Major Crop Pests Research Articles

Sublethal and transgenerational effects of dinotefuran on biological parameters and behavioural traits of the mirid bug Apolygus lucorum

The mirid bug, Apolygus lucorum, has become a major pest of many crops and fruit trees since the widespread adoption of Bt cotton in northern China. Neonicotinoid insecticides, such as dinotefuran, applied to control this pest may show sublethal effects, but evidence for such effects is lacking. Here, we investigated the sublethal and transgenerational effects of dinotefuran on biological parameters and feeding behavioural traits of A. lucorum using the age-stage, two-sex life table and electrical penetration graphs (EPGs), respectively. The LC10 and LC30 of dinotefuran against 3rd-instar nymphs of A. lucorum were 14.72 and 62.95 mg L−1, respectively. These two concentrations significantly extended the development duration from 3rd-instar nymph to adult in parent generation (F0). LC30 also increased the oviposition period and male adult longevity and reduced nymphal survival rate in the F0. For offspring generation (F1), the egg duration, preadult duration, and total preoviposition period were significantly lower at LC10 than in the control, and the egg duration, duration of 4th-instar nymphs, preadult duration, oviposition period, and fecundity were also decreased at LC30. However, the four demographic parameters of F1 generation, namely, net reproductive rate (R0), intrinsic rate of increase (r), finite rate of increase (λ), and mean generation time (T), were not affected by dinotefuran. The significant differences in the number of probes and duration of each of four feeding waveforms failed to be detected when A. lucorum nymphs treated by dinotefuran feed on Bt cotton plants without insecticide exposure. Overall, the dinotefuran concentrations tested here have sublethal, but no transgenerational impacts on A. lucorum.

Major crop pests identification research based on Convolutional Neural Network

There are many kinds of crop pests in China and they are prone to disasters. Agricultural pests pose a serious threat to crop growth, so how to effectively identify crop pests is crucial. With the development of computer vision technology and artificial intelligence, the combination of computer vision technology and classification and identification of pests has become a hot and difficult point for experts at home and abroad. In this paper, based on the bag-of-words model and the GoogLeNet model, 2200 pest images collected were used as experimental samples to study the identification of crop pests. The experimental results show that the average classification accuracy of the traditional bag-of-words model is about 56.41%, and the GoogLeNet model recognition accuracy can reach 96.35%. The GoogLeNet model based on transfer learning has higher precision and stronger anti-interference ability than the traditional bag-of-words model.

Soil conservation practices for insect pest management in highly disturbed agroecosystems – a review

AbstractDecline in soil health is a serious worldwide problem that decreases complexity and stability of agricultural ecosystems, commonly making them more prone to outbreaks of herbivorous insect pests. Potato (Solanum tuberosumL., Solanaceae) and onion (Allium cepaL., Amaryllidaceae) production is currently characterized by high soil disturbance and heavy reliance on synthetic inputs, including insecticides. Evidence suggests that adopting soil conservation techniques often (but not always) increases mortality and decreases reproductive output for the major insect pests of these important vegetable crops. Known mechanisms responsible for such an effect include increases in density and activity of natural enemy populations, enhanced plant defenses, and modified physical characteristics of respective agricultural habitats. However, most research efforts focused on mulches and organic soil amendments, with additional research needed on elucidating effects and their mechanisms for conservation tillage, cover crops, and arbuscular mycorrhizae.

Transcriptome and microbiome of coconut rhinoceros beetle (Oryctes rhinoceros) larvae

BackgroundThe coconut rhinoceros beetle, Oryctes rhinoceros, is a major pest of palm crops in tropical Asia and the Pacific Islands. Little molecular data exists for this pest, impeding our ability to develop effective countermeasures and deal with the species’ growing resistance to viral biocontrols. We present the first molecular biology analyses of this species, including a metagenomic assay to understand the microbiome of different sections of its digestive tract, and a transcriptomics assay to complement the microbiome data and to shed light on genes of interest like plant cell wall degrading enzymes and immunity and xenobiotic resistance genes.ResultsThe gut microbiota of Oryctes rhinoceros larvae is quite similar to that of the termite gut, as both species feed on decaying wood. We found the first evidence for endogenous beta-1,4-endoglucanase in the beetle, plus evidence for microbial cellobiase, suggesting the beetle can degrade cellulose together with its gut microfauna. A number of antimicrobial peptides are expressed, particularly by the fat body but also by the midgut and hindgut.ConclusionsThis transcriptome provides a wealth of data about the species’ defense against chemical and biological threats, has uncovered several potentially new species of microbial symbionts, and significantly expands our knowledge about this pest.

Crop pest control in China: Advances and perspectives

There are many different kinds of crop pests widely distributed in China, which are very complex in occurrence and difficult in prevention and control. They may outbreak suddenly, causing serious damages to crops, and thereby have a significant impact on food security and safety. In the past 70 years, the development of basic research in plant protection in China has made great progress and profound changes, starting from simple agricultural intervention measures to current integrated, biologically-based and environment-friendly protection measures to effectively prevent and control crop pests. These measures are mainly dependent on the progress of innovation in the following fields: better understanding of the epidemic and migration patterns of major crop pests and diseases, elucidation on mechanisms for causing damages to crop by pests, discovery of novel technology and products for control of crop diseases and pests, and establishment of surveillance, early warning and control systems for management of crop pests. With the improvement of the scientific and technological progress in plant protection, the innovation of the future plant protection research will focus on discovery of new epidemic pattern for crop pests; establishment of effective pest detection, monitoring and early warning system; development of green and effective pesticides, biological control products. Thus, sustainable management of crop pests and disease could be reached at local, regional and global levels. In conclusion, development of a full-scale national plant protection technical support system would meet the requirements of the food security and safety and natural environment and contribute to the global Sustainable Development Goals.

Conjugated linoleic acid as a novel insecticide targeting the agricultural pest Leptinotarsa decemlineata.

The Colorado Potato Beetle, Leptinotarsa decemlineata, is a major agricultural pest of solanaceous crops in the United States. Historically, a multitude of insecticides have been used to control problematic populations. Due to increasing resistance to insecticides, novel compounds and methodologies are warranted for the control of beetle populations. Mixed-isomer conjugated linoleic acid has been studied in-depth for its beneficial properties to mammalian systems. At the same time, studies have demonstrated that conjugated linoleic acid can manipulate fatty acid composition in non-mammalian systems, resulting in embryo mortality. Consequently, experiments were conducted to assess the effects of foliar-applied conjugated linoleic acid on larval growth, embryogenesis, and feeding preference in Colorado potato beetle. Both maternal and deterrent effects of dietary conjugated linoleic acid were assessed. Conjugated linoleic acid demonstrated desirable insecticidal properties, including increased larval mortality, slowed larval development, antifeedant effects, and decreased egg viability after maternal ingestion.

Changes in emergence phenology, fatty acid composition, and xenobiotic-metabolizing enzyme expression is associated with increased insecticide resistance in the Colorado potato beetle.

The Colorado potato beetle (Leptinotarsa decemlineata) is a major agricultural pest of solanaceous crops. An effective management strategy employed by agricultural producers to control this pest species is the use of systemic insecticides. Recent emphasis has been placed on the use of neonicotinoid insecticides. Despite efforts to curb resistance development through integrated pest management approaches, resistance to neonicotinoids in L. decemlineata populations continues to increase. One contributing factor may be alterations in insect fatty acids, which have multiple metabolic functions and are associated with the synthesis of xenobiotic‐metabolizing enzymes to mitigate the effects of insecticide exposure. In this study, we analyzed the fatty acid composition of L. decemlineata populations collected from an organic production field and from a commercially managed field to determine if fatty acid composition varied between the two populations. We demonstrate that a population of L. decemlineata that has a history of systemic neonicotinoid exposure (commercially managed) has a different lipid composition and differential expression of known metabolic detoxification mechanisms relative to a population that has not been exposed to neonicotinoids (organically managed). The fatty acid data indicated an upregulation of Δ6 desaturase in the commercially managed L. decemlineata population and suggest a role for eicosanoids and associated metabolic enzymes as potential modulators of insecticide resistance. We further observed a pattern of delayed emergence within the commercially managed population compared with the organically managed population. Variations in emergence timing together with specific fatty acid regulation may significantly influence the capacity of L. decemlineata to develop insecticide resistance.

Overwintering of the western flower thrips in outdoor strawberry crops

The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is a major pest of semi-protected strawberry crops in the UK. These crops are grown outdoors but sheltered by clear polythene tunnels during the growing season from about April to October. The aims of the study were (1) to test whether F. occidentalis overwinters in strawberry crops in central England, where overwintering in outdoor crops has not previously been demonstrated and (2) to test whether overwintering affects the thrips population during the following season. F. occidentalis was found breeding on several crop weeds that often flower throughout the year, including common chickweed (Stellaria media), groundsel (Senecio vulgaris) and dandelion (Taraxacum officinale). F. occidentalis female adults were found throughout the winter in flowers of these weeds and caught every month on blue sticky traps. Transparent emergence traps placed over various locations in a second-year crop in March caught adult thrips over the following month, showing that thrips survived within the crop. Second-year strawberry crops had earlier infestations and significantly more F. occidentalis adults per flower than nearby first-year crops at the start of the season, indicating that thrips that overwinter in and around retained crops contribute to pest build-up in the following season. Control of overwintering F. occidentalis after the end of first-year cropping before second-year cropping, or growing crops for only 1 year, is a potential strategy to improve thrips management in strawberry. The survival of F. occidentalis over winter on outdoor crops raises concerns that the species could in time become established on other outdoor crops.

Effects of Cold- and Hot-Pressed Neem Oil on Eggs of the Pod-Sucking Bug Clavigralla tomentosicollis Stål (Hemiptera: Coreidae) and Its Parasitoid Gryon fulviventre Crawford (Hymenoptera: Scelionidae) under Laboratory Conditions

The control of major insect crop pests of cowpea in Africa often involves synthetic pesticides to protect these crucial agricultural products. However, consequent harms to the environment, humans, animals and beneficial insects by these synthetic pesticides have driven a search for more sustainable integrated insect pest management (IPM) approaches, including the use of biological controls and neem (Azadirachta indica A. Juss) oil as alternatives to synthetic pesticides for the control of the pod-sucking bug Clavigralla tomentosicollis Stal on African cowpea crops. To date, however, no study to the authors' knowledge has investigated the compatibility and effectiveness of biological controls and neem approaches used together. In this study, we assessed the effects of two available preparations of neem oil (cold-pressed and hot-pressed) on the eggs of C. tomentosicollis and its parasitoid Gryon fulviventre Crawford. The main results of the study support the hypothesis that both cold-pressed and hot-pressed neem oil sprays are compatible with biological/IPM control efforts using G. fulviventre. While hot-pressed neem showed stronger effects on levels of egg hatchability and mortality for C. tomentosicollis compared to cold-pressed neem, no differences in outcomes across tested neem concentrations were observed. Future research, including field trials, will have the potential to elucidate any underlying mechanisms of these results and/or to more exactly identify appropriate concentrations needed to successfully integrate biological and non-synthetic controls for major cowpea pests in Africa.

Geographic distribution and abundance of the Afrotropical subterranean scale insect Stictococcus vayssierei (Hemiptera: Stictococcidae), a pest of root and tuber crops in the Congo basin.

Stictococcus vayssierei is a major pest of root and tuber crops in central Africa. However, data on its ecology are lacking. Here we provide an updated estimate of its distribution with the aim of facilitating the sustainable control of its populations. Surveys conducted in nine countries encompassing 13 ecological regions around the Congo basin showed that African root and tuber scale was present in Cameroon, Central African Republic, Congo, Democratic Republic of Congo, Equatorial Guinea, Gabon and Uganda. It was not found on the sites surveyed in Chad and Nigeria. The pest occurred in the forest and the forest-savannah mosaic as well as in the savannah where it was never recorded before. However, prevalence was higher in the forest (43.1%) where cassava was the most infested crop, compared to the savannah (9.2%) where aroids (cocoyam and taro) were the most infested crops. In the forest habitat, the pest was prevalent in all but two ecological regions: the Congolian swamp forests and the Southern Congolian forest-savanna mosaic. In the savannah habitat, it was restricted to the moist savannah highlands and absent from dry savannahs. The scale was not observed below 277 m asl. Where present, the scale was frequently (87.1% of the sites) attended by the ant Anoplolepis tenella. High densities (>1000 scales per plant) were recorded along the Cameroon-Gabon border. Good regulatory measures within and between countries are required to control the exchange of plant materials and limit its spread. The study provides information for niche modeling and risk mapping.

Fungal volatile organic compounds show promise as potent molluscicides.

BACKGROUNDSlugs and snails constitute major crop pests. Withdrawal of metaldehyde has prompted a search for more environmentally friendly yet fast acting molluscicides. This study investigated the response of representative molluscs to conidia and volatile organic compounds (VOCs) of the insect pathogenic fungus Metarhizium brunneum Petch.RESULTSConidia of M. brunneum had antifeedant/repellent properties with repellency being dependent upon the fungal strain and conidia concentration. Three commonly produced fungal VOCs, 1‐octene, 3‐octanone and 1‐octen‐3‐ol, were repellent at low doses (1–5 μL) but could kill slugs and snails on contact or fumigation. At the highest dose tested (10 μL), 100% mortality was achieved for Cornu aspersum Muller (garden snail) and Derocerus reticulatum Muller (grey field slug) within 1 h post‐treatment with the first deaths being recorded in <11 min. Aqueous formulations (20% v/v) of the most potent VOCs, 3‐octanone and 1‐octen‐3‐ol, could be sprayed onto plants to kill or drive the pest of the crop with no phytotoxic effects.CONCLUSIONThe sensitivity of terrestrial molluscs to 3‐octanone and 1‐octen‐3‐ol and the ephemeral nature of these compounds makes these excellent candidates for development as mollusc repellents or molluscicides. © 2019 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Egg-Laying Pattern of Helicoverpa zea1 in Sweet Corn: A New Pest Management Prospect

The corn earworm, Helicoverpa zea (Boddie), is a major insect pest of maize (Zea mays L.), cotton (Gossypium hirsutum L.), and vegetable crops. Maize silk is a favorite egg-laying site of H. zea. However, other parts of the maize plant might be even more attractive for oviposition by H. zea. Under field conditions and in insect-proof cages in a greenhouse, egg-laying distribution patterns were assessed on a late and an early sweet corn cultivar, i.e., Java (Technisem) and Garrison (Syngenta), respectively. Maize tassels on both cultivars were the main egg-laying sites of the pest. In insect-proof cages, at the maize silking stage, more than 60% of the total number of eggs collected were on tassels. In the field, oviposition by H. zea began at tassel emergence, and more than 80% of the total number of eggs were collected from tassels. Egg distribution on leaves and silk varied according to the sweet corn cultivar. The findings offer new prospects to control H. zea. The tassel emergence stage is the best period for controlling H. zea in maize fields and the best phenological stage to use maize as a trap crop for the pest.

Consumption of cereal leaf beetle, Oulema melanopus, by generalist predators in wheat fields detected by molecular analysis

AbstractThe cereal leaf beetle (CLB), Oulema melanopus L. (Coleoptera: Chrysomelidae), is a major pest of cereal crops that has recently been reported in western Canada. We developed a set of primers to detect CLB DNA in the gut of six common predator taxa in wheat fields: lady beetles (20 positives of 143 individuals), nabid bugs (73 positives of 206 individuals), and wolf spiders (2 positives of 25 individuals). Nabis americoferus Carayon (Hemiptera: Nabidae) and Coccinella septempunctata L. (Coleoptera: Coccinellidae) were the most abundant predators in cereal fields, with 0.35 and 0.05 proportion of samples positive for CLB DNA, respectively. The prey DNA half‐lives were used to adjust the estimates for N. americoferus to 0.22, due to its longer DNA detectability relative to C. septempunctata. Overall, Hippodamia parenthesis (Say) (Coleoptera: Coccinellidae) had the highest proportion of positives at 0.43. There was a positive association between CLB abundance and proportion of N. americoferus and C. septempunctata positives for CLB DNA. This study highlights the contribution of generalist predators to CLB mortality and their important role in integrated management for CLB. Furthermore, we provide a molecular tool that can be used to identify predators of CLB and predation frequency in agricultural fields.

Using de novo transcriptome assembly and analysis to study RNAi in Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae)

Phenacoccus solenopsis is one of the major polyphagous crop pests in India. Inadequate genomic or transcriptomic resources have limited the molecular studies in this insect despite its huge economic importance. The existing molecular sequence resources of this insect were supplemented through RNA sequencing, de novo transcriptome assembly and analysis, which generated 12, 925 CDS from 23,643 contigs with an average size of 1077.5 bp per CDS and 85.1% positive BLAST hits with NCBI Non redundant (nr) database. Twenty three genes involved in RNAi machinery identified through BLASTx search against NCBI nr database suggested the existence of robust RNAi in mealybug. RNAi in P. solenopsis was demonstrated through knockdown of IAP (Inhibitor of Apoptosis), AQP (Aquaporin), CAL (Calcitonin), VATPase (V-type proton ATPase subunit F 1), bursicon, chitin synthase, SNF7 and α-amylase by injecting sequence specific dsRNA of respective genes in adult female. Additionally, feeding RNAi has been demonstrated in 2nd instar nymph through dsRNA uptake in plant. The knockdown of core RNAi machinery genes such as Dicer, Argonaute and Staufen significantly hampered RNAi efficiency in this insect. However, downregulation of dsRNases improved RNAi efficiency. Sequential studies for understanding RNAi in P. solenopsis using transcriptome sequences have also been reported. The present study provides a base for future research on developing RNAi as strategy for management of this pest.

Global invasion history of the agricultural pest butterfly Pieris rapae revealed with genomics and citizen science

The small cabbage white butterfly, Pieris rapae, is a major agricultural pest of cruciferous crops and has been introduced to every continent except South America and Antarctica as a result of human activities. In an effort to reconstruct the near-global invasion history of P. rapae, we developed a citizen science project, the "Pieris Project," and successfully amassed thousands of specimens from 32 countries worldwide. We then generated and analyzed nuclear (double-digest restriction site-associated DNA fragment procedure [ddRAD]) and mitochondrial DNA sequence data for these samples to reconstruct and compare different global invasion history scenarios. Our results bolster historical accounts of the global spread and timing of P. rapae introductions. We provide molecular evidence supporting the hypothesis that the ongoing divergence of the European and Asian subspecies of P. rapae (∼1,200 y B.P.) coincides with the diversification of brassicaceous crops and the development of human trade routes such as the Silk Route (Silk Road). The further spread of P. rapae over the last ∼160 y was facilitated by human movement and trade, resulting in an almost linear series of at least 4 founding events, with each introduced population going through a severe bottleneck and serving as the source for the next introduction. Management efforts of this agricultural pest may need to consider the current existence of multiple genetically distinct populations. Finally, the international success of the Pieris Project demonstrates the power of the public to aid scientists in collections-based research addressing important questions in invasion biology, and in ecology and evolutionary biology more broadly.

Extracellular endonucleases in the midgut of Myzus persicae may limit the efficacy of orally delivered RNAi

Myzus persicae is a major pest of many crops including canola and Brassica vegetables, partly because it vectors plant viruses. Previously it has been reported that double-stranded RNA delivered to aphids by injection, artificial diet or transgenic plants has knocked down target genes and caused phenotypic effects. While these studies suggest that RNA interference (RNAi) might be used to suppress aphid populations, none have shown effects sufficient for field control. The current study analyses the efficacy of dsRNA directed against previously reported gene-targets on Green peach aphid (Myzus persicae) strains. No silencing effect was observed when dsRNA was delivered in artificial diet with or without transfection reagents. dsRNA produced in planta also failed to induce significant RNAi in M. persicae. Transcriptome analyses of the midgut suggested other potential targets including the Ferritin heavy chain transcripts, but they also could not be knocked down with dsRNA. Here we show that dsRNA is rapidly degraded by midgut secretions of Myzus persicae. Analysis of the transcriptome of the M. persicae midgut revealed that an ortholog of RNases from other insects was abundant.

Origin of resistance to pyrethroids in the redlegged earth mite (Halotydeus destructor) in Australia: repeated local evolution and migration.

Halotydeus destructor is a major pest of crops and pastures across southern parts of Australia. This invasive mite has been chemically controlled for over 50 years, but resistance to synthetic pyrethroids and organophosphates is developing. Understanding processes behind the emerging resistance is important for effective management efforts. We undertook a ddRAD pool-sequencing approach to analyse genome-wide single nucleotide polymorphism variation in H. destructor population samples at two scales: local resistance across a set of fields, and regional resistance across their Australian range, along with toxicology bioassays to screen for pyrethroid resistance. Spatial patterns of genomic variation and resistance at a local scale indicated that genetic similarity among samples was more closely correlated with distance along roads and fence-lines than with straight-line geographic distance. This pattern was particularly strong in resistant samples, which were also more related than susceptible samples, suggesting local spread of resistance within an area after it emerged. By contrast, regional data suggest resistance has emerged repeatedly within parts of Australia. Our de novo annotation of the H. destructor draft genome sequence and Bayesian analysis identified several candidate loci strongly associated with population-level resistance to pyrethroids, located in genomic regions that code for transmembrane transport and signalling proteins that have previously been linked to insecticide resistance in other arthropods. Our findings highlight multiple independent evolutionary events leading to resistance in H. destructor, and demonstrate the utility and cost-effectiveness of a cross-population, genome-wide association study to reveal processes underlying adaptive evolution in a non-model invasive species. © 2019 Society of Chemical Industry.

Draft Genome of Busseola fusca, the Maize Stalk Borer, a Major Crop Pest in Sub-Saharan Africa

The maize stalk borer, Busseola fusca, is an important Lepidopteran pest of cereal crops in Central, East, and Southern Africa. Crop losses due to B. fusca feeding activity vary by region, but can result in total crop loss in areas with high levels of infestation. Genomic resources provide critical insight into the biology of pest species and can allow for the development of effective management tools and strategies to mitigate their impact on agriculture. To this end, we sequenced, assembled, and annotated the genome of B. fusca. The total assembled genome size was 492.9 Mb with 19,417 annotated protein-coding genes. Using a comparative approach, we identified a putative expansion in the Chorion gene family, which is involved in the formation of the egg shell structure. Our analysis revealed high repeat content within the B. fusca genome, with LTR sequences comprising the majority of the repetitive sequence. We hope genomic resources will provide a foundation for future work aimed at developing an integrated pest management strategy to reduce B. fusca’s impact on food security.

Better biological control in glasshouses: synergies between biological control agents from different guilds and floral resources

The tomato/potato psyllid (TPP), Bactericera cockerelli (Hemiptera, Triozidae), is an adventive psyllid in New Zealand that is a major pest of solanaceous crops and a serious threat to growers in the glasshouse industry. Worldwide, evaluation of potential biological control (BC) agents is normally conducted using single species and this is the case with some potential BC agents for TPP. However, the idea that multiple species can act synergistically remains largely untested so that is the aim of the current work, which is funded by Tomatoes New Zealand. The introduced parasitoid Tamarixia triozae is a BC agent of TPP that attacks mainly late instars. It lives for just 1 day when provided with water but can live up to 11 days (and consume more pests) when nectar in the flowers of buckwheat (Fagopyrum esculentum) is provided. In addition, another potential BC agent, the mirid bug Engytatus nicotianae, prefers young nymphal instars, while the ladybird Cleobora mellyi is voracious and consumes all instars. We are testing combinations of these species to understand the potential for synergies between and within trophic levels for better biological control.

Parasitism of diamondback moth Plutella xylostella by the solitary parasitoid wasp Cotesia vestalis in Samoa

Plutella xylostella is a major pest of crucifier crops in Samoa and other Pacific islands. This pest has developed resistance to most insecticides available in the island nations so the objective of this study was to examine potential biological control options for P. xylostella in Samoa. Existing parasitism of P. xylostella on Chinese cabbage (Brassica rapa subspp.) was investigated at a farm in Alesia and at the USP farm in Alafua, and established populations of Cotesia vestalis were found at both locations. Plutella xylostella larvae turn light yellow and show sluggish behaviour after parasitism, and they could be easily differentiated from unparasitised ones. Developing C. vestalis larvae emerge from their hosts and spin white cocoon around their body. After 5–6 days, a single adult emerges from the C. vestalis cocoon. The average parasitism rate between April 2015 and March 2016 was 10–18% but was significantly higher at the USP farm than the Alesia farm. This result could be because no insecticides were applied to the crops at USP. Parasitism was highest between June and August when the lowest average daily temperatures occur.