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

New insights into changing honey bee (Apis mellifera) immunity molecules pattern and fatty acid esters, in responses to Ascosphaera apis infection

Monitoring of metabolite changes could provide valuable insights into disturbances caused by an infection and furthermore, could be used to define the status of an organism as healthy or diseased and define what could be defensive elements against the infection. The present investigation conducted a gas chromatography-mass spectrometry (GC/MS) for haemolymph of larval honey bees (Apis mellifera L.) infected with the fungal pathogen Ascosphaera apis in comparison with control haemolymph non-infected insects. Results revealed that the pathogen caused a general disturbance of metabolites detected in the haemolymph of the honey bee. The majority of metabolites identified before and after infection were fatty acid esters. The disease caused an elevation in levels of methyl oleate, methyl palmitate, and methyl stearate, respectively. Further, the disease drove to the disappearance of methyl palmitoleate, and methyl laurate. Conversely, methyl linolelaidate, and ethyl oleate were identified only in infected larvae. A high reduction in diisooctyl phthalate was recorded after the infection. Interestingly, antimicrobial activities were confirmed for haemolymph of infected honey bee larvae. In spite of the presence of some previously known bioactive compounds in healthy larvae there were no antimicrobial activities.

Transcriptome and Metabolome Analyses of Thitarodes xiaojinensis in Response to Ophiocordyceps sinensis Infection

Ophiocordyceps sinensis exhibits more than 5 months of vegetative growth in Thitarodes xiaojinensis hemocoel. The peculiar development process of O. sinensis has been elucidated through morphological observation and omics technology; however, little information has been reported regarding the changes that occur in the host T. xiaojinensis. The RNA sequencing data showed that when O. sinensis blastospores were in the proliferative stage, the greatest change in the infected larval fat body was the selectively upregulated immune recognition and antimicrobial peptide genes. When O. sinensis blastospores were in the stationary stage, the immune pathways of T. xiaojinensis reverted to normal levels, which coincides with the successful settlement of O. sinensis. Pathway enrichment analysis showed a higher expression of genes involved in energy metabolism pathway in this stage. Metabolomic analyses revealed a reduction of amino acids and lipids in hemolymph, but an upregulation of lipids in the fat body of the host larvae after O. sinensis infection. We present the first transcriptome integrated with the metabolome study of T. xiaojinensis infected by O. sinensis. It will improve our understanding of the interaction mechanisms between the host and entomopathogenic fungi, and facilitate future functional studies of genes and pathways involved in these interactions.

Lipids as a key element of insect defense systems

The relationship between insect pathogenic fungi and their insect hosts is a classic example of a co-evolutionary arms race between pathogen and target host: parasites evolve towards mechanisms that increase their advantage over the host, and the host increasingly strengthens its defenses. The present review summarizes the literature data describing the direct and indirect role of lipids as an important defense mechanism during fungal infection. Insect defense mechanisms comprise anatomical and physiological barriers, and cellular and humoral response mechanisms. The entomopathogenic fungi have the unique ability to digest the insect cuticle by producing hydrolytic enzymes with chitin-, lipo- and proteolytic activity; besides the oral tract, cuticle pays the way for fungal entry within the host. The key factor in insect resistance to fungal infection is the presence of certain types of lipids (free fatty acids, waxes or hydrocarbons) which can promote or inhibit fungal attachment to cuticle, and might also have antifungal activity. Lipids are considered as an important source of energy, and as triglycerides are stored in the fat body, a structure analogous to the liver and adipose tissue in vertebrates. In addition, the fat body plays a key role in innate humoral immunity by producing a range of bactericidal proteins and polypeptides, one of which is lysozyme. Energy derived from lipid metabolism is used by hemocytes to migrate to the site of fungal infection, and for phagocytosis, nodulation and encapsulation. One polyunsaturated fatty acid, arachidonic acid, is used in the synthesis of eicosanoids, which play several crucial roles in insect physiology and immunology. Apolipoprotein III is important compound with antifungal activity, which can modulate insect cellular response and is considered as important signal molecule.

Black soldier fly (Hermetia illucens) larvae as potential feedstock for the biodiesel production: Recent advances and challenges

Black soldier fly larvae (BSFL) Hermetia illucens is fastest growing and most promising insect species especially recommended to bring high-fat content as 5th generation bioenergy. The fat content can be fully optimized during the life-cycle of the BSFL through various organic dietary supplements and environmental conditions. Enriched fat can be obtained during the larval stages of the BSF. The presence of high saturated and unsaturated fatty acids in their body helps to produce 70 % of extractable oil which can be converted into biodiesel through transesterification. The first-generation biodiesel process mainly depends on catalytic transesterification, however, BSFL had 94 % of biodiesel production through non-catalytic transesterification. This increases the sustainability of producing biodiesel with less energy input in the process line. Other carbon emitting factors involved in the rearing of BSFL are less than the other biodiesel feedstocks including microalgae, cooking oil, and non-edible oil. Therefore, this review is focused on evaluating the optimum dietary source to produce fatty acid rich larvae and larval growth to accumulate C16-18 fatty acids in larger amounts from agro food waste. The process of optimization and biorefining of lipids using novel techniques have been discussed herein. The sustainability impact was evaluated from the cultivation to biodiesel conversion with greenhouse gas emissions scores in the entire life-cycle of process flow. The state-of-the-art in connecting circular bioeconomy loop in the search for bioenergy was meticulously covered.

The Potential Impacts by the Invasion of Insects Reared to Feed Livestock and Pet Animals in Europe and Other Regions: A Critical Review

While the use of alien insect species for food and feed can help to alleviate protein shortage and provide for a more sustainable feed production, their invasive potential should be considered since invasive alien species represent one of the five main global threats to biodiversity. In the European Union (EU), eight insect species have already been authorized to be used as feed ingredients for aquaculture organisms, pets, poultry, and pigs. These species were selected based on available national risk assessments, as most of them are non-native to Europe. However, it is not clear how these risk assessments truly consider all EU bioregions, given that the information used was mostly biased towards northern European regions. As a large proportion of invasive alien species already present in the EU were introduced unintentionally, it is therefore crucial to understand and manage the potential pathways of such introductions in a more effective way. Here, we provide a critical overview of the potential risks of rearing alien insect species as feed or as pet food (for both livestock and exotic pets) in the EU. The results showed that some of these insect species have an invasive potential, either due to their reproductive capacity in different climates or due to the fact that they have already established populations in areas where they were introduced, with negative effects on local ecosystems or causing economical losses. For this reason, it is recommended that risk assessments should be performed in other EU bioregions as well as monitoring programs to control the spread of insect species with invasive potential. In addition, other available native insect species with potential to be used as feed ingredients should be considered.

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.

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.

The Superworm, Zophobas morio (Coleoptera:Tenebrionidae): A 'Sleeping Giant' in Nutrient Sources

The aim of this review is to compile up-to-date information on the superworm, Zophobas morio (F.), regarding its biology and ecology, but also its further potential for use as a nutrient source for food and feed. We illustrate certain basic characteristics of the morphology and bio-ecology of this species, which is marginally considered as a 'pest' in durable amylaceous commodities. More recent data show that Z. morio can be a valuable nutrient and antimicrobial source that could be utilized further in insect-based feed and food production. The inclusion of this species in aquafeed has provided promising results in a wide range of feeding trials, both in terms of fish development and health. Additional data illustrate its potential for use in poultry, indicating that this species provides comparable results with those of other insect species that are used in feed. Moreover, Z. morio can be a viable waste management agent. This review aims to summarize the available data and underline data gaps for future research, toward the potential of the utilization of Z. morio for human food and animal feed. Based on the data presented, Z. morio appears to be a well-promising insect-based protein source, which potential still remains to be unfold.

Cuticular Chemistry of the Queensland Fruit Fly Bactrocera tryoni (Froggatt)

The cuticular layer of the insect exoskeleton contains diverse compounds that serve important biological functions, including the maintenance of homeostasis by protecting against water loss, protection from injury, pathogens and insecticides, and communication. Bactrocera tryoni (Froggatt) is the most destructive pest of fruit production in Australia, yet there are no published accounts of this species' cuticular chemistry. We here provide a comprehensive description of B. tryoni cuticular chemistry. We used gas chromatography-mass spectrometry to identify and characterize compounds in hexane extracts of B. tryoni adults reared from larvae in naturally infested fruits. The compounds found included spiroacetals, aliphatic amides, saturated/unsaturated and methyl branched C12 to C20 chain esters and C29 to C33 normal and methyl-branched alkanes. The spiroacetals and esters were found to be specific to mature females, while the amides were found in both sexes. Normal and methyl-branched alkanes were qualitatively the same in all age and sex groups but some of the alkanes differed in amounts (as estimated from internal standard-normalized peak areas) between mature males and females, as well as between mature and immature flies. This study provides essential foundations for studies investigating the functions of cuticular chemistry in this economically important species.

Chemistry and Sensory Characterization of a Bakery Product Prepared with Oils from African Edible Insects

Globally, there is growing interest to integrate insect-derived ingredients into food products. Knowledge of consumer perception to these food products is growing rapidly in the literature, but similar knowledge on the use of oils from African edible insects remains to be established. In this study, we (1) compared the chemistry of the oils from two commonly consumed grasshoppers, the desert locust Schistocerca gregaria and the African bush-cricket Ruspolia differens with those of olive and sesame oils; (2) compared the proximate composition of a baked product (cookie) prepared from the oils; (3) identified the potential volatiles and fatty acids contributing to the aroma and taste; and (4) examined acceptance and willingness to pay (WTP) for the baked product among consumers with no previous experience of entomophagy. Our results showed that the insect oils were compositionally richer in omega-3 fatty acids, flavonoids, and vitamin E than the plant oils. Proximate analysis and volatile chemistry revealed that differences in aroma and taste of the cookies were associated with their sources of oils. Consumers' acceptance was high for cookies prepared with R. differens (95%) and sesame (89%) oils compared to those with olive and S. gregaria oils. Notably, cookies prepared with insect oils had more than 50% dislike in aroma and taste. Consumers' willingness to pay for cookies prepared with insect oils was 6-8 times higher than for cookies containing olive oil, but 3-4 times lower than cookies containing sesame oil. Our findings show that integrating edible insect oils into cookies, entices people to ''take the first step" in entomophagy by decreasing insect-based food products neophobia, thereby, contributing to consumers' acceptance of the baked products. However, future research should explore the use of refined or flavored insect oils for bakery products to reduce off-flavors that might have been perceived in the formulated food products.