The use of chromatographic techniques for the separation and the identification of insect lipids

The effect of population density on the phenotype, metabolic and immunological adaptations in the cuticle of Spodoptera litura larvae

BACKGROUND

Species that experience outbreaks and those that display density-dependent phase polymorphism demonstrate density-dependent prophylaxis (DDP) by increasing their immune investment in response to increasing densities. Despite this phenomenon, the mechanisms of DDP remain largely unexplored.

RESULTS

Here, we showed that Spodoptera litura exhibited heightened cuticular melanization and enhanced cuticular immune responses when reared at higher population density. Transcriptomic analysis identified differentially expressed genes (DEGs) associated with immune responses, nutritional metabolism, and cuticular synthesis in the cuticle, revealing the molecular underpinnings of density-dependent plasticity in larval cuticles. Gregarious S. litura larvae exhibited significant up-regulation of immune-related genes, particularly those in the Toll and immune deficiency (IMD) signaling pathways and tyrosine metabolism, suggesting a strategic enhancement of immune defenses. Concurrently, a reduced lipid metabolism was observed in the cuticle of gregarious larvae, with suppressed expression of key genes in the fatty acid synthesis, leading to a decrease in integument triglyceride content. The immune defense of gregarious larvae was further amplified by increased expression of cuticle- and melanin formation-related genes, and reduced chitin degradation, reinforcing the cuticle as a physical barrier against pathogens.

CONCLUSION

Our findings clarify that shifts in phenotypic plasticity, metabolic pathways, and immune response mechanisms underscore the adaptability of insects to population density changes and their consequent vulnerability to pathogens, offering new directions and insights for uncovering the mechanisms underlying pest outbreaks and for enhancing the effectiveness of biological control measures by targeting gregarious immunity. © 2025 Society of Chemical Industry.

Unlocking the Secrets of Insects: The Role of Mass Spectrometry to Understand the Life of Insects

Chemical signaling is crucial during the insect lifespan, significantly affecting their survival, reproduction, and ecological interactions. Unfortunately, most chemical signals insects use are impossible for humans to perceive directly. Hence, mass spectrometry has become a vital tool by offering vital insight into the underlying chemical and biochemical processes in various variety of insect activities, such as communication, mate recognition, mating behavior, and adaptation (defense/attack mechanisms), among others. Here, we review different mass spectrometry-based strategies used to gain a deeper understanding of the chemicals involved in shaping the complex behaviors among insects and mass spectrometry-based research in insects that have direct impact in global economic activities.

Surface hydrophobicity mechanism of poultry red mite, Dermanyssus gallinae (Acari: Dermanyssidae), gives novel meaning to chemical control

Surface hydrophobicity of organisms provides biological self-protection. The hydrophobicity of pest surface, acting as a main obstacle for the pest control, can lead to low utilization and high loss of pesticides. Dermanyssus gallinae is a notorious pest in egg-laying hens, whose control primarily depends on acaricide spraying, while its surface hydrophobicity and potential influence on pesticide effectiveness are not clear. In the present study, the contact angle measurements revealed that the surface of D. gallinae was hydrophobic. Analysis using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the surface microstructures of D. gallinae consist of cuticular folds, with a lipid-rich outermost layer of the cuticle. Based on gas chromatography-mass spectrometry (GC-MS) and gas chromatography (GC), it was found that the major compositions of cuticular lipids were fatty acids and n-alkanes. Modifying the chemical compositions and microstructures of the D. gallinae surface resulted in a reduction in surface hydrophobicity and an increase in the permeation of Rhodamine B through the cuticle. This observation suggested that the chemical compositions and microstructures were pivotal in determining surface hydrophobicity, hindering compound penetration into the cuticle. Finally, it was found improving the wettability of pesticide solution by adding surfactants could overcome the surface hydrophobicity and enhance the efficacy of pesticide against the mites. This study sheds light on the surface hydrophobicity mechanism of D. gallinae and provides a novel strategy to improve the efficacy of acaricides against the mites.

Beauveria bassiana transcriptomics reveal virulence-associated shifts during insect lipid assimilation

Insect cuticular lipids, especially epicuticular hydrocarbons (CHC), have a significant role in insect ecology and interactions with other organisms, including fungi. The CHC composition of a specific insect species may influence the outcome of the interaction with a specific fungal strain. Some insects, such as Piezodorus guildinii, have low susceptibility towards fungal infections seemingly due to their CHC composition. The entomopathogenic fungus Beauveria bassiana can assimilate CHC and incorporate them as building blocks via cytochrome P450 monooxygenases (CYPs). However, little is known about other enzymes that promote the degradation/assimilation of these cuticular components. In this study, we performed a transcriptomic analysis to evaluate the in vitro response of two virulence-contrasting B. bassiana strains when grown on three different P. guildinii CHC sources. We found a different expression profile of virulence-related genes, as well as different GO and KEGG parameters enriched at 4 days post-inoculation, which could help account for the intrinsic virulence and for an alkane-priming virulence enhancement effect. The hypovirulent strain predominantly showed higher expression of cuticle penetration genes, including chitinases, proteases, and CYPs, with GO term categories of "heme binding," "monooxygenase activity," and "peroxisome" pathways enriched. The hypervirulent strain showed higher expression of cell wall remodeling and cell cycle genes, and cuticle adhesion and a distinct set of CYPs, with GO categories of "DNA-binding transcription factor activity" and KEGG pathways corresponding to "meiosis-yeast" and "cell cycle" enriched. These results suggest a delay and alternate routes in pathogenicity-related metabolism in the hypovirulent strain in comparison with the hypervirulent strain. KEY POINTS: •Transcriptomics of two B. bassiana strains grown in P. guildinii cuticular components •Virulence-related genes correlated with virulence enhancement towards P. guildinii •Differentially expressed genes, GOs and KEGGs showed different metabolic timelines associated with virulence.

Octanoic acid kills Lucilia sericata (Diptera: Calliphoridae) by affecting two major defence systems: cuticular free fatty acids and immunocompetent cells

This work examines the insecticidal activity of octanoic acid (C8:0), a short-chain fatty acid detected in entomopathogenic fungus - Conidiobolus coronatus medium, against Lucilia sericata larvae and adults. The LD50 value was calculated as 3.04±0.26 µg/mg (3040 mg/kg) of insect body mass, which places the compound in category 5 of acute toxicity (slightly hazardous). The presented research also describes its probable mechanism, with a particular focus on changes in two main insect defense mechanisms: (1) the composition of the cuticle (GC-MS analysis) and (2) immunocompetent cells (microscopic analysis of cultured hemocytes). More precisely, octanoic acid application resulted in changes in cuticular free fatty acid (FFA) profiles in both adults and larvae; generally, treatment increased short-chain FFAs, and a decrease of middle- and long-chain FFAs. Both in vivo and in vitro applications of octanoic acid resulted in vacuolisation, disintegration, and destruction of nets formed by plasmatocytes. As the compound has also previously been found to be toxic against Galleria mellonella, it appears to have lethal potential against insects in both the Orders Diptera and Lepidoptera, indicating it may have strong entomopathogenic potential. It is worth noting that octanoic acid is approved as a food additive with well-documented insecticidal activity, and hence may be a valuable component in the design of new insecticides that are safe for both humans and the environment.

Extraction and application of lipids from edible insects

Research on new food sources is a worldwide challenge due to the constant increase in the global population. In this scenario, insects and bug based products have been investigated as feasible food alternatives. They are nutritionally healthy and environmentally sustainable. Eating insects (entomophagy) or utilizing their macronutrients in food formulations can efficiently solve the demand for nutritious food. The benefits of insect-based foods are reported in the literature, mainly because they are viable sources of fat (∼38%) and proteins (∼68%). Fats and oils are recognized as essential nutrients in human nutrition, as they provide a concentrated source of energy and act as structural components of cell membranes and signaling pathways. The high levels of fats/oils of edible insects open the perspective in the food industry to be used as ingredients in the enrichment of several products, such as cookies, biscuits, butter, and margarine, among others, thus contributing to consumer acceptance. Insect fat/oil can be obtained using extraction techniques, such as solvent and supercritical CO2 methods. The method depends on the insect species, fat/oil yield, and process costs. Thus, this review aims to provide current information on the consumption, application, and extraction of edible insect oils.

Physicochemical properties and fatty acid profile of oil extracted from black soldier fly larvae (Hermetia illucens)

Background and Aim

Hermetia illucens, a black soldier fly, is widely recognized for sustainable recycling of organic waste. Black soldier fly larvae (BSFLs) can consume various types of biowastes and convert them into nutrient-rich biomass, including proteins, lipids, chitin, and minerals. This study investigated the best extraction method by comparing the fatty acid profiles, percentage yield, and antioxidant properties of BSFL oil extracted using different extraction methods.

Materials and Methods

The physicochemical properties, fatty acid profile, and free radical scavenging ability of BSFL oil were analyzed using six extraction methods.

Results

Ultrasonic extraction with hexane resulted in the highest yields compared with different extraction methods. Lauric acid (28%-37%) was the most abundant fatty acid in all extracts, followed by palmitic acid, myristic acid, oleic acid, and linoleic acid. Compared with other methods, aqueous extraction showed the highest lauric acid composition and free radical scavenging activities. In addition, high-temperature aqueous extraction resulted in higher oil yield and free radical scavenging activities than low-temperature extraction.

Conclusion

High-temperature aqueous extraction is the best extraction method because it is rich in lauric acid, has antioxidant ability, and can be further developed to produce novel sustainable biomaterials for humans and animals.

An Acyl Carrier Protein Gene Affects Fatty Acid Synthesis and Growth of Hermetia illucens

Acyl carrier protein (ACP) is an acyl carrier in fatty acid synthesis and is an important cofactor of fatty acid synthetase. Little is known about ACP in insects and how this protein may modulate the composition and storage of fatty acids. We used an RNAi-assisted strategy to study the potential function of ACP in Hermetia illucens (Diptera: Stratiomyidae). We identified a HiACP gene with a cDNA length of 501 bp and a classical conserved region of DSLD. This gene was highly expressed in the egg and late larval instars and was most abundant in the midgut and fat bodies of larvae. Injection of dsACP significantly inhibited the expression level of HiACP and further regulated the fatty acid synthesis in treated H. illucens larvae. The composition of saturated fatty acids was reduced, and the percentage of unsaturated fatty acids (UFAs) was increased. After interfering with HiACP, the cumulative mortality of H. illucens increased to 68.00% (p < 0.05). H. illucens growth was greatly influenced. The development duration increased to 5.5 days, the average final body weights of larvae and pupae were decreased by 44.85 mg and 14.59 mg, respectively, and the average body lengths of larvae and pupae were significantly shortened by 3.09 mm and 3.82 mm, respectively. The adult eclosion rate and the oviposition of adult females were also severely influenced. These results demonstrated that HiACP regulates fatty acid content and influences multiple biological processes of H. illucens.

Lipophorin receptor is required for the accumulations of cuticular hydrocarbons and ovarian neutral lipids in Locusta migratoria

Lipophorin is the most abundant lipoprotein particle in insect hemolymph. Lipophorin receptor (LPR) is a glycoprotein that binds to the lipophorin and mediates cellular uptake and metabolism of lipids by endocytosis. However, the roles of LPR in uptake of lipids in the integument and ovary remain unknown in the migratory locust (Locusta migratoria). In present study, we characterized the molecular properties and biological roles of LmLPR in L. migratoria. The LmLPR transcript level was high in the first 2 days of the adults after eclosion, then gradually declined. LmLPR was predominately expressed in fat body, ovary and integument. Using immuno-detection methods, we revealed that LmLPR was mainly localized in the membrane of oenocytes, epidermal cells, fat body cells and follicular cells. RNAi-mediated silencing of LmLPR led to a slight decrease of the cuticle hydrocarbon contents but with little effect on the cuticular permeability. However, the neutral lipid content was significantly decreased in the ovary after RNAi against LmLPR, which led to a retarded ovarian development. Taken together, our results indicated that LmLPR is involved in the uptake and accumulation of lipids in the ovary and plays a crucial role in ovarian development in L. migratoria. Therefore, LmLPR could be a promising RNAi target for insect pest management by disrupting insect ovarian development.

Fatty acid binding protein is required for chitin biosynthesis in the wing of Drosophila melanogaster

Chitin, the major structural polysaccharide in arthropods such as insects and mites, is a linear polymer of N-acetylglucosamine units. The growth and development of insects are intimately coupled with chitin biosynthesis. The membrane-bound β-glycosyltransferase chitin synthase is known to catalyze the key polymerization step of N-acetylglucosamine. However, the additional proteins that might assist chitin synthase during chitin biosynthesis are not well understood. Recently, fatty acid binding protein (Fabp) has been suggested as a candidate that interacts with the chitin synthase Krotzkopf verkehrt (Kkv) in Drosophila melanogaster. Here, using split-ubiquitin membrane yeast two-hybrid and pull-down assays, we have demonstrated that the Fabp-B splice variant physically interacts with Kkv in vitro. The global knockdown of Fabp in D. melanogaster using RNA interference (RNAi) induced lethality at the larval stage. Moreover, in tissue-specific RNAi experiments, silenced Fabp expression in the epidermis and tracheal system caused a lethal larval phenotype. Fabp knockdown in the wings resulted in an abnormal wing development and uneven cuticular surface. In addition to reducing the chitin content in the first longitudinal vein of wings, Fabp silencing also caused the loss of procuticle laminate structures. This study revealed that Fabp plays an important role in chitin synthesis and contributes to a comprehensive understanding of the complex insect chitin biosynthesis.

Octanoic Acid-An Insecticidal Metabolite of Conidiobolus coronatus (Entomopthorales) That Affects Two Majors Antifungal Protection Systems in Galleria mellonella (Lepidoptera): Cuticular Lipids and Hemocytes

The food flavour additive octanoic acid (C8:0) is also a metabolite of the entomopathogenic fungus Conidiobolus coronatus, which efficiently infects and rapidly kills Galleria mellonella. GC-MS analysis confirmed the presence of C8:0 in insecticidal fraction FR3 extracted from C. coronatus filtrate. Topical administration of C8:0 had a dose-dependent effect on survival rates of larvae but not on pupation or adult eclosion times of the survivors. Topically applied C8:0 was more toxic to adults than larvae (LD100 for adults 18.33 ± 2.49 vs. 33.56 ± 2.57 µg/mg of body mass for larvae). The administration of C8:0 on the cuticle of larvae and adults, in amounts corresponding to their LD50 and LD100 doses, had a considerable impact on the two main defense systems engaged in protecting against pathogens, causing serious changes in the developmental-stage-specific profiles of free fatty acids (FFAs) covering the cuticle of larvae and adults and damaging larval hemocytes. In vitro cultures of G. mellonella hemocytes, either directly treated with C8:0 or taken from C8:0 treated larvae, revealed deformation of hemocytes, disordered networking, late apoptosis, and necrosis, as well as caspase 1-9 activation and elevation of 8-OHdG level. C8:0 was also confirmed to have a cytotoxic effect on the SF-9 insect cell line, as determined by WST-1 and LDH tests.

Neglected Very Long-Chain Hydrocarbons and the Incorporation of Body Surface Area Metrics Reveal Novel Perspectives for Cuticular Profile Analysis in Insects

Simple Summary

The waxy layer covering the surface of most terrestrial insects is mainly composed of non-polar lipids termed cuticular hydrocarbons (CHCs). These have a long research history as important dual traits for both desiccation prevention and chemical communication. We analyzed CHC profiles of seven species of the insect order Blattodea (termites and cockroaches) with the most commonly applied chromatographic method, gas-chromatography coupled with mass spectrometry (GC-MS), and the more novel approach of silver-assisted laser desorption/ionization mass spectrometry (Ag-LDI-MS). Comparing these two analytical methods, we demonstrated that the conventional GC-MS approach does not provide enough information on the entire CHC profile range in the tested species. Ag-LDI-MS was able to detect very long-chain CHCs ranging up to C58, which remained undetected when solely relying on standard GC-MS analysis. Additionally, we measured the body surface areas of each tested species applying 3D scanning technology to assess their respective CHC amounts per mm². When adjusting for body surface areas, proportional CHC quantity distributions shifted considerably between our studied species, suggesting the importance of including this factor when conducting quantitative CHC comparisons, particularly in insects that vary substantially in body size.

Abstract

Most of our knowledge on insect cuticular hydrocarbons (CHCs) stems from analytical techniques based on gas-chromatography coupled with mass spectrometry (GC-MS). However, this method has its limits under standard conditions, particularly in detecting compounds beyond a chain length of around C40. Here, we compare the CHC chain length range detectable by GC-MS with the range assessed by silver-assisted laser desorption/ionization mass spectrometry (Ag-LDI-MS), a novel and rarely applied technique on insect CHCs, in seven species of the order Blattodea. For all tested species, we unveiled a considerable range of very long-chain CHCs up to C58, which are not detectable by standard GC-MS technology. This indicates that general studies on insect CHCs may frequently miss compounds in this range, and we encourage future studies to implement analytical techniques extending the conventionally accessed chain length range. Furthermore, we incorporate 3D scanned insect body surface areas as an additional factor for the comparative quantification of extracted CHC amounts between our study species. CHC quantity distributions differed considerably when adjusted for body surface areas as opposed to directly assessing extracted CHC amounts, suggesting that a more accurate evaluation of relative CHC quantities can be achieved by taking body surface areas into account.

The metabolism and role of free fatty acids in key physiological processes in insects of medical, veterinary and forensic importance

Insects are the most widespread group of organisms and more than one million species have been described. These animals have significant ecological functions, for example they are pollinators of many types of plants. However, they also have direct influence on human life in different manners. They have high medical and veterinary significance, stemming from their role as vectors of disease and infection of wounds and necrotic tissue; they are also plant pests, parasitoids and predators whose activities can influence agriculture. In addition, their use in medical treatments, such as maggot therapy of gangrene and wounds, has grown considerably. They also have many uses in forensic science to determine the minimum post-mortem interval and provide valuable information about the movement of the body, cause of the death, drug use, or poisoning. It has also been proposed that they may be used as model organisms to replace mammal systems in research. The present review describes the role of free fatty acids (FFAs) in key physiological processes in insects. By focusing on insects of medical, veterinary significance, we have limited our description of the physiological processes to those most important from the point of view of insect control; the study examines their effects on insect reproduction and resistance to the adverse effects of abiotic (low temperature) and biotic (pathogens) factors.

The Impact of the Entomopathogenic Fungus Conidiobolus coronatus on the Free Fatty Acid Profile of the Flesh Fly Sarcophaga argyrostoma

Simple Summary

The interaction between insect and fungus is characterised on the one hand by the parasite developing more effective strategies of host exploitation, and on the other, by the host mounting increasingly robust defences though Red Queen dynamics or coevolutionary arms races. Furthermore, depending on gene flow and differences in selection pressure between sites, both host and parasite may demonstrate local adaptation to their counterpart or develop more general resistance or offensive traits. As the cuticle is considered the first line of defence of the insect, changes in the FFA profile may well influence susceptibility or resistance to fungal invasion. Our findings indicate that Sarcophaga argyrostoma demonstrates stage-specific resistance to Conidiobolus coronatus infection and suggests that FFAs play a role in resistance to fungal infection in flesh flies. These findings not only increase our knowledge of the entomopatogenic potential of fungi, but also of the growing level of infection by C. coronatus in humans and other mammals. Also, the presented research suggests that FFAs demonstrate antifungal activity which may be helpful in designing new antifungal treatments.

Abstract

The chemical composition of the insect cuticle varies remarkably between species and their life stages. It can affect host resistance and substrate utilization by invading entomopathogen fungi, such as the soil fungus Conidiobolus coronatus. In this study, Sarcophaga argyrostoma flies were exposed to sporulating C. coronatus colonies for 24 h; the pupae were resistant, but the adults demonstrated 60% mortality. Although the pupae demonstrated no sign of infection nor any abnormal development, our findings indicate that after 24 h of contact with the fungus, the pupae demonstrated a 25.2-fold increase in total cuticular free fatty acids (FFAs) and a 1.9-fold decrease in total internal FFAs. Also, the cuticular FFA increased from 26 to 30, while the internal FFA class increased from 13 to 23. In exposed adults, the total mass of cuticular FFAs increased 1.7-fold, while the number of FFAs stayed the same (32 FFAs). Also, the internal FFA class increased from 26 to 35 and the total FFA mass increased 1.1-fold. These considerable differences between adults and pupae associated with C. coronatus exposure indicate developmental changes in the mechanisms governing lipid metabolism and spatial distribution in the organism, and suggest that cuticular lipids play a vital role in the defence against pathogenic fungi.

The Effect of Climate and Diet on Body Lipid Composition in the Oriental Hornet (Vespa orientalis)

Fatty acids (FA) are the primary metabolic fuel for many organisms and the fundamental component of membranes of all living organisms. FAs can be saturated (SFA), monounsaturated (MUFA), or polyunsaturated (PUFA). PUFA are not synthesized by most animals and are considered as essential nutrients. We examined the effect of climate on the saturation level of polar (mostly membranal) and neutral lipids in the body of the Oriental hornet (Vespa orientalis) from two extreme climatic zones: Mediterranean high elevation; and hot arid desert. In contrast to previous reports, the environmental temperature was shown to affect the hornet colonies’ thermal environments. The hornets nonetheless maintained their colony temperature within a narrow range. Analyses of the hornets’ unsaturation levels of polar and non-polar body lipids revealed caste differences: gynes and males contained less unsaturated lipids than workers. However, there were no differences in the respective castes between the two different climate zones tested. Experimentally manipulating the diet of queenless hornet colonies to a high Omega-3 diet (salmon) or a high Omega-6 diet (crickets) had only a minor effect on the worker-born males’ lipid composition. Although salmon-fed males had a higher Omega-3 content than cricket-fed ones, the proportion of these fatty acids was still low (below 1%). Cricket-fed males had significantly higher levels of Omega-6 than salmon-fed males. Our data show that the specific lipid composition of the hornet body is highly regulated and deficient in essential PUFA, even under different climates or high Omega-3 or Omega-6 PUFA diet. PUFA, especially Omega-3, is considered to have a beneficial effect on physiological processes. Our finding that these FA, when common in the diet, are almost absent in the body raises questions about how they affect animals’ physiology.

Dodecanol, metabolite of entomopathogenic fungus Conidiobolus coronatus, affects fatty acid composition and cellular immunity of Galleria mellonella and Calliphora vicina

One group of promising pest control agents are the entomopathogenic fungi; one such example is Conidiobolus coronatus, which produces a range of metabolites. Our present findings reveal for the first time that C. coronatus also produces dodecanol, a compound widely used to make surfactants and pharmaceuticals, and enhance flavors in food. The main aim of the study was to determine the influence of dodecanol on insect defense systems, i.e. cuticular lipid composition and the condition of insect immunocompetent cells; hence, its effect was examined in detail on two species differing in susceptibility to fungal infection: Galleria mellonella and Calliphora vicina. Dodecanol treatment elicited significant quantitative and qualitative differences in cuticular free fatty acid (FFA) profiles between the species, based on gas chromatography analysis with mass spectrometry (GC/MS), and had a negative effect on G. mellonella and C. vicina hemocytes and a Sf9 cell line in vitro: after 48 h, almost all the cells were completely disintegrated. The metabolite had a negative effect on the insect defense system, suggesting that it could play an important role during C. coronatus infection. Its high insecticidal activity and lack of toxicity towards vertebrates suggest it could be an effective insecticide.

The type of blood used to feed Aedes aegypti females affects their cuticular and internal free fatty acid (FFA) profiles

Aedes aegypti, the primary vector of various arthropod-borne viral (arboviral) diseases such as dengue and Zika, is a popular laboratory model in vector biology. However, its maintenance in laboratory conditions is difficult, mostly because the females require blood meals to complete oogenesis, which is often provided as sheep blood. The outermost layer of the mosquito cuticle is consists of lipids which protects against numerous entomopathogens, prevents desiccation and plays an essential role in signalling processes. The aim of this work was to determine how the replacement of human blood with sheep blood affects the cuticular and internal FFA profiles of mosquitoes reared in laboratory culture. The individual FFAs present in cuticular and internal extracts from mosquito were identified and quantified by GC-MS method. The normality of their distribution was checked using the Kolmogorov-Smirnov test and the Student's t-test was used to compare them. GC-MS analysis revealed similar numbers of internal and cuticular FFAs in the female mosquitoes fed sheep blood by membrane (MFSB) and naturally fed human blood (NFHB), however MFSB group demonstrated 3.1 times greater FFA concentrations in the cuticular fraction and 1.4 times the internal fraction than the NFHB group. In the MFSB group, FFA concentration was 1.6 times higher in the cuticular than the internal fraction, while for NFHB, FFA concentration was 1.3 times lower in the cuticular than the internal fraction. The concentration of C18:3 acid was 223 times higher in the internal fraction than the cuticle in the MHSB group but was absent in the NFHB group. MFSB mosquito demonstrate different FFA profiles to wild mosquitoes, which might influence their fertility and the results of vital processes studied under laboratory conditions. The membrane method of feeding mosquitoes is popular, but our research indicates significant differences in the FFA profiles of MFSB and NFHB. Such changes in FFA profile might influence female fertility, as well as other vital processes studied in laboratory conditions, such as the response to pesticides. Our work indicates that sheep blood has potential shortcomings as a substitute feed for human blood, as its use in laboratory studies may yield different results to those demonstrated by free-living mosquitoes.

Effects of the entomopathogenic fungi Metarhizium robertsii, Metarhizium flavoviride, and Isaria fumosorosea on the lipid composition of Galleria mellonella larvae

Galleria mellonella is a pest of the honey bee (Apis mellifera L.) and causes significant losses to the beekeeping industry; therefore, experiments are needed to decode the effects of entomopathogenic fungi on insect physiology. The gas chromatography-mass spectrometry (GC-MS) method was successful for the determination of the organic compounds of Galleria mellonella larvae, noninfected and infected by three fungal species: M. robertsii, M. flavoviride, and I. fumosorosea. A total of 46 compounds were identified in G. mellonella, including fatty acids, other acids, fatty acid methyl esters, monoacylglycerols, amino acids, sterols, and several other organic compounds. The lipids of G. mellonella larvae after M. robertsii, M. flavoviride, and I. fumosorosea exposure contained 40, 35, and 33 organic compounds, respectively. The following organic compounds, present in the noninfected larvae, were absent from the infected larvae: fatty acids C22:0 and C24:0, glutaric acid, urocanic acid, hydroxycinnamic acid, dihydroxycinnamic acid, 10-oxodecanoic acid, glycine, aspartic acid, glutamic acid, lysine, tyrosine, tryptophan, 2-aminobutyric acid, and tyramine. These compounds can be used by fungi as an exogenous source of carbon. The following organic compounds, present in the infected larvae, were absent from the noninfected larvae: fatty acids C10:0, C11:0, C13:0, and C20:0, suberic acid, phenylacetic acid, fatty acid methyl ester (FAME) C16:0, FAME C18:2, FAME C18:1, glycerol 2-monopalmitate, norvaline, proline, sitosterol, and 2-dekanal. These compounds can be synthesized as an insect response to fungal infection.

Metamorphosis-related changes in the free fatty acid profiles of Sarcophaga (Liopygia) argyrostoma (Robineau-Desvoidy, 1830)

The flies of the Sarcophagidae, widespread throughout the temperate zone, are of great significance in Medicine, Veterinary science, Forensics and Entomotoxicology. Lipids are important elements of cell and organelle membranes and a source of energy for embryogenesis, metamorphosis and flight. Cuticular lipids protect from desiccation and act as recognition cues for species, nest mates and castes, and are a source of various pheromones. The free fatty acid (FFA) profile of cuticular and internal extracts of Sarcophaga (Liopygia) argyrostoma (Robineau-Desvoidy, 1830) larvae, pupae and adults was determined by gas chromatography-mass spectrometry (GC-MS). The larvae, pupae and adults contained FFAs from C5:0 to C28:0. The extracts differed quantitatively and qualitatively from each other: C18:1 > C16:1 > C16:0 > C18:0 predominated in the cuticular and internal extracts from the larvae and adults, while 18:1 > C16:0 > C16:1 > C18:0 predominated in the pupae. The FFA profile of the cuticle varies considerably between each development stage: C23:0 and C25:0 are only present in larvae, C28:0 in the pupal cuticle, and C12:1 and C18:3 in internal extracts from adults. The mechanisms underlying this diversity are discussed herein.

Chemical composition and antimicrobial activity of cuticular and internal lipids of the insect Rhynchophorus palmarum

Insect cuticle lipids are involved in various types of chemical communication between species, and reduce the penetration of insecticides, chemicals, and toxins, as well as provide protection against the attack of microorganisms, parasitic insects, and predators. Ecological studies related to the insect Rhynchophorus palmarum are well-known; however, very little is known about its resistance mechanisms, which includes its lipid composition and its importance, specifically the cuticle layer. This study aimed to characterize the cuticle and internal lipid compounds of the male and female R. palmarum adult insects and to evaluate the presence of antimicrobial activity. We performed by gas chromatography coupled to mass spectrometry (GC-MS) analyzes of lipid extracts fractions and we identified 10 methyl esters of fatty acids esters of C14 to C23, with variation between the sexes of C22:0, C21:0, present only in male cuticle, and C20:2 in female. The lipid content of this insect showed relevant amount of C16:1, C18:1, and C18:2. The antimicrobial activity of the cuticular and internal fractions obtained was tested, which resulted in minimum inhibitory concentrations between 12.5 and 20 μg/ml against Gram-positive bacteria (Staphylococcus epidermidis, Enterococcus faecalis), Gram-negative (Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumonia), and fungal species (Candida albicans e Candida tropicalis). The antimicrobial effect of the R. palmarum cuticle open perspectives for a new source to bioinsecticidal strategies, in addition to elucidating a bioactive mixture against bacteria and fungi.

Apolipophorin-II/I Contributes to Cuticular Hydrocarbon Transport and Cuticle Barrier Construction in Locusta migratoria

Apolipophorins are carrier proteins that bind lipids and mediate their transport from tissue to tissue in animals. Apolipophorin I and II (apoLp-II/I) are the major apolipophorins in insects. The implication of apoLp-II/I in cuticle lipid-barrier formation in insects has not been addressed to date. In the present study, we investigated the function of apoLp-II/I in the migratory locust Locusta migratoria (LmapoLp-II/I). During the development of fifth instar nymphs, LmapoLp-II/I transcript levels increased until mid-instar, and then decreased gradually until molting to the adult stage. We found that LmapoLp-II/I was predominately expressed in the fat body and the integument including oenocytes and epidermal cells. Immunodetection experiments revealed that LmapoLp-I mainly localized in the cytoplasm of oenocytes and epidermal cells. Silencing of LmapoLp-II/I caused molting defects in nymphs. Importantly, RNA interference against LmapoLp-II/I resulted in a significant decrease in the content of cuticle surface lipids including alkanes and methyl alkanes. Cuticular permeability was significantly enhanced in these nymphs in Eosin Y penetration assays. By consequence, desiccation resistance and insecticide tolerance of dsLmapoLp-II/I-treated locusts were reduced. Taken together, our results indicate that LmapoLp-II/I is involved in the transport and deposition of surface-cuticular lipids that are crucial for maintaining normal cuticle barrier function in L. migratoria.

Preliminary Study on the Differences in Hydrocarbons Between Phosphine-Susceptible and -Resistant Strains of Rhyzopertha dominica (Fabricius) and Tribolium castaneum (Herbst) Using Direct Immersion Solid-Phase Microextraction Coupled with GC-MS

Phosphine resistance is a worldwide issue threatening the grain industry. The cuticles of insects are covered with a layer of lipids, which protect insect bodies from the harmful effects of pesticides. The main components of the cuticular lipids are hydrocarbon compounds. In this research, phosphine-resistant and -susceptible strains of two main stored-grain insects, T. castaneum and R. dominica, were tested to determine the possible role of their cuticular hydrocarbons in phosphine resistance. Direct immersion solid-phase microextraction followed by gas chromatography-mass spectrometry (GC-MS) was applied to extract and analyze the cuticular hydrocarbons. The results showed significant differences between the resistant and susceptible strains regarding the cuticular hydrocarbons that were investigated. The resistant insects of both species contained higher amounts than the susceptible insects for the majority of the hydrocarbons, sixteen from cuticular extraction and nineteen from the homogenized body extraction for T. castaneum and eighteen from cuticular extraction and twenty-one from the homogenized body extraction for R. dominica. 3-methylnonacosane and 2-methylheptacosane had the highest significant difference between the susceptible and resistant strains of T. castaneum from the cuticle and the homogenized body, respectively. Unknown5 from the cuticle and 3-methylhentriacontane from the homogenized body recorded the highest significant differences in R. dominica. The higher hydrocarbon content is a key factor in eliminating phosphine from entering resistant insect bodies, acting as a barrier between insects and the surrounding phosphine environment.

Concentration dependent cholesteryl-ester and wax-ester structural relationships and meibomian gland dysfunction

Background

With dry eye, the ratio of cholesteryl ester (CE) to wax ester (WE) decreases substantially in meibum, but the functional and structural consequences of this change are speculative. The aim of this study is to confirm this finding and to bridge this gap in knowledge by investigating the effect of varying CE/WE ratios on lipid structure and thermodynamics.

Methods

Infrared spectroscopy was use to quantify CE and WE in human meibum and to measure hydrocarbon chain conformation and thermodynamics in a cholesteryl behenate, stearyl stearate model system.

Results

The CE/WE molar ratio was 36% lower for meibum from donors with dry eye due to meibomian gland dysfunction compared with meibum from donors without dry eye. CE (5 mol %) dramatically increased the phase transition temperature of pure WE from -0.12 °C to 63 °C in the mixture. Above 5 mol % CB, the phase transition temperature increased linearly, from 68.5 °C to 85 °C. In the ordered state, CE caused an increase in lipid order from about 72% trans rotamers to about 86% trans rotamers. Above 10% CE, the hydrocarbon chains were arranged in a monoclinic geometry.

Conclusions

The CE/WE is lower in meibum from donors with dry eye due to meibomian-gland dysfunction. Major conformational changes in the hydrocarbon chains of wax and cholesteryl ester mixtures begin to occur with just 5% CB and above.

General significance

CE-WE interactions may be important for in understanding lipid layer structure and functional relationships on the surface of tears, skin and plants.

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The CE/WE is lower in meibum from donors with meibomian-gland dysfunction.

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CE may be important for the tear film lipid layer structure and function.

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CE-WE interactions may be important on the surface of tears, skin and plants.

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Conformational changes in WE and CE mixtures begin to occur with just 5% CE.

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CE, cholesteryl ester; WE, wax ester.

Effects of the entomopathogenic fungus Metarhizium flavoviride on the fat body lipid composition of Zophobas morio larvae (Coleoptera: Tenebrionidae)

Insects employ different defense strategies against fungal infections and chemicals. We aimed to identify the lipid compositions of the fat body of Zophobas morio larvae before and after fungal infection with the entomopathogenic fungus Metarhizium flavoviride. We used gas chromatography-mass spectrometry to analyze lipid extracts of the fat body isolated of Z. morio 2, 5, and 7 days after fungal infection (treatment group) and compared it with the lipid extracts in a control group injected with physiological isotonic saline. In all the samples, fatty acids were the most abundant compound found in the fat body extracts, with hexadecanoic acid/C16:0 being the most abundant lipid. However, the types and concentrations of lipids changed after fungal infection, likely as an immune response. The most considerable changes occurred in the concentrations of long-chain fatty acids, i.e., hexadecanoic acid/C16:0, octadecenoic acid/C18:1, and octadecanoic acid/C18:0. Contents of methyl ester increased significantly after infection, but that of other esters, especially octanoic acid decyl ester/OADE, decreased on the 5th day after infection. To the best of our knowledge, this is the first detailed analysis of the changes in the lipid composition of the fat body of Z. morio larvae as a result of fungal infection. Our results suggest that entomopathogenic fungal infection affects the internal lipid composition of insects, potentially as a way of adjusting to such infection. These results can help understand infection processes and defense strategies of insects against fungal infection. Ultimately, they can contribute to the creation of more effective chemicals against pest insects.

New Method of Analysis of Lipids in Tribolium castaneum (Herbst) and Rhyzopertha dominica (Fabricius) Insects by Direct Immersion Solid-Phase Microextraction (DI-SPME) Coupled with GC-MS

Lipids play an essential role in providing energy and other physiological functions for insects. Therefore, it is important to determine the composition of insect lipids from cuticular and internal tissues for a better understanding of insect biology and physiology. A novel non-derivatization method for the analysis of lipids including fatty acids, hydrocarbon waxes, sterols in Tribolium castaneum (Herbst) and Rhyzopertha dominica (Fabricius) was explored using the direct immersion solid-phase microextraction (DI-SPME) coupled with gas chromatography-mass spectrometry (GC-MS). Nine extraction solvents, acetonitrile, methanol, hexane, ethanol, chloroform, acetonitrile and ethanol (1:1 v/v), acetonitrile and water (1:1 v/v), ethanol and water (1:1 v/v) and acetonitrile and ethanol and water (2:2:1 v/v/v) were selected and evaluated for the extraction of insect lipids with DI-SPME fiber. Acetonitrile extraction offered the best qualitative, quantitative, and number of lipids extracted from insects samples results. Acetonitrile extracted high-boiling point compounds from both species of tested insects. The range of hydrocarbons was C25 (pentacosane) to C32 (dotriacontane) for T. castaneum and C26 (11-methylpentacosane) to C34 (tetratriacontane) for R. dominica. The major compounds extracted from the cuticular surface of T. castaneum were 11-methylheptacosane (20.71%) and 3-methylheptacosane (12.37%), and from R. dominica were 10-methyldotriacontane (14.0%), and 15-methyltritriacontane (9.93%). The limit of detection (LOD) for the n-alkane compounds ranged between 0.08 (nonacosane) and 0.26 (dotriacontane) µg/g and for the fatty acids between 0.65 (arachidic acid) to 0.89 (oleic acid) µg/g. The study indicated that DI-SPME GC-MS is a highly efficient extraction and a sensitive analytical method for the determination of non-derivatized insect lipids in cuticular and homogenized body tissues.

BgFas1: A fatty acid synthase gene required for both hydrocarbon and cuticular fatty acid biosynthesis in the German cockroach, Blattella germanica (L.)

Insect cuticular hydrocarbons (CHCs), the evolutionary products of aquatic hexapod ancestors expanding to terrestrial environment, are deposited on the surface of insect integument and originally functioned primarily as waterproofing agents. CHCs are derived from the conserved fatty acid synthesis pathway in insects. However, the pivotal fatty acid synthase (FAS) involved in hydrocarbon (HC) biosynthesis remains unknown in many insect orders including the primitive Blattodea. Here, we investigated functional FAS genes that modulate cuticular lipid biogenesis in the German cockroach, Blattella germanica (L.). Based on our full-length transcriptomic data and the available genomic data, seven FAS genes (BgFas1-7) were identified from B. germanica. Tissue-specific expression analysis revealed that BgFas1, BgFas3, BgFas4 and BgFas7 were highly expressed in the integument, whereas BgFas2 was dominantly expressed in the fat body. BgFas5/6 mRNA was almost negligible in the tested tissues. Systemic RNAi screen was performed against BgFas1-7, we found that only RNAi knockdown of BgFas1 caused a dramatic reduction of methyl-branched HCs (mbHCs) and a slight decrease of straight-chain HCs (scHCs) for both internal and external HCs. Significant reduction of cuticular free fatty acids (cFFAs) was also detected within BgFas1-repressed cockroaches, while repression of CYP4G19 resulted in dramatic increase of cFFAs. Moreover, we found that BgFas1 mRNA levels were correlated with insect molting cycles, and could be induced by long-term mild dryness treatment. Furthermore, desiccation assay revealed that BgFas1 suppression accelerated water loss and led to early death of cockroaches under desiccation. Our results indicate that BgFas1 is necessary for both HC and cFFA biosynthesis in B. germanica. In addition, our study also confirms that cuticular lipids, particularly mbCHCs, are critical for desiccation resistance in B. germanica.

Tissue damage and cytotoxic effects of Tagetes minuta essential oil against Lucilia cuprina

The blowfly Lucilia cuprina has great medico-sanitary and veterinary importance due to the ability of its larval form to develop in decaying organic matter, parasitizing vertebrates. Fly eradication is challenging and the essential oil (EO) of Tagetes minuta (TMEO) have been reported to have therapeutic properties. This study aimed to determine the activity of EO from the aerial parts of T. minuta against third instar larvae (L3) of L. cuprina. Groups of 20 L3 were placed on filter paper, which were impregnated with varying concentrations (0.19; 0.39; 0.79; 1.59; 2.38; 3.18; 4.77; and 6.36 μL/cm²) of TMEO solubilized in acetone, ethanol or Tween 20. Histological tissue damage of TMEO was measured in L3 after 24, 48 and 96 h of exposure. Dihydrotagetone (67.64%), trans-ocimene (16.23%), trans-tagetone (10.14%) and verbenone (2.98%) were obtained as major compounds of TMEO. Lethal concentrations of 50%, 24 and 48 h after TMEO exposure were 1.02 and 0.73 μL/cm² for acetone; 3.37 and 1.75 μL/cm² for ethanol; and 7.46 and 6.11 μL/cm² for Tween 20, respectively. TMEO had a significant L3 mortality of 96.6% in acetone, 48 h after contact. Cuticle abnormalities were observed, as well as the loss of digestive tract architecture and vacuolization in fat bodies. TMEO presented time and concentration-dependent effects against L. cuprina. As our study demonstrated a strong insecticide activity of TMEO, we consider that it could be developed into an ecofriendly product against L. cuprina.

Insect Adhesion Secretions: Similarities and Dissimilarities in Hydrocarbon Profiles of Tarsi and Corresponding Tibiae

Spatially controlled in vivo sampling by contact solid phase microextraction with a non-coated silica fiber combined with gas chromatography-mass spectrometry (GC-MS) was utilized for hydrocarbon profiling in tarsal adhesion secretions of four insect species (Nicrophorus vespilloides, Nicrophorus nepalensis, Sagra femorata, and Gromphadorhina portentosa) by using distinct adhesion systems, viz. hairy or smooth tarsi. For comparison, corresponding samples from tibiae, representing the general cuticular hydrocarbon profile, were analyzed to enable the statistical inference of active molecular adhesion principles in tarsal secretions possibly contributed by specific hydrocarbons. n-Alkanes, monomethyl and dimethyl alkanes, alkenes, alkadienes, and one aldehyde were detected. Multivariate statistical analysis (principal component and orthogonal partial least square discriminant analyses) gave insights into distinctive molecular features among the various insect species and between tarsus and tibia samples. In general, corresponding hydrocarbon profiles in tarsus and tibia samples largely resembled each other, both qualitatively and in relative abundances as well. However, several specific hydrocarbons showed significantly different relative abundances between corresponding tarsus and tibia samples, thus indicating that such differences of specific hydrocarbons in the complex mixtures might constitute a delicate mechanism for fine-tuning the reversible attachment performances in tarsal adhesive fluids that are composed of substances originating from the same pool as cuticular hydrocarbons. Caused by melting point depression, the multicomponent tarsal adhesion secretion, made up of straight chain alkanes, methyl alkanes, and alkenes will have a semi-solid, grease-like consistency, which might provide the basis for a good reversible attachment performance.

Regionalization of surface lipids in insects

Cuticular hydrocarbons (CHCs) play a critical role in the establishment of the waterproof barrier that prevents dehydration and wetting in insects. While rich data are available on CHC composition in different species, we know little about their distribution and organization. Here, we report on our studies of the surface barrier of the fruit fly Drosophila melanogaster applying a newly developed Eosin Y staining method. The inert Eosin Y penetrates different regions of the adult body at distinct temperatures. By contrast, the larval body takes up the dye rather uniformly and gradually with increasing temperature. Cooling down specimens to 25°C after incubation at higher temperatures restores impermeability. Eosin Y penetration is also sensitive to lipid solvents such as chloroform indicating that permeability depends on CHCs. As in D. melanogaster adult flies, Eosin Y penetration is regionalized in Tenebrio molitor larvae, whereas it is not in Locusta migratoria nymphs. Regionalization of the fly surface implies tissue-specific variation of the genetic or biochemical programmes of CHC production and deposition. The Eosin Y-based map of CHC distribution may serve to identify the respective factors that are activated to accommodate ecological needs.

Effect of exposure to chlorpyrifos on the cuticular and internal lipid composition of Blattella germanica males

The results of our research on the cuticular and internal lipids of Blattella germanica males provide new information on variation in the composition of the cuticular and internal lipids of B. germanica males after exposure to the presence of the insecticide. gas chromatography and gas chromatography-mass spectrometry analyses were used to identify and quantify the cuticular and internal lipid composition in males and males exposed to insecticide. There were significantly more acids having an even number of carbon atoms in the molecule, and these were also generally in higher concentrations. The following acids were in a higher concentration: C16:0 and C18:1, C18:2, C18:0. In both males and males exposed to insecticide, 24 fatty acids ranging from C6 to C22 were determined. However, there was a significantly higher content of fatty acids in the surface lipids of B. germanica males after exposure to insecticide. Our results indicate a higher content of n-alkanes, sterols, particularly cholesterol, fatty acids, and fatty acid methyl esters in the B. germanica surface after exposure to chlorpyrifos than in males that were not exposed.

Contact solid-phase microextraction with uncoated glass and polydimethylsiloxane-coated fibers versus solvent sampling for the determination of hydrocarbons in adhesion secretions of Madagascar hissing cockroaches Gromphadorrhina portentosa (Blattodea) by gas chromatography-mass spectrometry

Molecular profiles of adhesion secretions of Gromphadorrhina portentosa (Madagascar hissing cockroach, Blattodea) were investigated by gas chromatography mass spectrometry with particular focus on a comprehensive analysis of linear and branched hydrocarbons. For this purpose, secretions from the tarsi (feet), possibly contributing to adhesion on smooth surfaces, and control samples taken from the tibiae (lower legs), which contain general cuticular hydrocarbons that are supposed to be not involved in the biological adhesion function, were analyzed and their molecular fingerprints compared. A major analytical difficulty in such a study constitutes the representative, spatially controlled, precise and reproducible sampling from a living insect as well as the minute quantities of insect secretions on both tarsi and tibiae. Thus, three different in vivo sampling methods were compared in terms of sampling reproducibility and extraction efficiency by replicate measurement of samples from tarsi and tibiae. While contact solid-phase microextraction (SPME) with a polydimethylsiloxane (PDMS) fiber showed higher peak intensities, a self-made uncoated glass fiber had the best repeatability in contact-SPME sampling. Chromatographic profiles of these two contact-SPME sampling methods were statistically not significantly different. Inter-individual variances were larger than potentially existing minor differences in molecular patterns of distinct sampling methods. Sampling by solvent extraction was time consuming, showed lower sensitivities and was less reproducible. In general, sampling by contact-SPME with a cheap glass fiber turned out to be a viable alternative to PDMS-SPME sampling. Hydrocarbon patterns of the tarsal adhesion secretions were qualitatively similar to those of epicuticular hydrocarbon profiles of the tibiae. However, hydrocarbons were in general less abundant in tarsal secretions than secretions from tibiae.

Metabolite localization by atmospheric pressure high-resolution scanning microprobe matrix-assisted laser desorption/ionization mass spectrometry imaging in whole-body sections and individual organs of the rove beetle Paederus riparius

Mass spectrometry imaging provides for non-targeted, label-free chemical imaging. In this study, atmospheric pressure high-resolution scanning microprobe matrix-assisted laser desorption/ionization mass spectrometry imaging (AP-SMALDI MSI) was used for the first time to describe the chemical distribution of the defensive compounds pederin, pseudopederin, and pederon in tissue sections (16 μm thick) of the rove beetle Paederus riparius. The whole-insect tissue section was scanned with a 20-μm step size. Mass resolution of the orbital trapping mass spectrometer was set to 100,000 at m/z 200. Additionally, organ-specific compounds were identified for brain, nerve cord, eggs, gut, ovaries, and malpighian tubules. To confirm the distribution of the specific compounds, individual organs from the insect were dissected, and MSI experiments were performed on the dissected organs. Three ganglia of the nerve cord, with a dimension of 250–500 μm, were measured with 10-μm spatial resolution. High-quality m/z images, based on high spatial resolution and high mass accuracy were generated. These features helped to assign mass spectral peaks with high confidence. Mass accuracy of the imaging experiments was <3 ppm root mean square error, and mapping of different compound classes from a single experiment was possible. This approach improved the understanding of the biochemistry of P. riparius. Concentration differences and distributions of pederin and its analogues could be visualized in the whole-insect section. Without any labeling, we assigned key lipids for specific organs to describe their location in the body and to identify morphological structures with a specificity higher than with staining or immunohistology methods.