The comparative metabolic response of Bactrocera dorsalis larvae to azadirachtin, pyriproxyfen and tebufenozide

Effects of the Insect Growth Regulators Azadirachtin, Pyriproxyfen, and Tebufenozide on the Fatty Acid Metabolome of Bactrocera Dorsalis Larvae

Insects' lipids, including fatty acids, as the second largest constituents in insects, play a variety of fundamental and vital functions. However, there is a lack of reports on the effects of insect growth regulators on fatty acid profiles and metabolic mechanisms. Therefore, in this study, a comparative study of three growth regulators, azadirachtin, pyriproxyfen, and tebufenozide, on fatty acids was carried out using a targeted metabolomics approach to fill this gap. The results showed that when exposed to azadirachtin, pyriproxyfen, and tebufenozide, there were 14, 17, and 11 differentially regulated fatty acids, respectively. The pathway of biosynthesis of unsaturated fatty acids was the common shared pathway, while fatty acid biosynthesis and linoleic acid metabolism were the specific pathways affected by the 3 insect growth regulators. Therefore, the results could be helpful to deepen the effects of azadirachtin and insect growth regulators on terrestrial insects.

Integrated mass spectrometry imaging and metabolomics reveals sublethal effects of indoxacarb on the red fire ant Solenopsis invicta

BACKGROUND

Indoxacarb, representing an efficient insecticide, is normally made into a bait to spread the poison among red fire ants so that it can be widely applied in the prevention and control of Solenopsis invicta. However, the potential toxicity mechanism of S. invicta in response to indoxacarb remains to be explored. In this study, we integrated mass spectrometry imaging (MSI) and untargeted metabolomics methods to reveal disturbed metabolic expression levels and spatial distribution within the whole-body tissue of S. invicta treated with indoxacarb.

RESULTS

Metabolomics results showed a significantly altered level of metabolites after indoxacarb treatment, such as carbohydrates, amino acids and pyrimidine and derivatives. Additionally, the spatial distribution and regulation of several crucial metabolites resulting from the metabolic pathway and lipids can be visualized using label-free MSI methods. Specifically, xylitol, aspartate, and uracil were distributed throughout the whole body of S. invicta, while sucrose-6'-phosphate and glycerol were mainly distributed in the abdomen of S. invicta, and thymine was distributed in the head and chest of S. invicta. Taken together, the integrated MSI and metabolomics results indicated that the toxicity mechanism of indoxacarb in S. invicta is closely associated with the disturbance in several key metabolic pathways, such as pyrimidine metabolism, aspartate metabolism, pentose and glucuronate interconversions, and inhibited energy synthesis.

CONCLUSION

Collectively, these findings provide a new perspective for the understanding of toxicity assessment between targeted organisms S. invicta and pesticides. © 2023 Society of Chemical Industry.

Mechanism of Rotenone Toxicity against Plutella xylostella: New Perspective from a Spatial Metabolomics and Lipidomics Study

The botanical pesticide rotenone can effectively control target pest Plutella xylostella, yet insights into in situ metabolic regulation of P. xylostella toward rotenone remain limited. Herein, we demonstrated metabolic expression levels and spatial distribution of rotenone-treated P. xylostella using spatial metabolomics and lipidomics. Specifically, rotenone significantly affected purine and amino acid metabolisms, indicating that adenosine monophosphate and inosine were distributed in the whole body of P. xylostella with elevated levels, while guanosine 5'-monophosphate and tryptophan were significantly downregulated. Spatial lipidomics results indicated that rotenone may significantly destroy glycerophospholipids in cell membranes of P. xylostella, inhibit fatty acid biosynthesis, and consume diacylglycerol to enhance fat oxidation. These findings revealed that high toxicity of rotenone toward P. xylostella may be ascribed to negative effects on energy production and amino acid synthesis and damage to cell membranes, providing guidelines for the toxicity mechanism of rotenone on target pests and rational development of botanical pesticide candidates.

Prior infection of Galleria mellonella with sublethal dose of Bt elicits immune priming responses but incurs metabolic changes

Invertebrate immune priming has attracted wide attention of biologists in recent years because it challenges core notions about the disparate nature of acquired and innate immunity. However, the metabolic switch and energetic cost during eliciting immune priming are poorly investigated issues, which could widen and deepen our understanding of the physiological mechanism of immune priming. In this study, using sublethal dose of Bacillus thuringiensis (Bt) as an elicitor, we detected typical immune priming responses in Galleria mellonella. We found that the intensity of immune priming is positively correlated with the levels of antimicrobial peptides and phagocytosis ability of hemocytes. Subsequently, we employed LC-MS/MS-based untargeted metabolomics techniques to analyze the metabolic changes in the fat body of G. mellonella larvae during immune priming. The results showed that there were 74 and 56 significantly altered metabolites in positive and negative ion mode, respectively, after Bt priming. Most of the differential metabolites were enriched in the following metabolic pathways: amino acid biosynthesis, carbon metabolism, aminoacyl-tRNA biosynthesis and ABC transporters. The energetic cost of immune priming was depicted mainly in the slow growth of body mass and decreased levels of sucrose, lactose, D-ribulose 1,5-bisphosphate, Glycerate-3P and isocitric acid, which are enriched in carbon metabolism and involved in energy production. Meanwhile, correlation and interaction network analysis showed negative correlations between carbohydrates and metabolites involved in amino acid biosynthesis, suggesting that amino acids acted as the main energy source and helped the organisms synthesize immune effectors to participate in the immune priming response. Our results pave the way for uncovering the physiological mechanism of insect immune priming and discovering novel targets for Bt insecticide.

Effects of camptothecin on histological structures and gene expression profiles of fat bodies in Spodoptera frugiperda

Spodoptera frugiperda is a serious threat to global food production. Our previous study demonstrated that Camptothecin (CPT), a bioactive secondary metabolite from Camptotheca acuminata (Decne: Nyssaceae), exhibits adverse impact on the larval midgut of S. frugiperda and inhibits insect growth. However, effects of CPT on fat bodies of S. frugiperda larvae have not been examined yet. In the present study, we found that histological structures of fat bodies of S. frugiperda larvae were damaged in insects treated with CPT. Comparative transcriptomic analyses among different fat body samples from controls and insects treated with 1.0 and 5.0 μg/g CPT were performed. A total of 4212 and 5044 differentially expressed genes (DEGs) were identified in the samples treated with 1.0 and 5.0 μg/g CPT, respectively. Our data indicated that the pathways of detoxification, immune response, fatty acids, chitin, and hormone biosynthesis in fat bodies were affected by CPT treatments based on DEGs. These results provided a comprehensive view of the damage and gene expression changes in fat bodies of S. frugiperda after CPT exposure, which shall be useful to reveal the mechanism of CPT toxicity against S. frugiperda in future.

Identification of azadirachtin responsive genes in Spodoptera frugiperda larvae based on RNA-seq

The fall armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae) is a polyphagous pest with 353 plant species as its hosts, including maize, sorghum, cotton, and rice. Azadirachtin is one of the most effective botanical insecticides. The effect of azadirachtin against S. frugiperda remains to be determined. Here we report strong growth inhibition of azadirachtin on S. frugiperda larvae under either 1.0 or 5.0 μg/g azadirachtin. To explore the relevant mechanisms, the larvae fed with normal artificial diet and with 1.0 μg/g azadirachtin exposure for 3 days were collected as samples for RNA-Seq. RNA-Seq on S. frugiperda larvae under different treatments identified a total of 24,153 unigenes, including 3494 novel genes, were identified. Among them, 1282 genes were affected by 1.0 μg/g azadirachtin exposure, with 672 up-regulated and 610 down-regulated. The impacted genes include 61 coding for detoxification enzymes (31 P450s, 7 GSTs, 11 CarEs, 7 UGTs and 5 ABC transporters), 31 for cuticle proteins, and several proteins involved in insect chitin and hormone biosynthesis. Our results indicated that azadirachtin could regulate the growth of S. frugiperda by affecting insect chitin and hormone biosynthesis pathway. The enhanced expression of detoxification enzymes might be related to detoxifying azadirachtin. These findings provided a foundation for further delineating the molecular mechanism of growth regulation induced by azadirachtin in S. frugiperda larvae.

Integrated LC-MS and GC-MS-based untargeted metabolomics studies of the effect of azadirachtin on Bactrocera dorsalis larvae

Azadirachtin exhibits excellent bioactivities against several hundred arthropods. However, current knowlege of its biochemical effect on B. dorsalis larvae is not deep enough. In this study, integrated LC-MS and GC-MS-based untargeted metabolomics were used to analyze the changes of endogenous metabolites and the biochemical effects of azadirachtin on B. dorsalis larvae. Azadirachtin has excellent bioactivities against B. dorsalis larvae in this study, leading to a longer developmental duration, lower survival rate, and low pupa weight. The effect of azadirachtin was investigated on a total of 22 and 13 differentially abundant metabolites in the LC-MS and GC-MS-based metabolomics results, are selected respectively. Pathway analysis indicated that 14 differentially enriched metabolic pathways, including seven influential pathways, are worthy of attention. Further integrated key metabolic pathway analysis showed that histidine metabolism, D-glutamine and D-glutamate metabolism, biotin metabolism, ascorbate and aldarate metabolism, pentose and glucuronate interconversions, and alanine, aspartate and glutamate metabolism in B. dorsalis larvae are significantly relevant pathways affected by azadirachtin. Although extrapolating the bioactivity results in this study to the practical project of B. dorsalis pest management in the field has limitations, it was found that azadirachtin has a significant effect on the primary metabolism of B. dorsalis larvae.