insect pests, including aphids. In this study, the effects of sub-lethal concentrations of imidacloprid on the life table traits of the rose-grain aphid Metopolophium dirhodum (Walker) were evaluated on parental and first filial generations. The results showed that sub-lethal concentrations of imidacloprid significantly reduced the fecundity, adult longevity, and reproductive period of M. dirhodum in parental generation (F₀). However, the imidacloprid-induced hormetic effects on development and reproduction were detected in the F₁ generation. These hormetic effects were indicated by significantly higher adult longevity, fecundity, survival rate, intrinsic and finite rates of increase, and net reproductive rate of first filial generation (F₁) of M. dirhodum. Our finding indicated that the application of sub-lethal concentrations of imidacloprid inhibited parental generation (F₀), but it significantly stimulated the population growth of filial generation (F₁) in the M. dirhodum. The results support the inclusion of insecticides in integrated pest management programs for managing wheat aphids.

Sublethal Effects of Thiamethoxam on Biological Traits and Detoxification Enzyme Activities in the Small Brown Planthopper, Laodelphax striatellus (Fallén)

The small brown planthopper (Laodelphax striatellus (Fallén), Hemiptera: Delphacidae), is an important agricultural pest of rice, and neonicotinoid insecticides are commonly used for controlling L. striatellus. However, the sublethal effects of thiamethoxam on L. striatellus remain relatively unknown. In this study, an age-stage life table procedure was used to evaluate the sublethal effects of thiamethoxam on the biological parameters of L. striatellus. Additionally, activities of carboxylesterase, glutathione S-transferase, and cytochrome P450 monooxygenase in the third instar nymphs were analyzed. The results indicated that the survival time of F0 adults and the fecundity of female adults decreased significantly after the third instar nymphs were treated with sublethal concentrations of thiamethoxam (LC15 0.428 mg/liter and LC30 0.820 mg/liter). The developmental duration, adult preoviposition period, total preoviposition period, and mean generation time of the F1 generation increased significantly, whereas the fecundity of the female adults, intrinsic rate of increase (ri), and finite rate of increase (λ) decreased significantly. The oviposition period was significantly shorter for the insects treated with LC30 than for the control insects. Neither sublethal concentrations had significant effects on the adult longevity, net reproduction rate (R0), or gross reproduction rate (GRR) of the F1 generation. The activities of carboxylesterase, glutathione-S-transferase, and cytochrome P450 monooxygenase increased significantly after the thiamethoxam treatments. These results indicate that sublethal concentrations of thiamethoxam can inhibit L. striatellus population growth and enhance detoxification enzyme activities.

Assessment of sublethal and transgenerational effects of spirotetramat, on population growth of cabbage aphid, Brevicoryne brassicae L. (Hemiptera: Aphididae)

The cabbage aphid (Brevicoryne brassicae L.) is a devastating pest of cruciferous crops causing economic damage worldwide and notably owing to its increasing resistance to commonly used pesticides. Such resistance prompts the development of integrated pest management (IPM) programs that include novel pesticides being effective against the aphids. Spirotetramat is a novel insecticide used against sap-sucking insect pests, particularly aphids. This study evaluated the toxicity of spirotetramat to adult apterous B. brassicae after 72 h using the leaf dipping method. According to the toxicity bioassay results, the LC₅₀ value of spirotetramat to B. brassicae was 1.304 mgL^-1. However, the sublethal concentrations (LC₅ and LC₁₅) and transgenerational effects of this novel insecticide on population growth parameters were estimated using the age-stage, two-sex life table theory method. The sublethal concentrations (LC₅; 0.125 mgL^-1 and LC₁₅; 0.298 mgL^-1) of spirotetramat reduced the adult longevity and fecundity of the parent generation (F₀). These concentrations prolonged the preadult developmental duration while decreasing preadult survival, adult longevity and reproduction of the F₁ generation. The adult pre-reproductive period was also extended by spirotetramat treatment groups. Subsequently, the population growth parameters such as the intrinsic rate of increase r, finite rate of increase λ and net reproductive rate R ₀ of the F₁ generation were decreased in spirotetramat treatment groups whereas, the mean generation time T of the F₁ generation was not affected when compared to the control. These results indicated the negative effect of sublethal concentrations of spirotetramat on the performance of B. brassicae by reducing its nymphal survival, extending the duration of some immature stages and suppressing the population growth of B. brassicae. Overall, we demonstrated that spirotetramat is a pesticide showing both sublethal activities, and transgenerational effects on cabbage aphid; it may be useful for implementation in IPM programs against this aphid pest.

Hormetic and transgenerational effects in spotted-wing Drosophila (Diptera: Drosophilidae) in response to three commonly-used insecticides

Although insecticide formulations and spray rates are optimized to achieve lethal exposure, there are many factors in agricultural settings that can reduce the effective exposure of insect pests. These include weather patterns, timing of application, chemical degradation/volatilization, plant structural complexity, and resistant populations. While sub-lethal exposure to insecticides can still have negative impacts on pest populations, they can also lead to stimulatory, or hormetic, responses that can increase the fitness of surviving insects. Sub-lethal concentrations may also produce increased tolerance in the offspring of surviving adults through transgenerational effects. Sub-lethal effects are pertinent for the invasive fruit pest, spotted-wing Drosophila, Drosophila suzukii (Matsumura), because its small size, diurnal movement patterns, and utilization of hosts with complex plant structures, such as caneberries and blueberries, make effective insecticide applications tenuous. In this study, we measured spotted-wing Drosophila survivorship, reproductive performance, and offspring tolerance in flies exposed to sub-lethal concentrations of three commonly-used insecticides (zeta-cypermethrin, spinetoram, and pyrethrin). We found some evidence for hormesis, with survival effects being sex- and concentration-dependent for all insecticides. Males were far more susceptible to insecticides than females, which in some cases exhibited higher eclosion success and reproductive rates when exposed to sub-lethal doses. We did not observe significant transgenerational effects at sub-lethal concentrations, despite trends of increased offspring viability for zeta-cypermethrin and spinetoram. More research, however, is needed to fully understand the role that sub-lethal effects may play in pest population dynamics, insecticide efficacy, and the development of genetic resistance.

Exposures to deltamethrin on immature Chironomus columbiensis drive sublethal and transgenerational effects on their reproduction and wing morphology

Sublethal exposure to insecticides can trigger unintended responses in non-target insects that may disrupt reproductive and developmental performances of these organisms. Here, we assessed whether sublethal exposure to the pyrethroid insecticide deltamethrin in early life had sublethal and transgenerational effects on the reproduction (i.e., fecundity and fertility) and wing morphology of Chironomus columbiensis, an aquatic insect used as a water quality indicator. We first conducted concentration-response bioassays to evaluate the susceptibility of C. columbiensis larvae to deltamethrin. Our results revealed that deltamethrin toxicity was approximately 7-fold higher when C. columbiensis larvae where exposed to 96 h (LC₅₀ = 0.17 [0.15-0.20] μg/L) than to 24 h (LC₅₀ = 1.17 [0.97-1.43] μg/L). Furthermore, the sublethal exposures (at LC₁ = 0.02 μg/L or LC₁₀ = 0.05 μg/L) of immature C. columbiensis resulted in lower fecundity (e.g., reduced eggs production) and morphometric variation wing shapes. Further reduction in fertility rates (quantity of viable eggs) occurred at deltamethrin LC₁₀ (0.05 μg/L). Almost 80% of the fecundity was recovered with only a single recovery generation; however, two subsequent recovery generations were not sufficient to fully recover fecundity in C. columbiensis. Specimens recovered from 98.5% of wing morphometric variation after two consecutive generations without deltamethrin exposure. Collectively, our findings demonstrates that sublethal exposure to synthetic pyrethroids such as deltamethrin detrimentally affect the reproduction and wing shape of C. columbiensis, but also indicate that proper management of these compounds (e.g., concentration and frequency of application) would suffice for these insects' population recovery.

Transcriptome analysis in the thiamethoxam resistance of seven-spot ladybird beetle, Coccinella septempunctata (Coleoptera: Coccinellidae)

The seven-spot ladybird beetle, Coccinella septempunctata Linnaeus (Coleoptera: Coccinellidae) has been used as the main biological control agent against all kinds of aphids in farmland and greenhouse. In this study, a thiamethoxam-resistant strain (ThR) and a susceptible strain (SS) of seven-spot ladybird beetle were established, and differentially expressed genes (DEGs) associated with thiamethoxam resistance were recorded through de novo Illumina HiSeq 4000 sequencing. A total of 53.5 Gb of clean data were obtained and finally assembled into 21,217 unigenes from ThR and SS transcriptomes. 1798 DEGs were identified between the ThR libraries and the SS libraries, including 560 up-regulated genes and 1238 down-regulated genes. Some cytochrome p450 monooxygenases (CYP450s), UDP-glycosyltransferases (UGTs), esterases (ESTs) and ATP-binding cassette (ABC) transporters were observed to be up-regulated and the nicotinic acetylcholine receptors (nAChRs) α subunit gene down-regulated in the ThR strain compared to the SS strain. This study provides genetic information for further studies on thiamethoxam resistance mechanisms in the seven-spot ladybird beetle.

Insect Epigenetic Mechanisms Facing Anthropogenic-Derived Contamination, an Overview

Currently, the human species has been recognized as the primary species responsible for Earth's biodiversity decline. Contamination by different chemical compounds, such as pesticides, is among the main causes of population decreases and species extinction. Insects are key for ecosystem maintenance; unfortunately, their populations are being drastically affected by human-derived disturbances. Pesticides, applied in agricultural and urban environments, are capable of polluting soil and water sources, reaching non-target organisms (native and introduced). Pesticides alter insect's development, physiology, and inheritance. Recently, a link between pesticide effects on insects and their epigenetic molecular mechanisms (EMMs) has been demonstrated. EMMs are capable of regulating gene expression without modifying genetic sequences, resulting in the expression of different stress responses as well as compensatory mechanisms. In this work, we review the main anthropogenic contaminants capable of affecting insect biology and of triggering EMMs. EMMs are involved in the development of several diseases in native insects affected by pesticides (e.g., anomalous teratogenic reactions). Additionally, EMMs also may allow for the survival of some species (mainly pests) under contamination-derived habitats; this may lead to biodiversity decline and further biotic homogenization. We illustrate these patterns by reviewing the effect of neonicotinoid insecticides, insect EMMs, and their ecological consequences.

Actinomycetes Rhodococcus ruber CGMCC 17550 degrades neonicotinoid insecticide nitenpyram via a novel hydroxylation pathway and remediates nitenpyram in surface water

Neonicotinoid insecticides are neurotoxicants that cause serious environmental pollution and ecosystem risks. In the present study, a nitenpyram-degrading bacterium, Rhodococcus ruber CGMCC 17550, was isolated from a nitenpyram production sewage treatment tank. Liquid chromatography-mass spectrometry analysis revealed R. ruber degraded nitenpyram via a novel hydroxylation pathway to form three different metabolites, one of which was confirmed to hydroxylate nitenpyram at the C3 site of the 6-chlorpyridine cycle by nuclear magnetic resonance analysis. The nitenpyram degradation rate increased as the biomass of resting R. ruber CGMCC 17550 cells increased, reaching 98.37% at an OD₆₀₀ of 9 in transformation broth containing 100 mg L^-1 nitenpyram after 72 h of incubation. Nitenpyram degradation by R. ruber CGMCC 17550 was insensitive to dissolved oxygen levels. Use of glucose, fructose and pyruvate as co-substrates slightly increased nitenpyram degradation. The cytochrome P450 inhibitor 1-aminobenzotriazole strongly inhibited nitenpyram degradation, indicating that P450 enzymes may mediate nitenpyram hydroxylation. Inoculation of R. ruber CGMCC 17550 enhanced nitenpyram degradation in surface water. Additionally, R. ruber cells immobilized by calcium-alginate remediated 87.11% of 100 mg L^-1 NIT in 8 d. Genome sequencing analysis confirmed that R. ruber CGMCC 17550 has metabolic diversity and abundant KEGG genes involved in xenobiotics biodegradation and metabolism. These findings demonstrate that R. ruber CGMCC 17550 is capable of unique biodegradation of nitenpyram via the hydroxylation pathway and is a promising bacterium for bioremediation of contaminants.

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).

Comparative selectivity of nano and commercial formulations of pirimicarb on a target pest, Brevicoryne brassicae, and its predator Chrysoperla carnea

Nanotechnology is a new field in the pesticide industry. Nanopesticides represent an emerging technological tool that offers a range of benefits including increased efficacy, durability, and reduction in the amounts of used active ingredients. However, due to the lack of studies on the toxicity and the sublethal effects on pests and natural enemies, the extent of action and fate of these nanopesticdes is still not fully understood limitting thus their wide use. In this study, we encapsulated the pirimicarb insecticide using nanostructured lipid carriers (NLC) and investigated the toxicity and sublethal effects (LC₂₅) of the resulting nanocapsules against the cabbage aphid, Brevicoryne brassicae (Linnaeus) (Hemiptera: Aphididae) and its natural enemy the green lacewings Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae). Nanoencapsulation of pirimicarb enhanced 12.6-fold its toxicity to cabbage aphids compared to its commercial formulation. Furthermore, analysis of the age-stage, two-sex life table showed that negative effects on the B. brassicae aphid population growth were observed on F0 and F1 generations when aphids of parental (F0) generation were exposed to subelethal dose (LC₂₅) of both formulations of pirimicarb. However, negative effects from sublethal exposure to the commercial and nanoformulated pirimicarb resulted in significant reduction on the net reproductive rate, intrinsic rate of natural increase, and finite rate of increase of the green lacewings C. carnea. Our findings indicate that the approaches and assumptions used to assess the risks of conventional insecticides may not apply for nanopesticides. Further research is still needed to better understand the environmental impact of these compounds.

Oxidative stress and genotoxicity of nitenpyram to earthworms (Eisenia foetida)

In this study, the artificial soil poisoning method was used to explore the antioxidative stress mechanism and gene changes of earthworms (Eisenia foetida) after application of nitenpyram. The toxic effects of nitenpyram on earthworms were combined with the method called the second-generation integrated biomarker response index method (IBRv2) to be comprehensively analyzed by studying the reactive oxygen species (ROS) content, superoxide dismutase (SOD) activity, catalase (CAT) activity, glutathione S-transferase (GST) activity, malondialdehyde (MDA) content and DNA damage degree in earthworms. The results showed that the ROS content in the high-concentration (2.5 mg/kg) nitenpyram treatment group changed significantly. The changes of antioxidant enzymes in earthworms were also obvious. In terms of SOD enzyme activity, under the induction of nitenpyram, SOD activity in the 1 mg/kg and 2.5 mg/kg treatment groups was significantly enhanced. The concentration-treated group could all affect the activity of earthworm detoxifying enzyme GST. Earthworm DNA olive tail in the nitenpyram treatment group with different concentrations was mainly concentrated at low and medium levels at 21d, and the proportion was the largest during the whole exposure period, showing a significant dose-effect relationship. This study confirms that nitenpyram not only has a toxic effect on the physiological and biochemical indicators of earthworms, but also cannot be underestimated on its genetic level.

Genome-wide identification of neuropeptides and their receptor genes in Bemisia tabaci and their transcript accumulation change in response to temperature stresses

Insect neuropeptides play an important role in regulating physiological functions such as growth, development, behavior and reproduction. We identified temperature-sensitive neuropeptides and receptor genes of the cotton whitefly, Bemisia tabaci. We identified 38 neuropeptide precursor genes and 35 neuropeptide receptors and constructed a phylogenetic tree using additional data from other insects. As temperature adaptability enables B. tabaci to colonize a diversity of habitats, we performed quantitative polymerase chain reaction with two temperature stresses (low = 4 °C and high = 40 °C) to screen for temperature-sensitive neuropeptides. We found many neuropeptides and receptors that may be involved in the temperature adaptability of B. tabaci. This study is the first to identify B. tabaci neuropeptides and their receptors, and it will help to reveal the roles of neuropeptides in temperature adaptation of B. tabaci.

Functional and evolutionary characterization of chemosensory protein CSP2 in the whitefly, Bemisia tabaci

BACKGROUND

Chemosensory proteins (CSPs) are thought to play essential roles in insect chemical communication, but their exact physiological functions remain unclear.

RESULTS

In this study, we investigated the functions of the CSP2 gene in the whitefly Bemisia tabaci using protein expression and the binding affinity spectrum of CSP2 to different types of odor molecules. Moreover, the evolutionary characteristics of the CSP2 gene were studied. The data obtained using binding assay showed that the CSP2 protein can bind to a broad range of plant volatiles including the homoterpene (E)-3,8-dimethyl-1,4,7-nonatriene (DMNT) and its analogs. In addition, using a behavioral experimental approach we identified that DMNT can repel the selection and oviposition of B. tabaci. Furthermore, protein structure modeling, molecular docking analyses and a functional mutation experiment were carried out resulting in the final identification of key amino acid residue Y11, which displayed important roles in the binding of CSP2 to DMNT. The results also showed that Y11 is located in the pocket region where CSP2 has a pi-alkyl interaction with DMNT. Meanwhile, comparative and evolutionary analyses indicated that CSP2 shared a high sequence similarity with CSPs of other insect family members such as Sternorrhyncha and Auchenorrhyncha including aphids, whiteflies and planthoppers.

CONCLUSION

These results suggested that CSP2 likely contributes to mediating responses of B. tabaci to plant volatiles, which may play a pivotal role in its feeding and oviposition preferences. Moreover, these findings could provide key information for exploring efficiency monitoring and integrated pest management strategies of B. tabaci.

Detrimental sublethal effects hamper the effective use of natural and chemical pesticides in combination with a key natural enemy of Bemisia tabaci on tomato

BACKGROUND

Bemisia tabaci (Hemiptera: Aleyrodidae) represents one of the greatest threats to agricultural crops. Chemical control is the primary tool used in integrated pest management (IPM) programs. However, release of the predator Nesidiocoris tenuis (Hemiptera: Miridae) on tomato plants is a highly recommended control tactic. The objective of this study was to evaluate the efficacy of a commercial borax plus citrus oil (BCO) product against B. tabaci in the presence and absence of N. tenuis. The synthetic insecticide lambda-cyhalothrin was used as a positive control. We also evaluated the sublethal effects of BCO on the behavior and predation rate of N. tenuis.

RESULTS

Our results demonstrated that BCO, alone and at its maximum recommended field rate for B. tabaci, was not effective in controlling the pest under laboratory conditions. Application of BCO simultaneous with N. tenuis release did not reduce the increase in the B. tabaci population. Effective control of B. tabaci was achieved using only N. tenuis. However, synthetic lambda-cyhalothrin pyrethroid, used here as a control, caused high pest mortality and led to on-site extinction of N. tenuis, which did not occur for insects exposed to BCO. Lambda-cyhalothrin and BCO significantly affected the foraging behavior of N. tenuis, reducing the predation rate, especially following exposure to lambda-cyhalothrin.

CONCLUSION

The insecticide lambda-cyhalothrin achieved satisfactory results in suppressing B. tabaci, but was harmful to N. tenuis. Additionally, lambda-cyhalothrin and BCO affected predator behavior. © 2020 Society of Chemical Industry.

Low herbicide doses can change the responses of weeds to subsequent treatments in the next generation: metamitron exposed PSII-target-site resistant Chenopodium album as a case study

BACKGROUND

It is well known that exposure to mild stress can precondition organisms to better tolerate subsequent stress exposure in the same or future generations. Since herbicide hormesis also represents a moderate stress to exposed plants, a transgenerational priming is likely but not proven. Especially in herbicide-resistant weeds showing enhanced reproductive fitness after regular herbicide treatments, the ability to induce resilient offspring phenotypes via hormesis may hasten the evolution of herbicide resistance in weeds. This hypothesis was studied for the triazinone metamitron in an F1 offspring generation of PSII target-site resistant (TSR) plants of Chenopodium album propagated after parental conditioning with various metamitron doses.

RESULTS

In two independent dose-response greenhouse trials, there was a positive correlation between the strength of the stimulatory response during parental preconditioning and the magnitude of transgenerational changes in herbicide sensitivity and hormesis expression. Parental conditioning at subhormetic and toxic concentrations lead to less resilient offspring, while conditioning doses that induced a pronounced hormetic effect in F0 plants had a sensitivity-reducing and hormesis-promoting effect on the offspring. The observed reduction in sensitivity in F1 plants compared to unconditioned F1 plants was up to 2.2-fold.

CONCLUSIONS

This study demonstrates that hormetic herbicide treatments have the ability to prime weeds for enhanced tolerance to subsequent treatments in the next generation. Effects proved dose sensitive and may act in concert with other stimulatory adaptations in plant populations. This is relevant for weed control and herbicide resistance evolution, but also for herbicide side-effects that go beyond the exposed area. © 2020 The Author. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Target and non-target impact of systemic insecticides on a polyphagous aphid pest and its parasitoid

Systemic insecticides are used to control agricultural pests globally and their non-target impact at non-lethal doses on beneficial arthropods has been recognized. We assessed the baseline toxicity of imidacloprid, thiamethoxam and sulfoxaflor-based insecticides on the polyphagous aphid pest, Aphis gossypii (Hemiptera: Aphididae), and their non-target effects on its main parasitoid, Aphidius colemani (Hymenoptera: Braconidae), evaluated by residual contact exposure to the median lethal (LC₅₀), the low lethal (LC₂₀) and the sublethal (LC₁) concentrations of the three tested insecticides, earlier estimated for the target pest. The results showed that the LC₅₀s for the aphid were 6.4 × 10^-3, 5 × 10^-3, 2.9 × 10^-2 times lower compared to the label concentrations of imidacloprid, thiamethoxam and sulfoxaflor, respectively. LC₅₀ of thiamethoxam caused the highest mortality rate on the parasitoid followed by sulfoxaflor, while imidacloprid had the lowest impact. No significant sublethal effects on reprodution were observed for A. colemani survived to the insecticide exposure. Our findings highlight the importance of case-specific evaluation to optimize pesticide applications in Integrated Pest Management packages taking into account the ecological services provided by biological control agents.

Fitness costs in chlorfenapyr-resistant populations of the chive maggot, Bradysia odoriphaga

The chive maggot, Bradysia odoriphaga (Yang and Zhang) is an economically important insect pest, affecting many key vegetables, including Chinese chive, especially in northern China. Chlorfenapyr, a halogenated pyrrole insecticide that interferes with mitochondrial oxidative phosphorylation is widely used against B. odoriphaga. In this study, we evaluated selection-induced resistance to chlorfenapyr and fitness costs in B. odoriphaga. The results showed that B. odoriphaga developed 43.32-fold resistance after continuous exposure to chlorfenapyr for over 10 consecutive generations. The life-history traits of chlorfenapyr-resistant and susceptible strains were compared using age-stage, two-sex life table approach. No significant effects were observed on the longevity and pre-adult period. However, reduction in the total pre-oviposition period (TPOP) and fecundity (eggs/female) were observed in the resistant strain. Moreover, the demographic parameters such as intrinsic rate of increase (r), net reproductive rate (R₀) and finite rate of increase (λ) were also decreased significantly in the resistant strain compared to the susceptible strain. These results showed the potential of B. odoriphaga to develop resistance against chlorfenapyr under continuous selection pressure. Furthermore, there was a fitness cost linked with chlorfenapyr resistance in B. odoriphaga. We conclude that a better knowlegde on the trade-off at play between resistance degree and fitness cost could be crucial for developing further management of B. odoriphaga in China.

Endophytic Isolates of Cordyceps fumosorosea to Enhance the Growth of Solanum melongena and Reduce the Survival of Whitefly (Bemisia tabaci)

This study reports the effects of seed treatment with Cordyceps fumosorosea on seed germination, growth, colonization of eggplant (Solanum melongena), and growth of Bemisia tabaci (feeding on fungal colonized eggplant leaves). Germination rates of eggplant seeds were similar among different treatments. The growth parameters such as root length, shoot length, and number of leaves) differed significantly after 15, 30, and 60 days of seed treatment. The total dry weight of eggplant in response to treatment with C. fumosorosea isolates increased significantly when compared with the control. Both isolates of C. fumosorosea colonized different plant tissues, although the extent of colonization decreased during the experimental period. The colonization of eggplants by both C. fumosorosea isolates resulted in a significant reduction of B. tabaci incidence. This study possibly provides the first report of increased plant growth and increased insect mortality in eggplants inoculated with C. fumosorosea isolates.

Cloning and Functional Analysis of Two Ca2+-Binding Proteins (CaBPs) in Response to Cyantraniliprole Exposure in Bemisia tabaci (Hemiptera: Aleyrodidae)

Ca²⁺-binding proteins (CaBPs) are widely distributed as Ca²⁺ sensor relay proteins that regulate various cellular processes, including Ca²⁺ homeostasis. Diamide insecticides such as cyantraniliprole kill insects by disrupting the Ca²⁺ homeostasis in muscle cells. However, less attention has been paid to the roles of CaBPs in response to insecticides. In this study, two CaBP genes (BtCaBP1 and BtCaBP2) were identified in the whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), and their functions in response to cyantraniliprole were investigated. After expression of BtCaBP1 and BtCaBP2 in vitro, the results of Ca²⁺ imaging and cytotoxicity assay revealed that the overexpression of each of the BtCaBPs stabilized Ca²⁺ concentration in the cytoplasm after exposure to cyantraniliprole and decreased the toxicity of cyantraniliprole against Sf9 cells. However, the knockdown of BtCaBP1 or BtCaBP2 in vivo significantly increased the toxicity of cyantraniliprole to B. tabaci. Taken together, these results provide evidence that BtCaBP1 and BtCaBP2 play a role in response to cyantraniliprole exposure through stabilization of Ca²⁺ concentration in whiteflies.

Spatio-temporal variations in wheat aphid populations and their natural enemies in four agro-ecological zones of Pakistan

Aphids are major pests of wheat crop in Pakistan inflicting considerable economic losses. A better knowledge of landscape scale spatial distribution of aphids and their natural enemies could be used to improve integrated pest management programs. Therefore, the present study aimed to document spatio-temporal variations in populations of wheat aphids and their natural enemies in Pakistan. The 2-year survey study was carried out at ten experimental farms located in five districts of four contrasted agro-ecological zones of eastern Pakistan (Punjab area) i.e. District Chakwal in arid zone, Gujranwala in rice-cropped zone, Faisalabad in central mixed-cropped zone, and Khanewal and Multan in cotton-cropped zone. The dominant aphid species i.e. Schizaphis graminum, Rhopalosiphum padi, R. maidis and Sitobion avenae varied significantly among the five districts surveyed. The population of S. graminum was observed more abundant in arid, R. padi in rice, S. avenae in aird and rice, and R. maidis in cotton-I zones. Aphids ended their population dynamics on 25^th March in central mixed-cropped zone and 12^th April in other three zones. Various species of natural enemies, mainly Coccinella septumpunctata, C. undecimpunctata, Menochilus sexmaculata, Chrysoperla carnea, Syrphidae and parasitoid mummies were inconsistently observed in four agro-ecological zones. The population of C. septumpunctata, was observed more abundant in rice zone, C. undecimpunctata and C. carnea in cotton-I and arid zones, M. sexmaculata in cotton-I and II zones, Syrphidae in cotton-I zone and parasitoid mummies in rice and arid zones. There were no clear relationships between aphid and the natural enemy populations. The present study may serve as a baseline regarding distribution of wheat aphids and their natural enemies and the results provided insights for further studies on the potential top-down (natural enemies) versus bottom-up (fertilization and irrigation regimes) forces in management of wheat aphids in eastern Pakistan.

Selectivity of novel and traditional insecticides used for management of whiteflies on the parasitoid Encarsia formosa

BACKGROUND

Encarsia formosa Gahan is the most important parasitoid exploited for the control of whitefly pests of vegetable crops. However, the non-target effects of recently developed insecticides for controlling whiteflies toward this biocontrol agent is little documented. Here we evaluated the susceptibility of E. formosa adults and juveniles to eight commonly used insecticides against whiteflies.

RESULTS

Residual toxicity tests on glass showed that E. formosa adults were susceptible (over 98% mortality after 6 h treated) to field concentrations of the tested neonicotinoids (imidacloprid, acetamiprid, nitenpyram and thiamethoxam), abamectin, cyantraniliprole, and sulfoxaflor at their field concentrations. Pyriproxyfen was harmless to both adult and pupae of E. formosa. A risk quotient analysis showed that toxicity of pyriproxyfen to E. formosa adults was the lowest, followed by acetamiprid and cyantraniliprole. In the leaf residues test, mortality of E. formosa adults under all insecticides decreased when the residue age increased. Interestingly, E. formosa experiencing contact with the residues of most insecticides, except pyriproxyfen and abamectin, parasitized significantly more hosts 5-days after treatment, suggesting a hormetic effect on parasitism.

CONCLUSION

The risk assessment of insecticides indicated that pyriproxyfen and cyantraniliprole were the least toxic to E. formosa. Our results suggest that the inclusion of the insecticides in sustainable integrated pest management programs of whiteflies should be carefully evaluated on a case-by-case basis. © 2019 Society of Chemical Industry.

Effects of Propoxur Exposure on Insecticidal Susceptibility and Developmental Traits in Culex pipiens quinquefasciatus

Propoxur-sel strains of Culex pipiens quinquefasciatus were derived from a lab-bred strain following 16 generations of propoxur exposure under sublethal concentrations of LC₂₅ (lethal concentration of 25%) and LC₅₀ (lethal concentration of 50%), respectively. This resulted in resistance development in F16 with ratios of 8.8× and 6.3×, respectively, compared with F0. The fecundity, longevity, sex ratio (F/M), and hatchability of the propoxur-exposed Cx. quinquefasciatus adult survivors and their offspring were decreased, with no effect on the emergence ratio and pupa survival rate. In addition, the intrinsic rates of increase (r), the net reproduction (R₀), and the finite rate of increase (λ) of the Cx. quinquefasciatus offspring generations were also decreased significantly compared to F0. Correspondingly, the mean generation time (T) and the population double time (DT) in propoxur-sels were increased. Enhanced activities of cytochrome P450 monooxygenase and esterase were also observed in propoxur-sels, indicating that a detoxification mechanism might be responsible for resistance development in Cx. quinquefasciatus. Except for the three genes cyp4d42v1, cyp4c52v1, and cyp6aa9 which displayed a coincidence in some degree in different treatments, induction by different doses of propoxur and constitutive expression in different generations of propoxur-sel strains resulted in an inconsistent identification of the P450 genes probably related with resistance.

Characterization of nitenpyram resistance in Nilaparvata lugens (Stål)

Nitenpyram is very effective in controlling Nilaparvata lugens (brown planthopper, BPH), and its resistance has been reported in field populations; however, the resistance mechanism remains unclear. In the present study, cross-resistance and resistance mechanisms in nitenpyram-resistant BPH were investigated. A resistant strain (NR) with a high resistance level (164.18-fold) to nitenpyram was evolved through successive selection for 42 generations from a laboratory susceptible strain (NS). The bioassay results showed that the NR exhibited cross-resistance to imidacloprid (37.46-fold), thiamethoxam (71.66-fold), clothianidin (149.17-fold), dinotefuran (98.13-fold), sulfoxaflor (47.24-fold), cycloxaprid (9.33-fold), etofenprox (10.51-fold) and isoprocarb (9.97-fold) but not to triflumezopyrim, chlorpyrifos and buprofezin. The NR showed a 3.21-fold increase in cytochrome P450 monooxygenase (P450) activity compared to that in the NS, while resistance was also synergized (4.03-fold) with the inhibitor piperonyl butoxide (PBO), suggesting a role of P450. Furthermore, the mRNA expression levels of cytochrome P450 (CYP) genes by quantitative real-time PCR results indicated that twelve P450 genes were significantly overexpressed in the NR strain, especially CYP6ER1 (203.22-fold). RNA interference (RNAi) suppression of CYP6ER1 through injection of dsCYP6ER1 led to significant susceptibility in the NR strain. The current study expands our understanding of the nitenpyram resistance mechanism in N. lugens, provides an important reference for integrated pest management (IPM), and enriches the theoretical system of insect toxicology.

Sublethal Effects of Imidacloprid on the Population Development of Western Flower Thrips Frankliniella occidentalis (Thysanoptera: Thripidae)

The Western flower thrips (WFT, Frankliniella occidentalis) is a global polyphagous pest that is often dependent on chemical control. Imidacloprid has been a commonly used chemical insecticide for effective control of WFT. Low concentrations of insecticides can have sublethal effects on individual insects. However, no more information is known about the effects of exposure at low concentrations of imidacloprid on WFT. Here, we evaluated the effects of imidacloprid at sublethal concentrations on WFT population growth parameters. We first exposed the parental generation to LC₁₀ (56.8 mg/L) and LC₂₅ (79.2 mg/L) concentrations of imidacloprid. We then quantified various parameters related to the development, survival, and fecundity of the F₁ generation also exposed to these same concentrations. The development time of the treatment groups exposed to imidacloprid was significantly shorter than the control group, and the net reproductive rate (R₀) was significantly higher for treatment groups than for the control group. For both variables, there was no significant difference between LC₁₀ and LC₂₅ exposure. The generational survival rate was significantly higher for the control group, followed by the LC₁₀ treatment group and then the LC₂₅ treatment group. However, the opposite was true for fecundity and intrinsic rate of increase (r_m) of WFT. In summary, exposure to low concentrations of imidacloprid was positive for the population development of WFT, which may contribute to the development of insecticide resistance and cause resurgence in WFT populations.

Effects of high temperature on insecticide tolerance in whitefly Bemisia tabaci (Gennadius) Q biotype

Bemisia tabaci (Gennadius) Q biotype (BTQ) has spread to many tropical and subtropical regions over the past several decades. This may reflect an advantage biotype Q has over closely related forms in having greater thermal and/or insecticide resistance, although the effects of higher temperatures on insecticide tolerance of BTQ has, to date, been largely ignored. In this study, the effects of elevated temperatures on BTQ's tolerance to the insecticide thiamethoxam were investigated. The effect on the activities of detoxifying enzymes [carboxylesterase (CarE), glutathione S-transferase (GST), and cytochrome P450 monooxygenase (P450)] and expression profiling of eleven genes of detoxifying enzymes were also determined. In addition, RNA interference (RNAi) and bioassay methods were used to further identify the function of CYP6CM1 in tolerance to thiamethoxam following exposure to higher temperatures. The results showed that elevated temperatures were responsible for causing different outcomes in the tolerance of BTQ to thiamethoxam: Temperatures of 35 °C or higher decreased the tolerance of BTQ to thiamethoxam, while a moderately high temperature of 31 °C increased the tolerance. The high temperature influenced the tolerance of BTQ by affecting the activity of P450. Quantitative real-time PCR (qPCR) showed that CYP6CM1 was significantly up-regulated in most treatments at 31 °C, but was suppressed at 35 °C, which was closely associated with the mortality rates. Feeding on double-stranded RNA (dsRNA) of CYP6CM1 significantly reduced the mRNA levels of the target gene in the adults, and dramatically decreased tolerance to thiamethoxam induced by a temperature of 31 °C for 6 h. Our finding provides useful information to better understand the invasion mechanism of BTQ.

Does multigenerational exposure to hormetic concentrations of imidacloprid precondition aphids for increased insecticide tolerance?

BACKGROUND

Hormetic preconditioning, whereby exposure to mild stress primes an organism to better tolerate subsequent stress, is well documented. It is unknown if exposure to hormetic concentrations of insecticide can trans-generationally prime insects to better tolerate insecticide exposure, or whether exposure to hormetic concentrations of insecticide can induce mutations in genes responsible for insecticide resistance. Using the aphid Myzus persicae (Sulzer) and the insecticide imidacloprid as a model, we examined if exposure to mildly toxic and hormetic concentrations of imidacloprid reduced aphid susceptibility to insecticides across four generations, and whether such exposures induced mutations in the imidacloprid binding site in post-synaptic nicotinic acetylcholine receptors.

RESULTS

Chronic, multigenerational exposure of aphids to hormetic concentrations of imidacloprid primed offspring to better survive exposure to certain concentrations of imidacloprid, but not exposure to spirotetramat, an insecticide with a different mode of action. Exposure to hormetic and mildly toxic concentrations of imidacloprid did not result in mutations in any of the examined nicotinic acetylcholine receptor subunits.

CONCLUSION

Our findings demonstrate that exposure to hormetic concentrations of insecticide can prime insects to better withstand subsequent chemical stress, but this is dependent upon the insecticide exposure scenario, and may be subtle over generations. © 2017 Society of Chemical Industry.

Sublethal effects of buprofezin on development and reproduction in the white-backed planthopper, Sogatella furcifera (Hemiptera: Delphacidae)

In the present study, the effects of sublethal concentrations of buprofezin on life-table traits of S. furcifera were evaluated for two consecutive generations (F0 and F1). Our results exhibited that the fecundity, life span (longevity) and hatchability of the F0 and F1 generations were significantly decreased at LC₃₀ compared to the control. However, copulation was not significantly affected for the F0 or F1 generations at sublethal concentrations. The female life span was affected negatively at both treatments in F0 and at LC₃₀ in F1, compared to the control. Furthermore, significant effects of the sublethal concentrations were found on the developmental rate of all instars except the 3^rd instar of F1. However, the pre-adult period, total pre-oviposition period (TPOP) and adult pre-oviposition period (APOP) significantly increased in F1 individuals at LC₃₀ and LC₁₀ compared to the control. Our findings revealed that demographic characters (survival rate, intrinsic rate of increase (ri), finite rate of increase (λ), net reproductive rate (R₀), and gross reproductive rate (GRR)) of the F1 generation (from F0 parents) significantly decreased compared to the untreated group; however, the generation time (T) increased at LC₁₀. Therefore, the results suggested that buprofezin could adversely affect individuals in the successive generation.

Silence of inositol 1,4,5-trisphosphate receptor expression decreases cyantraniliprole susceptibility in Bemisia tabaci

Cyantraniliprole is the second active ingredient of anthranilic diamide insecticide, and the first to control a cross-spectrum of chewing and sucking pests such as sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). The inositol 1,4,5-trisphosphate receptor (IP3R) and ryanodine receptor (RyR) are two families of Ca²⁺ release channels to raise the cytoplasmic free calcium concentration when it is activated by various extracellular stimuli. Previous study proved the over-expression of ryanodine receptor (RyR) was associated with the resistance to diamide insecticides, while the roles of IP3R in diamide resistance remain unknown. In this study, a full-length cDNA sequence of IP3R was cloned from B. tabaci through RT-PCR and rapid amplification of cDNA ends (RACE). The gene (named BtIP3R) is 9922bps long, with an open reading frame (ORF) of 8202bps, encoding a predicted IP3R of 2733 amino acids. The BtIP3R shares 47-78% identity with other insect IP3Rs. Quantitative real-time PCR (qRT-PCR) analysis showed that the BtIP3R was highly expressed in larva, pseudopupa, and female adult, while lowly expressed in egg and male adult. RNA interference (RNAi) by dietary introduction of double-stranded RNA (dsRNA) of BtIP3R significantly reduced the mRNA levels of the target gene in the adult, and dramatically decreased the susceptibility of adult B. tabaci to cyantraniliprole. The results shed light on further understanding of cyantraniliprole resistance mechanisms in B. tabaci as well as in other insects.

Nitenpyram seed treatment effectively controls against the mirid bug Apolygus lucorum in cotton seedlings

The mirid bug Apolygus lucorum (Meyer-Dür) has become a major pest in cotton fields and has led to significant yield losses due to the widespread use of transgenic Bt cotton in China. Eight neonicotinoid seed treatments were investigated to determine their effects on the management of A. lucorum in cotton fields. All neonicotinoid seed treatments reduced the cotton damage caused by A. lucorum, and nitenpyram at the rate of 4 g/kg seed showed the most favorable efficacy in suppressing A. lucorum populations throughout the cotton seedling stage. The neonicotinoid seed treatments had no effect on the emergence rate of cotton seeds. Although the neonicotinoid seed treatments were not significantly different from the spray treatments in the cotton yield, the seed treatments reduced the need for three pesticide applications and showed a tremendous advantage in labor costs throughout the cotton seedling stage. Overall, the neonicotinoid seed treatments, particularly the nitenpyram seed treatment, can provide effective protection and should play an important role in the management of early season A. lucorum in Bt cotton fields.

Toxicological and biochemical basis of synergism between the entomopathogenic fungus Lecanicillium muscarium and the insecticide matrine against Bemisia tabaci (Gennadius)

The sweetpotato whitefly Bemisia tabaci (Gennadius) was challenged with different combinations of matrine (insecticide) and Lecanicillium muscarium (entomopathogenic fungus). Our results revealed a synergistic relationship between matrine and L. muscarium on mortality and enzyme activities of B. tabaci. To illustrate the biochemical mechanisms involved in detoxification and immune responses of B. tabaci against both control agents, activities of different detoxifying and antioxidant enzymes were quantified. After combined application of matrine and L. muscarium, activities of carboxylestrease (CarE), glutathione-s-transferase (GSTs) and chitinase (CHI) decreased during the initial infection period. Acetylcholinestrase (AChE) activities increased during the entire experimental period, whereas those of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) decreased during the later infection period. The increased mortality and suppression of enzymatic response of B. tabaci following matrine and L. muscarium application suggests a strong synergistic effect between both agents. The strong synergistic effect is possibly related to the disturbance of acetylcholine balance and changes in AchE activities of the whitefly as both matrine and L. muscarium target insect acetylcholine (Ach) receptors which in turn effects AchE production. Therefore, our results have revealed the complex biochemical processes involved in the synergistic action of matrine and L. muscarium against B. tabaci.

Modification of Flight and Locomotion Performances, Respiratory Metabolism, and Transcriptome Expression in the Lady Beetle Harmonia axyridis through Sublethal Pesticide Exposure

Biological control is usually used in combination with chemical control for practical agricultural applications. Thus, the influence of insecticides on the natural predators used for biological control should be investigated for integrated pest management. The ladybird Harmonia axyridis is an effective predator on aphids and coccids. Beta-cypermethrin is a broad-spectrum insecticide used worldwide for controlling insect pests. H. axyridis is becoming increasingly threatened by this insecticide. Here, we investigated the effect of a sublethal dose of beta-cypermethrin on flight, locomotion, respiration, and detoxification system of H. axyridis. After exposure to beta-cypermethrin, succinic female adults flew more times, longer distances, and during longer time periods. Exposure to a sublethal dose of beta-cypermethrin also promoted an increase in walking rate, walking distance, walking duration, and also an increase in respiratory quotient and respiratory rate. To investigate the effects of beta-cypermethrin on H. axyridis detoxification system, we analyzed the transcriptome of H. axyridis adults, focusing on genes related to detoxification systems. De novo assembly generated 65,509 unigenes with a mean length of 799 bp. From these genes, 26,020 unigenes (40.91% of all unigenes) exhibited clear homology to known genes in the NCBI non-redundant database. In addition, 10,402 unigenes were annotated in the Cluster of Orthologous Groups database, 12,088 unigenes were assigned to the Gene Ontology database and 12,269 unigenes were in the Kyoto Encyclopedia of Genes and Genome (KEGG) database. Exposure to beta-cypermethrin had significant effects on the transcriptome profile of H. axyridis adult. Based on uniquely mapped reads, 3,296 unigenes were differentially expressed, 868 unigenes were up-regulated and 2,248 unigenes were down-regulated. We identified differentially-expressed unigenes related to general detoxification systems in H. axyridis. This assembled, annotated transcriptome provides a valuable genomic resource for further understanding the molecular basis of detoxification mechanisms in H. axyridis.

Dynamics of Bemisia tabaci biotypes and insecticide resistance in Fujian province in China during 2005-2014

The whitefly Bemisia tabaci (Gennadius) is an important agricultural insect pest worldwide. The B and Q biotypes are the two most predominant and devastating biotypes prevalent across China. However, there are few studies regarding the occurrence of the Q biotype in Fujian Province, China, where high insecticide resistance has been reported in the B biotype. Differences in some biological characteristics between the B and Q biotypes, especially insecticide resistance, are considered to affect the outcome of their competition. Extensive surveys in Fujian revealed that the B biotype was predominant during 2005–2014, whereas the Q biotype was first detected in some locations in 2013 and widely detected throughout the province in 2014. Resistance to neonicotinoids (that have been used for more than 10 years) exhibited fluctuations in open fields, but showed a continual increasing trend in protected areas. Resistance to lambda-cyhalothrin, chlorpyrifos, and abamectin exhibited a declining trend. Resistance to novel insecticides, such as nitenpyram, pymetrozine, sulfoxaflor, and cyantraniliprole, in 2014 was generally below a moderate level. A decline in insecticide resistance in the B biotype and the rapid buildup of protected crops under global temperature increase may have promoted the establishment of the Q biotype in Fujian.

Pesticide-mediated interspecific competition between local and invasive thrips pests

Competitive interactions between species can be mitigated or even reversed in the presence of anthropogenic influences. The thrips species Frankliniella occidentalis and Thrips tabaci are highly invasive and damaging agricultural pests throughout the world. Where the species co-occur, one species tends to eventually predominate over the other. Avermectin and beta-cypermethrin are commonly used insecticides to manage thrips in China, and laboratory bioassays demonstrated that F. occidentalis is significantly less susceptible than T. tabaci to these insecticides. In laboratory cage trials in which both species were exposed to insecticide treated cabbage plants, F. occidentalis became the predominant species. In contrast, T. tabaci completely displaced F. occidentalis on plants that were not treated with insecticides. In field trials, the species co-existed on cabbage before insecticide treatments began, but with T. tabaci being the predominant species. Following application of avermectin or beta-cypermethrin, F. occidentalis became the predominant species, while in plots not treated with insecticides, T. tabaci remained the predominant species. These results indicate that T. tabaci is an intrinsically superior competitor to F. occidentalis, but its competitive advantage can be counteracted through differential susceptibilities of the species to insecticides. These results further demonstrate the importance of external factors, such as insecticide applications, in mediating the outcome of interspecific interactions and produce rapid unanticipated shifts in the demographics of pest complexes.

Sublethal and transgenerational effects of sulfoxaflor on the biological traits of the cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae)

Sulfoxaflor is a novel insecticide belonging to sulfoximine chemical class that can be used to control sap-feeding insects, notably Aphis gossypii Glover. In addition to its acute toxicity, it is also important to consider the possible sublethal effects when establishing a comprehensive understanding of the toxicity of a new insecticide. We assessed the effects of a low lethal concentration (LC₂₅) of sulfoxaflor on biological parameters of A. gossypii adults (F0) and subsequent transgenerational effects, i.e., on the progeny (F1 generation). The data were analyzed using an age-stage life table procedure. The results showed that the longevity and fecundity were not significantly affected by the LC₂₅ of sulfoxaflor in the F0 or F1 generations. In addition, no significant differences were observed on the developmental time of each instar, the adult pre-oviposition period, and on the longevity of F1 individuals. However, the duration of their pre-adult stage and total pre-oviposition period, as well as their mean generation time were significantly increased. These observed effects affected aphid demographic traits; the survival rate, the intrinsic rate of increase (r _i ), the finite rate of increase (λ), the net reproductive rate (R₀), and the gross reproduction rate (GRR) of the F1 individuals (i.e., from F0 mothers) were significantly lower compared to the control. Our results showed that sublethal effects of sulfoxaflor significantly slowed down A. gossypii population growth; they indicated that effects of sulfoxaflor might be increased (beyond lethal effect) through sublethal effects when concentrations decreased in sulfoxaflor-treated areas after initial application in field.

Sublethal effects of imidacloprid on the predatory seven-spot ladybird beetle Coccinella septempunctata

The seven-spot ladybird beetle, Coccinella septempunctata, is a major natural enemy of aphids in the field and in greenhouses in China and is part of integrated pest management (IPM). Imidacloprid, a highly efficient insecticide that not only kills aphids at lethal concentrations, but also can cause various sublethal effects in nontarget organisms. To strengthen IPM and its sustainability, it is important assessing possible side effects on natural enemies. When the effects of sublethal concentrations (LC5 and 10%LC5) of imidacloprid on C. septempunctata were evaluated, the adult longevity was shortened by 23.97 and 28.68 %, and the fecundity reduced by 52.81 and 56.09 % compared to control population. In the F₁ generation (i.e., the progeny of the exposed individuals), the juvenile development was slower by 1.44 days and 0.66 days, and the oviposition period was shortened by 10 and 13 days, respectively. The fecundity of the F₁ generation decreased by 17.88, 44.03 and 51.69 % when exposed to 1%LC5, 10%LC5, and LC5, respectively. The results of demographical growth estimates showed that the intrinsic rate of increase (r _m ) and net reproductive rate (R ₀ ) were lower in C. septempunctata populations that had been exposed to sublethal concentrations of imidacloprid. The results emphasize the importance of assessing side effects of low imidacloprid concentrations on such predator species, even at the transgenerational level.

Feeding preference of Plutella xylostella for leaves treated with plant extracts

Plutella xylostella L. is one of the main agents to cause damages to plants of Brassica genus, provoking negative impacts in cultures. The use of botanical extracts in plants protection has been related in literature, however, their use in the species analyzed in this study is not yet reported. We assessed the effect of aqueous and methanolic extracts of the species: Schinus terebinthifolius Raddi (Pink Pepper), Annona coriacea Mart. (Araticum), Duguetia furfuracea (A. St.-Hil.) Benth. & Hook. (Pindaúva do campo) and Trichilia silvatica C. DC. (Catiguá-branco), occuring in the state of Mato Grosso do Sul and whose feeding preference of P. xylostella larvae of 3rd instar. We intend to answer the following questions: (1) Are the plant species analyzed fagodeterrentes? (2) what type of extract produces the least food preferrence? To answer these questions, we treated cabbage disks with aqueous extracts stored in a refrigerator in periods of 0, 7, 14 and 21 days and the methanolic extracts were treated at concentrations of 0.5 mg/mL, 1.0 mg/mL, 2.0mg/mL. The aqueous and methanolic extracts of T. silvatica presented the lowest values of feeding preference, 0.113 and 0.06, respectively, compared to other extracts.

Sublethal Concentration of Beta-Cypermethrin Influences Fecundity and Mating Behavior of Carposina sasakii (Lepidoptera: Carposinidae) Adults

The purpose of this study was to evaluate the sublethal effects of the beta-cypermethrin on calling behavior and fecundity of a major fruit-boring pest of apple, Carposina sasakii Matsumura. The mating rate, fertility (total number of eggs laid per female), and adult longevity of adults were remarkably decreased as compared with that in control when the adults were exposed to 10% lethal concentrations (LC10) of beta-cypermethrin (LC10♀ × LC10♂), and the age-specific survival rate (lx) was also negatively affected by sublethal beta-cypermethrin especially for the LC10♀× LC10♂ mating combination. However, the age-specific fecundity (mx) was stimulated particularly in the combination of CK♀× LC10♂. Furthermore, the oviposition period was prolonged and the number of eggs was significantly increased for combinations of CK♀× LC10♂ and LC10♀× CK♂. In the mating experiments, males in control or LC10-beta-cypermethrin treatments preferred to mate with females in control. It might be because of lower calling rate of female survivors treated with sublethal beta-cypermethrin. Our data indicate that treatment of beta-cypermethrin had a sublethal effect on the development and production of C. sasakii, and their mating behavior changes in surviving adults that may contribute to assortative mating.

Evaluation of Bioinsecticides for Management of Bemisia tabaci (Hemiptera: Aleyrodidae) and the Effect on the Whitefly Predator Delphastus catalinae (Coleoptera: Coccinellidae) in Organic Squash

Organic zucchini squash is a high-value vegetable crop in Florida and potential exists to expand its production throughout the state. A lack of knowledge on the effectiveness of organic products and their integration with natural enemies is an important constraint to the regulation of pest populations in organic squash production in Florida. The objectives of this study were to evaluate the effect of insecticides labeled for organic production that can be used for management of Bemisia tabaci (Gennadius) biotype B, on organically grown squash; and to determine the effects of the most efficient insecticides on a key natural enemy, Delphastus catalinae (Horn). Experiments were conducted in the greenhouse in exclusion cages. The first experiment compared the effects of four bioinsecticides on whitefly densities. Insecticides include 1) AzaSol (azadirachtin), 2) PyGanic EC 1.4 (pyrethrin), 3) M-Pede (insecticidal soap), and 4) Entrust (spinosad). The second experiment investigated the effects of bioinsecticides on D. catalinae Treatment effectiveness was evaluated 1, 3, and 5 d posttreatment. PyGanic and M-Pede were highly effective in controlling whitefly populations on organic squash, while moderate control was provided by AzaSol and there was no control provided by Entrust. PyGanic and M-Pede treatments reduced D. catalinae populations when adults were released 1 d post pesticide application. However, when adults were released 5 d post application, there was no reduction. The importance of using bioinsecticides in combination with natural enemies to regulate pest populations in organic cropping systems is discussed.

Deep Sequencing-Based Transcriptome Analysis Reveals the Regulatory Mechanism of Bemisia tabaci (Hemiptera: Aleyrodidae) Nymph Parasitized by Encarsia sophia (Hymenoptera: Aphelinidae)

The whitefly Bemisia tabaci is a genetically diverse complex with multiple cryptic species, and some are the most destructive invasive pests of many ornamentals and crops worldwide. Encarsia sophia is an autoparasitoid wasp that demonstrated high efficiency as bio-control agent of whiteflies. However, the immune mechanism of B. tabaci parasitization by E. sophia is unknown. In order to investigate immune response of B. tabaci to E. Sophia parasitization, the transcriptome of E. sophia parasitized B. tabaci nymph was sequenced by Illumina sequencing. De novo assembly generated 393,063 unigenes with average length of 616 bp, in which 46,406 unigenes (15.8% of all unigenes) were successfully mapped. Parasitization by E. sophia had significant effects on the transcriptome profile of B. tabaci nymph. A total of 1482 genes were significantly differentially expressed, of which 852 genes were up-regulated and 630 genes were down-regulated. These genes were mainly involved in immune response, development, metabolism and host signaling pathways. At least 52 genes were found to be involved in the host immune response, 33 genes were involved in the development process, and 29 genes were involved in host metabolism. Taken together, the assembled and annotated transcriptome sequences provided a valuable genomic resource for further understanding the molecular mechanism of immune response of B. tabaci parasitization by E. sophia.

Mixed release of two parasitoids and a polyphagous ladybird as a potential strategy to control the tobacco whitefly Bemisia tabaci

A mixed species release of parasitoids is used to suppress outbreaks of tobacco whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae); however, this biocontrol may be inhibited by interspecific interactions. We investigated the effects of mixed releases of natural enemies of B. tabaci on predation rates, parasite performance and adult parasitoid emergence under greenhouse conditions. We tested the polyphagous predatory ladybird Harmonia axyridis (Coleoptera: Coccinellidae) and two whitefly-specific parasitoids, namely Encarsia formosa and Encarsia sophia (both, Hymenoptera: Aphelinidae). Harmonia axyridis exhibited the lowest rates of predation when released with each parasitoid than with both parasitoid species together and showed a significant preference for non-parasitized nymphs as prey. Both E. formosa and E. sophia parasitized more B. tabaci when released with the ladybird than when the wasps were released either alone or mixed with the other parasitoid. We also found that the presence of H. axyridis significantly reduced adult parasitoid emergence; the highest rate of adult emergence was obtained with parasitoids released alone. Our results indicate that different combinations of natural enemies can influence observed rates of predation, parasitism, and parasitoid emergence. Therefore, the combination of natural enemies to be used for a particular biological control program should depend on the specific objectives.

Pesticide-Induced Stress in Arthropod Pests for Optimized Integrated Pest Management Programs

More than six decades after the onset of wide-scale commercial use of synthetic pesticides and more than fifty years after Rachel Carson's Silent Spring, pesticides, particularly insecticides, arguably remain the most influential pest management tool around the globe. Nevertheless, pesticide use is still a controversial issue and is at the regulatory forefront in most countries. The older generation of insecticide groups has been largely replaced by a plethora of novel molecules that exhibit improved human and environmental safety profiles. However, the use of such compounds is guided by their short-term efficacy; the indirect and subtler effects on their target species, namely arthropod pest species, have been neglected. Curiously, comprehensive risk assessments have increasingly explored effects on nontarget species, contrasting with the majority of efforts focused on the target arthropod pest species. The present review mitigates this shortcoming by hierarchically exploring within an ecotoxicology framework applied to integrated pest management the myriad effects of insecticide use on arthropod pest species.

Foraging behaviour of the parasitoid Eretmocerus eremicus under intraguild predation risk by Macrolophus pygmaeus

BACKGROUND

Intraguild predation (IGP), predation between species that use a common resource, can affect the populations of a pest, of the pest's natural enemy (IG prey) and of the predator of the pest's natural enemy (IG predator). In this study, we determined whether the parasitoid Eretmocerus eremicus (Hymenoptera: Aphelinidae) (IG prey), modifies its foraging behaviour under the risk of IGP by Macrolophus pygmaeus (Hemiptera: Miridae) (IG predator). Parasitoid behaviour was analysed using two bioassays (choice and no-choice) with the following treatments: (i) control, tomato leaf infested with whitefly nymphs; and (ii) PEP, tomato leaf infested with whitefly nymphs and previously exposed to the IG predator; and (iii) PP, tomato leaf infested with whitefly nymphs, with both, the IG predator and the IG prey present.

RESULTS

In both bioassays, we found that E. eremicus did not significantly modify the number of ovipositions, time of residence, duration of oviposition or behavioural sequence. However, in the no-choice bioassay, the number of attacks was higher and their duration shorter in the PEP treatment than in the control.

CONCLUSION

Our results indicate that the parasitoid may detect IGP risk to a certain extent, but it did not significantly modify its foraging behaviour, suggesting that simultaneous release of the two natural enemies can be successfully employed.

Demonstration of an adaptive response to preconditioning Frankliniella occidentalis (Pergande) to sublethal doses of spinosad: a hormetic-dose response

Sublethal doses of some insecticides have been reported to either stimulate or reduce the survival and fecundity of insects. Many sublethal-effect studies have been conducted after exposure of only one generation to sublethal insecticides, and there is little information about the sublethal effects on insects after long-term exposure to sublethal insecticides. In this study, changes in biological characteristics were investigated in spinosad-susceptible (Spin-S) and sublethal-spinosad-treated (Spin-Sub) strains of Frankliniella occidentalis (Pergande) after exposure to their corresponding sublethal concentrations of spinosad. The results showed that for the Spin-S strain, the LC10 concentration of spinosad slightly affected the biotic fitness both in parents and offspring of F. occidentalis. The LC25 concentration of spinosad prolonged the development time, reduced the fecundity, and significantly reduced the intrinsic rate of increase, the net reproductive rate and the finite rate of increase in the Spin-S strain. However, the negative effects were not as pronounced in the offspring (F1 generation) as in the parent generation. For the Spin-Sub strain, the LC10 and LC25 concentrations of spinosad had little negative effect on the development and fecundity, and no significant difference was found between the effects of the LC10 and LC25 treatments on the Spin-Sub strain. The Spin-Sub strain exhibited a shorter developmental time, and larger intrinsic rates of increase and net reproductive rates, compared with the corresponding treatments of the Spin-S strain. These findings combined with our previous studies suggest that the biotic fitness increased in the Spin-Sub strain and the strain became more adaptable to sublethal doses of spinosad, compared with the Spin-S strain. Physiological and biochemical adaptation may contribute to these changes after long treatment times at sublethal doses.

Sublethal effects of insecticide seed treatments on two nearctic lady beetles (Coleoptera: Coccinellidae)

Predatory insects often feed on plants or use plant products to supplement their diet, creating a potential route of exposure to systemic insecticides used as seed treatments. This study examined whether chlorantraniliprole or thiamethoxam might negatively impact Coleomegilla maculata and Hippodamia convergens when the beetles consumed the extrafloral nectar of sunflowers grown from treated seed. We reared both species on eggs of Ephestia kuehniella and then switched adult H. convergens to a diet of greenbugs, Schizaphis graminum, in order to induce oviposition in this species. Excised sunflower stems, either treated or control and refreshed every 48 h, were provided throughout larval development, or for the first week of adult life. Exposure of C. maculata larvae to chlorantraniliprole and thiamethoxam applied as seed treatments delayed adult emergence by prolonging the pupal period. When adults were exposed, thiamethoxam reduced the preoviposition period compared to chlorantraniliprole, whereas the latter treatment cause females to produce fewer clutches during the observation period. Larvae of C. maculata did not appear to obtain sufficient hydration from the sunflower stems and their subsequent fecundity and fertility were compromised in comparison to the adult exposure experiment where larvae received supplemental water during development. Exposure of H. convergens larvae to thiamethoxam skewed the sex ratio in favor of females; both materials reduced the egg viability of resulting adults and increased the period required for eclosion. Exposure of H. convergens adults to chlorantraniliprole reduced egg eclosion times compared to thiamethoxam and exposure to both insecticides reduced pupation times in progeny. The results indicate that both insecticides have negative, sublethal impacts on the biology of these predators when they feed on extrafloral nectar of sunflower plants grown from treated seed.