Field-evolved resistance to beta-cyfluthrin in the boll weevil: Detection and characterization

Bacillus thuringiensis Bt_UNVM-84, a Novel Strain Showing Insecticidal Activity against Anthonomus grandis Boheman (Coleoptera: Curculionidae)

Bacillus thuringiensis is a Gram-positive bacterium known for its insecticidal proteins effective against various insect pests. However, limited strains and proteins target coleopteran pests like Anthonomous grandis Boheman, causing substantial economic losses in the cotton industry. This study focuses on characterizing a Bacillus sp. strain, isolated from Oncativo (Argentina), which exhibits ovoid to amorphous parasporal crystals and was designated Bt_UNVM-84. Its genome encodes genes for the production of two pairs of binary Vpb1/Vpa2 proteins and three Cry-like proteins showing similarity with different Cry8 proteins. Interestingly, this gene content was found to be conserved in a previously characterized Argentine isolate of B. thuringiensis designated INTA Fr7-4. SDS-PAGE analysis revealed a major band of 130 kDa that is proteolytically processed to an approximately 66-kDa protein fragment by trypsin. Bioassays performed with spore-crystal mixtures demonstrated an interesting insecticidal activity against the cotton boll weevil A. grandis neonate larvae, resulting in 91% mortality. Strain Bt_UNVM-84 is, therefore, an interesting candidate for the efficient biological control of this species, causing significant economic losses in the cotton industry in the Americas.

Planting Date of Cotton in the Brazilian Cerrado Drives Boll Weevil (Coleoptera: Curculionidae) Infestation

Although the boll weevil (BW), Anthonomus grandis grandis (Coleoptera: Curculionidae) has been attributed to the significant losses caused to cotton yield in the Americas, the categorization as a quarentenary pest in places where it is still not occurring has increased its relevance worldwide. In areas where it is widespread, pest suppression relies on many broad-spectrum insecticide applications. However, other control tactics are sought. Considering that early-flowering cultivars escape from boll weevil infestation, we investigated if three different planting dates (November, December, and January) could alter the plant life cycle, allowing the plants to escape from boll weevil infestation. Field trials were run in two seasons (2014/2015 and 2017/2018), and variables (days required to reach each flowering stage, fruiting plant structures-undamaged and damaged by the BW, and totals-number of boll weevils on plants and that had emerged from fallen structures on the ground) were assessed over 29 and 33 weeks, respectively. Based on the number of days required to initiate and terminate the flowering stage, the time to reach the economic threshold (ET), the number of undamaged, damaged, and the total reproductive structures, we concluded that planting dates in December for the Central Cerrado of Brazil should be preferred over the other two tested dates. Cultivations run at this planting date, anticipating the flowering period initiation and termination, reduced infested flowering structures, and delayed the decision making to control the pest, when compared to the other two planting dates.

Lethal and Sublethal Effects of Contact Insecticides and Horticultural Oils on the Hibiscus Bud Weevil, Anthonomus testaceosquamosus Linell (Coleoptera: Curculionidae)

In 2017, the hibiscus bud weevil (HBW), Anthonomus testaceosquamosus Linell (Coleoptera: Curculionidae), was found outside of its native range of Mexico and Texas, infesting hibiscus plants in Florida. Therefore, we selected 21 different insecticide and horticultural oil products to evaluate their effects on the reproductive rate, feeding, and oviposition behavior of the HBW. In laboratory experiments, significant mortality was observed in adult weevils exposed to diflubenzuron-treated hibiscus leaves and buds, and hibiscus buds treated with diflubenzuron contained the fewest number of eggs and feeding/oviposition holes. Among horticultural oil products, significant mortality was only observed in experiments in which adult weevils were directly sprayed (direct experiments). Pyrethrins and spinetoram plus sulfoxaflor reduced the oviposition rate and caused significant mortality in direct experiments. Diflubenzuron, pyrethrins, spinetoram plus sulfoxaflor, and spirotetramat were further tested via contact toxicity experiments and greenhouse experiments. Contact toxicity experiments demonstrated that the tested insecticides (except diflubenzuron) were highly toxic to HBW adults. In greenhouse experiments, only those hibiscus plants treated with pyrethrins had significantly fewer feeding/oviposition holes and larvae within their flower buds when compared to control (water-treated) plants. These results constitute an important first step in the identification of effective chemical control options for the HBW.

The Transcriptomic Response of the Boll Weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), following Exposure to the Organophosphate Insecticide Malathion

Insecticide tolerance and resistance have evolved countless times in insect systems. Molecular drivers of resistance include mutations in the insecticide target site and/or gene duplication, and increased gene expression of detoxification enzymes. The boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), is a pest of commercial cotton and has developed resistance in the field to several insecticides; however, the current organophosphate insecticide, malathion, used by USA eradication programs remains effective despite its long-term use. Here, we present findings from an RNA-seq experiment documenting gene expression post-exposure to field-relevant concentrations of malathion, which was used to provide insight on the boll weevil's continued susceptibility to this insecticide. Additionally, we incorporated a large collection of boll weevil whole-genome resequencing data from nearly 200 individuals collected from three geographically distinct areas to determine SNP allele frequency of the malathion target site, as a proxy for directional selection in response to malathion exposure. No evidence was found in the gene expression data or SNP data consistent with a mechanism of enhanced tolerance or resistance adaptation to malathion in the boll weevil. Although this suggests continued effectiveness of malathion in the field, we identified important temporal and qualitative differences in gene expression between weevils exposed to two different concentrations of malathion. We also identified several tandem isoforms of the detoxifying esterase B1 and glutathione S-transferases, which are putatively associated with organophosphate resistance.

Population genomic insights into invasion success in a polyphagous agricultural pest, Halyomorpha halys

Invasive species are increasingly threatening ecosystems and agriculture by rapidly expanding their range and adapting to environmental and human-imposed selective pressures. The genomic mechanisms that underlie such rapid changes remain unclear, especially for agriculturally important pests. Here, we used genome-wide polymorphisms derived from native, invasive, and intercepted samples and populations of the brown marmorated stink bug (BMSB), Halyomorpha halys, to gain insights into population genomics processes that have promoted the successful global invasion of this polyphagous pest. Our analysis demonstrated that BMSB exhibits spatial structure but admixture rates are high among introduced populations, resulting in similar levels of genomic diversity across native and introduced populations. These spatial genomic patterns suggest a complex invasion scenario, potentially with multiple bridgehead events, posing a challenge for accurately assigning BMSB incursions to their source using reduced-representation genomic data. By associating allele frequencies with the invasion status of BMSB populations, we found significantly differentiated single nucleotide polymorphisms (SNPs) located in close proximity to genes for insecticide resistance and olfaction. Comparing variations in allele frequencies among populations for outlier SNPs suggests that BMSB invasion success has probably evolved from standing genetic variation. In addition to being a major nuisance of households, BMSB has caused significant economic losses to agriculture in recent years and continues to expand its range. Despite no record of BMSB insecticide resistance to date, our results show high capacity for potential evolution of such traits, highlighting the need for future sustainable and targeted management strategies.

Simultaneous silencing of juvenile hormone metabolism genes through RNAi interrupts metamorphosis in the cotton boll weevil

The cotton boll weevil (CBW) (Anthonomus grandis) is one of the major insect pests of cotton in Brazil. Currently, CBW control is mainly achieved by insecticide application, which is costly and insufficient to ensure effective crop protection. RNA interference (RNAi) has been used in gene function analysis and the development of insect control methods. However, some insect species respond poorly to RNAi, limiting the widespread application of this approach. Therefore, nanoparticles have been explored as an option to increase RNAi efficiency in recalcitrant insects. Herein, we investigated the potential of chitosan-tripolyphosphate (CS-TPP) and polyethylenimine (PEI) nanoparticles as a dsRNA carrier system to improve RNAi efficiency in the CBW. Different formulations of the nanoparticles with dsRNAs targeting genes associated with juvenile hormone metabolism, such as juvenile hormone diol kinase (JHDK), juvenile hormone epoxide hydrolase (JHEH), and methyl farnesoate hydrolase (MFE), were tested. The formulations were delivered to CBW larvae through injection (0.05-2 µg), and the expression of the target genes was evaluated using RT-qPCR. PEI nanoparticles increased targeted gene silencing compared with naked dsRNAs (up to 80%), whereas CS-TPP-dsRNA nanoparticles decreased gene silencing (0%-20%) or led to the same level of gene silencing as the naked dsRNAs (up to 50%). We next evaluated the effects of targeting a single gene or simultaneously targeting two genes via the injection of naked dsRNAs or dsRNAs complexed with PEI (500 ng) on CBW survival and phenotypes. Overall, the gene expression analysis showed that the treatments with PEI targeting either a single gene or multiple genes induced greater gene silencing than naked dsRNA (∼60%). In addition, the injection of dsJHEH/JHDK, either naked or complexed with PEI, significantly affected CBW survival (18% for PEI nanoparticles and 47% for naked dsRNA) and metamorphosis. Phenotypic alterations, such as uncompleted pupation or malformed pupae, suggested that JHEH and JHDK are involved in developmental regulation. Moreover, CBW larvae treated with dsJHEH/JHDK + PEI (1,000 ng/g) exhibited significantly lower survival rate (55%) than those that were fed the same combination of naked dsRNAs (30%). Our findings demonstrated that PEI nanoparticles can be used as an effective tool for evaluating the biological role of target genes in the CBW as they increase the RNAi response.

Exploring China stepping into the dawn of chemical pesticide-free agriculture in 2050

China has implemented a series of policies to reduce the usage of chemical pesticides to maintain food production safety and to reduce water and soil pollution. However, there is still a huge gap in developing biological pesticides to replace chemical agents or managing pests to prevent crop production loss. It is necessary to predict the future use of chemical pesticides and to exploit the potential ways to control pests and crop diseases. Pesticide usage is affected by seasonal changes and analyzed by using a seasonal autoregressive integrated moving average (ARIMA) model (a statistical model that predicts future trends using time-series data). The future development of biopesticides in China was predicted using the compound annual growth rate (CAGR), which is calculated via the equation [(Final value/Starting value)1/years - 1] according to the annual growth rate of target products over time. According to the reducing trend of pesticide and biological pesticide usage annually, China is predicted possibly step into the era of pesticide-free agriculture in 2050 based on the analysis of the ARIMA model. With CAGR calculation, China will produce from 500 thousand to one million tons of biopesticides in 2050, which can meet the need to replace chemical pesticides in agriculture to prevent the present crop production loss. To achieve the goal, China still has the greatest challenges to develop biopesticides and use various strategies to control pest and crop diseases. China may step into the dawn of chemical pesticide-free agriculture in 2050 if biopesticides can be developed smoothly and pests can be controlled well using various strategies.

Insecticides in Use and Risk of Control Failure of Boll Weevil (Coleoptera: Curculionidae) in the Brazilian Cerrado

Growers rely on synthetic insecticides to control the boll weevil throughout the reproductive cotton stage. An average of 19.6 insecticide applications (range: 10 to 30) for control of boll weevil were found in a survey with growers in the Brazilian Cerrado, covering an area of 494,100 hectares of cotton. Twenty-one insecticides were applied, with 64.8% of the applications made with malathion, fipronil, carbosulfan, and thiamethoxam + lambda-cyhalothrin. These four insecticides were used by 100, 76, 70, and 62% of the growers, with respectively 7.2, 2.1, 1.8, and 1.6 applications. Growers classified their boll weevil control achieved into four categories (fair, good, very good, or excellent), without correlation between these categories with the number of insecticide applications. Control of cotton regrowth and volunteer cotton plants were the major obstacles for effective boll weevil management, followed by the low efficacy of insecticides. Five registered insecticides to spray cotton against other pests than boll weevil were enlisted by growers with potential for recommendation. A boll weevil standard population for susceptibility was assayed with 27 insecticides and the results presented within a failure risk quotient (FRQ). The FRQ of eight, six, and 13 of the 27 tested insecticides was high, intermediate, and low, respectively. The high FRQ included 7 of 10 pyrethroid formulations, pymetrozine, and methomyl. On the opposite end, fipronil had the lowest FRQ value.

Susceptibility of Boll Weevil (Coleoptera: Curculionidae) to Ethiprole, Differential Toxicity Against Selected Natural Enemies, and Diagnostic Concentrations for Resistance Monitoring

Synthetic insecticide application is one tactic for reducing boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), infestations during the cotton, Gossypium hirsutum L., reproductive stage. We assessed the susceptibility of the boll weevil and its natural enemies to ethiprole (mode of action 2B), a phenylpyrazole insecticide, and diagnostic concentrations of ethiprole indicative of boll weevil susceptibility. Differences in the lethal concentrations of ethiprole were calculated with susceptibility ratios based on LC50 ranging from 2.89- to 10.34-fold relative to a natural susceptible population. The lowest and the highest recommended field rates of ethiprole, 100 and 200 g a.i./ha, produced residues that caused 83.3% and 93.7% mortality of weevils caged with cotton leaves from field-treated plants for 8 d. We found that ethiprole was less toxic than fipronil to the boll weevil parasitoid Bracon vulgaris Ashmead (Hymenoptera: Braconidae) and to the red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), while fipronil was highly toxic to both. Adult earwigs, Euborellia annulipes Lucas (Dermaptera: Anisolabididae), were relatively tolerant to ethiprole and fipronil at the highest field rates. Pooled LC50-and LC95-concentrations of ethiprole calculated from studied populations were used as diagnostic for boll weevil mortality, and the outcome fitted to the expected mortality for boll weevil populations from different locations serving for further control failure assessment. Ethiprole appears to be suitable for boll weevil control with low impact on natural enemy communities.

Formulation of nanopesticide with graphene oxide as the nanocarrier of pyrethroid pesticide and its application in spider mite control

Nanopesticides with controlled release can achieve more effective utilization of pesticides. Here, to enhance the adsorption of pesticides onto the target organisms, the formulation of pesticides with temperature-responsive release was proposed by combing graphene oxide (GO) and existing pyrethroid pesticides (cyhalothrin, bifenthrin and fenpropathrin). Pesticides were loaded onto GO nanosheets as a carrier via a simple physisorption process, and the GO–pesticide nanocomposites exhibited temperature-responsive release and excellent storage stability, which are of vital importance to the practical application. Furthermore, we assessed the bioactivity of the GO–pesticide nanocomposites against spider mites (Tetranychus urticae Koch) indoors and in the field. As a result, GO–pesticide nanocomposites had many folds higher bioactivity than individual pesticides, and could be adsorbed on the cuticle of T. urticae and surface of bean leaves with highly uniform dispersibility. The easy preparation and higher bioactivity of GO–pesticide nanocomposites indicate their promising application potential in pest control and green agriculture.

Nanopesticides with controlled release can achieve more effective utilization of pesticides.