Adult Locusts Research Articles

Formulation and bio-efficacy of different isolates of Beauveria bassiana against adults and third nymphal instar of desert locust (Schistocerca gregaria Forskål)

Recently, the Horn of Africa witnessed a swift increase in the incidence of desert locust (Schistocerca gregaria) invasion. During outbreaks, pesticides are applied through aerial or ground spraying to kill the insects, and/or to prevent their spread to new grounds. However, after decades of extensive use, many drawbacks such as contamination of the environment, toxicity to non-target organisms, harmful residues on food, pest resistance, and bioaccumulation in the food chains emerged. Entomopathogenic fungi offer viable alternatives to chemical pesticides against many insect invasions, but few studies have tested their bio-efficacy in desert locusts. Therefore, the current study aimed at isolating, formulating local isolates 231, 334, 333, 341, 349, 351, 339 of Beauveria bassiana, and testing their bio-efficacy against larval and adult desert locusts. The 21-day experiment was conducted under controlled conditions in a greenhouse. Soil samples were collected from two agroecological zones in Isiolo and Laikipia Counties in Kenya. B. bassiana was isolated from the soil samples using the Galleria bait method and cultivated in Sabouraud Dextrose Agar Yeast (SDAY). The isolates were identified based on molecular techniques (DNA and PCR amplification). The conidia of the isolates were screened and bioassays on 30 locusts was conducted for 14 days. The best isolates eliciting over 90 % mortality during screening were used for formulations using three carrier materials (liquid paraffin, Diatomaceous Earth, and whey) which were again tested against adult and 3rd nymphal instars of the locusts. The stability of the formulations was also tested after 1 and 2 months. All the tested isolates of B. bassiana significantly outperformed the control and thus pathogenic to the adults and 3rd nymphal instars of S. gregaria under laboratory conditions. They caused mortality ranging from 57.8–100 % after 14 days post-incubation. The isolates 341, 231, and, 334 elicited 50 % mortality responses at concentrations 1.1 × 105 conidia/ml, 2.5 × 105 conidia/ml and 1.7 × 106 conidia/ml respectively in adults and 1.1 × 105 conidia/ml, 2.5 × 105 conidia/ml and, 1.7 × 106 conidia/ml respectively in 3rd nymphal instars. Formulations with 341–1, 341–2, and, 334–1 had the highest efficacy (>99 %) against the adult locusts. There was a significant 3-way interaction (P < 0.05) of isolate for the formulation, carrier material and, time in determining the Cfu of the B. bassiana formulations. After 1 month, the best Cfu occurred in formulation with isolates 231 and 341 formulated using Diatomaceous Earth, while the highest Cfu was observed in formulation with isolate 334 formulated with either liquid paraffin or whey. After 2 months, the highest Cfu occurred in formulation with isolates 231, 341, and, 334 formulated using liquid paraffin. This study provides encouraging data for the development of potential biopesticides formulated with different carrier materials against desert locusts.

The miRNA-mRNA modules enhance juvenile hormone biosynthesis for insect vitellogenesis and egg production.

In addition to preventing precocious larval metamorphosis, juvenile hormone (JH), synthesized in corpora allata (CA), is known to stimulate female reproduction of insects. JH titer is extremely low or absent during metamorphosis, but thereafter rapidly increases in the previtellogenic stage and rises to a peak in the vitellogenic phase. However, the mechanisms underlying the biosynthesis of high levels of JH in adults remain unclear. We found in this study that 12 genes involved in JH synthesis pathway were highly expressed in the CA of adult locusts. By transcriptome analysis and quantitative real-time - polymerase chain reaction validation, a total of 106 evolutionary conserved micro RNAs (miRNAs) and 163 species-specific miRNAs were identified in locust CA. Dual-luciferase assay revealed that 17 miRNAs bound to 10 JH synthesis genes (JHSGs) and downregulated their expression. These miRNAs were expressed in low levels during vitellogenic stage, which was oppositive from that of targeting JHSGs. Six miRNAs including miR-971-3p, miR-31a, miR-9-5p, miR-1-3p, miR-315, and miR-282 were selected for function study. Co-application of agomiRs resulted in significantly decreased levels of targeting JHSGs, accompanied by significantly reduced vitellogenin expression as well as arrested ovarian development. The data suggest that multiple miRNAs expressed synchronously at low levels in the vitellogenic phase, thereby ensuring the high levels of JHSG expression to facilitate JH biosynthesis required for JH-dependent female reproduction. The findings provide important information for deciphering miRNA-messenger RNA modules for JH biosynthesis as well as JH regulation of insect metamorphosis and reproduction.

Transcriptome-based analysis reveals chromatin remodeling in post-adult eclosion reconstruction of the insect fat body

The insect fat body is comparable to the liver and adipose tissue in vertebrates, and plays a pivotal role in energy metabolism, nutrient storage, and reproduction. During metamorphosis, the fat body is disassembled via programmed cell death and cell dissociation. After adult eclosion, the fat body is reconstructed either by repopulation from the remaining juvenile fat body cells or by differentiation from adult progenitor cells. This reconstruction is a prerequisite for initiating the extensive synthesis of vitellogenin (Vg), which is necessary for the maturation of eggs. Despite its significance, the underlying mechanisms of this reconstruction remain inadequately understood. Transcriptome analysis of the fat bodies from migratory locusts at 0-5 days post adult emergence revealed 79 genes associated with chromatin remodeling. Weighted gene co-expression network analysis indicated a positive correlation between chromatin remodeling and fat body reconstitution. Protein-protein interaction analysis revealed that brahma, which encodes the catalytic subunit of the SWI/SNF chromatin remodeling complex, is crucial for post-adult-eclosion fat body development. qRT-PCR analysis demonstrated that the levels of brahma mRNA in the fat body are progressively increased during the previtellogenic stage, then reach the peak and remain elevated in the vitellogenic phase. Furthermore, brahma is expressed in response to gonadotropic juvenile hormone (JH). Knockdown of brahma led to a marked reduction in Vg expression within the fat body, along with arrested ovarian growth. These findings shed light on the involvement of brahma-mediated chromatin remodeling in JH-stimulated fat body reconstruction and reproduction of adult female locusts.

Comparative analysis of nutritional quality and color properties of flours derived from Locusta migratoria at different developmental stages.

This study was conducted to determine the variation in the chemical composition of flours derived from Locusta migratoria at two distinct developmental stages: the fourth instar and adult stages. Adult locust flour exhibited approximately two times higher fat content, similar protein content, ash content, CHNS elemental composition, and 45.7% lower total phenolic content compared to fourth instar locust flour. The flour from the adult locust was lighter, more red, and yellow than the fourth instar locust flour. Nineteen fatty acids were detected in both flours, with oleic acid, palmitic acid, and linoleic acid being the major ones. The ΣPUFA/ΣSFA of fourth instar and adult locusts was 0.82 and 0.78, respectively. The ratio of ω-6/ω-3 fatty acids was 2.1 for the fourth instar locust flour and 1.7 for the adult locust flour. Apart from gamma-aminobutyric acid (GABA), similar amino acids were found in both the flours. However, significant differences were detected in the levels of some of these amino acids between the fourth instar and adult locust flours. Of particular interest, adult locust flour showcased a GABA content of 25.4 mg/100 g dry weight, making it a valuable alternative protein source in developing innovative and nutritious food products.

The mechanical properties of different cross-veins in the hind wing of locust Locusta migratoria under uniaxial tensile and stress relaxation tests.

Locust Locusta migratoria exhibits remarkable aerial performances, relying predominantly on its hind wings that generate most of lift and thrust for flight. The mechanical properties of the cross-veins determine the deformation of the hind wing, which greatly affect the aerodynamic performance of flapping flight. However, whether the mechanical behaviours of the locust cross-veins change with loading rate is still unknown. In this study, cross-veins in four physiological regions (anterior-medial, anterior-lateral, posterior-medial and posterior-lateral) of the hind wing from adult locusts were investigated using uniaxial tensile test, stress relaxation test and fluorescence microscopy. It was found that the cross-veins were a type of viscoelastic material (including rate-independent elastic modulus and obvious stress relaxation). The cross-veins in the two anterior regions of the hind wing had significantly higher elastic moduli and higher ultimate tensile stress than those of its two posterior regions. This difference might be attributed to different resilin distribution patterns in the cross-veins. These findings furnish new insights into the mechanical characteristics of the locust cross-veins, which might deepen our understanding of the aerodynamic mechanisms of locust flapping flight.

Adipokinetic hormone signaling regulates adult dehydration resistance in the migratory locust

Drought events have become more severe under climate change, and this can pose a major threat to the survival of various organisms. The molecular mechanisms involved in dehydration resistance are not well known. Here, adults of the migratory locust, Locusta migratoria, were subjected to food-mediated dehydration, and adipokinetic hormone (AKH) signaling was found to play a key role in regulating dehydration resistance. Specifically, dehydration shortened the lifespan, increased the body weight loss, and reduced the water loss rate in adult locusts. Global transcriptome profiles revealed variations in tissue-specific gene expression between dehydration-resistant locusts and normal locusts. Importantly, dehydration selection and exposure induced prominent expression of AKH genes in the retrocerebral complex of adult locusts. Furthermore, individual knockdown of AKH1, AKH2, or AKH receptor (AKHR) accelerated water loss and shortened the lifespan of adult locusts under dehydration conditions, and trehalose supplementation ameliorated the negative effects caused by interference with AKH or AKHR. These findings demonstrated that AKH/AKHR signaling-dependent trehalose metabolism plays a crucial role in regulating locust dehydration resistance and thus provide novel insights into the regulatory mechanism underlying drought resistance.

Characterisation of the myosin light chain kinase (MLCK) gene of Locusta migratoria and the encoded MLCK.

Myosin light chain kinase (MLCK) is a dedicated kinase of myosin regulatory light chain (RLC), playing an essential role in the regulation of muscle contraction and cell motility. Much of the knowledge about MLCK comes from the study of vertebrate MLCK, and little is known about insect MLCK. Here, we identified the single MLCK gene in the locust Locusta migratoria, which spans over 1400 kb, includes 62 exons and accounts for at least five transcripts. We found that the five distinct transcripts of the locust MLCK gene are expressed in a tissue-specific manner, including three muscle-specific isoforms and two generic isoforms. To characterise the kinase activity of locust MLCK, we recombinantly expressed LmMLCK-G, the smallest locust MLCK isoform, in insect Sf9 cells. We demonstrated that LmMLCK-G is a Ca2+/calmodulin-dependent kinase that specifically phosphorylates serine 50 of locust muscle myosin RLC (LmRLC). Additionally, we found that almost all LmRLC molecules in the flight muscle and the hindleg muscles of adult locusts are phosphorylated.

Olfactory system structure and function in newly hatched and adult locusts

An important question in neuroscience is how sensory systems change as animals grow and interact with the environment. Exploring sensory systems in animals as they develop can reveal how networks of neurons process information as the neurons themselves grow and the needs of the animal change. Here we compared the structure and function of peripheral parts of the olfactory pathway in newly hatched and adult locusts. We found that populations of olfactory sensory neurons (OSNs) in hatchlings and adults responded with similar tunings to a panel of odors. The morphologies of local neurons (LNs) and projection neurons (PNs) in the antennal lobes (ALs) were very similar in both age groups, though they were smaller in hatchlings, they were proportional to overall brain size. The odor evoked responses of LNs and PNs were also very similar in both age groups, characterized by complex patterns of activity including oscillatory synchronization. Notably, in hatchlings, spontaneous and odor-evoked firing rates of PNs were lower, and LFP oscillations were lower in frequency, than in the adult. Hatchlings have smaller antennae with fewer OSNs; removing antennal segments from adults also reduced LFP oscillation frequency. Thus, consistent with earlier computational models, the developmental increase in frequency is due to increasing intensity of input to the oscillation circuitry. Overall, our results show that locusts hatch with a fully formed olfactory system that structurally and functionally matches that of the adult, despite its small size and lack of prior experience with olfactory stimuli.

Comparison of the Virulence of Space Mutants of Aspergillus oryzae XJ-1 against Adult Locusta migratoria

Biological control methods provide a sustainable approach for reducing agricultural losses caused by locust plagues. Space mutagenesis can generate high numbers of mutations using satellites and spacecrafts, including beneficial and stable mutants. Aspergillus oryzae XJ-1 was recently reported to show high virulence against locusts. We subjected this fungal pathogen to space mutagenesis to obtain more effective strains. Pathogen conidia powder was mutated in the China Space Station for 6 months. We obtained five mutants of A. oryzae XJ-1, TQ201, TQ238, TQ302, TQ549, and TQ555, and all mutants were identified as A. oryzae by molecular techniques. TQ549 showed the highest virulence against adult L. migratoria (LT50: 4.97 ± 0.21 days); the LT50 of A. oryzae XJ-1 was 5.67 ± 0.06 days. Both TQ549 and A. oryzae XJ-1 grew most rapidly at 33 °C on potato dextrose agar (PDA) plates. There was no significant difference in the growth rate of TQ549 and A. oryzae XJ-1 at 24 °C. The colony morphological characteristics of the five mutants on PDA plates differed from that of A. oryzae XJ-1. The space mutant TQ549, which showed high virulence against adult locusts, could be used as a biological control agent for the control of locust infestations.

Towards early response to desert locust swarming in eastern Africa by estimating timing of hatching

Desert locust (Schistocerca gregaria) plagues threaten agricultural production, food security and the environment across Africa, the Middle East, and Southwest Asia. Control methods targeting adult desert locusts present significant challenges and financial costs. Recognizing this, we developed a ground-breaking fuzzy set Mamdani type inference model that provides an innovative solution for early warning alerts. The model aids in predicting the juvenile stages of locust development, thereby preventing wide-scale locust swarming and mitigating its extensive damages and socioeconomic costs. The novelty of our approach lies in our unique application of environmental variables relevant for locust breeding to estimate the timing and location of desert locust hatching. Additionally, we improved the algorithmic handling of these variables, with localized desert locust bands data used as a proxy for hatching timing with a temporal offset of 35 days. The model's boundary conditions were determined using a training area in Sudan, where comprehensive ground data was available. This rule set was subsequently applied to Turkana County in Kenya, a data-scarce region, demonstrating the model's applicability and success in different contexts. The model's accuracy, assessed by data from the Sudan training site, demonstrated a remarkable score of 82% for true predictions. Furthermore, the model correctly identified the months of highest hatching probabilities in Turkana during 2020, demonstrating its real-world effectiveness and practical value. A correlation analysis affirmed that hatching was associated with increases in chlorophyll levels and precipitation accumulations. Our study marks a significant advancement in predicting the timing of hatching using fuzzy logic in data-scarce environments. By operationalizing more targeted early responses to desert locust infestations, our model facilitates more effective locust control. This study stands as an important contribution to locust management strategies, with substantial implications for agricultural production and food security in affected regions.

Eco-friendly postharvest irradiation strategy with 131I isotope for environmental management of populations of migratory locust, Locusta migratoria

Purpose Irradiation of food is promising for control of pests to minimize postharvest losses of yields and thus improvement of food safety, shelf life of produce. It is a method of choice that induces a series of lethal biochemical and molecular changes culminating into the engagement of a downstream cascade to cause abnormalities in irradiated pests. In this study, the effects of iodine-131 (131I) isotope radiation on the male gonad development of the migratory locust, Locusta migratoria, were evaluated. Materials and methods Newly emerged adult male locusts, less than one-day-old, were divided into two groups, control and irradiated. Locusts in the control group (n = 20 insects) didn’t drink irradiated water and were reared under normal environmental conditions for one week. Locusts in the irradiated group (n = 20 insects) were exposed to irradiated water at a dose of 30 mCi and they were subsequently observed until they drank the whole quantity. Results At the end of the experiment, scanning and electron microscopic examination of testes obtained from irradiated locusts revealed several major abnormalities, including malformed nuclei of spermatozoa, irregular plasma membranes, shrinkage of testicular follicles, vacuolated cytoplasm, disintegrated nebenkern and agglutinations of spermatids. Flow cytometry analysis revealed that 131I radiation induced both early and late apoptosis, but not necrosis, in testicular tissues. Testes of irradiated insects also exhibited a burst in reactive oxygen species (ROS), as indicated by significant elevation in amounts of malondialdehyde (MDA), a marker for peroxidation of lipids. In contrast, irradiation coincided with significant reductions in activities of enzymatic antioxidant biomarkers. Relative to controls, a three-fold upregulation of expression of mRNA of heat shock protein, Hsp90, was observed in testicular tissue of irradiated locusts. 131I-irradiated insects exhibited genotoxicity, as indicated by significant increases in various indicators of DNA damage by the comet assay, including tail length (7.80 ± 0.80 µm; p < .01), olive tail moment (40.37 ± 8.08; p < .01) and tail DNA intensity % (5.1 ± 0.51; p < .01), in testicular cells compared to the controls. Conclusion This is the first report on elucidation of I131-irradiation-mediated histopathological, biochemical and molecular mechanisms in gonads of male L. migratoria. Herein, the findings underscore the utility of 131I radiation as an eco-friendly postharvest strategy for management of insect pests and in particular for control of populations of L. migratoria.

Virulence of the fungal pathogen, Aspergillus oryzae XJ-1 in adult locusts (Orthoptera: Acrididae) in both laboratory and field trials.

Locusts and grasshoppers are pests of many agricultural crops, and their frequent outbreaks worldwide threaten food security. Microbial control agents are currently used to suppress the early (nymphal) stages of pests, but they are often less effective against adults, which are primarily responsible for locust plagues. The fungal pathogen Aspergillus oryzae XJ-1 has high pathogenicity in locust nymphs. To assess its potential for controlling locust adults, we evaluated the virulence of A. oryzae XJ-1 (i.e., locust Aspergillus, LAsp) in locust adults using laboratory, field-cage experiments, and a field trial. The lethal concentration of LAsp in adult Locusta migratoria was 3.58±0.09×105 conidia/ml 15 days after inoculation in the laboratory. A field-cage experiment showed that the mortalities of adult L. migratoria were 92.0±4.6% and 90.1±3.2% 15 days after inoculation with 3×105 and 3×103 conidia/m2 of LAsp, respectively. A large-scale field trial of 666.6 ha was conducted, in which a LAsp water suspension was applied at a concentration of 2×108 conidia/ml in 15 L/ha by aerial spraying via drones. The densities of mixed populations of L. migratoria and Epacromius spp. were significantly reduced by 85.4±7.9%-94.9±5.1%. In addition, the infection rates of surviving locusts collected from the treated plots were 79.6% and 78.3% on the 17th and 31st day after treatment, respectively. These results indicate that A. oryzae XJ-1 is highly virulent in adult locusts and that it has high potential for the control of locusts.

RNAi-mediated CrebA silencing inhibits reproduction and immunity in Locusta migratoria manilensis

Locusta migratoria manilensis is a major agricultural pest that causes severe direct and indirect damage to several crops. Thus, to provide a theoretical foundation for pest control, the role of CrebA in the reproduction and immune regulation of L. migratoria was investigated. CrebA is a bZIP transcription factor that critically regulates intracellular protein secretion. In this study, CrebA was widely expressed in the brain, fat body, integument, midgut, and reproductive tissues of different maturity stages of adult locusts, especially in the female fat body. RNA interfering (RNAi)-mediated silencing of CrebA inhibited locusts ovarian development, and key reproduction gene expressions, Vgs, VgRs, Chico, and JHAMT were downregulated. After the locusts were injected with Micrococcus luteus or Escherichia coli, M. luteus activated lysozyme expression, while the E. coli activated both phenol oxidase cascade and lysozyme expression. Furthermore, both bacteria stimulated the upregulation of the antimicrobial peptide genes DEF3 and DEF4. However, CrebA silencing is fatal to locusts infection with E. coli, with a mortality rate of up to 96.3%, and resulted in a significant decrease in the expression of DEF3 and DEF4 and changes in the activities of phenol oxidase and lysozyme of locusts infected by bacteria. Collectively, CrebA may be involved in diverse biological processes, including reproduction and immunity. CrebA inhibited locusts reproduction by regulating JH signaling pathway and inhibits the expression of immune genes TLR6, IMD, and AMPs. These results demonstrate CrebA seems to play a crucial role in reproduction and innate immunity.

Effect of entomopathogenic nematodes Steinernema species (steinernematidae: rhabditida) and Heterorhabditis bacteriophora (heterorhabditidae: rhabditida) on the digestive enzymes and midgut histology of the African migratory locust Locusta migratoria migratorioides (acrididae: orthoptera)

In some governorates of Egypt, the African migratory locust L. migratoria migratorioides is in a gregarious phase. Swarm development was successfully prevented by biological control agents. In this work, the two entomopathogenic nematode species, Steinernema sp. (SII)and Heterorhabditis bacteriophora (HP88) were investigated as natural enemies against the fifth nymph and adult African locusts at various concentrations (300, 600, 900, 1200, and 1500 Infected juveniles/100 g. soil). To ascertain fatal activity at 25 °C, the nematode-inoculated sand method was used. The two nematode species were semi-field administered against fifth nymphs and adult stages at (25 ± 2 °C) and 55–60% relative humidity with concentrations (3000, 6000, 9000, 12000, and 15000 Infected juveniles/kg. soil). Protease, amylase, invertase, and trehalase levels in the digestive enzymes of both fifth nymphs and adults fed with LC50 of both nematodes significantly decreased, but lipase and chitinase levels significantly increased. Adult locusts treated with the LC50 of S. sp. SII had basophilic epithelial cells, severe lumen hemorrhage, and highly aberrant proliferating cytoplasm, whereas the LC50 of H. bacteriophora HP88 displayed necrosis in an epithelial cell with vacuoles, loss of nucleus, and loss of goblet cells.

Fungal-Based Biopesticide Formulations to Control Nymphs and Adults of the Desert Locust, Schistocerca gregaria Forskål (Orthoptera: Acrididae): A Laboratory and Field Cage Study

This is the first field study in which we have tested the efficacy of four different entomopathogenic fungal (EPF) formulations together in single study—i.e., Green Muscle, Green Guard, Metarhizium anisopliae, and an isolate of Beauveria bassiana (isolate WG-11)—against nymphs and adults of the desert locust, Schistocerca gregaria Forskål (Orthoptera: Acrididae). We conducted several different studies: (a) lethal bioassay against the 3rd, 5th, and adult stages under laboratory conditions; (b) sublethal effects on the reproduction, diet consumption, fecal production, and weight gain; (c) a greenhouse trial; and (d) a field cage trial. Under laboratory conditions, all EPF formulations caused significant mortality, and the highest efficacy was observed with Green Muscle, followed by Green Guard, B. bassiana, and M. anisopliae. Susceptibility was found to be greatest in 3rd-instar nymphs, followed by 5th instars, and then adults. Along with lethal effects, sublethal doses of EPF reduced the number of egg pods per female, total eggs per pod, and egg hatching, while extending nymphal developmental time and reducing adult longevity; again, Green Muscle performed better. Sublethal doses not only retarded reproduction, but also caused behavioral changes, including reductions in food consumption, fecal production, and weight gain. All EPF formulations not only produced significant mortality in laboratory conditions, but also performed very well under the greenhouse and field conditions. The maximum mortality against 3rd-instar (81.7% and 74.0%), 5th-instar (73.3% and 65.1%), and adult locusts (67.5% and 58.9%) was observed when using Green Muscle under greenhouse and field trials, respectively. The current study showed that all of the EPF formulations have the potential to reduce pest populations, and could be used in the integrated pest management program.

DEAD-Box RNA Helicase DDX47 Maintains Midgut Homeostasis in Locusta migratoria.

Tissue homeostasis is critical for maintaining organ shape, size, and function. The condition is regulated by the balance between the generation of new cells and the loss of senescent cells, and it involves many factors and mechanisms. The midgut, an important part of the intestinal tract, is responsible for digestion and nutrient absorption in insects. LmDDX47, the ortholog of DEAD-box helicase 47 from Locusta migratoria, is indispensable for sustaining a normal midgut in the nymphs. However, the underlying cellular and molecular mechanisms remain to be elucidated. In this study, LmDDX47 knockdown resulted in atrophy of the midgut and gastric cecum in both nymph and adult locusts. After LmDDX47 knockdown, the number of regenerative and columnar cells in the midgut was significantly reduced, and cell death was induced in columnar tissue. LmDDX47 was localized to the nucleolus; this was consistent with the reduction in 18S rRNA synthesis in the LmDDX47 knockdown group. In addition, the acetylation and crotonylation levels of midgut proteins were significantly increased. Therefore, LmDDX47 could be a key regulator of midgut homeostasis, regulating 18S rRNA synthesis as well as protein acetylation and crotonylation in the migratory locust.

Replication protein A is required for juvenile hormone-dependent vitellogenesis and oocyte maturation in locusts

Aside from inhibiting insect metamorphosis, juvenile hormone (JH) has a well-known role in stimulating various aspects of insect reproduction. Replication protein A (RPA), a heterotrimeric complex comprised of RPA1, RPA2 and RPA3 subunits plays an essential role in DNA replication and DNA repair. Here we report that RPAs are highly expressed in the fat body of adult female locust, Locusta migratoria. While RPA1 is upregulated by the JH receptor Methoprene-tolerant (Met), RPA2 and RPA3 expression appears to be primarily controlled by Forkhead box O transcription factor (FoxO). Knockdown of RPA1, RPA2 or RPA3 results in markedly reducd vitellogenin (Vg) expression in the fat body, accompanied by arrested ovarian growth and inhibited oocyte maturation. In addition, depletion of an RPA subunit leads to increased expression of other RPA subunits as well as a pro-apoptotic gene, Smac that is involved in DNA repair and apoptosis. The data indicate a crucial role of RPAs in JH-dependent vitellogenesis and oocyte maturation.

Humoral immunity of the adult desert locust, Schistocerca gregaria developed following bacterial infection

The haemolymph plasma of adult desert locust, Schistocerca gregaria was analyzed in order to detect the induction of antibacterial activity following injection with a sublethal dose of Bacillus thuringiensis israelensis (Bti). A slight activity was demonstrated in the normal locust plasma, while a significant increase of this activity was appeared in both control and immune plasma, when tested by the agar-disk diffusion method. The maximum activity was attained after 24 h post-injection. Analysis of proteins by SDS polyacrylamide gel electrophoresis showed disappearance of some protein bands and appearance of other new ones in the injected adult locusts. Some of these new proteins may affect adult immunity. The phenoloxidase (PO) activity was significantly higher at 6 and 12 h after injection with Bti, but at 24 and 48 h, the activity was significantly lower than that of the controls. However, no significant changes in lysozyme activity were detected at all time intervals post-injection compared with the control insects.

NO Synthesis in Immune-Challenged Locust Hemocytes and Potential Signaling to the CNS.

Simple SummaryInsects, in the same way as vertebrates, are exposed to a broad variety of pathogens but lack their adaptive immune system. Relying on their innate immune system, they respond to pathogens by phagocytosis, melanization, and the synthesis of antimicrobial or cytotoxic compounds. In this study, we evaluated the production of the cytotoxic gaseous radical nitric oxide (NO) in hemocytes, the immune cells of the model insect Locusta migratoria in response to various immune stimuli. Both sessile and circulating hemocytes responded to gram-negative Escherichia coli and gram-positive Streptococcus suis injection with a strong increase in NO production. In contrast, the gram-positive bacterium Staphylococcus aureus elicited only a minor response. In addition, bacteria were encapsulated by hemocytes. Since NO is an important neurotransmitter, NO-producing hemocytes were tested on the locust central nervous system (CNS) in an embryo culture model. CNS neurons responded with a distinct increase in production of the second messenger, cGMP. This is indicative of the influence of the immune response on the CNS. Our findings show that NO production in hemocytes and capsule formation need complex stimuli and contribute to the understanding of neuroimmune interactions in insects.Similar to vertebrates, insects are exposed to a broad variety of pathogens. The innate insect immune system provides several response mechanisms such as phagocytosis, melanization, and the synthesis of antimicrobial or cytotoxic compounds. The cytotoxic nitric oxide (NO), which is also a neurotransmitter, is involved in the response to bacterial infections in various insects but has rarely been shown to be actually produced in hemocytes. We quantified the NO production in hemocytes of Locusta migratoria challenged with diverse immune stimuli by immunolabeling the by-product of NO synthesis, citrulline. Whereas in untreated adult locusts less than 5% of circulating hemocytes were citrulline-positive, the proportion rose to over 40% after 24 hours post injection of heat-inactivated bacteria. Hemocytes surrounded and melanized bacteria in locust nymphs by forming capsules. Such sessile hemocytes also produced NO. As in other insect species, activated hemocytes were found dorsally, close to the heart. In addition, we frequently observed citrulline-positive hemocytes and capsules near the ventral nerve cord. Neurites in the CNS of sterile locust embryos responded with elevation of the second messenger cGMP after contact with purified adult NO-producing hemocytes as revealed by immunofluorescence. We suggest that hemocytes can mediate a response in the CNS of an infected animal via the NO/cGMP signaling pathway.

Extraction of lipids from insect powders using a one-step organic solvent extraction process

The extraction efficiency, fatty acid profiles (FAP) and classes of lipids separated from insect powders by a one-step process were studied. Hexane (H), chloroform (C), methyl-tert-butyl ether (MTBE), and 3:2 hexane-isopropanol (HI) were used as extraction solvents and results were compared to 2:1 chloroform-methanol (CM). A 1:10 sample:solvent was mixed and centrifuged to separate the lipid layer which was then filtered and dried. Extraction was best (P<0.05) using CM as the solvent for adult cricket and locust; however, MTBE had the greatest efficiency (P<0.05) for silkworm pupae. The lipid classes extracted from silkworm were most like the initial powder (p>0.05), regardless of solvent. H and MTBE extracted lipid classes like (P>0.05) the initial cricket and locust, respectively. The FAP for cricket lipid was like the initial (P>0.05) when CM was used; however, the FAPs of locust and silkworm lipid were most like the initial powders (P>0.05) when MTBE and C were used as the solvent, respectively.