Identification and RNAi-based function analysis of trehalase family genes in Frankliniella occidentalis (Pergande).

BACKGROUND: Insects utilize trehalases (TREs) to regulate energy metabolism and chitin biosynthesis, which are essential for their growth, development, and reproduction. TREs can therefore be used as potential targets for future insecticide development. However, the roles of TREs in Frankliniella occidentalis (Pergande), a serious widespread agricultural pest, remain unclear. RESULTS: Three TRE genes were identified in F. occidentalis and cloned, and their functions were then investigated via feeding RNA interference (RNAi) and virus-induced gene silencing (VIGS) assays. The results showed that silencing FoTRE1-1 or FoTRE1-2 significantly decreased expression levels of FoGFAT, FoPGM, FoUAP, and FoCHS, which are members of the chitin biosynthesis pathway. Silencing FoTRE1-1 or FoTRE2 significantly down-regulated FoPFK and FoPK, which are members of the energy metabolism pathway. These changes resulted in 2-fold decreases in glucose and glycogen content, 2-fold increases in trehalose content, and 1.5- to 2.0-fold decreases in chitinase activity. Furthermore, knocking down FoTRE1-1 or FoTRE1-2 resulted in deformed nymphs and pupae as a result of hindered molting. The VIGS assay for the three FoTREs revealed that FoTRE1-1 or FoTRE2 caused shortened ovarioles, and reduced egg-laying and hatching rates. CONCLUSION: The results suggest that FoTRE1-1 and FoTRE1-2 play important roles in the growth and development of F. occidentalis, while FoTRE1-1 and FoTRE2 are essential for its reproduction. These three genes could be candidate targets for RNAi-based management and control of this destructive agricultural pest. © 2024 Society of Chemical Industry.

Combinatorial expression of ebony and tan generates body color variation from nymph through adult stages in the cricket, Gryllus bimaculatus.

Insect body colors and patterns change markedly during development in some species as they adapt to their surroundings. The contribution of melanin and sclerotin pigments, both of which are synthesized from dopamine, to cuticle tanning has been well studied. Nevertheless, little is known about how insects alter their body color patterns. To investigate this mechanism, the cricket Gryllus bimaculatus, whose body color patterns change during postembryonic development, was used as a model in this study. We focused on the ebony and tan genes, which encode enzymes that catalyze the synthesis and degradation, respectively, of the precursor of yellow sclerotin N-ß-alanyl dopamine (NBAD). Expression of the G. bimaculatus (Gb) ebony and tan transcripts tended to be elevated just after hatching and the molting period. We found that dynamic alterations in the combined expression levels of Gb'ebony and Gb'tan correlated with the body color transition from the nymphal stages to the adult. The body color of Gb'ebony knockout mutants generated by CRISPR/Cas9 systemically darkened. Meanwhile, Gb'tan knockout mutants displayed a yellow color in certain areas and stages. The phenotypes of the Gb'ebony and Gb'tan mutants probably result from an over-production of melanin and yellow sclerotin NBAD, respectively. Overall, stage-specific body color patterns in the postembryonic stages of the cricket are governed by the combinatorial expression of Gb'ebony and Gb'tan. Our findings provide insights into the mechanism by which insects evolve adaptive body coloration at each developmental stage.

SPARC plays an important role in the oviposition and nymphal development in Nilaparvata lugens Stål.

BACKGROUND: The brown planthopper (Nilaparvata lugens Stål)is a notorious rice pest in many areas of Asia. Study on the molecular mechanisms underlying its development and reproduction will provide scientific basis for effective control. SPARC (Secreted Protein, Acidic and Rich in Cysteine) is one of structural component of the extracellular matrix, which influences a diverse array of biological functions. In this study, the gene for SPARC was identified and functionally analysed from N.lugens. RESULTS: The result showed that the NlSPARC mRNA was highly expressed in fat body, hemolymph and early embryo. The mortality increased significantly when NlSPARC was downregulated after RNA interference (RNAi) in 3 ~ 4th instar nymphs. Downregulation of NlSPARC in adults significantly reduced the number of eggs and offspring, as well as the transcription level of NlSPARC in newly hatched nymphs and survival rate in progeny. The observation with microanatomy on individuals after NlSPARC RNAi showed smaller and less abundant fat body than that in control. No obvious morphological abnormalities in the nymphal development and no differences in development of internal reproductive organ were observed when compared with control. CONCLUSION: NlSPARC is required for oviposition and nymphal development mainly through regulating the tissue of fat body in N.lugens. NlSPARC could be a new candidate target for controlling the rapid propagation of N.lugens population. Our results also demonstrated that the effect of NlSPARC RNAi can transfer to the next generation in N.lugens.

The Function of Nilaparvata lugens (Hemiptera: Delphacidae) E74 and Its Interaction With ßFtz-F1.

Drosophila E74 is an early gene located in the polytene chromosome 74EF puff position. E74 controls the production of late genes, indicating that it plays a crucial role in this cascade model. Nilaparvata lugens E74 is closely related to Diaphorina citri, Bemisia tabaci, and Laodelphax striatellus. After downregulating E74, molting, and nymphal mortality were increased, and ovarian development was delayed. Moreover, the expression of Vg was reduced at the transcriptional level, as measured by qRT-PCR, and the content of Vg protein was reduced, as detected by Western blotting. After downregulating E74, the expression of hormone-related genes, including Tai, ßFtz-F1, Met, Kr-h1, UspA, UspB, E93, and Br, was changed. The expression of E74 was significantly decreased after downregulating hormone-related genes. When the expression of E74 and ßFtz-F1 was downregulated together, nymph mortality and molting mortality were higher than those when E74 or ßFtz-F1 was downregulated alone. Thus, E74 probably interacts with ßFtz-F1 at the genetic level. In summary, this study showed that E74 plays a crucial role in the development, metamorphosis and reproduction of N. lugens, possibly via the interaction with ßFtz-F1 at the genetic level. This study provides a basis for the development of new target-based pesticides and new methods for the effective control of N. lugens.

Notch is an alternative splicing gene in brown planthopper, Nilaparvata lugens.

Much research has assumed that Notch codes one protein. Then the protein will be cleaved into two parts and regenerates a heterodimers receptor to construct Notch signal pathways to regulate development in the past three decades. Here, we show that Notch in brown planthopper is a complex alternatively spliced gene has at least three transcriptional start sites, four exon skips, and 21 transcriptional endpoints that uses these to form variants and codes a series of proteins. When used dsRNAs to suppression different regions of the full-length variant NlNF resulted in a similar phenotype. Insects were molting after treatment, sensation circles on antennas near to root decayed, bristles on wings shortened, thickened or disappeared, accompanied by thickening veins and blades of fore-wing apex regions thickened. These results suggested that Notch influenced developmental of sensation circles, bristles, veins, and blades in nymph late periods. This study has deepened our understanding of Notch.

Abdominal-B contributes to abdominal identity in the brown planthopper, Nilaparvata lugens (Hemiptera: Delphacidae).

The homeotic complex gene Abdominal-B (Abd-B) is involved in regulating the development of posterior abdomens and has been extensively studied in holometabolous insects. However, the function of Abd-B in hemimetabolous insects is not fully understood. Here, we functionally characterize an Abd-B homologue in the brown planthopper (BPH), Nilaparvata lugens. The full-length cDNA of the N. lugens Abd-B homologue (NlAbd-B) is 2334 nt, with an open reading frame of 1113 bp. NlAbd-B has the highest expression level at the egg stage relative to the nymphal and adult stages and is mainly expressed in the fourth to the ninth abdominal segment of embryos. RNA interference (RNAi)-mediated knockdown of NlAbd-B in nymphs disrupted the development of genitalia both in females and males and caused a genitalia-to-leg transformation. Parental RNAi of NlAbd-B in both female and male adults caused an extra abdominal segment in offspring nymphs, while parental RNAi of the N. lugens abdominal-A homologue in both female and males adults led to embryos with leg-like appendages on the second to the eighth abdominal segment. These findings suggest that NlAbd-B plays a pivotal role in genital development and posterior abdominal patterning and thus highlight the conservational role of Abd-B in holometabolous and hemimetabolous insects.

Rice Defense against Brown Planthopper Partially by Suppressing the Expression of Transferrin Family Genes of Brown Planthopper.

Transferrins are multifunctional proteins, but their role in the interaction of rice and brown planthopper (BPH) remains unclear. In this study, the full-length cDNA of transferrin genes NlTsf1, NlTsf2, and NlTsf3 was cloned. Reverse transcription quantitative polymerase chain reaction showed that the expressions of NlTsf1 and NlTsf3 were significantly suppressed in BPH reared on the resistant rice R1 by 68.0 and 86.7%, respectively, compared with that on the susceptible S9. The survival rate decreased to 3.3% for dsNlTsf3-treated nymphs, to 58.9% for dsNlTsf1, and to 56.7% for dsNlTsf2 on day 11. RNAi of NlTsf3 against females largely reduced the number of eggs by 99.4%, and it decreased by 48.6% for dsNlTsf1 but did not significantly decrease for dsNlTsf2. Collectively, NlTsf1, NlTsf2, and NlTsf3 are essential for the survival and fecundity of BPH and are differentially involved in the interaction between rice and BPH. Therefore, NlTsf1 and NlTsf3 may be used as targets to control BPH.

V-ATPase subunit a is required for survival and midgut development of Locusta migratoria.

The vacuolar-type H+ -ATPase (V-ATPase) is an ATP-dependent proton pump, which regulates various cellular processes. To date, most functional studies on V-ATPases of insects have focused on subunits of the V1 complex, and there is little information on the VO genes. In this study, two cDNA sequences of LmV-ATPase a were identified in Locusta migratoria. RT-qPCR analysis revealed that LmV-ATPase a1 and LmV-ATPase a2 are differentially expressed in various tissues and developmental stages. Injection of dsRNA for the common region of LmV-ATPase a1 and LmV-ATPase a2 into third-instar nymphs resulted in a significant suppression of LmV-ATPase a. The injected nymphs ceased feeding, lost body weight and finally died at a mortality of 98.6%. Furthermore, aberrations of midgut epithelial cells, the accumulation of electron-lucent vesicles in the cytoplasm, and a partially damaged brush border were observed in dsLmV-ATPase a-injected nymphs using transmission electron microscopy. Especially, the mRNA level of wingles, and notch genes were dramatically down-regulated in the dsLmV-ATPase a-injected nymphs. Taken together, our results suggest that LmV-ATPase a is required for survival and midgut development of L. migratoria. Hence, this gene could be a good target for RNAi-based control against locusts.

Neofunctionalization of a second insulin receptor gene in the wing-dimorphic planthopper, Nilaparvata lugens.

A single insulin receptor (InR) gene has been identified and extensively studied in model species ranging from nematodes to mice. However, most insects possess additional copies of InR, yet the functional significance, if any, of alternate InRs is unknown. Here, we used the wing-dimorphic brown planthopper (BPH) as a model system to query the role of a second InR copy in insects. NlInR2 resembled the BPH InR homologue (NlInR1) in terms of nymph development and reproduction, but revealed distinct regulatory roles in fuel metabolism, lifespan, and starvation tolerance. Unlike a lethal phenotype derived from NlInR1 null, homozygous NlInR2 null mutants were viable and accelerated DNA replication and cell proliferation in wing cells, thus redirecting short-winged-destined BPHs to develop into long-winged morphs. Additionally, the proper expression of NlInR2 was needed to maintain symmetric vein patterning in wings. Our findings provide the first direct evidence for the regulatory complexity of the two InR paralogues in insects, implying the functionally independent evolution of multiple InRs in invertebrates.

Identification and characterization of microRNAs in the immature stage of the beneficial predatory bug Arma chinensis Fallou (Hemiptera: Pentatomidae).

MicroRNAs (miRNAs) are a type of small noncoding RNAs that regulate gene expression at the posttranscriptional level and can influence significant biological processes. Arma chinensis (Hemiptera: Pentatomidae) is a predaceous insect species that preys upon a wide variety of insect pests. It is important to explore and understand the molecular mechanisms involving miRNAs in regulating developmental and other gene expression for beneficial insects. However, examination of miRNAs associated with Hemiptera, especially predatory bugs, has been absent or scarce. This study represents the first comprehensive analysis of predatory bug A. chinensis encoded miRNAs through high throughput sequencing and predicts genes and biological processes regulated by the newly identified miRNAs through analyzing their differential expression in and across five nymphal instars. A total of 64 A. chinensis miRNAs, including 46 conserved miRNAs and 18 novel miRNAs, were identified by analysis of high throughput sequence reads mapped to the genome. A total of 2913 potential gene targets for these 64 miRNAs were predicted by comprehensive analyses utilizing miRanda, PITA, and RNAhybrid. Gene Ontology annotation of predicted target genes of A. chinensis suggested the key processes regulated by miRNAs involved biological processes, regulation of cellular processes, and transporter activity. Kyoto Encyclopedia of Genes and Genomes pathway predictions included the Toll and Imd signaling pathway, Valine, leucine and isoleucine degradation, Steroid biosynthesis, the AGE-RAGE signaling pathway in diabetic complications, and Alanine, aspartate and glutamate metabolism. This newly identified miRNAs through analyzing their differential expression, assessment of their predicted functions forms a foundation for further investigation of specific miRNAs.

The transcription factor of the Hippo signaling pathway, LmSd, regulates wing development in Locusta migratoria.

Scalloped (Sd) is transcription factor that regulates cell proliferation and organ growth in the Hippo pathway. In the present research, LmSd was identified and characterized, and found to encode an N-terminal TEA domain and a C-terminal YBD domain. qRT-PCR showed that the LmSd transcription level was highest in the fifth-instar nymphs and very little was expressed in embryos. Tissue-specific analyses showed that LmSd was highly expressed in the wing. Immunohistochemistry indicated that LmSd was highly abundant in the head, prothorax, and legs during embryonic development. LmSd dsRNA injection resulted in significantly down-regulated transcription and protein expression levels compared with dsGFP injection. Gene silencing of LmSd resulted in deformed wings that were curved, wrinkled, and failed to fully expand. Approximately 40% of the nymphs had wing pads that were not able to close normally during molting from fifth-instar nymphs into adults. After silencing of LmSd, the transcription levels of cell division genes were suppressed and the expression levels of apoptosis genes were significantly up-regulated. Our results reveal that LmSd plays an important role in wing formation and development by controlling cell proliferation and inhibiting apoptosis.

Molecular characterizations and expression profiles of transient receptor potential channels in the brown planthopper, Nilaparvata lugens.

Transient receptor potential (TRP) is a superfamily of important cation channels located on the cell membrane. It can regulate almost all sensory modality and control a series of behaviors, including hearing, locomotion, gentle touch, temperature sensation, dry air and food texture detection. The expression profiles of TRP channels have been well documented in the model insect Drosophila melanogaster. However, little is known about the TRP channels of agricultural pests. In this study, we cloned 9 TRP ion channel genes from brown planthopper. Their amino acid sequences are highly conserved with homologues of other insects and have typical TRP channel characteristics: six transmembrane domains (TM1 - TM6) and a pore region between TM5 and TM6. These TRP channels of N. lugens were expressed in all developmental stages and various body parts. The expression levels of almost all TRP channels were relatively higher in adults than nymph stages, and lowest in the eggs. Antenna and abdomen were the main body parts with high expression of these genes. Furthermore, the mRNA levels of these TRP genes were significantly decreased in the third-instar nymphs injected with double-stranded RNA (dsRNA). The survival rate of different TRP dsRNA injected nymphs all exceeded 81%, which was no significant difference compared with the control group. These results suggested that these 9 TRP channels are expressed throughout the body and all ages of the brown planthopper, and are involved in regulating multiple physiological and behavioral processes. The identification of TRP channel genes in this study not only provides a foundation for further exploring the potential roles of TRP channels, but also serves as targets to develop new insecticides for the control of agricultural pests.

Distinct chemical blends produced by different reproductive castes in the subterranean termite Reticulitermes flavipes.

The production of royal pheromones by reproductives (queens and kings) enables social insect colonies to allocate individuals into reproductive and non-reproductive roles. In many termite species, nestmates can develop into neotenics when the primary king or queen dies, which then inhibit the production of additional reproductives. This suggests that primary reproductives and neotenics produce royal pheromones. The cuticular hydrocarbon heneicosane was identified as a royal pheromone in Reticulitermes flavipes neotenics. Here, we investigated the presence of this and other cuticular hydrocarbons in primary reproductives and neotenics of this species, and the ontogeny of their production in primary reproductives. Our results revealed that heneicosane was produced by most neotenics, raising the question of whether reproductive status may trigger its production. Neotenics produced six additional cuticular hydrocarbons absent from workers and nymphs. Remarkably, heneicosane and four of these compounds were absent in primary reproductives, and the other two compounds were present in lower quantities. Neotenics therefore have a distinct 'royal' blend from primary reproductives, and potentially over-signal their reproductive status. Our results suggest that primary reproductives and neotenics may face different social pressures. Future studies of these pressures should provide a more complete understanding of the mechanisms underlying social regulation in termites.

Matrix metalloproteinases are involved in eclosion and wing expansion in the American cockroach, Periplaneta americana.

Matrix metalloproteinases (MMPs) are the major proteinases that process or degrade numerous extracellular matrix (ECM) components and are evolutionarily conserved from nematodes to humans. During molting in insects, the old cuticle is removed and replaced by a new counterpart. Although the regulatory mechanisms of hormones and nutrients in molting have been well studied, very little is known about the roles of ECM-modifying enzymes in this process. Here, we found that MMPs are necessary for imaginal molting of the American cockroach, Periplaneta americana. Inhibition of Mmp activity via inhibitor treatment led to the failure of eclosion and wing expansion. Five Mmps genes were identified from the P. americana genome, and PaMmp2 played the dominant roles during molting. Further microscopic investigations showed that newly formed adult cuticles were attenuated and that then chitin content was reduced upon Mmp inhibition. Transcriptomic analysis of the integument demonstrated that multiple signaling and metabolic pathways were changed. Microscopic investigation of the wings showed that epithelial cells were restrained together because they were incapable of degrading the ECM upon Mmp inhibition. Transcriptomic analysis of the wing identified dozens of possible genes functioned in wing expansion. This is the first study to show the essential roles of Mmps in the nymph-adult transition of hemimetabolous insects.

Effectiveness of orally-delivered double-stranded RNA on gene silencing in the stinkbug Plautia stali.

Development of a reliable method for RNA interference (RNAi) by orally-delivered double-stranded RNA (dsRNA) is potentially promising for crop protection. Considering that RNAi efficiency considerably varies among different insect species, it is important to seek for the practical conditions under which dsRNA-mediated RNAi effectively works against each pest insect. Here we investigated RNAi efficiency in the brown-winged green stinkbug Plautia stali, which is notorious for infesting various fruits and crop plants. Microinjection of dsRNA into P. stali revealed high RNAi efficiency-injection of only 30 ng dsRNA into last-instar nymphs was sufficient to knockdown target genes as manifested by their phenotypes, and injection of 300 ng dsRNA suppressed the gene expression levels by 80% to 99.9%. Knockdown experiments by dsRNA injection showed that multicopper oxidase 2 (MCO2), vacuolar ATPase (vATPase), inhibitor of apoptosis (IAP), and vacuolar-sorting protein Snf7 are essential for survival of P. stali, as has been demonstrated in other insects. By contrast, P. stali exhibited very low RNAi efficiency when dsRNA was orally administered. When 1000 ng/µL of dsRNA solution was orally provided to first-instar nymphs, no obvious phenotypes were observed. Consistent with this, RT-qPCR showed that the gene expression levels were not affected. A higher concentration of dsRNA (5000 ng/µL) induced mortality in some cohorts, and the gene expression levels were reduced to nearly 50%. Simultaneous oral administration of dsRNA against potential RNAi blocker genes did not improve the RNAi efficiency of the target genes. In conclusion, P. stali shows high sensitivity to RNAi with injected dsRNA but, unlike the allied pest stinkbugs Halyomorpha halys and Nezara viridula, very low sensitivity to RNAi with orally-delivered dsRNA, which highlights the varied sensitivity to RNAi across different species and limits the applicability of the molecular tool for controlling this specific insect pest.

Roles of LmCDA1 and LmCDA2 in cuticle formation in the foregut and hindgut of Locusta migratoria.

Chitin deacetylases (CDAs, including CDA1 and CDA2) are considered key enzymes for body cuticle formation and tracheal morphogenesis in various insect species. However, their functions in the formation of the cuticular intima of the foregut and hindgut are unclear. Here, we investigated the roles of their respective genes LmCDA1 and LmCDA2 in this process, in the hemimetabolous insect Locusta migratoria. Transcripts of LmCDA1 and LmCDA2 were highly expressed both before and after molting in the foregut. In the hindgut, their expression was high only before molting. In both the foregut and hindgut, LmCDA1 protein was localized in the basal half of the chitin matrix (procuticle), whereas LmCDA2 was detected in the upper half of the procuticle. Knockdown of LmCDA1 by RNA interference (RNAi) in 5th-instar nymphs caused no visible defects of the hindgut cuticle. By contrast, the chitinous lamellae of the cuticular intima in the foregut of knockdown animals were less compact than in control animals. RNAi against LmCDA2 led to thickening of both the foregut and hindgut cuticles, with a greater number of thinner laminae than in the respective control cuticles. Taken together, our results show that LmCDA1 and LmCDA2 have distinct, but overlapping, functions in chitin organization in the foregut cuticle. However, in the hindgut, this process seems independent of LmCDA1 activity but requires LmCDA2 function. Thus, the CDAs reflect tissue-specific differences in cuticular organization and function, which need further detailed molecular and histological analyses for full comprehension.

Parental RNA interference as a tool to study genes involved in rostrum development in the Neotropical brown stink bug, Euschistus heros.

In insects, the identity of body segments is controlled by homeotic genes and the knockdown of these genes during embryogenesis can lead to an abnormal development and/or atypical phenotypes. The main goal of this study was to investigate the involvement of labial (lab), deformed (dfd), sex comb reduced (scr), extradenticle (exd) and proboscipedia (pb) in rostrum development in the Neotropical brown stink bug Euschistus heros, using parental RNAi (pRNAi). To achieve this objective, 10-days-old adult females were first microinjected with double-stranded RNAs (dsRNA) targeting these five genes. Then, the number of eggs laid per female, the percentage of hatched nymphs with normal or abnormal phenotype and target gene silencing were evaluated. Except for the dsDfd-treatment, the number of eggs laid per female per day was not affected by the different dsRNA-treatments compared to the control (dsGFP). However, treatment with either dsLab, dsDfd, dsScr or dsExd caused a strong reduction in egg hatching. The dsExd-treatment caused no apparent change in phenotype in the nymphs while hatched nymphs from the dsDfd, dsScr and dsPb-treatment showed abnormalities in the rostrum. Particularly for the dsPb-treatment, 91% of the offspring displayed a bifurcated rostrum with a leg-like structure. Overall, these results indicate that these five genes are involved in E. heros embryonic development and that the knockdown of dfd, scr and pb leads to an abnormal development of the rostrum. Additionally, this study demonstrates the efficiency of pRNAi in studying genes involved in embryogenesis in E. heros, with clear phenotypes and a strong target gene silencing in the next generation, after treatment of the parent female adult with gene-specific dsRNA.

Aerobic Metabolism Alterations as an Evidence of Underlying Deltamethrin Resistance Mechanisms in Triatoma infestans (Hemiptera: Reduviidae).

Triatoma infestans (Klug, 1834), the main vector of Chagas disease in Latin America, is regularly controlled by spraying the pyrethroid deltamethrin, to which some populations have developed resistance. The three main mechanisms of resistance are 1) metabolic resistance by overexpression or increased activity of detoxifying enzymes, 2) target site mutations, and 3) cuticle thickening/modification. We use open-flow respirometry to measure real-time H2O loss rate (V˙H2O) and CO2 production rate (V˙CO2), on nymphs from susceptible and resistant populations before and after exposure to the insecticide to understand the underlying mechanisms of resistance in live insects. Lack of differences in V˙H2O between populations suggested that cuticular thickness/composition is not acting as a relevant resistance mechanism. Similarly, there was no difference in resting V˙CO2, suggesting a trade-off between resistance mechanisms and other physiological processes. The increment in V˙CO2 after application of deltamethrin was similar in both populations, which suggested that while enhanced enzymatic detoxification may play a role in resistance expression in this population, the main mechanism involved should be a passive one such as target site mutations. Open-flow respirometry provided useful evidence for evaluating the mechanisms involved in deltamethrin resistance. Using this technique could improve efficiency of scientific research in the area of insecticide resistance management, leading to a faster decision making and hence improved control results.

Silencing of ATG6 and ATG8 promotes increased levels of triacylglycerol (TAG) in the fat body during prolonged starvation periods in the Chagas disease vector Rhodnius prolixus.

Rhodnius prolixus is an obligatorily hematophagous insect known as an important vector of Chagas disease. Autophagy is a conserved cellular mechanism that acts in response to nutrient starvation, where components of the cytoplasm are sequestered by a double membrane organelle, named autophagosome, which is targeted to fuse with the lysosome for degradation. Lipophagy is the process of lipid degradation by selective autophagy, where autophagosomes sequester lipid droplets and degrade triacylglycerol (TAG) generating free fatty acids for ß-oxidation. Here, two essential genes of the autophagic pathway, Atg6/Beclin1 (RpAtg6) and Atg8/LC3 (RpAtg8), were silenced and the storage of lipids during starvation in Rhodnius prolixus was monitored. We found that RNAi knockdown of both RpAtg6 and RpAtg8 resulted in higher levels of TAG in the fat body and the flight muscle, 24 days after the blood meal, as well as a larger average diameter of the lipid droplets in the fat body, as seen by Nile Red staining under the confocal fluorescence microscope. Silenced starved insects had lower survival rates when compared to control insects. Accordingly, when examined during the starvation period for monitored activity, silenced insects had lower spontaneous locomotor activity and lower forced flight rates. Furthermore, we found that some genes involved in lipid metabolism had their expression levels altered in silenced insects, such as the Brummer lipase (down regulated) and the adipokinetic hormone receptor (up regulated), suggesting that, as previously observed in mammalian models, the autophagy and neutral lipolysis machineries are interconnected at the transcriptional level. Altogether, our data indicate that autophagy in the fat body is important to allow insects to mobilize energy from lipid stores.

E93-depleted adult insects preserve the prothoracic gland and molt again.

Insect metamorphosis originated around the middle Devonian, associated with the innovation of the final molt; this occurs after histolysis of the prothoracic gland (PG; which produces the molting hormone) in the first days of adulthood. We previously hypothesized that transcription factor E93 is crucial in the emergence of metamorphosis, because it triggers metamorphosis in extant insects. This work on the cockroach Blattella germanica reveals that E93 also plays a crucial role in the histolysis of PG, which fits the above hypothesis. Previous studies have shown that the transcription factor FTZ-F1 is essential for PG histolysis. We have found that FTZ-F1 depletion towards the end of the final nymphal instar downregulates the expression of E93, whereas E93-depleted nymphs molt to adults that retain a functional PG. Interestingly, these adults are able to molt again, which is exceptional in insects. The study of insects able to molt again in the adult stage may reveal clues about how nymphal epidermal cells definitively become adult cells, and whether it is possible to reverse this process.