Adaptation to nicotine in the facultative tobacco-feeding hemipteran Bemisia tabaci

The role of the Bemisia tabaci and Trialeurodes vaporariorum cytochrome-P450 clade CYP6DPx in resistance to nicotine and neonicotinoids

The alkaloid, nicotine, produced by tobacco and other Solanaceae as an anti-herbivore defence chemical is one of the most toxic natural insecticides in nature. However, some insects, such as the whitefly species, Trialeurodes vaporariorum and Bemisia tabaci show strong tolerance to this allelochemical and can utilise tobacco as a host. Here, we used biological, molecular and functional approaches to investigate the role of cytochrome P450 enzymes in nicotine tolerance in T. vaporariorum and B. tabaci. Insecticide bioassays revealed that feeding on tobacco resulted in strong induced tolerance to nicotine in both species. Transcriptome profiling of both species reared on tobacco and bean hosts revealed profound differences in the transcriptional response these host plants. Interrogation of the expression of P450 genes in the host-adapted lines revealed that P450 genes belonging to the CYP6DP subfamily are strongly upregulated in lines reared on tobacco. Functional characterisation of these P450s revealed that CYP6DP1 and CYP6DP2 of T. vaporariorum and CYP6DP3 of B. tabaci confer resistance to nicotine in vivo. These three genes, in addition to the B. tabaci P450 CYP6DP5, were also found to confer resistance to the neonicotinoid imidacloprid. Our data provide new insight into the molecular basis of nicotine resistance in insects and illustrates how divergence in the evolution of P450 genes in this subfamily in whiteflies may have impacted the extent to which different species can tolerate a potent natural insecticide.

A novel gene REPTOR2 activates the autophagic degradation of wing disc in pea aphid

Wing dimorphism in insects is an evolutionarily adaptive trait to maximize insect fitness under various environments, by which the population could be balanced between dispersing and reproduction. Most studies concern the regulatory mechanisms underlying the stimulation of wing morph in aphids, but relatively little research addresses the molecular basis of wing loss. Here, we found that, while developing normally in winged-destined pea aphids, the wing disc in wingless-destined aphids degenerated 30-hr postbirth and that this degeneration was due to autophagy rather than apoptosis. Activation of autophagy in first instar nymphs reduced the proportion of winged aphids, and suppression of autophagy increased the proportion. REPTOR2, associated with TOR signaling pathway, was identified by RNA-seq as a differentially expressed gene between the two morphs with higher expression in the thorax of wingless-destined aphids. Further genetic analysis indicated that REPTOR2 could be a novel gene derived from a gene duplication event that occurred exclusively in pea aphids on autosome A1 but translocated to the sex chromosome. Knockdown of REPTOR2 reduced autophagy in the wing disc and increased the proportion of winged aphids. In agreement with REPTOR's canonical negative regulatory role of TOR on autophagy, winged-destined aphids had higher TOR expression in the wing disc. Suppression of TOR activated autophagy of the wing disc and decreased the proportion of winged aphids, and vice versa. Co-suppression of TOR and REPTOR2 showed that dsREPTOR2 could mask the positive effect of dsTOR on autophagy, suggesting that REPTOR2 acted as a key regulator downstream of TOR in the signaling pathway. These results revealed that the TOR signaling pathway suppressed autophagic degradation of the wing disc in pea aphids by negatively regulating the expression of REPTOR2.

Larvicidal and repellent potential of Ageratum houstonianum against Culex pipiens

Mosquitoes are unquestionably the most medic arthropod vectors of disease. Culex pipiens, usually defined as a common house mosquito, is a well-known carrier of several virus diseases. Crude ethanol extracts of different organs of Agratum houstonianum are tested with Culex pipiens Linnaeus (Diptera: Culicidae) to determine their larvicidal, antifeedant, and repellency effects. Alongside biochemical analysis, the activity of the AChE, ATPase, CarE, and CYP-450 is detected in the total hemolymph of the C. pipiens larvae to examine the enzymatic action on the way to explain their neurotoxic effect and mode of action. Through HPLC and GC-MS analysis of the phytochemical profile of A. houstonianum aerial parts is identified. The larvicidal activity of aerial parts; flower (AF), leaf (AL), and stem (AS) of A. houstonianum extracts are evaluated against the 3rd instar larvae of C. pipiens at 24-, 48- and 72-post-treatment. A. houstonianium AF, AL, and AS extracts influenced the mortality of larvae with LC50 values 259.79, 266.85, and 306.86 ppm, respectively after 24 h of application. The potency of AF and AL extracts was 1.69- and 1.25-folds than that of AS extract, respectively. A high repellency percentage was obtained by AF extract 89.10% at a dose of 3.60 mg/cm². A. houstonianium AF prevailed inhibition on acetylcholinesterase and decrease in carboxylesterase activity. Moreover, a significant increase in the ATPase levels and a decrease in cytochrome P-450 monooxegenase activity (- 36.60%) are detected. HPLC analysis prevailed chlorogenic and rosmarinic acid as the major phenolic acids in AL and AF, respectively. GC-MS analysis of A. houstonianum results in the identification of phytol as the major makeup. Precocene I and II were detected in AF. Linoleic, linolenic, and oleic acid were detected in comparable amounts in the studied organs. Overall, results suggest that the A. houstonianum flower extract (AF) exhibits significant repellent, antifeedant, and larvicidal activities.

Metabolization and sequestration of plant specialized metabolites in insect herbivores: Current and emerging approaches

Herbivorous insects encounter diverse plant specialized metabolites (PSMs) in their diet, that have deterrent, anti-nutritional, or toxic properties. Understanding how they cope with PSMs is crucial to understand their biology, population dynamics, and evolution. This review summarizes current and emerging cutting-edge methods that can be used to characterize the metabolic fate of PSMs, from ingestion to excretion or sequestration. It further emphasizes a workflow that enables not only to study PSM metabolism at different scales, but also to tackle and validate the genetic and biochemical mechanisms involved in PSM resistance by herbivores. This review thus aims at facilitating research on PSM-mediated plant-herbivore interactions.

Silencing of cytochrome P450 gene CYP321A1 effects tannin detoxification and metabolism in Spodoptera litura

Cytochrome P450 monooxygenase (P450 or CYP) plays an important role in the metabolism of insecticides and plant allelochemicals by insects. CYP321B1, a novel Spodoptera litura P450 gene, was identified and characterized. CYP321B1 contains a 1488 bp open reading frame (ORF) that encodes a 495 amino acid protein. In fourth instar larvae, the highest CYP321B1 expression levels were found in the midgut and fat body. In the tannin feeding test, tannin can significantly induce the expression of CYP321B1 in the midgut and fat body of 4th instar larvae. To verify the function of CYP321B1, RNA interference and metabolome analysis were performed. The results showed that silencing CYP321B1 significantly reduced the rate of weight gain under tannin induction. Metabolome analysis showed silencing affected 47 different metabolites, mainly involved in secondary metabolite biosynthesis and amino acid metabolism, including amino acids, lipid fatty acids, organic acids and their derivatives. Henoxyacetic acid and cysteamine are the most highly regulated metabolites, respectively. These findings demonstrate that CYP321B1 plays an important role in tannin detoxification and metabolism. Functional knowledge about metabolite detoxification genes in this major herbivorous insect pest can provide new insights into this biological process and provide new targets for agricultural pest control.

Natural variation in wild tomato trichomes; selecting metabolites that contribute to insect resistance using a random forest approach

BACKGROUND

Plant-produced specialised metabolites are a powerful part of a plant's first line of defence against herbivorous insects, bacteria and fungi. Wild ancestors of present-day cultivated tomato produce a plethora of acylsugars in their type-I/IV trichomes and volatiles in their type-VI trichomes that have a potential role in plant resistance against insects. However, metabolic profiles are often complex mixtures making identification of the functionally interesting metabolites challenging. Here, we aimed to identify specialised metabolites from a wide range of wild tomato genotypes that could explain resistance to vector insects whitefly (Bemisia tabaci) and Western flower thrips (Frankliniella occidentalis). We evaluated plant resistance, determined trichome density and obtained metabolite profiles of the glandular trichomes by LC-MS (acylsugars) and GC-MS (volatiles). Using a customised Random Forest learning algorithm, we determined the contribution of specific specialised metabolites to the resistance phenotypes observed.

RESULTS

The selected wild tomato accessions showed different levels of resistance to both whiteflies and thrips. Accessions resistant to one insect can be susceptible to another. Glandular trichome density is not necessarily a good predictor for plant resistance although the density of type-I/IV trichomes, related to the production of acylsugars, appears to correlate with whitefly resistance. For type VI-trichomes, however, it seems resistance is determined by the specific content of the glands. There is a strong qualitative and quantitative variation in the metabolite profiles between different accessions, even when they are from the same species. Out of 76 acylsugars found, the random forest algorithm linked two acylsugars (S3:15 and S3:21) to whitefly resistance, but none to thrips resistance. Out of 86 volatiles detected, the sesquiterpene α-humulene was linked to whitefly susceptible accessions instead. The algorithm did not link any specific metabolite to resistance against thrips, but monoterpenes α-phellandrene, α-terpinene and β-phellandrene/D-limonene were significantly associated with susceptible tomato accessions.

CONCLUSIONS

Whiteflies and thrips are distinctly targeted by certain specialised metabolites found in wild tomatoes. The machine learning approach presented helped to identify features with efficacy toward the insect species studied. These acylsugar metabolites can be targets for breeding efforts towards the selection of insect-resistant cultivars.

Gene Expression and Diet Breadth in Plant-Feeding Insects: Summarizing Trends

Transcriptomic studies lend insights into the role of transcriptional plasticity in adaptation and specialization. Recently, there has been growing interest in understanding the relationship between variation in herbivorous insect gene expression and the evolution of diet breadth. We review the studies that have emerged on insect gene expression and host plant use, and outline the questions and approaches in the field. Many candidate genes underlying herbivory and specialization have been identified, and a few key studies demonstrate increased transcriptional plasticity associated with generalist compared with specialist species. Addressing the roles that transcriptional variation plays in insect diet breadth will have important implications for our understanding of the evolution of specialization and the genetic and environmental factors that govern insect-plant interactions.

Characterization of UDP-Glucuronosyltransferases and the Potential Contribution to Nicotine Tolerance in Myzus persicae

Uridine diphosphate (UDP)-glycosyltransferases (UGTs) are major phase II detoxification enzymes involved in glycosylation of lipophilic endobiotics and xenobiotics, including phytoalexins. Nicotine, one of the most abundant secondary plant metabolites in tobacco, is highly toxic to herbivorous insects. Plant-herbivore competition is the major impetus for the evolution of large superfamilies of UGTs and other detoxification enzymes. However, UGT functions in green peach aphid (Myzus persicae) adaptation are unknown. In this study, we show that UGT inhibitors (sulfinpyrazone and 5-nitrouracil) significantly increased nicotine toxicity in M. persicae nicotianae, suggesting that UGTs may be involved in nicotine tolerance. In total, 101 UGT transcripts identified in the M. persicae genome/transcriptome were renamed according to the UGT Nomenclature Committee guidelines and grouped into 11 families, UGT329, UGT330, UGT339, UGT341-UGT345, and UGT348-UGT350, with UGT344 containing the most (57). Ten UGTs (UGT330A3, UGT339A2, UGT341A6, UGT342B3, UGT343C3, UGT344D5, UGT344D8, UGT348A3, UGT349A3, and UGT350A3) were highly expressed in M. persicae nicotianae compared to M. persicae sensu stricto. Knockdown of four UGTs (UGT330A3, UGT344D5, UGT348A3, and UGT349A3) significantly increased M. persicae nicotianae sensitivity to nicotine, suggesting that UGT expression in this subspecies may be associated with nicotine tolerance and thus host adaptation. This study reveals possible UGTs relevant to nicotine adaptation in tobacco-consuming M. persicae nicotianae, and the findings will facilitate further validation of the roles of these UGTs in nicotine tolerance.

Effect of Pesticides on Biological Control Potential of Neoscona theisi (Araneae: Araneidae)

The present study was designed to record the effect of λ-cyhalothrin, Bifenthrin, and Glyphosate on the mortality, avoidance behavior, foraging activity, and activity of Acetylcholine esterase (AChE) and Carboxylesterase (CarE) in Neoscona theisi (Walckenaer, 1841). Highest mortality (70%) in N. theisi was recorded against λ-cyhalothrin. However, Glyphosate was found to be least toxic. Spider spent less time on insecticides/herbicide-treated surfaces. Insecticides/herbicide-treated N. theisi consumed less prey than untreated control spiders. Similarly, when N. theisi were offered insecticide/herbicide-treated prey, they consumed significantly less. Increased AChE and CarE activities were recorded in insecticides/herbicide-treated spiders as compared to control group. Total protein contents were less in insecticides/herbicide-treated spiders than control group. The results revealed that λ-cyhalothrin is more harmful to spiders as compared to Bifenthrin and Glyphosate. It is suggested that the effect of all pesticides used in agro-ecosystem on beneficial insects should be evaluated before using them in the fields.

The metabolic fate of dietary nicotine in the cabbage looper, Trichoplusia ni (Hübner)

Cabbage looper (Trichoplusia ni) larvae are generalist herbivores that feed on numerous cultivated plants and weeds including crucifers, other vegetables, flowers, and field crops. Consuming plant material from a wide range of plant species exposes these larvae to a considerable variety of plant secondary metabolites involved in chemical defense against herbivory. The ability of the cabbage looper larvae to detoxify plant secondary metabolites, such as nicotine, has been attributed to the rapid induction of excretion via the Malpighian tubules. However, the role of metabolism in the detoxification of plant secondary metabolites in cabbage looper larvae is not well studied. We investigated nicotine metabolism in 4th larval instar cabbage looper using UPLC-MS/MS analysis to resolve the time course of nicotine metabolism, the kinetic distribution of nicotine, and the presence or absence of major metabolites of nicotine in larval tissue and excretions. The major metabolite found in our analysis was cotinine, with trace amounts of cotinine N-oxide and nicotine N-oxide. The nicotine metabolites detected are similar to those of the nicotine-tolerant Lepidopteran tobacco hornworm (Manduca sexta). The results of our study demonstrate that the 5'C-oxidation of nicotine to cotinine is the primary pathway for nicotine metabolism in cabbage looper larvae. This study showed that metabolism of nicotine and subsequent excretion of nicotine and its metabolites occurs in the larvae of the cabbage looper. Our results suggest that 5'C-oxidation in lepidopteran insects is a conserved metabolic pathway for the detoxification of plant secondary metabolites.

Transcriptional profile and differential fitness in a specialist milkweed insect across host plants varying in toxicity

Interactions between plants and herbivorous insects have been models for theories of specialization and co-evolution for over a century. Phytochemicals govern many aspects of these interactions and have fostered the evolution of adaptations by insects to tolerate or even specialize on plant defensive chemistry. While genomic approaches are providing new insights into the genes and mechanisms insect specialists employ to tolerate plant secondary metabolites, open questions remain about the evolution and conservation of insect counterdefences, how insects respond to the diversity defences mounted by their host plants, and the costs and benefits of resistance and tolerance to plant defences in natural ecological communities. Using a milkweed-specialist aphid (Aphis nerii) model, we test the effects of host plant species with increased toxicity, likely driven primarily by increased secondary metabolites, on aphid life history traits and whole-body gene expression. We show that more toxic plant species have a negative effect on aphid development and lifetime fecundity. When feeding on more toxic host plants with higher levels of secondary metabolites, aphids regulate a narrow, targeted set of genes, including those involved in canonical detoxification processes (e.g., cytochrome P450s, hydrolases, UDP-glucuronosyltransferases and ABC transporters). These results indicate that A. nerii marshal a variety of metabolic detoxification mechanisms to circumvent milkweed toxicity and facilitate host plant specialization, yet, despite these detoxification mechanisms, aphids experience reduced fitness when feeding on more toxic host plants. Disentangling how specialist insects respond to challenging host plants is a pivotal step in understanding the evolution of specialized diet breadths.

Biochemical evaluation of interactions between synergistic molecules and phase I enzymes involved in insecticide resistance in B- and Q-type Bemisia tabaci (Hemiptera: Aleyrodidae)

BACKGROUND

Metabolic resistance is an important consideration in the whitefly Bemisia tabaci, where an esterase-based mechanism has been attributed to pyrethroid resistance and over-expression of the cytochrome P450, CYP6CM1, has been correlated to resistance to imidacloprid and other neonicotinoids.

RESULTS

In vitro interactions between putative synergists and CYP6CM1, B and Q-type esterases were investigated, and structure-activity relationship analyses allowed the identification of chemical structures capable of acting as inhibitors of esterase and oxidase activities. Specifically, methylenedioxyphenyl (MDP) moieties with a polyether chain were preferable for optimum inhibition of B-type esterase, whilst corresponding dihydrobenzofuran structures were potent for the Q-esterase variation. Potent inhibition of CYP6CM1 resulted from structures which contained an alkynyl chain with a terminal methyl group.

CONCLUSIONS

Synergist candidates could be considered for field control of B. tabaci, especially to abrogate neonicotinoid resistance. © 2017 Society of Chemical Industry.

The metabolic fate of nectar nicotine in worker honey bees

Honey bees (Apis mellifera) are generalist pollinators that forage for nectar and pollen of a very large variety of plant species, exposing them to a diverse range of secondary metabolites produced as chemical defences against herbivory. Honey bees can tolerate high levels of many of these toxic compounds, including the alkaloid nicotine, in their diet without incurring apparent fitness costs. Very little is known about the underlying detoxification processes mediating this tolerance. We examined the metabolic fate of nicotine in newly emerged worker bees using radiolabeled nicotine and LC-MS/MS analysis to determine the kinetic distribution profile of nicotine as well as the absence or presence and identity of any nicotine-derived metabolites. Nicotine metabolism was extensive; virtually no unmetabolised nicotine were recovered from the rectum. The major metabolite found was 4-hydroxy-4-(3-pyridyl) butanoic acid, the end product of 2'C-oxidation of nicotine. It is the first time that 4-hydroxy-4-(3-pyridyl) butanoic acid has been identified in an insect as a catabolite of nicotine. Lower levels of cotinine, cotinine N-oxide, 3'hydroxy-cotinine, nicotine N-oxide and norcotinine were also detected. Our results demonstrated that formation of 4-hydroxy-4-(3-pyridyl) butanoic acid is quantitatively the most significant pathway of nicotine metabolism in honey bees and that the rapid excretion of unmetabolised nicotine does not contribute significantly to nicotine tolerance in honey bees. In nicotine-tolerant insects that do not rely on the rapid excretion of nicotine like the Lepidoptera, it is possible that the 2'C-oxidation of nicotine is the conserved metabolic pathway instead of the generally assumed 5'C-oxidation pathway.

Proteomic and metabolomic analysis reveals rapid and extensive nicotine detoxification ability in honey bee larvae

Despite potential links between pesticides and bee declines, toxicology information on honey bee larvae (Apis mellifera) is scarce and detoxification mechanisms in this development stage are virtually unknown. Larvae are exposed to natural and synthetic toxins present in pollen and nectar through consumption of brood food. Due to the characteristic intensive brood care displayed by honey bees, which includes progressive feeding throughout larval development, it is generally assumed that larvae rely on adults to detoxify for them and exhibit a diminished detoxification ability. We found the opposite. We examined the proteomic and metabolomic responses of in vitro reared larvae fed nicotine (an alkaloid found in nectar and pollen) to understand how larvae cope on a metabolic level with dietary toxins. Larvae were able to effectively detoxify nicotine through an inducible detoxification mechanism. A coordinated stress response complemented the detoxification processes, and we detected significant enrichment of proteins functioning in energy and carbohydrate metabolism, as well as in development pathways, suggesting that nicotine may promote larval growth. Further exploration of the metabolic fate of nicotine using targeted mass spectrometry analysis demonstrated that, as in adult bees, formation of 4-hydroxy-4-(3-pyridyl) butanoic acid, the result of 2'C-oxidation of nicotine, is quantitatively the most significant pathway of nicotine metabolism. We provide conclusive evidence that larvae are capable of effectively catabolising a dietary toxin, suggesting that increased larval sensitivity to specific toxins is not due to diminished detoxification abilities. These findings broaden the current understanding of detoxification biochemistry at different organizational levels in the colony, bringing us closer to understanding the capacity of the colony as a superorganism to tolerate and resist toxic compounds, including pesticides, in the environment.

Different Narrow-Band Light Ranges Alter Plant Secondary Metabolism and Plant Defense Response to Aphids

Light of different wavelengths affects various physiological processes in plants. Short-wavelength radiation (like UV) can activate defense pathways in plants and enhance the biosynthesis of secondary metabolites (such as flavonoids and glucosinolates) responsible for resistance against certain herbivorous insects. The intensity of light-induced, metabolite-based resistance is plant- and insect species-specific and depends on herbivore feeding guild and specialization. In this study, broccoli (Brassica oleracea var. italica) plants were grown for 4 weeks in a climate chamber under conventional fluorescent tubes and were additionally treated with UV-B (310 nm), UV-A (365 or 385 nm), or violet (420 nm) light generated with UV-B tubes or light-emitting diodes (LEDs). The objective was to determine the influence of narrow bandwidths of light (from UV-B to violet) on plant secondary metabolism and on the performance of the cabbage aphid Brevicoryne brassicae (a specialist) and the green peach aphid Myzus persicae (a generalist). Among flavonol glycosides, specific quercetin and kaempferol glycosides increased markedly under UV-B, while among glucosinolates only 4-methoxy-3-indolylmethyl showed a 2-fold increase in plants exposed to UV-B and UV-A. The concentration of 3-indolylmethyl glucosinolate in broccoli plants increased with UV-B treatment. Brevicoryne brassicae adult weights and fecundity were lower on UV-B treated plants compared to UV-A or violet light-treated plants. Adult weights and fecundity of M. persicae were increased under UV-B and UV-A treatments. When specific light wavelengths are used to induce metabolic changes in plants, the specificity of the induced effects on herbivores should be considered.

Reduced abundance of the CYP6CY3-targeting let-7 and miR-100 miRNAs accounts for host adaptation of Myzus persicae nicotianae

Nicotine is one of the most abundant and toxic secondary plant metabolites in nature and is defined by high toxicity to plant-feeding insects. Studies suggest that increased expression of cytochrome P450 (CYP6CY3) and the homologous CYP6CY4 genes in Myzus persicae nicotianae is correlated with tolerance to nicotine. Indeed, through expression analyses of the CYP6CY3 and CYP6CY4 genes of different M. persicae subspecies, we determined that the mRNA levels of these two genes were much higher in M. persicae nicotianae than in M. persicae sensu stricto. We hypothesized that the expression of these two genes is subject to post-transcriptional regulation. To investigate the underlying mechanism, the miRNA profile of M. persicae nicotianae was sequenced, and twenty-two miRNAs were predicted to target CYP6CY3. Validation of these miRNAs identified two miRNAs, let-7 and miR-100, whose abundance was highly inversely correlated with the abundance of the CYP6CY3 gene. This result implies that the let-7 and miR-100 miRNAs play a major role in the post-transcriptional regulation of the CYP6CY3 gene. Modulation of the abundance of let-7 and miR-100 through the addition of inhibitors/mimics of let-7 or miR-100 to artificial diet significantly altered the tolerance of M. persicae nicotianae to nicotine, further confirming the regulatory role of these two miRNAs. Interestingly, after decreasing the transcript levels of CYP6CY3 by modulating regulatory miRNAs, the transcript levels of the homologous isozyme CYP6CY4 were significantly elevated, suggesting a compensatory mechanism between the CYP6CY3 gene and its homologous CYP6CY4 gene. Our findings provide insight into the molecular drivers of insect host shifts and reveal an important source of genetic variation for adaptive evolution in insect species.

How active ingredient localisation in plant tissues determines the targeted pest spectrum of different chemistries

BACKGROUND

The efficacies of four commercial insecticides and of two research compounds were tested against aphids (Aphis craccivora and Myzus persicae), whiteflies (Bemisia tabaci) and red-spotted spider mites (Tetranychus urticae) in intrinsic (oral administration), curative (direct contact spray) and translaminar (arthropods infested on untreated leaf underside) assays. With a new translaminar model, the transport across the leaf cuticle and tissues and the electrochemical distribution of test compounds in cellular compartments and apoplast were calculated.

RESULTS

The comparison of both information sets revealed that the intracellular localisation of active ingredients determines the performance of test compounds against different target pests because of different feeding behaviours: mites feed on mesophyll, and aphids and whiteflies mostly in the vascular system. Polar compounds have a slow adsorption into leaf cells and thus a favourable distribution into apoplast and xylem sap. Slightly lipophilic bases get trapped in vacuoles, which is a less suited place to control hemipteran pests but appropriate to control mites. Non-favourable cellular localisation led to a strong reduction in translaminar efficacy against phloem feeders.

CONCLUSION

Prediction and optimisation of intracellular localisation of pesticides add valuable new information for targeted bioavailability and can indicate directions for improved pesticide design.

Fluorescent in situ hybridization for the localization of viruses, bacteria and other microorganisms in insect and plant tissues

Methods for the localization of cellular components such as nucleic acids, proteins, cellular vesicles and more, and the localization of microorganisms including viruses, bacteria and fungi have become an important part of any research program in biological sciences that enable the visualization of these components in fixed and live tissues without the need for complex processing steps. The rapid development of microscopy tools and technologies as well as related fluorescent markers and fluorophores for many cellular components, and the ability to design DNA and RNA sequence-based molecular probes and antibodies which can be visualized fluorescently, have rapidly advanced this field. This review will focus on some of the localizations methods which have been used in plants and insect pests in agriculture, and other microorganisms, which are rapidly advancing the research in agriculture-related fields.

Detoxification mechanisms of honey bees (Apis mellifera) resulting in tolerance of dietary nicotine

Insecticides are thought to be among the major factors contributing to current declines in bee populations. However, detoxification mechanisms in healthy, unstressed honey bees are poorly characterised. Alkaloids are naturally encountered in pollen and nectar, and we used nicotine as a model compound to identify the mechanisms involved in detoxification processes in honey bees. Nicotine and neonicotinoids have similar modes of action in insects. Our metabolomic and proteomic analyses show active detoxification of nicotine in bees, associated with increased energetic investment and also antioxidant and heat shock responses. The increased energetic investment is significant in view of the interactions of pesticides with diseases such as Nosema spp which cause energetic stress and possible malnutrition. Understanding how healthy honey bees process dietary toxins under unstressed conditions will help clarify how pesticides, alone or in synergy with other stress factors, lead to declines in bee vitality.

Adaptation to nicotine feeding in Myzus persicae

Lineages of the generalist hemipteran herbivore Myzus persicae (green peach aphid) that have expanded their host range to include tobacco often have elevated nicotine tolerance. The tobacco-adapted M. persicae lineage used in this study was able to reproduce on nicotine-containing artificial diets at concentrations that were 15-fold higher than those that were lethal to a non-adapted M. persicae lineage. Fecundity of the nicotine-tolerant M. persicae lineage was increased by 100 μM nicotine in artificial diet, suggesting that this otherwise toxic alkaloid can serve as a feeding stimulant at low concentrations. This lineage also was pre-adapted to growth on tobacco, exhibiting no drop in fecundity when it was moved onto tobacco from a different host plant. Although growth of the non-tobacco-adapted M. persicae lineage improved after three generations on tobacco, this higher reproductive rate was not associated with increased nicotine tolerance. Myzus persicae gene expression microarrays were used to identify transcripts that are up-regulated in response to nicotine in the tobacco-adapted lineage. Induced expression was found for CYP6CY3, which detoxifies nicotine in M. persicae, other genes encoding known classes of detoxifying enzymes, and genes encoding secreted M. persicae salivary proteins.