Herbivorous Pests Research Articles

Zoophytophagous mirids provide pest control by inducing direct defences, antixenosis and attraction to parasitoids in sweet pepper plants.

In addition to their services as predators, mirid predators are able to induce plant defences by phytophagy. However, whether this induction occurs in sweet pepper and whether it could be an additional benefit to their role as a biological control agent in this crop remain unknown. Here, these questions were investigated in two model insects, the mirids Nesidiocoris tenuis and Macrolophus pygmaeus. Plant feeding behaviour was observed in both N. tenuis and M. pygmaeus on sweet pepper and occupied 33% and 14% of total time spent on the plant, respectively. The punctures caused by mirid plant feeding induced the release of a blend of volatile organic compounds (VOCs) which repelled the herbivore pests Frankliniella occidentalis and Bemisia tabaci and attracted the whitefly parasitoid Encarsia formosa. The repellent effect on B. tabaci was observed for at least 7 days after initial exposure of the plant to N. tenuis, and attraction of E. formosa remained functional for 14 days. Plant defences induced by the feeding of mirid predators, their subsequent effects on the behaviour of both pests and natural enemies, and the persistence of these observed effects open the door to new control strategies in the sweet pepper crop. Further application of this research is discussed, such as the vaccination of plants by zoophytophagous mirids in the nursery before transplantation. © 2017 Society of Chemical Industry.

Shy herbivores forage more efficiently than bold ones regardless of information-processing overload

The neural constraint hypothesis is central to understanding decision-making by foraging herbivorous insects which make decisions less efficiently when they face multiple choices for numerous resource types and/or at high densities instead of a fewer choices. Previous studies have also shown the relationship between personality type and decision-making style. How personality types correlate with foraging efficiency among herbivores is however, largely untested. To answer this question, we used a widespread, polyphagous, floriphilic katydid, Phaneroptera brevis (Orthoptera: Tettigoniidae) and two naturalised, Asteraceae, food plants, Bidens pilosa and Sphagneticola trilobata, as model systems. After we determined each katydid’s exploration and boldness levels, we examined its foraging efficiency across different combinations of floral resource choice and density. We showed: (1) For the first time within the Tettigonioidea lineage that this katydid exhibits different personality types in exploration and boldness. (2) Contrary to our prediction, we did not find any support for the neural constraint hypothesis because more floral resource choice at a high density did not reduce foraging efficiency. (3) Surprisingly, bold katydids tend to be less efficient foragers than shy ones. Our findings have enhanced understanding of herbivore behavioural ecology and knowledge to better deal with potential pest herbivores.

Edge-biased distributions of insects. A review

Spatial ecology includes research into factors responsible for observed distribution patterns of organisms. Moreover, the spatial distribution of an animal at a given spatial scale and in a given landscape may provide valuable insight into its host preference, fitness, evolutionary adaptation potential, and response to resource limitations. In agro-ecology, in-depth understanding of spatial distributions of insects is of particular importance when the goals are to (1) promote establishment and persistence of certain food webs, (2) maximize performance of pollinators and natural enemies, and (3) develop precision-targeted monitoring and detection of emerging outbreaks of herbivorous pests. In this article, we review and discuss a spatial phenomenon that is widespread among insect species across agricultural systems and across spatial scales—they tend to show “edge-biased distributions” (spatial distribution patterns show distinct “edge effects”). In the conservation and biodiversity literature, this phenomenon has been studied and reviewed intensively in the context of how landscape fragmentation affects species diversity. However, possible explanations of, and also implications of, edge-biased distributions of insects in agricultural systems have not received the same attention. Our review suggests that (1) mathematical modeling approaches can partially explain edge-biased distributions and (2) abiotic factors, crop vegetation traits, and environmental parameters are factors that are likely responsible for this phenomenon. However, we argue that more research, especially experimental research, is needed to increase the current understanding of how and why edge-biased distributions of insects are so widespread. We argue that the fact that many insect pests show edge-biased distribution patterns may be used to optimize both pest monitoring practices and precision targeting of pesticide applications and releases of natural enemies.

耕作方式对玉-豆轮作地表节肢动物多样性及其营养结构的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 耕作方式对玉-豆轮作地表节肢动物多样性及其营养结构的影响 DOI: 10.5846/stxb201709221712 作者: 作者单位: 中国科学院东北地理与农业生态研究所,吉林大学;吉林大学,商丘师范学院,中国科学院东北地理与农业生态研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41501263，41430857）；中国博士后科学基金面上项目（2016M590269）；河南省科技厅科技攻关项目（172102410054）；商丘师范学院骨干教师项目（2015GGJS15）；2014年河南省哲学社会科学规划项目（2014CJJ087） Response of ground-dwelling arthropod community diversity and its trophic structure in relation tillage regimes under maize-soybean rotation Author: Affiliation: College of Surveying and Planning,Shangqiu Normal University,,,Northeast Institute of Geography and Agroecology Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为阐明长期不同耕作方式对轮作种植模式黑土农田地表节肢动物多样性及其营养结构的影响，2015年5月至9月间，利用陷阱法对连续13年玉米大豆轮作模式的定位试验站三种耕作方式（免耕、垄作、秋翻）的地表节肢动物群落进行了调查。共捕获动物1002只，隶属于3纲11目29科37个类群，凹唇蚁、玉米毛蚁和直角通缘步甲为优势类群。免耕（NT，no tillage）有利于增加蜘蛛类群密度，垄作（RT，ridge tillage）和秋翻（MP，mould board plough）显著增加了玉米毛蚁密度。耕作方式仅对群落密度有显著影响显著影响（P < 0.05），而大豆不同生育阶段显著或极显著的影响地表节肢动物群落组成特征（P < 0.05；P < 0.001）。长期玉米大豆轮作种植的地表节肢动物群落营养功能群在不同耕作方式中所占比例不同，保护性耕作方式（NT、RT）更有利于捕食性和植食性动物的生存和繁殖，常规耕作（MP）则是杂食性动物占据优势，明显呈现对不稳定环境的适应。大豆不同生育期，各功能群的个体数与类群数的动态变化不尽一致，不具有明显的规律性。研究结果表明，免耕轮作对维持地表节肢动物群落内部物种间的关系及其营养结构有着较为重要的作用，保护性耕作和轮作种植模式相结合可维持农田生态系统平衡。 Abstract:Conservation tillage, such as reduced tillage or no-tillage, may play an important role in increasing soil organic matter, reducing soil erosion, and providing a more complex and favorable habitat for soil-dwelling organisms. Aboveground arthropods are important components of ecosystems, promoting a number of key functions, such as decomposition of organic matter and some herbivorous pest control. The abundance and diversity of food web components depends highly on the rotation system and soil management. To reveal the effect of tillage regimes on the diversity and trophic structure of ground-dwelling arthropods under maize-soybean rotation in the black soil of Northeast China, five field investigations were conducted with three tillage regimes (no tillage, NT; ridge tillage, RT; mould board plough, MP) at a 13-year tillage regime experiment station. A total of 1002 arthropod individuals belonging to 3 classes, 11 orders, 29 families, and 37 groups were collected. Formica sanguinea Letreille, Lasius alienus Foerster, and Poecilus gebleri Dejean were the dominant species and accounted for 60.58% of the total individuals. The results showed that NT was beneficial to the spider population resulting in increased densities, and RT and MP significantly increased the density of Lasius alienus. Tillage regimes only significantly affected the density of arthropod communities in different growth stages (P < 0.05), whereas different growth stages of soybeans significantly or highly significantly affected the density, groups, and diversity of the arthropod community under different tillage regimes (P < 0.05; P < 0.001). In the long-term, under the maize and soybean rotation system, the proportion of trophic functional groups was different under the different tillage practices. The results indicated that the long-term conservation tillage (NT and RT) was more conducive to the survival of predators and herbivorous arthropods. Omnivores were dominant in the MP system, showing obvious adaptation to the unstable environment. In the different growth stages of the soybeans, the variation in all functional groups was not consistent, and there was no obvious pattern. It is obvious that no-tillage with rotation play an important role in maintaining the relationship between the species within the community and the trophic structure of the food web. 参考文献 相似文献 引证文献

QTL mapping of antixenosis resistance to common cutworm (Spodoptera litura Fabricius) in wild soybean (Glycine soja).

The common cutworm (CCW; Spodoptera litura Fabricius) is a serious herbivorous insect pest of soybean (Glycine max) in Asia and Oceania. Previously, we identified quantitative trait loci (QTLs) for CCW-antibiosis-resistance, CCW-1 and CCW-2, and antixenosis-resistance, qRslx1 and qRslx2, in the cultivar ‘Himeshirazu’. The effects of these QTLs are useful in the breeding of CCW-resistant cultivars. In this study, we conducted an antixenosis bioassay on CCW using recombinant inbred lines derived from a cross between a wild soybean (Glycine soja) and the leading cultivar ‘Fukuyutaka’ to identify CCW-resistance genes in G. soja. The QTL analysis revealed six and four novel antixenosis-resistance QTLs in 2012 and 2013, respectively. Among them, the QTLs on chromosomes 2 and 7, designated qRslx4 and qRslx3, respectively, were stably detected in both years. qRslx3 exhibited the largest effect in both years, suggesting that qRslx3 can be exploited in the breeding of CCW-resistant soybean. Furthermore, qRslx3 and qRslx4 can be used, along with previously reported QTLs from ‘Himeshirazu’, to enhance the CCW-resistance of soybean cultivars because their chromosomal positions are unique. These new CCW-resistance QTLs from G. soja should play important roles in the breeding of CCW-resistant soybean cultivars.

A comparison of the molecular mechanisms underpinning high-intensity, pulsed polychromatic light and low-intensity UV-C hormesis in tomato fruit

Postharvest treatment of tomato fruit with high-intensity, pulsed polychromatic light (HIPPL) has previously been shown to induce delayed ripening and disease resistance comparable to that of low-intensity UV-C (LIUV). Little, however, is known of the mechanisms underpinning postharvest HIPPL hormesis in tomato fruit. Expression of genes involved in plant hormone biosynthesis, defence, secondary metabolism and ripening were monitored 24h post treatment (24 HPT), 10 d post treatment (10 DPT) and 12h post inoculation with Botrytis cinerea (12 HPI). All genes monitored were constitutively expressed and changes in expression profiles following treatment were highly similar for both HIPPL and LIUV treatments. Expression of pathogenesis-related proteins P4, β-1,3,-Glucanase and Chitinase 9 and a jasmonate biosynthesis enzyme (OPR3), were significantly upregulated at 10 DPT and 12 HPI. Both treatments significantly downregulated the expression of polygalacturonase and flavonol synthase at 10 DPT and 12 HPI. Ethylene biosynthesis enzyme ACO1 and β-carotene hydroxylase were significantly upregulated at 24 HPT, and phenylalanine ammonia-lyase (PAL) was significantly upregulated at 12 HPI. Both HIPPL and LIUV treatments stimulate defence responses that are mediated by salicylic acid, jasmonic acid and ethylene. This may lead to broad range resistance against both necrotrophic and biotrophic pathogens as well as abiotic stresses and herbivorous pests. Following inoculation with B. cinerea only PAL showed indication of a gene priming response for HIPPL- and LIUV-treated fruit.

Plant-to-plant communication triggered by systemin primes anti-herbivore resistance in tomato

Plants actively respond to herbivory by inducing various defense mechanisms in both damaged (locally) and non-damaged tissues (systemically). In addition, it is currently widely accepted that plant-to-plant communication allows specific neighbors to be warned of likely incoming stress (defense priming). Systemin is a plant peptide hormone promoting the systemic response to herbivory in tomato. This 18-aa peptide is also able to induce the release of bioactive Volatile Organic Compounds, thus also promoting the interaction between the tomato and the third trophic level (e.g. predators and parasitoids of insect pests). In this work, using a combination of gene expression (RNA-Seq and qRT-PCR), behavioral and chemical approaches, we demonstrate that systemin triggers metabolic changes of the plant that are capable of inducing a primed state in neighboring unchallenged plants. At the molecular level, the primed state is mainly associated with an elevated transcription of pattern -recognition receptors, signaling enzymes and transcription factors. Compared to naïve plants, systemin-primed plants were significantly more resistant to herbivorous pests, more attractive to parasitoids and showed an increased response to wounding. Small peptides are nowadays considered fundamental signaling molecules in many plant processes and this work extends the range of downstream effects of this class of molecules to intraspecific plant-to-plant communication.

A Gene Family Coding for Salivary Proteins (SHOT) of the Polyphagous Spider Mite Tetranychus urticae Exhibits Fast Host-Dependent Transcriptional Plasticity

The salivary protein repertoire released by the herbivorous pest Tetranychus urticae is assumed to hold keys to its success on diverse crops. We report on a spider mite-specific protein family that is expanded in T. urticae. The encoding genes have an expression pattern restricted to the anterior podocephalic glands, while peptide fragments were found in the T. urticae secretome, supporting the salivary nature of these proteins. As peptide fragments were identified in a host-dependent manner, we designated this family as the SHOT (secreted host-responsive protein of Tetranychidae) family. The proteins were divided in three groups based on sequence similarity. Unlike TuSHOT3 genes, TuSHOT1 and TuSHOT2 genes were highly expressed when feeding on a subset of family Fabaceae, while expression was depleted on other hosts. TuSHOT1 and TuSHOT2 expression was induced within 24 h after certain host transfers, pointing toward transcriptional plasticity rather than selection as the cause. Transfer from an 'inducer' to a 'noninducer' plant was associated with slow yet strong downregulation of TuSHOT1 and TuSHOT2, occurring over generations rather than hours. This asymmetric on and off regulation points toward host-specific effects of SHOT proteins, which is further supported by the diversity of SHOT genes identified in Tetranychidae with a distinct host repertoire.

Plant sex effects on insect herbivores and biological control in a Short Rotation Coppice willow

In the wild, plant sex can affect plant-herbivore interactions and higher trophic levels, including natural enemies of the herbivores. However, the possibility of manipulating plant sex to improve biological control and reduce herbivory in domesticated dioecious crops remains unexplored. The dioecious bioenergy crop, Salix viminalis, is often planted in monoclonal, and thus monosexual, fields. We investigated whether using plant clones of either sex, or mixing plants of both sexes, reduced the performance and abundance of the herbivorous pest insect Phratora vulgatissima and its main natural enemy, Anthocoris nemorum, and whether predation was affected. The herbivore laid more eggs, and the predator survived longer, on female plants in the lab. However, these effects did not translate into differences in predation rates in laboratory experiments or differential insect abundances on plants of either sex or plantation sex composition in the field. Plant genotype did have a significant effect on insect abundances, but this was due to plant traits other than sex. The results indicate that manipulating plant sex will not lead to improved biological control or reduced insect herbivory in S. viminalis energy forestry, but suggest that a focus on plant genotypic differences offers promise for improving management practices.

Egg Parasitoids ofDalbulus maidison Wild Teosintes in Mexico

Little is known about parasitoids that attack insect pests on wild host plants, including wild teosintes. Sentinel teosinte plants with eggs of the specialist herbivore pest, the corn leafhopper, Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae), were used to attract and capture egg parasitoid species in natural habitats of annual teosinte Zea mays ssp. parviglumis Iltis & Doebley, which is the direct ancestor of maize (Zea mays ssp. mays L.), and perennial teosinte Zea perennis (Hitchc.) Reeves & Mangelsdorf in central Mexico. In annual teosinte, eggs of D. maidis were parasitized by Anagrus incarnatus Haliday and Anagrus columbi Perkins (Hymenoptera: Mymaridae), as well as Paracentrobia sp. near subflava (Girault) and Pseudoligosita sp. near longifrangiata (Viggiani) (Hymenoptera: Trichogrammatidae); in perennial teosinte, they were parasitized by A. incarnatus and Pseudoligosita sp. near longifrangiata. All the egg parasitoids, recorded for the first time from wild teosintes, have been previously known from the same leafhopper pest on cultivated maize. Thus, their conservation in wild teosinte habitats may be important for enhancing natural biological control of the corn leafhopper in adjacent maize fields.

Plant parasite victims share insect pest alerts

Wizard’s net, devil’s guts, and witch’s hair are just a few of the common names for dodder, a nefarious rootless and leafless parasitic plant that sucks the water and nutrients out of its plant victims using a penetrating organ called a haustorium. Masses of the spaghetti-like dodder can smother crops, including soybeans, clover, and alfalfa. New research suggests that dodder’s victims try to make the best of a miserable situation. Because dodder’s haustoria bridge the vasculatures of multiple plants, the victims can use the parasite as a conduit to share chemical information about herbivorous insect pests when they try to invade, reports a team led by Ian T. Baldwin of the Max Planck Institute for Chemical Ecology and Jianqiang Wu of the Chinese Academy of Sciences’ Kunming Institute of Botany (Proc. Natl. Acad. Sci. USA 2017, DOI: 10.1073/pnas.1704536114). Working with two soybean plants connected by dodder, the team found that

Identification and characterization of ace1-type acetylcholinesterase in insecticide-resistant and -susceptible Propylaea japonica (Thunberg).

Characterization and gene cloning of acetylecholinesterase (AChE) in the insecticide-resistant (R) and -susceptible (S) insects have been reported in the past. However, the studies focused mostly on herbivorous pests, rather than predacious species, such as ladybird beetles. Using R and S Propylaea japonica (thunberg), a full-length cDNA sequence (2928 bp) of the ace1-type AChE gene was determined for the first time. The ace1 encoding a protein of 645 amino acids contained typical conserved motifs, such as FGESAG domains, catalytic triad, acyl pocket, oxyanino hole, choline binding site, peripheral anionic site, omega loop and conserved aromatic residues. R P. japonica displayed 50-times greater resistance to chlorpyrifos or mathamidophos with a significantly lower AChE sensitivity to paraoxon, malaoxon, chlorpyrifos or methamidophos than its S counterpart. Five amino acids in the ace1 of R P. japonica differed from those found in S P. japonica. One of them, F358S, located in the acyl-binding pocket, might play a crucial role in the resistance of the insect to organophosphates (OPs). Whereas, K493E and I538V, which were close to some of the conserved aromatic amino acids (i.e., H509, Y511, and W499) in the gorge, and G571R and T576A near C593 that formed the disulfide bonds with C471, might also involve in the change of insecticide resistance in P. japonica. AChE insensitivity and amino acid replacements, particularly F358S, might be the determining factors in the alteration of OPs-resistance in P. japonica.

Protocols for the delivery of small molecules to the two-spotted spider mite, Tetranychus urticae

The two-spotted spider mite, Tetranychus urticae, is a chelicerate herbivore with an extremely wide host range and an extraordinary ability to develop pesticide resistance. Due to its responsiveness to natural and synthetic xenobiotics, the spider mite is becoming a prime pest herbivore model for studies of the evolution of host range, plant-herbivore interactions and mechanisms of xenobiotic resistance. The spider mite genome has been sequenced and its transcriptional responses to developmental and various biotic and abiotic cues have been documented. However, to identify biological and evolutionary roles of T. urticae genes and proteins, it is necessary to develop methods for the efficient manipulation of mite gene function or protein activity. Here, we describe protocols developed for the delivery of small molecules into spider mites. Starting with mite maintenance and the preparation of the experimental mite populations of developmentally synchronized larvae and adults, we describe 3 methods for delivery of small molecules including artificial diet, leaf coating, and soaking. The presented results define critical steps in these methods and demonstrate that they can successfully deliver tracer dyes into mites. Described protocols provide guidelines for high-throughput setups for delivery of experimental compounds that could be used in reverse genetics platforms to modulate gene expression or protein activity, or for screens focused on discovery of new molecules for mite control. In addition, described protocols could be adapted for other Tetranychidae and related species of economic importance such as Varroa, dust and poultry mites.

Functional evolution of Lepidoptera olfactory receptors revealed by deorphanization of a moth repertoire

Insects detect their hosts or mates primarily through olfaction, and olfactory receptors (ORs) are at the core of odorant detection. Each species has evolved a unique repertoire of ORs whose functional properties are expected to meet its ecological needs, though little is known about the molecular basis of olfaction outside Diptera. Here we report a pioneer functional analysis of a large array of ORs in a lepidopteran, the herbivorous pest Spodoptera littoralis. We demonstrate that most ORs are narrowly tuned to ubiquitous plant volatiles at low, relevant odorant titres. Our phylogenetic analysis highlights a basic conservation of function within the receptor repertoire of Lepidoptera, across the expansive evolutionary radiation of different major clades. Our study provides a reference for further studies of olfactory mechanisms in Lepidoptera, a historically crucial insect order in olfactory research.

The Effects of Salinity on the Herbivorous Crop Pest Tetranychus urticae (Trombidiformes: Tetranychidae) on Soybean and Corn.

Many environmental factors, including soil characteristics, are critical for plants, herbivorous arthropods, and their interactions. Despite increasing evidence that soil salinity drastically impacts plants, little is known about how salinity affects the herbivorous arthropod pests feeding on those plants. We investigated how soil salinity affects the twospotted spider mite (Tetranychus urticae Koch) feeding on corn (Zea mays L.) and soybean (Glycine max L.). We performed two greenhouse studies, one focusing on the impact of salinity on individual mite fecundity over a period of 3 d and the other focusing on population growth of T. urticae over 7 d. Both experiments were performed across varying salinity levels; electrical conductivity values ranged from 0.84 to 8.07 dS m-1. We also performed the 3-d fecundity experiment in the field, across naturally varying saline conditions. Overall, the twospotted spider mite performed better as salinity increased; both fecundity and population growth tended to have a positive linear correlation with salinity. These studies suggest that salinity can be important for herbivores, just as it is for plants. Moreover, the negative effects of soil salinity on crop plants in agroecosystems may be further compounded by a greater risk of pest problems. Salinity may be another important environmental stressor that can directly influence crop production while also indirectly influencing herbivorous pests.

Herbivorous Insects Diversity at Miscanthus × Giganteus in Ukraine

Abstract Miscanthus × giganteus is considered as a perspective energy crop for biomass production in Ukraine where its commercial production has been observed. The herbivorous pest may pose a risk of yield reduction when an energy crop is growing on monoculture. The herbivorous diversity, species composition and potential damage associated with growing M. × giganteus were studied on seven experimental sites at three locations in Ukraine. The different life stages of herbivorous insects from seven orders representing thirteen families were found on M. × giganteus during the herbivorous survey and most of the insects had a pest status. Research indicated that crop was an alternate host for key cereal pest the Hessian fly Mayetiola destructor (Say) (Diptera: Cecidomyiidae). A comparative analysis of the biodiversity of herbivorous insects across research locations was done using statistical analysis. It was found that site location played a significant role in the level of biodiversity and an increase in the insect’s herbivores diversity was associated with the type of researched lands. The massive scale commercial use of M. × giganteus should take into account a responsible consideration of the benefits and risks associated with that crop in order to protect agroecosystems.

A global synthesis of the effects of diversified farming systems on arthropod diversity within fields and across agricultural landscapes.

Agricultural intensification is a leading cause of global biodiversity loss, which can reduce the provisioning of ecosystem services in managed ecosystems. Organic farming and plant diversification are farm management schemes that may mitigate potential ecological harm by increasing species richness and boosting related ecosystem services to agroecosystems. What remains unclear is the extent to which farm management schemes affect biodiversity components other than species richness, and whether impacts differ across spatial scales and landscape contexts. Using a global metadataset, we quantified the effects of organic farming and plant diversification on abundance, local diversity (communities within fields), and regional diversity (communities across fields) of arthropod pollinators, predators, herbivores, and detritivores. Both organic farming and higher in-field plant diversity enhanced arthropod abundance, particularly for rare taxa. This resulted in increased richness but decreased evenness. While these responses were stronger at local relative to regional scales, richness and abundance increased at both scales, and richness on farms embedded in complex relative to simple landscapes. Overall, both organic farming and in-field plant diversification exerted the strongest effects on pollinators and predators, suggesting these management schemes can facilitate ecosystem service providers without augmenting herbivore (pest) populations. Our results suggest that organic farming and plant diversification promote diverse arthropod metacommunities that may provide temporal and spatial stability of ecosystem service provisioning. Conserving diverse plant and arthropod communities in farming systems therefore requires sustainable practices that operate both within fields and across landscapes.

Epifluorescence and Stereomicroscopy of Trichomes Associated with Resistant and Susceptible Host Plant Genotypes of the Asian Citrus Psyllid (Hemiptera: Liviidae), Vector of Citrus Greening Disease Bacterium.

Background and Significance:Foliar trichomes (tiny hair-like structures) are part of the plant defense mechanisms that may confer resistance to some herbivore pests. Trifoliate orange, Poncirus trifoliata, is a genotype resistant to infestations by the Asian citrus psyllid, Diaphorina citri (Hemiptera: Liviidae), vector of the economically important citrus greening (huanglongbing) disease bacterium. We discovered that dense trichomes are associated with young leaves of trifoliate orange plants and hypothesized that these might be responsible for reduced infestation by this psyllid.Materials and Methods:Epifluorescence and stereomicroscopy were used to study the density and structure of trichomes associated with young flush leaves and stems of trifoliate orange and of five other plant genotypes that are highly susceptible to colonization by the psyllid: lemon, grapefruit, sweet orange, curry leaf, and orange jasmine.Results:Simple unicellular trichomes were observed at moderate-to-large densities on young leaves and stems of each genotype except lemon and sweet orange, which had considerably fewer trichomes. Trichomes were generally abundant on young leaves of curry leaf and orange jasmine, two genotypes that are often heavily colonized by the psyllid. Although we did not quantify oviposition rates on these genotypes, we observed that psyllid females deposited eggs on young leaves, buds, and stems regardless of the density of trichomes present, sometimes directly within or close to a dense bed of trichomes.Conclusions:While trichomes were moderately abundant on young leaves of trifoliate orange, our results strongly suggest that these trichomes may play little or no role in reduced colonization by the psyllid on this genotype.

Accumulation of amino acids and phenolic compounds in biochemical plant responses to feeding of two different herbivorous arthropod pests

The study aimed at comparing the changes in the content of free amino acids, phenolic compounds and the activity of PAL and TAL caused by two piercing-sucking arthropods: the grape mealybug (Pseudococcus maritimus Ehrh.) and the two-spotted spider mite (Tetranychus urticae Koch) in the leaves of orchid and strawberry, respectively. The obtained results show that the amino acid content and the ratio of amino acids to phenolic compounds increased in both plant species infested by the mealybug and the mite. However, such response was weakly dependent on changes in activity of the analysed enzymes. The pest feeding affected accumulation of the phenolic compounds, since the induction of the PAL activity in mealybug-infested orchid leaves during the first 5 h of the experiment preceded the increase in phenolic compounds during the first week of insect feeding. Instead, the increased activity of TAL was accompanied by elevated levels of phenolic compounds in the leaves of strawberry infested by mites. Mechanisms of biochemical plant responses induced by infestation of the studied herbivorous arthropods are discussed.

Biochemical mechanisms of acaricidal activity of 2,4-di-tert-butylphenol and ethyl oleate against the carmine spider mite Tetranychus cinnabarinus

Tetranychus cinnabarinus (Boisduval) is one of the most economically important and highly polyphagous herbivorous pests in fields and greenhouses worldwide. We previously reported that 2,4-di-tert-butylphenol (DTBP) and ethyl oleate (EO) showed significantly acaricidal, repellent and oviposition deterrent properties against T. cinnabarinus via an unknown mechanism. In this study, the acaricidal activities of DTBP and EO and their biochemical mechanisms in controlling T. cinnabarinus were investigated at different time points by assessing the associated changes in toxic symptoms, potential target-related enzyme activities and seven neurotransmitters belonging to the biogenic amines (BAs). The results showed that the median lethal times (LT50) for DTBP and EO were 8 and 15 h after treatment, respectively. Using dynamic symptomatology observations, typical neurotoxic symptoms including excitation, convulsion and paralysis were observed in the mites treated with DTBP and EO. Furthermore, the two compounds exerted significant inhibitory activity on monoamine oxidase (MAO) in adult T. cinnabarinus females in vitro and in vivo and had little effect on acetylcholinesterase (AChE) activity. The content levels of the seven BAs analyzed by UPLC-3QMS were higher in the mites treated with DTBP and EO than in the controls, except for phenethylamine (PEA) (for DTBP and EO) and octopamine (OA) (for EO). These results demonstrate that both DTBP and EO exert effects on T. cinnabarinus that are possibly consequences of their preventive effects on the deamination of BAs in the nervous system, most likely through inhibitory effects on MAO or MAO-like enzymes and/or interactions with certain special biogenic amine G protein-coupled receptors.