Cuticular lipids of insects

Hygiene-Eliciting Brood Semiochemicals as a Tool for Assaying Honey Bee (Hymenoptera: Apidae) Colony Resistance to Varroa (Mesostigmata: Varroidae)

Despite numerous interventions, the ectoparasitic mite Varroa (Varroa destructor Anderson and Trueman [Mesostigmata: Varroidae]) and the pathogens it vectors remain a primary threat to honey bee (Apis mellifera Linnaeus [Hymenoptera: Apidae]) health. Hygienic behavior, the ability to detect, uncap, and remove unhealthy brood from the colony, has been bred for selectively for over two decades and continues to be a promising avenue for improved Varroa management. Although hygienic behavior is expressed more in Varroa-resistant colonies, hygiene does not always confer resistance to Varroa. Additionally, existing Varroa resistance selection methods trade efficacy for efficiency, because those achieving the highest levels of Varroa resistance can be time-consuming, and thus expensive and impractical for apicultural use. Here, we tested the hypothesis that hygienic response to a mixture of semiochemicals associated with Varroa-infested honey bee brood can serve as an improved tool for predicting colony-level Varroa resistance. In support of our hypothesis, we demonstrated that a mixture of the compounds (Z)-10-tritriacontene, (Z)-8-hentriacontene, (Z)-8-heptadecene, and (Z)-6-pentadecene triggers hygienic behavior in a two-hour assay, and that high-performing colonies (hygienic response to ≥60% of treated cells) have significantly lower Varroa infestations, remove significantly more introduced Varroa, and are significantly more likely to survive the winter compared to low-performing colonies (hygienic response to <60% of treated cells). We discuss the relative efficacy and efficiency of this assay for facilitating apiary management decisions and selection of Varroa-resistant honey bees, as well as the relevance of these findings to honey bee health, pollination services, and social insect communication.

Desiccation Resistance and Micro-Climate Adaptation: Cuticular Hydrocarbon Signatures of Different Argentine Ant Supercolonies Across California

Cuticular hydrocarbons (CHCs), the dominant fraction of the insects' epicuticle and the primary barrier to desiccation, form the basis for a wide range of chemical signaling systems. In eusocial insects, CHCs are key mediators of nestmate recognition, and colony identity appears to be maintained through a uniform CHC profile. In the unicolonial Argentine ant Linepithema humile, an unparalleled invasive expansion has led to vast supercolonies whose nestmates can still recognize each other across thousands of miles. CHC profiles are expected to display considerable variation as they adapt to fundamentally differing environmental conditions across the Argentine ant's expanded range, yet this variation would largely conflict with the vastly extended nestmate recognition based on CHC uniformity. To shed light on these seemingly contradictory selective pressures, we attempt to decipher which CHC classes enable adaptation to such a wide array of environmental conditions and contrast them with the overall CHC profile uniformity postulated to maintain nestmate recognition. n-Alkanes and n-alkenes showed the largest adaptability to environmental conditions most closely associated with desiccation, pointing at their function for water-proofing. Trimethyl alkanes, on the other hand, were reduced in environments associated with higher desiccation stress. However, CHC patterns correlated with environmental conditions were largely overriden when taking overall CHC variation across the expanded range of L. humile into account, resulting in conserved colony-specific CHC signatures. This delivers intriguing insights into the hierarchy of CHC functionality integrating both adaptation to a wide array of different climatic conditions and the maintenance of a universally accepted chemical profile.

Chemical compositions and characteristics of organic compounds in propolis from Yemen

Propolis is a gummy material made by honeybees for protecting their hives from bacteria and fungi. The main objective of this study is to determine the chemical compositions and concentrations of organic compounds in the extractable organic matter (EOM) of propolis samples collected from four different regions in Yemen. The propolis samples were extracted with a mixture of dichloromethane and methanol and analyzed by gas chromatography–mass spectrometry (GC–MS). The results showed that the total extract yields ranged from 34% to 67% (mean = 55.5 ± 12.4%). The major compounds were triterpenoids (254 ± 188 mg g⁻¹, mainly α-, β-amyryl and dammaradienyl acetates), n-alkenes (145 ± 89 mg g⁻¹), n-alkanes (65 ± 29 mg g⁻¹), n-alkanoic acids (40 ± 26 mg g⁻¹), long chain wax esters (38 ± 25 mg g⁻¹), n-alkanols (8 ± 3 mg g⁻¹) and methyl n-alkanoates (6 ± 4 mg g⁻¹). The variation in the propolis chemical compositions is apparently related to the different plant sources. The compounds of these propolis samples indicate that they are potential sources of natural bio-active compounds for biological and pharmacological applications.

Molecular Characterization of Two Fatty Acyl-CoA Reductase Genes From Phenacoccus solenopsis (Hemiptera: Pseudococcidae)

Fatty acyl-CoA reductases (FARs) are key enzymes involved in fatty alcohol synthesis. Here, we cloned and characterized full-length cDNAs of two FAR genes from the cotton mealybug, Phenacoccus solenopsis. The results showed PsFAR I and PsFAR II cDNAs were 1,584 bp and 1,515 bp in length respectively. Both PsFAR I and PsFAR II were predicted to be located in the endoplasmic reticulum by Euk-mPLoc 2.0 approach. Both of them had a Rossmann folding region and a FAR_C region. Two conservative motifs were discovered in Rossmann folding region by sequence alignment including a NADPH combining motif, TGXXGG, and an active site motif, YXXXK. A phylogenetic tree made using MEGA 6.06 indicated that PsFAR I and PsFAR II were placed in two different branches. Gene expression analysis performed at different developmental stages showed that the expression of PsFar I is significantly higher than that of PsFar II in first and second instar nymphs and in male adults. Spirotetramat treatment at 125 mg/liter significantly increased the expression of PsFar I in third instar nymphs, but there was no effect in the expression of PsFar II Our results indicated these two FAR genes showed different expression patterns during insect development and after pesticide treatment, suggesting they play different roles in insect development and detoxification against pesticides.

The origin and evolution of queen and fertility signals in Corbiculate bees

Background

In social Hymenoptera (ants, bees and wasps), various chemical compounds present on the cuticle have been shown to act as fertility signals. In addition, specific queen-characteristic hydrocarbons have been implicated as sterility-inducing queen signals in ants, wasps and bumblebees. In Corbiculate bees, however, the chemical nature of queen-characteristic and fertility-linked compounds appears to be more diverse than in ants and wasps. Moreover, it remains unknown how queen signals evolved across this group and how they might have been co-opted from fertility signals in solitary ancestors.

Results

Here, we perform a phylogenetic analysis of fertility-linked compounds across 16 species of solitary and eusocial bee species, comprising both literature data as well as new primary data from a key solitary outgroup species, the oil-collecting bee Centris analis, and the highly eusocial stingless bee Scaptotrigona depilis. Our results demonstrate the presence of fertility-linked compounds belonging to 12 different chemical classes. In addition, we find that some classes of compounds (linear and branched alkanes, alkenes, esters and fatty acids) were already present as fertility-linked signals in the solitary ancestors of Corbiculate bees, while others appear to be specific to certain species.

Conclusion

Overall, our results suggest that queen signals in Corbiculate bees are likely derived from ancestral fertility-linked compounds present in solitary bees that lacked reproductive castes. These original fertility-linked cues or signals could have been produced either as a by-product of ovarian activation or could have served other communicative purposes, such as in mate recognition or the regulation of egg-laying.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-015-0509-8) contains supplementary material, which is available to authorized users.

Chemical basis of unwettability in Liacaridae (Acari, Oribatida): specific variations of a cuticular acid/ester-based system

Oribatid mites of the family Liacaridae comprise a large number of species with smooth and shiny body surfaces that display extraordinary anti-wetting properties. The principle of liacarid unwettability is not related to micro-structured surfaces as present in many Oribatida ("Lotus effect") but the formation of raincoat-like lipid layers covering the epicuticle. We here conducted a comparative study on the chemistry of cuticular lipid layers in a selection of Liacaridae, including representatives of all major Central European genera, Liacarus, Dorycranosus, Adoristes, and Xenillus. Cuticular lipids of unwettable individuals were removed from mite bodies by hexane extraction, and were analyzed by GC-MS. Basically, two chemically distinguishable systems were found. Type I: cuticular lipids of Liacarus subterraneus, L. coracinus, L. nitens, Dorycranosus curtipilis, and Xenillus tegeocranus contained different carboxylic acids (C8-, C10-, C10:1-, C10:2-acids) and their corresponding di-glycerides in species-specific combinations. Type II: Adoristes ovatus exhibited a system of cuticular lipids composed of esters of pentanoic- and heptanoic acids with C14-, C15-, C16- and C17-alcohols. Interestingly, the chemistry of surface lipids did not reflect the morphology of the cuticle in the species investigated. Smooth and shiny cuticles, though exhibiting a specific pattern of round or slit-like pores, were found in representatives of Liacarus, Dorycranosus (all of which exhibiting cuticular chemistry of type I) and Adoristes (exhibiting cuticular chemistry of type II). Xenillus, possessing a rough, cerotegumental cement layer-covered surface, showed type I-chemistry. The acid-esters systems herein investigated are considered characteristic for the cuticular chemistry of Liacaridae or a lineage of these, and provide first insights into the comparative chemistry of the inner (=lipid) layer of the oribatid cerotegument.

Organic Tracers from Asphalt in Propolis Produced by Urban Honey Bees, Apis mellifera Linn

Propolis is a gummy material produced by honey bees to protect their hives and currently has drawn the attention of researchers due to its broad clinical use. It has been reported, based only on observations, that honey bees also collect other non-vegetation substances such as paint or asphalt/tar to make propolis. Therefore, propolis samples were collected from bee hives in Riyadh and Al-Bahah, a natural area, Saudi Arabia to determine their compositional characteristics and possible sources of the neutral organic compounds. The samples were extracted with hexane and analyzed by gas chromatography-mass spectrometry. The results showed that the major compounds were n-alkanes, n-alkenes, methyl n-alkanoates, long chain wax esters, triterpenoids and hopanes. The n-alkanes (ranging from C₁₇ to C₄₀) were significant with relative concentrations varying from 23.8 to 56.8% (mean = 44.9+9.4%) of the total extracts. Their odd carbon preference index (CPI) ranged from 3.6 to 7.7, with a maximum concentration at heptacosane indicating inputs from higher plant vegetation wax. The relative concentrations of the n-alkenes varied from 23.8 to 41.19% (mean = 35.6+5.1%), with CPI = 12.4-31.4, range from C₂₅ to C₃₅ and maximum at tritriacontane. Methyl n-alkanoates, ranged from C₁₂ to C₂₆ as acids, with concentrations from 3.11 to 33.2% (mean = 9.6+9.5%). Long chain wax esters and triterpenoids were minor. The main triterpenoids were α- and β-amyrins, amyrones and amyryl acetates. The presence of hopanes in some total extracts (up to 12.5%) indicated that the bees also collected petroleum derivatives from vicinal asphalt and used that as an additional ingredient to make propolis. Therefore, caution should be taken when considering the chemical compositions of propolis as potential sources of natural products for biological and pharmacological applications. Moreover, beekeepers should be aware of the proper source of propolis in the flight range of their bee colonies.

Characteristics and chemical compositions of propolis from Ethiopia

Introduction

Propolis is a sticky material mixed by honeybees to utilize it in protecting their hives from infection by bacteria and fungi. The therapeutic properties of propolis are due to its chemical composition with bio-active compounds; therefore, researchers are interested in studying its chemical constituents and biological properties. The main objective of this study is to determine the chemical compositions, characteristics and relative concentrations of organic compounds in the extractable organic matter of propolis samples collected from four different areas in Ethiopia.

Results

The propolis samples were extracted with a mixture of dichloromethane and methanol and analyzed by gas chromatography–mass spectrometry (GC-MS).The results showed that the total extract yields ranged from 27.2% to 64.2% (46.7 ± 19.1%). The major compounds were triterpenoids (85.5 ± 15.0% of the total extracts, mainly α-, β-amyrins and amyryl acetates), n-alkanes (5.8 ± 7.5%), n-alkenes (6.2 ± 7.0%,), methyl n-alkanoates (0.4 ± 0.2%), and long chain wax esters (0.3 to 2.1%).

Conclusion

The chemical compositions of these propolis samples indicate that they are potential sources of natural bio-active compounds for biological and pharmacological applications.

Cuticular fatty acid profile analysis of three Rhipicephalus tick species (Acari: Ixodidae)

Cuticular fatty acids (CFA) are important constituents of the arthropod exoskeleton, serving as structural and defense components, and participating in intra-species communication. Here we describe for the first time a comparative analysis of the CFA profiles of three tick species of the genus Rhipicephalus: R. annulatus, R. bursa and R. sanguineus. CFA profiles were determined for R. bursa and R. sanguineus grown both on rabbit or calf, and for R. annulatus grown on calf. CFA composition was compared for each species before and after ethanol treatment, for different hosts of each species, and between the different species. Our data suggest that adsorption of the host's fatty acids changes the apparent CFA composition. Ethanol treatment efficiently removed the unbound fatty acids from the ticks and revealed the actual composition. Comparison between ticks grown on rabbit versus calf showed significant difference in the relative abundance of fatty acids C14 and 9,12-C18:2 for R. bursa, and a difference in the relative abundance of C14 for R. sanguineus. Comparison of the CFA between the three species revealed significant differences in the abundance of fatty acids C16, 9,12-C18:2, 9-C18:1, C18 and C20. Our results show that while the host had a minor effect on CFA composition within each species, significant differences were observed in the CFA profiles of different species. We suggest that CFA profiles may be used to distinguish between related species. CFA analysis can also be used in studies of communication and defense mechanisms in ticks and other arthropods.

Free fatty acids in the cuticular and internal lipids of Calliphora vomitoria and their antimicrobial activity

The cuticular and internal lipid composition in Calliphora vomitoria larvae, pupae, and male and female adults was studied. The free fatty acid (FA) compositions of the lipids were chemically characterized using gas chromatography (GC) and gas chromatography-electron impact mass spectrometry (GC-MS). Analyses of cuticular extracts from larvae, pupae, and male and female adults revealed that the carbon numbers of the acids ranged from C7:0 to C22:0, from C8:0 to C24:0, from C7:0 to C24:0 and from C7:0 to C22:0 respectively. The internal lipids of C. vomitoria larvae, pupae, male and female adults contained FAs ranging from C8:0 to C20:0, from C9:0 to C22:0, from C8:0 to C24:0 and from C9:0 to C22:0 respectively. Nine FAs with odd-numbered carbon chains from C7:0 to C21:0 were identified in the cuticular lipids of the larvae. The internal lipids of C. vomitoria larvae contained 8 odd-numbered FAs ranging from C9:0 to C19:0. Eight odd-numbered FAs from C9:0 to C21:0 were identified in the cuticular and internal lipids of pupae, while nine such FAs were found in the cuticular lipids of male and female adults. The internal lipids of adult males and females respectively contained nine and seven odd-numbered FAs, while both larvae and pupae contained eight such compounds. Eight unsaturated FAs were identified in the cuticular lipids of larvae, adult males and females and also in the internal lipids of females. Seven unsaturated FAs were identified in the cuticular lipids of pupae. The internal lipids of larvae, pupae and males contained 10, 11 and 12 unsaturated FAs respectively. Developmental changes were found both in the amounts of extracted cuticular and internal FAs and in their profiles. Four cuticular FAs (C7:0, C9:0, C10:0 and C15:1), identified as being male-specific, were either absent in the female cuticle or present there only in trace amounts. Cuticular and internal extracts obtained from larvae, pupae, adult males and females were tested for their potential antimicrobial activity. The minimal inhibitory concentrations of extracts against reference strains of bacteria and fungi were determined. Antimicrobial activity was the strongest against Gram-positive bacteria; Gram-negative bacteria, on the other hand, turned out to be resistant to all the lipids tested. Overall, the activities of the internal lipids were stronger. All the lipid extracts were equally effective against all the fungal strains examined. In contrast, crude extracts containing both cuticular and internal lipids displayed no antifungal activity against the entomopathogenic fungus Conidiobolus coronatus, which efficiently killed adult flies, but not larvae or pupae.

Composition and antimicrobial activity of fatty acids detected in the hygroscopic secretion collected from the secretory setae of larvae of the biting midge Forcipomyia nigra (Diptera: Ceratopogonidae)

The hygroscopic secretion produced by the secretory setae of terrestrial larvae of the biting midge Forcipomyia nigra (Winnertz) was analysed using gas chromatography coupled with mass spectrometry (GC-MS). The viscous secretion is stored at the top of each seta and absorbs water from moist air. GC-MS analyses (four independent tests) showed that the secretion contained 12 free fatty acids, the most abundant of which were oleic (18:1), palmitic (16:0), palmitoleic (16:1) and linoleic (18:2). Other acids identified were valeric (5:0), enanthic (7:0), caprylic (8:0), pelargonic (9:0), capric (10:0), lauric (12:0), myristic (14:0) and stearic (18:0). Two other compounds, glycerol and pyroglutamic acid, were also found. The antibacterial activity of the fatty acids and pyroglutamic acid was tested using the agar disc diffusion method and targeted Gram positive (Bacillus cereus, Bacillus subtilis, Enterococcus faecalis) and Gram negative bacterial strains (Citrobacter freundii, Pseudomonas aeruginosa, Pseudomonas fluorescens). The antifungal activity was tested by determining minimal inhibitory concentration (MIC) of examined compounds. Fatty acids were tested against enthomopathogenic fungi (Paecilomyces lilacinus, Paecilomyces fumosoroseus, Lecanicillium lecanii, Metarhizium anisopliae, Beauveria bassiana (Tve-N39), Beauveria bassiana (Dv-1/07)). The most effective acids against bacterial and fungal growth were C(9:0), C(10:0) and C(16:1), whereas C(14:0), C(16:0,) C(18:0) and C(18:1) demonstrated rather poor antifungal activity and did not inhibit the growth of bacteria. The antimicrobial assay investigated mixtures of fatty and pyroglutamic acids (corresponding to the results of each GC-MS test): they were found to be active against almost all the bacteria except P. fluorescens and also demonstrated certain fungistatic activity against enthomopathogenic fungi. The hygroscopic secretion facilitates cuticular respiration and plays an important role in the antimicrobial protection of F. nigra larvae living in moist terrestrial habitats.

1,2-Octanediol, a novel surfactant, for treating head louse infestation: identification of activity, formulation, and randomised, controlled trials

BACKGROUND

Interest in developing physically active pediculicides has identified new active substances. The objective was to evaluate a new treatment for clinical efficacy.

METHODS AND FINDINGS

We describe the selection of 1,2-octanediol as a potential pediculicide. Clinical studies were community based. The main outcome measure was no live lice, after two treatments, with follow up visits over 14 days. Study 1 was a proof of concept with 18/20 (90%) participants cured. Study 2 was a multicentre, parallel, randomised, observer-blind study (520 participants) that compared 0.5% malathion liquid with 1,2-octanediol lotion (20% alcohol) applied 2-2.5 hours or 8 hours/overnight. 1,2-octanediol lotion was significantly (p<0.0005) more effective with success for 124/175 (70.9%) RR = 1.50 (97.5% CI, 1.22 to 1.85) for 2-2.5 hours, and 153/174 (87.9%) RR = 1.86 (97.5% CI, 1.54 to 2.26) for 8 hours/overnight compared with 81/171 (47.4%) for malathion. Study 3, a two centre, parallel, randomised, observer-blind study (121 participants), compared 1,2-octanediol lotion, 2-2.5 hours with 1,2-octanediol alcohol free mousse applied for 2-2.5 hours or 8 hours/overnight. The mousse applied for 8 hours/overnight cured 31/40 (77.5%), compared with 24/40 (60.0%) for lotion (RR = 1.29, 95% CI, 0.95 to 1.75; NNT = 5.7) but mousse applied for 2-2.5 hours 17/41 (41.5%) was less effective than lotion (RR = 0.69, 95% CI, 0.44 to 1.08). Adverse events were more common using 1,2-octanediol lotion at both 2-2.5 hours (12.0%, p = 0.001) and 8 hours/overnight (14.9%, p<0.0005), compared with 0.5% malathion (2.3%). Similar reactions were more frequent (p<0.045) using lotion compared with mousse.

CONCLUSIONS

1,2-octanediol was found to eliminate head louse infestation. It is believed to disrupt the insect's cuticular lipid, resulting in dehydration. The alcohol free mousse is more acceptable exhibiting significantly fewer adverse reactions.

TRIAL REGISTRATIONS

Controlled-Trials.com ISRCTN66611560, ISRCTN91870666, ISRCTN28722846.

Differences in cuticular lipid composition of the antennae of Helicoverpa zea, Heliothis virescens, and Manduca sexta

Analyses of the hexane washes of antennae, forelegs and whole bodies of Helicoverpa zea, Heliothis virescens, and Manduca sexta revealed notable differences in the components of the cuticular coatings of each species. Most striking were the differences between the cuticular coatings of male and female antennae of both H. zea and H. virescens. Novel esters of short-chain acids (C2-C4) and long-chain secondary alcohols (C25-C32) were identified in the hexane washes of the male antenna and forelegs of H. zea and H. virescens. These compounds were found in only small amounts or were completely absent on the female antennae of both species. In H. zea, butyrates of 7- and 8-pentacosanol and 8- and 9-heptacosanol were found, whereas, in the foreleg extracts of H. virescens, acetates and propionates were detected in addition to butyrates. While cholesterol is a major component of antennal washes (10-15%), only traces were found in the foreleg extracts. Although the composition of the cuticular coating of M. sexta differed greatly from that of the other two species, the extractable coatings of the antennae of male and female M. sexta were nearly identical.

Electrospray mass spectrometry of human hair wax esters

Wax esters extracted from human hair have been examined by capillary GC-MS and by nano electrospray ionization (ESI) mass spectrometry using a tandem quadrupole mass spectrometer. Initially, the wax esters were examined by capillary GC-MS using conventional means, thus revealing an incomplete chromatographic resolution of the complex array of >200 wax esters ranging from 28 to 40 carbons in length, including saturated/straight-chained, unsaturated/straight-chained, saturated/branched, and unsaturated/branched molecular species. ESI of wax esters produced ammonium adduct ions [M+NH4]+, and collisional activation of these ions formed abundant [RCO2H2]+ product ions. Wax esters containing a double bond in the fatty acyl or fatty alcohol portion of the molecule revealed identical behavior, suggesting little influence of the double bond on the ionization process or subsequent decomposition. The wax ester mixture was analyzed by ESI and tandem mass spectrometry using multiple reaction monitoring and neutral loss scanning. The neutral loss experiment [loss of NH3 and CH2=CH-(CH2)nCH3] was particularly effective at rapidly surveying the complex biological mixture, identifying>160 different wax esters that range from 24 to 42 total carbons.

Quantification of n-alkanes in stratum corneum in the hereditary ichthyoses

Chromatographic assay of n-alkanes in skin showed detectable levels in normal controls and in patients with various forms of hereditary ichthyosis. Raised n-alkanes were found in some, but not all, patients with non-bullous and bullous ichthyosiform erythroderma and in individual patients with lamellar ichthyosis, ichthyosis vulgaris and Netherton's syndrome. The finding of elevated scale n-alkanes is neither consistent in ichthyosis, nor specific to any one type of ichthyosis, and n-alkane assay is not helpful in distinguishing one type of hereditary ichthyosis from another. The source of n-alkanes in ichthyotic scale and their role, if any, in the pathogenesis of ichthyosis remain obscure.

Fine structure of the Gene's organ in the camel tick Hyalomma (Hyalomma) dromedarii (Ixodoidea: Ixodidae)

Gene's organ of the camel tick Hyalomma (Hyalomma) dromedarii is located in the anterodorsal region of the body cavity ventrad to the scutum. It consists of a short stalk, dividing posteriorly into 2 pairs of horns and then into tubular glands. In unfed ticks, the epithelial layer of both the stalk and horns is lined internally by 2 cuticular layers; an inner, thin, greatly folded, dense layer surrounds the organ main lumen, and an outer, thick, slightly folded, less dense layer abuts the cell apices. Only the inner cuticular layer extends into the horn posterior region and appears perforated with numerous pore canals and covered with fine, cuticular projections. The horn and tubular glands epithelium is structurally consistent with a secretory function that apparently increases as feeding progresses. During oviposition, the inner cuticular layer unfolds and inflates into a pair of balloonlike structures that evert through the organ external aperture to receive and manipulate each egg as it is laid, coating it with a waxy layer that prevents desiccation. The fine cuticular projections may have a function in gripping the eggs as they leave the vagina. This organ appears to be everted by hydrostatic pressure from the hemolymph and is retracted by muscles.

The ichthyoses--pathogenesis and prenatal diagnosis: a review of recent advances

Disturbances in the process of normal cornification leading to pathologic scaling provide the pathophysiologic basis for the ichthyoses. These disturbances may result from either abnormalities in protein metabolism (keratinization) (i.e., the "bricks") or in lipid metabolism (i.e., the "mortar") (Fig. 1). The evidence linking the various ichthyoses to defects in protein or lipid metabolism have been reviewed. It is likely that future advances will lead not only to a more complete understanding of the pathogenesis of these disorders, but also will shed significant light on the normal stratum corneum functions of barrier formation and desquamation, as well as lead the way to more rational and effective therapies. In recent years, prenatal diagnosis has been successfully performed in several of the ichthyoses. It is likely that improvements in our ability to prenatally diagnose those disorders will advance hand-in-hand with further progress in unraveling their underlying causes.