Rapid quantification of juvenile hormones and their metabolites in insect haemolymph by liquid chromatography?mass spectrometry (LC-MS)

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

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

The making of the defensive caste: Physiology, development, and evolution of the soldier differentiation in termites

Termites (Blattodea, Termitoidea, or Isoptera) constitute one of the major lineages of eusocial insects. In termite societies, multiple types of functional individuals, that is, castes, perform divisions of labors to coordinate social behaviors. Among other castes, the soldier caste is distinctive since it is sterile and exclusively specialized into defensive behavior with largely modified morphological features. Therefore, many of the previous studies have been focused on soldiers, in terms of ecology, behavior, and evolution as well as developmental and physiological mechanisms. This article overviews the accumulation of studies especially focusing on the developmental and physiological mechanisms underlying the soldier differentiation in termites. Furthermore, the evolutionary trajectories that have led the acquisition of soldier caste and have diversified the soldier characteristics in association with the social evolution are discussed.

Reproductive workers insufficiently signal their reproductive ability in a paper wasp

Why workers forfeit direct reproduction is a crucial question in eusocial evolution. Worker reproduction provides an excellent opportunity to understand the mechanism of kin conflict resolution between the queen and workers. We evaluated behavioral and physiological differences among females in the paper wasp Polistes chinensis antennalis to examine why some workers reproduce under queenright conditions. Reproductive workers were old and foraged less early in the season; their cuticular hydrocarbon (CHC) profiles overlapped with those of queens but were significantly different. The distinct CHC profile of the eggs of the queen likely represented a cue for policing against those by workers. Juvenile hormone (JH) and dopamine seemed to be associated with gonadotropic function, and the JH level of reproductive workers was similar to that of the queen. The high JH level of reproductive workers likely facilitated their reproduction even under queenright conditions. Gene expression levels of the queen and reproductive workers differed only in vitellogenin. These results suggest that worker reproduction is facilitated by an increase in JH level; however, CHC is not a fertility-linked signal, but a queen-linked signal; consequently, reproductive workers without a queen-linked signal might be allowed to stay within the colony.

Common structural features facilitate the simultaneous identification and quantification of the five most common juvenile hormones by liquid chromatography-tandem mass spectrometry

This study reports the development and application of a liquid chromatography method coupled to electrospray tandem mass spectrometry (LC-MS/MS) for the identification and quantification of the five most common juvenile hormone (JH) homologs and methyl farnesoate (MF). The protocol allows the simultaneous analysis in a single LC run of JH I, JH II, JH III, JH III bisepoxide (JHB₃) and JH III skipped bisepoxide (JHSB₃). The identification of JHs is based on multiple reaction monitoring (MRM), using two of the most abundant fragmentation transitions for each hormone. Addition of deuterated JH III as an internal standard permits the absolute quantification of the different JHs. The JH homologs common structural features led to similar chromatographic behavior, as well as related fragmentation patterns, which facilitated the simultaneous detection of all the homologs in a single LC-MS/MS run. The protocol detects JHs in the low femtomole range, allowing often the analysis of JH in individual insects. Fragmentation of each of the JH homologs generates unique diagnostic ions that permitted the identification and quantification of JHs from samples of different species of Diptera, Lepidoptera, Heteroptera and Hymenoptera. Having a simple protocol, which can undisputedly determine the identity of the homologs present in a particular species, provides us with the opportunity to identify and quantify JHs existing in insects that are pests, vector of diseases or important research models.

Epigenetic Regulator CoREST Controls Social Behavior in Ants

Ants acquire distinct morphological and behavioral phenotypes arising from a common genome, underscoring the importance of epigenetic regulation. In Camponotus floridanus, "Major" workers defend the colony, but can be epigenetically reprogrammed to forage for food analogously to "Minor" workers. Here, we utilize reprogramming to investigate natural behavioral specification. Reprogramming of Majors upregulates Minor-biased genes and downregulates Major-biased genes, engaging molecular pathways fundamental to foraging behavior. We discover the neuronal corepressor for element-1-silencing transcription factor (CoREST) is upregulated upon reprogramming and required for the epigenetic switch to foraging. Genome-wide profiling during reprogramming reveals CoREST represses expression of enzymes that degrade juvenile hormone (JH), a hormone elevated upon reprogramming. High CoREST, low JH-degrader expression, and high JH levels are mirrored in natural Minors, revealing parallel mechanisms of natural and reprogrammed foraging. These results unveil chromatin regulation via CoREST as central to programming of ant social behavior, with potential far-reaching implications for behavioral epigenetics.

Insights into the effect on silkworm (Bombyx mori) cocooning and its potential mechanisms following non-lethal dose tebuconazole exposure

Silkworm (Bombyx mori) is one of the most important economic insects in the world, while pesticides impact its economic benefits. Tebuconazole is a fungicide that has been frequently detected in agriculture systems at concentrations that affect endocrine function in organisms. In the present study, silkworm larvae at different instar stages were exposed to tebuconazole, respectively. Cocoon weight, cocoon shell weight and cocoon shell rate were significantly decreased by 6.8%, 11.8% and 4.4% respectively, after exposure to 0.40 mg/L tebuconazole at 2nd -3rd instar stage. Vacuolization was found in the exposure silkworm under histopathological study at all stages exposures, indicating potential damage to silk gland. Downregulation of genes transcription (Fibh, Fibl, P25, Ser2, Ser3) involved with protein synthesis in the silk gland were further observed, and the results showed significant decreasing in mRNA expression among the tebuconazole treatments. Ecdysteroid levels in silkworm were changed with pronounced decreases after exposed to tebuconazole. In contrast, exposure to tebuconazole significantly increased juvenile hormone 1 concentrations and the maximum increasing fold of juvenile hormone 1 was up to 3.73 which was observed at stage I exposure. In addition, co-exposure to 2 and 10 mg/L forskolin able to mitigate tebuconazole-induced downregulate of mRNA expression of Sgf1 in the present study, indicating the potential mechanism of tebuconazole-induced chronic toxicity in silkworm may relative to PI3K/AKT/TORC1/Sgf1 pathway.

Juvenile hormone as a physiological regulator mediating phenotypic plasticity in pancrustaceans

Phenotypic plasticity and polyphenism, in which phenotypes can be changed depending on environmental conditions, are common in insects. Several studies focusing on physiological, developmental, and molecular processes underlying the plastic responses have revealed that similar endocrine mechanisms using juvenile hormone (JH) are used to coordinate the flexible developmental processes. This review discusses accumulated knowledge on the caste polyphenism in social insects (especially termites), the wing and the reproductive polyphenisms in aphids, and the nutritional polyphenism and sexual dimorphism in stag beetles. For the comparison with non-insect arthropods, extensive studies on the inducible defense (and reproductive polyphenism) in daphnids (crustacean) are also addressed. In all the cases, JH (and methyl farnesoate in daphnids) plays a central role in mediating environmental stimuli with morphogenetic processes. Since the synthetic pathways for juvenoids, i.e., the mevalonate pathway and downstream pathways to sesquiterpenoids, are conserved across pancrustacean lineages (crustaceans and hexapods including insects), the evolution of developmental regulation by juvenoids that control molting (ecdysis) and metamorphosis is suggested to have occurred in the ancestral arthropods. The discontinuous postembryonic development (i.e., molting) and the regulatory physiological factors (juvenoids) would have enabled plastic developmental systems observed in many arthropod lineages.

Sex Differences in 20-Hydroxyecdysone Hormone Levels Control Sexual Dimorphism in Bicyclus anynana Wing Patterns

In contrast to the important role of hormones in the development of sexual traits in vertebrates (Cox RM, Stenquist DS, Calsbeek R. 2009. Testosterone, growth and the evolution of sexual size dimorphism. J Evol Biol. 22(8):1586-1598.), the differentiation of these traits in insects is attributed almost exclusively to cell-autonomous mechanisms controlled by members of the sex determination pathway (Verhulst EC, van de Zande L. 2015. Double nexus - doublesex is the connecting element in sex determination. Brief Funct Genomics 14(6):396-406.), such as doublesex. Although hormones can shape the development of sexual traits in insects, variation in hormone levels are not conclusively known to cause dimorphism in these traits (Prakash A, Monteiro A. 2016. Molecular mechanisms of secondary sexual trait development in insects. Curr Opin Insect Sci. 17:40-48.). Here, we show that butterflies use sex-specific differences in 20-hydroxyecdysone hormone titers to create sexually dimorphic wing ornaments. Females of the dry season (DS) form of Bicyclus anynana display a larger sexual ornament on their wings than males, whereas in the wet season form both sexes have similarly sized ornaments (Prudic KL, Jeon C, Cao H, Monteiro A. 2011. Developmental plasticity in sexual roles of butterfly species drives mutual sexual ornamentation. Science 331(6013):73-75.). High levels of circulating 20-hydroxyecdysone during larval development in DS females and wet season forms cause proliferation of the cells fated to give rise to this wing ornament, and results in sexual dimorphism in the DS forms. This study advances our understanding of how the environment regulates sex-specific patterns of plasticity of sexual ornaments and conclusively shows that hormones can play a role in the development of secondary sexual traits in insects, just like they do in vertebrates.

Upregulation of Juvenile Hormone Titers in Female Drosophila melanogaster Through Mating Experiences and Host Food Occupied by Eggs and Larvae

Juvenile hormone (JH) plays a crucial role in the determination of developmental timing in insects. In Drosophila melanogaster, reports indicate that JH titers are the highest immediately following eclosion and that the mating experience increases the titers in females. However, the titers have not been successively measured for an extended period of time after eclosion. This study reveals that JH titers are increased after eclosion in virgin females when supplied with food that is occupied by eggs and larvae as well as in mated females. With the presence of eggs and larvae, food induced the virgin females to lay unfertilized eggs. When combined with previous work indicating that females are attracted to such food where they prefer to lay eggs, these results suggest that flies can prepare themselves to lay eggs by changing the titers of JH under the presence of growing larvae, ensuring that the food is an appropriate place to oviposit.

Steroid hormone signaling during development has a latent effect on adult male sexual behavior in the butterfly Bicyclus anynana

It is well established that steroid hormones regulate sexual behavior in vertebrates via organizational and activational effects. However, whether the organizational/activational paradigm applies more broadly to the sexual behavior of other animals such as insects is not well established. Here we describe the hormonal regulation of a sexual behavior in the seasonally polyphenic butterfly Bicyclus anynana is consistent with the characteristics of an organizational effect. By measuring hormone titer levels, quantifying hormone receptor gene expression in the brain, and performing hormone manipulations, we demonstrate steroid hormone signaling early in pupal development has a latent effect on adult male sexual behavior in B. anynana. These findings suggest the organizational/activational paradigm may be more highly conserved across animal taxa than previously thought.

Discovery of methylfarnesoate as the annelid brain hormone reveals an ancient role of sesquiterpenoids in reproduction

Animals require molecular signals to determine when to divert resources from somatic functions to reproduction. This decision is vital in animals that reproduce in an all-or-nothing mode, such as bristle worms: females committed to reproduction spend roughly half their body mass for yolk and egg production; following mass spawning, the parents die. An enigmatic brain hormone activity suppresses reproduction. We now identify this hormone as the sesquiterpenoid methylfarnesoate. Methylfarnesoate suppresses transcript levels of the yolk precursor Vitellogenin both in cell culture and in vivo, directly inhibiting a central energy–costly step of reproductive maturation. We reveal that contrary to common assumptions, sesquiterpenoids are ancient animal hormones present in marine and terrestrial lophotrochozoans. In turn, insecticides targeting this pathway suppress vitellogenesis in cultured worm cells. These findings challenge current views of animal hormone evolution, and indicate that non-target species and marine ecosystems are susceptible to commonly used insect larvicides.

DOI:http://dx.doi.org/10.7554/eLife.17126.001

All organisms need energy to survive and grow. However, sources of energy are limited and so organisms need to decide how to spend the resources they have available. For instance, animals must choose whether they should continue to grow or if they should invest energy into reproduction instead. This decision becomes even more important for animals that reproduce in an “all-or-nothing” manner and invest all their available energy into reproduction and die soon after.

Bristle worms live in coastal areas around world. In mass spawning events, thousands of individuals raise from the sea floor to the surface, to release sperm and eggs. While the fertilized eggs start to develop in the water, the parents invariably die. The female worms spend roughly half their body mass in producing eggs and supplying them with yolk as a source of energy. It has been known for decades that the brains of bristle worms produce a master hormone that promotes growth and suppresses reproduction. Yet the identity of this hormone that controls the life-or-death decision was not clear.

Schenk et al. took advantage of new molecular tools to solve this puzzle. The experiments show that this hormone directly regulates how much yolk the female animals produce. This allowed Schenk et al. to design a new molecular assay that helped to identify the hormone itself. Unexpectedly, the hormone – called methylfarnesoate – belongs to a family of small molecules called sesquiterpenoids, which researchers previously thought were only found in insects and related groups. Hence, many insecticides have been developed to target sesquiterpenoid signaling and they are used in massive amounts to fight pests like the tiger mosquito (which transmits the Zika virus). Schenk et al. also found that these insecticides also cause severe problems in bristle-worms.

These findings challenge current views of how animal hormones have evolved and indicate that common insecticides may be harming bristle worms and other animals in marine environments. The next steps are to find out whether methylfarnesoate is found in other closely related animals, such as snails and mussels, and whether the insecticides are harmful to these animals too. Another future challenge will be to investigate how this hormone actually promotes animal growth.

DOI:http://dx.doi.org/10.7554/eLife.17126.002

Determination of juvenile hormone titers by means of LC-MS/MS/MS and a juvenile hormone-responsive Gal4/UAS system in Aedes aegypti mosquitoes

In anautogenous mosquitoes, juvenile hormone III (JH) plays an essential role in female post-eclosion (PE) development, preparing them for subsequent blood feeding and egg growth. We re-examined the JH titer during the reproductive cycle of female Aedes aegypti mosquitoes. Using liquid chromatography coupled with triple tandem mass spectrometry (LC-MS/MS/MS), we have shown that it reaches its peak at 48-54 h PE in the female hemolymph and at 72 h PE in whole body extracts. This method represents an effective assay for determination of JH titers. The 2.1-kb 5' promoter region of the Early Trypsin (ET) gene, which is specifically expressed in the female midgut under the control of JH during the PE phase, was utilized to genetically engineer the Ae. aegypti mosquito line with the ET-Gal4 activator. We then established the ET-GAL4>UAS-enhanced green fluorescent protein (EGFP) system in Ae. aegypti. In ET-Gal4>UAS-EGFP female mosquitoes, the intensity of the midgut-specific EGFP signal was observed to correspond to the ET gene transcript level and follow the JH titer during the PE phase. The EGFP signal and the EGFP transcript level were significantly diminished in midguts of transgenic female mosquitoes after RNA interference depletion of the JH receptor Methoprene-tolerant (Met), providing evidence of the control of ET gene expression by Met. Topical JH application caused premature enhancement of the EGFP signal and the EGFP transcript level in midguts of newly eclosed ET-Gal4>UAS-EGFP female mosquitoes, in which endogenous JH titer is still low. Hence, this novel ET-Gal4>UAS system permits JH-dependent gene overexpression in the midgut of Ae. aegypti female mosquitoes prior to a blood meal.

Fast, ultra-trace detection of juvenile hormone III from mosquitoes using mass spectrometry

In the present work, a new protocol for fast separation and quantification of JH III from biological samples using liquid chromatography coupled to electrospray tandem mass spectrometry is described. In particular, the proposed protocol improves existing methodologies by combining a limited number of sample preparation steps with fast LC-MS/MS detection, providing lower limits of detection and demonstrated matrix effect control, together with high inter and intraday reproducibility. A limit of detection of 8pg/mL (0.32pg on column) was achieved, representing a 15-fold gain in sensitivity with respect to previous LC-MS based protocols. The performance of the LC-MS/MS protocol is comparable to previously described JH III quantitation protocol based on fluorescence detection, with the added advantage that quantification is independent of the availability of fluorescent tags that are often unavailable or show quite diverse responses on a batch-to-batch basis. Additionally, a detailed description of the JH III fragmentation pathway is provided for the first time, based on isolation of the molecular ion and their intermediate fragments using in-source MS/MS, MS/MS(n) and FT-ICR MS/MS measurements. The JH III workflow was evaluated as a function of developmental changes, sugar feeding and farnesoic acid stimulation in mosquitoes and can be applied to the detection of other juvenile hormones.

Differential Expression of Ecdysone Receptor Leads to Variation in Phenotypic Plasticity across Serial Homologs

Bodies are often made of repeated units, or serial homologs, that develop using the same core gene regulatory network. Local inputs and modifications to this network allow serial homologs to evolve different morphologies, but currently we do not understand which modifications allow these repeated traits to evolve different levels of phenotypic plasticity. Here we describe variation in phenotypic plasticity across serial homologous eyespots of the butterfly Bicyclus anynana, hypothesized to be under selection for similar or different functions in the wet and dry seasonal forms. Specifically, we document the presence of eyespot size and scale brightness plasticity in hindwing eyespots hypothesized to vary in function across seasons, and reduced size plasticity and absence of brightness plasticity in forewing eyespots hypothesized to have the same function across seasons. By exploring the molecular and physiological causes of this variation in plasticity across fore and hindwing serial homologs we discover that: 1) temperature experienced during the wandering stages of larval development alters titers of an ecdysteroid hormone, 20-hydroxyecdysone (20E), in the hemolymph of wet and dry seasonal forms at that stage; 2) the 20E receptor (EcR) is differentially expressed in the forewing and hindwing eyespot centers of both seasonal forms during this critical developmental stage; and 3) manipulations of EcR signaling disproportionately affected hindwing eyespots relative to forewing eyespots. We propose that differential EcR expression across forewing and hindwing eyespots at a critical stage of development explains the variation in levels of phenotypic plasticity across these serial homologues. This finding provides a novel signaling pathway, 20E, and a novel molecular candidate, EcR, for the regulation of levels of phenotypic plasticity across body parts or serial homologs.

One of the most exquisite types of organismal adaptations in nature occurs when organisms are able to change the way they develop in anticipation of the different selective environments they will experience as adults. This leads to variation in adult morphologies that are adaptive. Environmental cues experienced during development often lead to variation in hormonal titers that can have profound effect on the way genes are regulated and on the adult morphology. Here we examine the hormonal and molecular mechanisms that allow specific traits that are repeated in an organism (butterfly eyespots) to either be sensitive to environmental cues–and develop different morphologies—or insensitive to these cues and develop the same morphology. We discover that a specific gene, a hormone receptor, that is expressed in the sensitive eyespots but absent in the insensitive eyespots, is responsible for regulating the level of sensitivity of each of the eyespots to an environmental cue. We identify a molecule that is regulating levels of environmental sensitivity, or phenotypic plasticity, across repeated traits in an organism.

Neuropeptides affecting the transfer of juvenile hormones from males to females during mating in Spodoptera frugiperda

In the polyandric moth, Spodopterafrugiperda, juvenile hormone (JH) is transferred from the male accessory reproductive glands (AG) to the female bursa copulatrix (BC) during copulation (see Hassanien et al., 2014). Here we used the RNA interference technique to study the role of allatoregulating neuropeptides in controlling the synthesis and transfer of JH during mating. Knockdown of S. frugiperda allatostatin C (Spofr-AS type C) in freshly emerged males leads to an accumulation of JH in the AG beyond that in the control and mating results in a higher transport of JH I and JH II into the female BC. Knockdown of S. frugiperda allatotropin 2 (Spofr-AT2) significantly reduces the amount of JH in the AG as well as its transfer into the female BC during copulation. Knockdown of S. frugiperda allatostatin A (Spofr-AS type A) and S. frugiperda allatotropin (Spofr-AT; Hassanien et al., 2014) only slightly affects the accumulation of JH in the AG and its transfer from the male to the female. We conclude that Spofr-AS type C and Spofr-AT2 act as true allatostatin and true allatotropin, respectively, on the synthesis of JH I and JH II in the male AG. Moreover, both peptides seem to control the synthesis of JH III in the corpora allata of adult males and its release into the hemolymph.

Social interactions affecting caste development through physiological actions in termites

A colony of social insects is not only an aggregation of individuals but also a functional unit. To achieve adaptive social behavior in fluctuating environmental conditions, in addition to coordination of physiological status in each individual, the whole colony is coordinated by interactions among colony members. The study on the regulation of social-insect colonies is termed "social physiology." Termites, a major group of social insects, exhibit many interesting phenomena related to social physiology, such as mechanisms of caste regulation in a colony. In their colonies, there are different types of individuals, i.e., castes, which show distinctive phenotypes specialized in specific colony tasks. Termite castes comprise reproductives, soldiers and workers, and the caste composition can be altered depending on circumstances. For the regulation of caste compositions, interactions among individuals, i.e., social interactions, are thought to be important. In this article, we review previous studies on the adaptive meanings and those on the proximate mechanisms of the caste regulation in termites, and try to understand those comprehensively in terms of social physiology. Firstly, we summarize classical studies on the social interactions. Secondly, previous studies on the pheromone substances that mediate the caste regulatory mechanisms are overviewed. Then, we discuss the roles of a physiological factor, juvenile hormone (JH) in the regulation of caste differentiation. Finally, we introduce the achievements of molecular studies on the animal sociality (i.e., sociogenomics) in terms of social physiology. By comparing the proximate mechanisms of social physiology in termites with those in hymenopterans, we try to get insights into the general principles of social physiology in social animals.

RNA interference of a putative S-adenosyl-L-homocysteine hydrolase gene affects larval performance in Leptinotarsa decemlineata (Say)

In Leptinotarsa decemlineata, juvenile hormones (JHs) play primary roles in the regulation of metamorphosis, reproduction and diapause. In JH biosynthetic pathway in insect corpora allata, methylation of farnesoic acid or JH acid using S-adenosyl-L-methionine generates a potent feedback inhibitor S-adenosyl-L-homocysteine (AdoHcy). Rapid removal of AdoHcy is hypothesized to be essential for JH synthesis. AdoHcy hydrolase (SAHase) is the only eukaryotic enzyme catalyzing the removal. In the present paper, we firstly cloned a putative LdSAHase gene from L. decemlineata. The cDNA consists of 1806 bp and encodes a 525 amino acid protein. LdSAHase was expressed in all developmental stages. The gene had the highest and the lowest level of transcription respectively in the 3rd- and 4th-instars' heads that contain corpora allata, which was positively correlated with JH titer in the haemolymph and the mRNA level of a JH early-inducible gene, the Krüppel homolog 1 gene (Kr-h1). Secondly, dietary ingestion of bacterially-expressed LdSAHase-dsRNA significantly decreased LdSAHase and LdKr-h1 mRNA levels, reduced JH titer, and caused the death of the larvae, and the failure of pupation and adult emergence. After continuous exposure for 12 days, 42% of the larvae died, 65% of the prepupae failed to pupate and 100% of the pupae failed to emerge. Moreover, RNAi-mediated LdSAHase knockdown also reduced larval developing time, and decreased larval weight. Lastly, application of JH analogue pyriproxyfen to LdSAHase-dsRNA-exposed larvae did not greatly increase LdSAHase expression level and JH content, but up-regulated LdKr-h1 mRNA level. Expectedly, pyriproxyfen application could partially rescue the negative effects on the survival and the development. Thus, our results support the hypothesis that SAHase plays a critical role in JH biosynthesis in insects.

Interplay between insulin signaling, juvenile hormone, and vitellogenin regulates maternal effects on polyphenism in ants

Polyphenism is the phenomenon in which alternative phenotypes are produced by a single genotype in response to environmental cues. An extreme case is found in social insects, in which reproductive queens and sterile workers that greatly differ in morphology and behavior can arise from a single genotype. Experimental evidence for maternal effects on caste determination, the differential larval development toward the queen or worker caste, was recently documented in Pogonomyrmex seed harvester ants, in which only colonies with a hibernated queen produce new queens. However, the proximate mechanisms behind these intergenerational effects have remained elusive. We used a combination of artificial hibernation, hormonal treatments, gene expression analyses, hormone measurements, and vitellogenin quantification to investigate how the combined effect of environmental cues and hormonal signaling affects the process of caste determination in Pogonomyrmex rugosus. The results show that the interplay between insulin signaling, juvenile hormone, and vitellogenin regulates maternal effects on the production of alternative phenotypes and set vitellogenin as a likely key player in the intergenerational transmission of information. This study reveals how hibernation triggers the production of new queens in Pogonomyrmex ant colonies. More generally, it provides important information on maternal effects by showing how environmental cues experienced by one generation can translate into phenotypic variation in the next generation.

A quantitative assay for the juvenile hormones and their precursors using fluorescent tags

BACKGROUND

The juvenile hormones (JHs) are sesquiterpenoid compounds that play a central role in insect reproduction, development and behavior. The lipophilic nature of JHs and their precursors, in conjunction with their low concentration in tissues and susceptibility to degradation had made their quantification difficult. A variety of methods exist for JH quantification but few can quantify on the femtomole range. Currently applied methods are expensive and time consuming. In the present study we sought to develop a novel method for accurate detection and quantification of JHs and their precursors.

METHODS

A sensitive and robust method was developed to quantify the precursor, farnesoic acid (FA) and juvenile hormone III (JH III) in biological samples. The assay is based on the derivatization of analytes with fluorescent tags, with subsequent analysis by reverse phase high performance liquid chromatography coupled to a fluorescent detector (HPLC-FD). The carboxyl group of FA was derivatized with 4-Acetamido-7-mercapto-2,1,3-benzoxadiazole (AABD-SH). Tagging the epoxide group of JH III required a two-step reaction: the opening of the epoxide ring with sodium sulfide and derivatization with the fluorescent tag 4-(N,N-Dimethylaminosulfonyl)-7-(N-chloroformylmethyl-N-methylamino)-2,1,3-benzoxadiazole (DBD-COCl).

CONCLUSIONS

The method developed in the present study showed high sensitivity, accuracy and reproducibility. Linear responses were obtained over the range of 10-20 to 1000 fmols. Recovery efficiencies were over 90% for JH III and 98% for FA with excellent reproducibility.

SIGNIFICANCE

The proposed method is applicable when sensitive detection and accurate quantification of limited amount of sample is needed. Examples include corpora allata, hemolymph and whole body of female adult Aedes aegypti and whole body Drosophila melanogaster. A variety of additional functional groups can be targeted to add fluorescent tags to the remaining JH III precursors.

Liquid chromatography coupled to ion trap-tandem mass spectrometry to evaluate juvenile hormone III levels in bee hemolymph from Nosema spp. infected colonies

It has been described a fast, simple and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to measure juvenile hormone III (JH III), which was used to study of the effects of Nosema spp. infection on JH III levels in bee hemolymph. Honey bee hemolymph was extracted by centrifugation and mixed with a solution of phenylthiourea in methanol. This mixture was then centrifuged and the supernatant removed and evaporated to dryness. The residue was reconstituted in methanol containing the internal standard (methoprene) and injected onto an LC-MS/MS (ion-trap) system coupled to electrospray ionization (ESI) in positive mode. Chromatography was performed on a Synergi Hydro-RP column (4 μm, 30 mm × 4.60 mm i.d.) using a mobile phase of 20 mM ammonium formate and methanol in binary gradient elution mode. The method was fully validated and it was found to be selective, linear from 15 to 14,562 pg/μL, precise and accurate, with %RSD values below 5%. The limits of detection and quantification were: LOD, 6 pg/μL; LOQ, 15 pg/μL. Finally, the proposed LC-MS/MS method was used to analyze JH III levels in the hemolymph of worker honey bees (Apis mellifera iberiensis) experimentally infected with different Nosema spp. (Nosema apis, Spanish and Dutch Nosema ceranae strains). The highest concentrations of JH III were detected in hemolymph from bees infected with Spanish N. ceranae.

UHPLC-MS analysis of juvenile hormone II in Mediterranean corn borer (Sesamia nonagrioides) hemolymph using various ionization techniques

The juvenile hormones (JHs) have been considered the most versatile hormones in the animal kingdom. JH-II is the most abundant JH in Sesamia nonagrioides, important maize pests in the Mediterranean basin. This study compared the sensitivities and matrix effects of four ionization modes on analyzing JH-II in S. nonagrioides hemolymph using ultrahigh-performance liquid chromatography-mass spectrometry (UHPLC-MS) in single ion monitoring (SIM) mode. The ionization techniques tested were electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI), and APPI with the lamp turned off, which corresponds to atmospheric pressure thermospray ionization (APTSI). ESI was discarded because of the high matrix effect. APPI was discarded because the correlation responses between solvent and matrix on the instrumental quality parameters were worse than those for APTSI and APCI. In our analytical conditions, APCI has shown the best validation parameter values. APCI ionization is widely available in instrumental laboratories.

Juvenile hormone titre and related gene expression during the change of reproductive modes in the pea aphid

Most aphids show reproductive polyphenism, i.e. they alternate their reproductive modes from parthenogenesis to sexual reproduction in response to short photoperiods. Although juvenile hormone (JH) has been considered a likely candidate for regulating the transition from asexual to sexual reproduction after photoperiod sensing, there are few studies investigating the direct relationship between JH titres and the reproductive-mode change. In addition, the sequencing of the pea aphid genome has allowed identification of the genes involved in the JH pathway, which in turn allows us to examine their expression levels in relation to the reproductive-mode change. Using liquid chromatography-mass spectrometry in the pea aphid, JHIII titre was shown to be lower in aphids producing sexual morphs under short-day conditions than in aphids producing parthenogenetic morphs under long-day conditions. The expression levels of genes upstream and downstream of JH action were quantified by real-time quantitative reverse-transcription-PCR across the reproductive-mode change. The expression level of JH esterase, which is responsible for JH degradation, was significantly higher in aphids reared under short-day conditions. This suggests that the upregulation of the JH degradation pathway may be responsible for the lower JHIII titre in aphids exposed to short-days, leading to the production of sexual morphs.

Juvenile hormone regulates extreme mandible growth in male stag beetles

The morphological diversity of insects is one of the most striking phenomena in biology. Evolutionary modifications to the relative sizes of body parts, including the evolution of traits with exaggerated proportions, are responsible for a vast range of body forms. Remarkable examples of an insect trait with exaggerated proportions are the mandibular weapons of stag beetles. Male stag beetles possess extremely enlarged mandibles which they use in combat with rival males over females. As with other sexually selected traits, stag beetle mandibles vary widely in size among males, and this variable growth results from differential larval nutrition. However, the mechanisms responsible for coupling nutrition with growth of stag beetle mandibles (or indeed any insect structure) remain largely unknown. Here, we demonstrate that during the development of male stag beetles (Cyclommatus metallifer), juvenile hormone (JH) titers are correlated with the extreme growth of an exaggerated weapon of sexual selection. We then investigate the putative role of JH in the development of the nutritionally-dependent, phenotypically plastic mandibles, by increasing hemolymph titers of JH with application of the JH analog fenoxycarb during larval and prepupal developmental periods. Increased JH signaling during the early prepupal period increased the proportional size of body parts, and this was especially pronounced in male mandibles, enhancing the exaggerated size of this trait. The direction of this response is consistent with the measured JH titers during this same period. Combined, our results support a role for JH in the nutrition-dependent regulation of extreme mandible growth in this species. In addition, they illuminate mechanisms underlying the evolution of trait proportion, the most salient feature of the evolutionary diversification of the insects.

Modification of hormonal balance in larvae of the corn borer Sesamia nonagrioides (Lepidoptera: Noctuidae) due to sublethal Bacillus thuringiensis protein ingestion

Bacillus thuringiensis (Bt) corn, Zea mays L., is highly efficient against the corn borer Sesamia nonagrioides (Lefèbvre) (Lepidoptera: Noctuidae) when the larvae feed only on the transgenic plants. However, when they feed on Bt leaves during only part of their development, thus ingesting sublethal amounts of Bt toxins, some larvae survive. A previous study reported a prolonged development and precocious diapause induction in larvae fed on a diet with sublethal amounts of Cry1Ab protein. To determine whether these effects were accompanied by a modification of the hormonal balance, S. nonagrioides larvae were fed on sublethal amounts of Bt protein provided in Bt leaves or in the diet. The larvae that survived had higher levels of juvenile hormone (JH), whereas their level of ecdysteroids did not increase sufficiently to allow pupation, leading to a longer larval development and more larval molts. This response may be considered a defense mechanism that allows some larvae to survive toxin ingestion; it is similar the response to insecticidal toxins or viruses observed in other larvae. Changes in the hormone levels in diapausing larvae were undetectable, probably because these changes were masked by the higher level of JH in the hemolymph of diapausing larvae and because of lack of ecdysteroid titer increase, a phenomenon that is usually observed a few days before pupation in nondiapausing larvae. These results should be taken into account in the establishment of non-Bt refuges to prevent development of Bt-resistance in S. non-agrioides populations.

Soldier presence suppresses presoldier differentiation through a rapid decrease of JH in the termite Reticulitermes speratus

The regulation of caste differentiation is essential to insect eusociality. Termite soldiers are sterile and cannot eat by themselves because they have specialized mouth morphology. Almost all termite species have a soldier caste, and the soldier ratio per colony is maintained at a low level, probably by elaborate regulatory mechanisms. Although the soldier presence is considered to negatively affect soldier differentiation in all examined species, the detailed mechanism remains unclear. Presoldier differentiation can be induced artificially by juvenile hormone (JH) application to workers, showing that JH is a key factor underlying the regulation of soldier differentiation. In this study, to elucidate physiological changes in workers because of the soldier presence during the molt into presoldiers, JH III applications and JH titer quantifications were carried out in the rhinotermitid termite Reticulitermes speratus. Firstly, the effects of soldier presence before the molt into presoldiers induced by JH III application to workers were investigated. The rates of presoldier molt induced by the treatments with soldiers were significantly lower than those without soldiers. Secondly, worker JH titers in the presence or absence of soldiers were quantified by LC-MS on day 0, 5, 10, and 15 after JH application. Results indicated that the worker JH titers (endogenous+applied JH III) in the presence of soldiers were significantly lower than those without soldiers on day 5 after the JH treatment. On days 10 and 15, such soldier effects were not observed. Finally, the effective duration of soldier presence after the JH application was elucidated. A 4 day period of co-existence with soldiers suppressed presoldier differentiation, suggesting that the soldier presence rapidly decreased the JH titer in other colony members (i.e., workers), resulting in the inhibition of presoldier production.

Functional genomics of life history variation in a butterfly metapopulation

In fragmented landscapes, small populations frequently go extinct and new ones are established with poorly understood consequences for genetic diversity and evolution of life history traits. Here, we apply functional genomic tools to an ecological model system, the well-studied metapopulation of the Glanville fritillary butterfly. We investigate how dispersal and colonization select upon existing genetic variation affecting life history traits by comparing common-garden reared 2-day adult females from new populations with those from established older populations. New-population females had higher expression of abdomen genes involved in egg provisioning and thorax genes involved in the maintenance of flight muscle proteins. Physiological studies confirmed that new-population butterflies have accelerated egg maturation, apparently regulated by higher juvenile hormone titer and angiotensin converting enzyme mRNA, as well as enhanced flight metabolism. Gene expression varied between allelic forms of two metabolic genes (Pgi and Sdhd), which themselves were associated with differences in flight metabolic rate, population age and population growth rate. These results identify likely molecular mechanisms underpinning life history variation that is maintained by extinction-colonization dynamics in metapopulations.

Nitric oxide/cGMP signaling in the corpora allata of female grasshoppers

The corpora allata (CA) of various insects express enzymes with fixation resistant NADPHdiaphorase activity. In female grasshoppers, juvenile hormone (JH) released from the CA is necessary to establish reproductive readiness, including sound production. Previous studies demonstrated that female sound production is also promoted by systemic inhibition of nitric oxide (NO) formation. In addition, allatotropin and allatostatin expressing central brain neurons were located in close vicinity of NO generating cells. It was therefore speculated that NO signaling may contribute to the control of juvenile hormone release from the CA. This study demonstrates the presence of NO/cGMP signaling in the CA of female Chorthippus biguttulus. CA parenchymal cells exhibit NADPHdiaphorase activity, express anti NOS immunoreactivity and accumulate citrulline, which is generated as a byproduct of NO generation. Varicose terminals from brain neurons in the dorsal pars intercerebralis and pars lateralis that accumulate cGMP upon stimulation with NO donors serve as intrinsic targets of NO in the CA. Both accumulation of citrulline and cyclic GMP were inhibited by the NOS inhibitor aminoguanidine, suggesting that NO in CA is produced by NOS. These results suggest that NO is a retrograde transmitter that provides feedback to projection neurons controlling JH production. Combined immunostainings and backfill experiments detected CA cells with processes extending into the CC and the protocerebrum that expressed immunoreactivity against the pan-neural marker anti-HRP. Allatostatin and allatotropin immunopositive brain neurons do not express NOS but subpopulations accumulate cGMP upon NO-formation. Direct innervation of CA by these peptidergic neurons was not observed.

Rapid direct analysis in real time (DART) mass spectrometric detection of juvenile hormone III and its terpene precursors

Direct analysis in real time (DART) is a plasma-based ambient ionization technique that enables rapid ionization of small molecules with high sample throughput. In this work, DART was coupled to an orthogonal (oa) time-of-flight (TOF) mass spectrometer and the system was optimized for analyzing a vital hormonal regulator in insects, juvenile hormone (JH) III and its terpene precursors, namely, farnesol, farnesoic acid, and methyl farnesoate. Optimization experiments were planned using design of experiments (DOE) full factorial models to identify the most significant DART variables contributing to JH III analysis sensitivity by DART-TOF mass spectrometry (MS). The optimized DART-TOF MS method had femtomole to sub-picomole detection limits for terpene standards, along with mass accuracies below 5 ppm. Finally, the possibility of distinguishing between two farnesol isomers by in-source-collision-induced dissociation (CID) in the first differentially pumped region of the oaTOF mass spectrometer was investigated. DART-MS enabled high-throughput, sensitive analysis with acquisition times ranging from 30 s to a minute. To the best of our knowledge, this is the first report on the application of DART-MS to the detection and identification of volatile or semi-volatile insect terpenoids, and on the use of DOE approaches to optimize DART-MS analytical procedures.

Translating environmental gradients into discontinuous reaction norms via hormone signalling in a polyphenic butterfly

Polyphenisms-the expression of discrete phenotypic morphs in response to environmental variation-are examples of phenotypic plasticity that may potentially be adaptive in the face of predictable environmental heterogeneity. In the butterfly Bicyclus anynana, we examine the hormonal regulation of phenotypic plasticity that involves divergent developmental trajectories into distinct adult morphs for a suite of traits as an adaptation to contrasting seasonal environments. This polyphenism is induced by temperature during development and mediated by ecdysteroid hormones. We reared larvae at separate temperatures spanning the natural range of seasonal environments and measured reaction norms for ecdysteroids, juvenile hormones (JHs) and adult fitness traits. Timing of peak ecdysteroid, but not JH titres, showed a binary response to the linear temperature gradient. Several adult traits (e.g. relative abdomen mass) responded in a similar, dimorphic manner, while others (e.g. wing pattern) showed a linear response. This study demonstrates that hormone dynamics can translate a linear environmental gradient into a discrete signal and, thus, that polyphenic differences between adult morphs can already be programmed at the stage of hormone signalling during development. The range of phenotypic responses observed within the suite of traits indicates both shared regulation and independent, trait-specific sensitivity to the hormone signal.

The genetic, morphological, and physiological characterization of a dark larval cuticle mutation in the butterfly, Bicyclus anynana

Studies on insect melanism have greatly contributed to our understanding of natural selection and the ultimate factors influencing the evolution of darkly pigmented phenotypes. Research on several species of melanic lepidopteran larvae have found that low levels of circulating juvenile hormone (JH) titers are associated with a melanic phenotype, suggesting that genetic changes in the JH biosynthetic pathway give rise to increased deposition of melanin granules in the cuticle in this group. But does melanism arise through different molecular mechanisms in different species? The present study reports on a Bicyclus anynana (Lepidoptera: Nymphalidae) dark larvae single locus mutation, in which larvae exhibit a darker cuticle relative to wild type. Unlike other lepidopteran melanic larvae mutations, this one is autosomal recessive and does not appear to involve a deficiency in JH titers. Unlike JH deficiency mutants, dark larvae mutants display similar growth rates and sexual behaviors as wild type, and topical application of a JH analogue failed to rescue the wild type cuticular coloration. Finally, transmission electron microscopy showed that sclerotization or deposition of diffuse melanin, rather than deposition of melanin granules, produces the dark coloration found in the cuticle of this species. We conclude that different molecular mechanisms underlie larval melanism in different species of Lepidoptera.

Hemolymph extraction from various developmental stages of the African butterfly Bicyclus anynana

This protocol describes procedures for the extraction of hemolymph from larvae, pupae, and adults of the African butterfly Bicyclus anynana. The hemolymph can subsequently be used for various purposes; the method for processing the hemolymph depends on the question under investigation.

Juvenile hormone titres and winged offspring production do not correlate in the pea aphid, Acyrthosiphon pisum

Pea aphids, Acyrthosiphon pisum, reproduce parthenogenetically and are wing-dimorphic such that offspring can develop into winged (alate) or unwinged (apterous) adults. Alate induction is maternal and offspring phenotype is entirely determined by changes in the physiology and environment of the mother. Juvenile hormones (JHs) have been implicated in playing a role in wing differentiation in aphids, however until recently, methods were not available to accurately quantify these insect hormones in small insects such as aphids. Using a novel LC-MS approach we were able to quantify JH III in pea aphids that were either producing a high proportion of winged morphs among their offspring or mainly unwinged offspring. We measured JH III titres by pooling the hemolymph of 12 or fewer individuals (1 microL hemolymph) treated identically. Levels of JH ranged from 30 to 163 pg/microL. While aphids in the two treatments strongly differed in the proportion of winged morphs among their offspring, their JH III titres did not differ significantly. There was also no correlation between JH III titre and the proportion of winged offspring in induced aphids. This supports earlier findings that wing dimorphism in aphids may be regulated by other physiological mechanisms.

Effects of temperature on reproductive output, egg provisioning, juvenile hormone and vitellogenin titres in the butterfly Bicyclus anynana

Environmentally induced phenotypic plasticity is common in nature. Hormones, affecting multiple traits and signaling to a variety of distant target tissues, provide a mechanistic link between environments, genes and trait expression, and may therefore well be involved in the regulation phenotypic plasticity. Here, we investigate whether in the tropical butterfly Bicyclus anynana temperature-mediated plasticity in egg size and number, with fewer but larger eggs produced at lower temperatures and vice versa, is under control of juvenile hormone, and whether different temperatures cause differences in egg composition. Female B. anynana butterflies showed the expected response to temperature, however, we found no evidence for an involvement of juvenile hormone. Neither haemolymph JH II and JH III titres nor vitellogenin levels differed across temperatures. The smaller eggs produced at the higher temperature contained relatively higher amounts of water, free carbohydrates and proteins, but relatively lower amounts of lipids. While these smaller eggs had a lower absolute energy content, total reproductive investment was higher at the higher temperature (due to a higher fecundity). Overall, our study indicates that temperature-mediated plasticity in reproduction in B. anynana is mechanistically related to a biophysical model, with oocyte production (differentiation) and oocyte growth (vitellogenesis) having differential temperature sensitivities.

Juvenile hormone titers and caste differentiation in the damp-wood termite Hodotermopsis sjostedti (Isoptera, Termopsidae)

Termites are social insects, presenting morphologically distinct castes, performing specific tasks in the colony. The developmental processes underlying caste differentiation are mainly controlled by juvenile hormone (JH). Although many fragmentary data support this fact, there was no comparative work on JH titers during the caste differentiation processes. In this study, JH titer variation was investigated using a liquid chromatography-mass spectrometry (LC-MS) quantification method in all castes of the Japanese damp-wood termite Hodotermopsis sjostedti, especially focusing on the soldier caste differentiation pathway, which was induced by treatment with a JH analog. Hemolymph JH titers fluctuated between 20 and 720pg/microl. A peak of JH was observed during molting events for the pseudergate stationary molt and presoldier differentiation, but this peak was absent prior to the imaginal molt. Soldier caste differentiation was generally associated with high JH titers and nymph to alate differentiation with low JH titers. However, JH titer rose in females during alate maturation, probably in relation to vitellogenesis. In comparison, JH titer was surprisingly low in neotenics. On the basis of these results in both natural and artificial conditions, the current model for JH action on termite caste differentiation is discussed and re-appraised.

RNA interference with the allatoregulating neuropeptide genes from the fall armyworm Spodoptera frugiperda and its effects on the JH titer in the hemolymph

The juvenile hormone (JH) titer was measured by liquid chromatography-mass spectrometry (LC-MS) with electrospray ionization (ESI). Three JH homologs, the JH I-III were detected in various amounts in larvae, prepupae and virgin adult females of Spodoptera frugiperda. In penultimate larvae, the JH II and III titers were relatively high, but decreased continuously during the 3 days of that stage, whereas JH I was detectable at low amounts only on the first 2 days. At the beginning of the last larval stage almost no JH could be detected but thereafter, a consistent low amount of JH III was present until the prepupal stage. In adult virgins, the JH titer peaked on the 2nd and 6th day after the imaginal molt. The measured hormone titers well agree with general lepidopteran physiology, because in larvae the JH titer should be high to prevent premature metamorphosis, but decrease in last instar larvae before pupation, whereas in adults JH returns to control various aspects of reproduction. JH biosynthesis is thought to be the main factor influencing the JH titer in the hemolymph and there is evidence that neuropeptides either act stimulatory (allatotropins) or inhibitory (allatostatins) on this process. After silencing of either the allatostatin AS-C-type (Spofr/Manse-AS) or the allatotropin AT 2 (Spofr-AT 2) gene the transcript level was reduced in brain and gut of last instar larvae as well as of adult S. frugiperda. This suppression led to an increased JH titer in larvae, suggesting an allatostatic activity of both the peptides in this stage. As a result of the elevated hormone titer, the last larval stage was prolonged. In prepupae, the JH titer was decreased, but the animals pupated and molted normally. In adult female virgin moths the effect on the JH titer was inversely dependent on the age of the moths and varied among the JH homologs, indicating that the peptides act either allatostatic or allatotropic. For both peptides, gene silencing clearly reduced the oviposition rates of adult females.

Effects of the NMDA receptor antagonist MK-801 on female reproduction and juvenile hormone biosynthesis in the cricket Gryllus bimaculatus and the butterfly Bicyclus anynana

Apart from regulating insect development, juvenile hormones (JHs) play an important role in insect reproduction, where they initiate vitellogenin synthesis and regulate the uptake of yolk by the ovary. JH synthesis is a tightly regulated process controlled by neurons and peptidergic neurosecretory cells. One of the known stimulatory regulators of JH biosynthesis is glutamate, and its N-methyl-d-aspartate (NMDA) receptor has been recently found in the cockroach Diploptera punctata. In this study we demonstrate a strong reduction in reproductive output in the tropical butterfly Bicyclus anynana and the Mediterranean field cricket Gryllus bimaculatus caused by the NMDA receptor antagonist MK-801. Such inhibiting effects on reproduction could be overruled by the application of JH mimics. In G. bimaculatus, MK-801 inhibits in vitro JH biosynthesis in the corpora allata and reduces in vivo JH haemolymph titres in a dose-dependent manner. These results suggest that JH biosynthesis in the corpora allata is at least in part controlled by an NMDA receptor with Ca2+ as a second level messenger. Based on our findings we consider NMDA receptor antagonists as important tools for manipulating juvenile hormone biosynthesis and therefore for gaining a better understanding of the mechanistic basis of reproduction.

Endocrine analysis in evolutionary-developmental studies of insect polymorphism: hormone manipulation versus direct measurement of hormonal regulators

"Hormone manipulation" is being used increasingly in evo-devo studies as the sole or primary technique to investigate the regulation of insect polymorphism by hormones, most notably juvenile hormone (JH). This manuscript critically evaluates the limitations and strengths of this indirect method for inferring aspects of endocrine regulation, and conclusions derived from recent endocrine studies of evolution and development in which data have been obtained primarily or exclusively by this method. The main conclusions of this critique are as follows: first, when used alone, or as the primary empirical technique, hormone manipulation is a superficial method that is fraught with problems with respect to identifying a hormone that regulates developmental-morphological variation, let alone identifying its mode of action. Second, conclusions reported in studies using this technique as the exclusive, or nearly exclusive experimental approach, most notably recent studies of JH regulation of horn polymorphism in dung beetles, and some studies of wing polymorphism should be considered, at best, weakly supported until substantiated by well-validated, direct methods. Finally, there are many reliable and well-validated techniques that can be used to directly and accurately quantify JH levels, and activities of JH regulators, in many insects, even in small, nonmodel species. Some of the most important of these assays will be briefly described and their strengths and weaknesses will be discussed.

Comparison of radioimmunoassay and liquid chromatography tandem mass spectrometry for determination of juvenile hormone titers

This paper compares the results of juvenile hormone (JH) titer determinations in two insect species, Melanoplus sanguinipes, a migratory grasshopper, and Acyrthosiphon pisum, the pea aphid, using a chiral-specific JH radioimmunoassay (RIA) and liquid chromatography tandem mass spectrometry (LC-MS/MS), after extraction of JH with either hexane or isooctane-methanol. We compared results of JH titer determinations done on extracts of M. sanguinipes hemolymph taken from animals flown to exhaustion in tethered flight tests or unflown controls and from whole body extracts of A. pisum raised at two different temperatures. In each case the two different treatments experienced by the experimental animals were expected to result in widely differing JH titers. Methoprene and precocene II were used as internal standards. Samples were split and titers determined simultaneously with both the LC-MS/MS and RIA procedures. Unambiguous detection of JH III by LC-MS/MS was done by identification of its specific parent ion and its mass fingerprint (m/z 289, 267, 249, 235, 217, and 189). We conclude that isooctane-methanol-extracted JH samples can be accurately analyzed by LC-MS/MS, but not by RIA without further separation of JH from contaminating lipids. Hexane extracted JH samples from hemolymph can be analyzed accurately by both RIA and LC-MS/MS. However, the RIA results from whole body extracts of aphids reared at two different temperatures were initially obscured with excess lipids even when hexane was the extraction solvent. Thus samples were further purified by Waters Sep-Pak C18 column, but contaminating phospholipids continued to cause problems with the RIA assay. The detection limit of JH III standard for RIA was 13.75+/-2.39 pg whereas that for LC-M/MS was 8.25+/-1.44 pg in our experimental conditions.

Enantioselective separation of racemic juvenile hormone III by normal-phase high-performance liquid chromatography and preparation of [(2)H(3)]juvenile hormone III as an internal standard for liquid chromatography-mass spectrometry quantification

Juvenile hormone III (JH III) racemate was prepared from methyl (2E,6E)-farnesoate via epoxidation with 3-chloroperbenzoic acid (mCPBA). Enantioselective separation of JH III was conducted using normal-phase high-performance liquid chromatography (HPLC) on a chiral stationary phase. [(2)H(3)]Methyl (2E,6E)-farnesoate was also prepared from (2E,6E)-farnesoic acid and [(2)H(4)]methanol (methanol-d(4)) using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and 4-dimethylaminopyridine (DMAP); the conjugated double bond underwent isomerization to some degree. Epoxidation of [(2)H(3)]methyl (2E,6E)-farnesoate with mCPBA gave a novel deuterium-substituted internal standard [(2)H(3)]JH III (JH III-d(3)). The standard curve was produced by linear regression using the peak area ratios of JH III and JH III-d(3) in liquid chromatography-mass spectrometry (LC-MS).

Juvenile Hormone III Influences Task-Specific Cuticular Hydrocarbon Profile Changes in the Ant Myrmicaria eumenoides

We investigated the influence of juvenile hormones (JH) on the composition of cuticular hydrocarbons (CHCs) and the division of labor in colonies of the African ant Myrmicaria eumenoides. CHCs have long been implicated in nestmate recognition in social insect colonies. In M. eumenoides, the CHC profiles also vary with the task performed from brood-tender-type to forager type. The endocrine factors regulating the task allocation as well as the intracolonial recognition cues are not well understood, but JHs are prime candidates. Only JH III was identified in the hemolymph of M. eumenoides workers. Foragers had significantly higher JH III titers than brood tenders. The application of exogenous JH III and a JH analogue (methoprene) to M. eumenoides workers did not result in an observable acceleration of task change in our study. However, longevity of the focus workers, and thus the observational period, was reduced by the applications. Changes from a brood-tender-type to a forager-type CHC profile were accelerated by the application of JH III and methoprene, resulting in brood-tending workers that displayed forager-type CHC profiles. We present the first data supporting that recognition cues of an eusocial Hymenopteran are influenced by JH III, which could thus play a major role in the regulation of the dynamic nature of social insect colonies. JH III is connected to at least two key processes: the acceleration of CHC changes and the more long-term modulation of task shifting. Moreover, this indicates that changes in CHC recognition cues do not trigger task allocation in social insect colonies.