Acta Entomologica Sinica

Insect symbionts: Research progresses and prospects

LUAN Jun-Bo, WANG Si-Bao

2023, 66(10): 1271-1281. doi:10.16380/j.kcxb.2023.10.001

Abstract ( 26 )

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Insect symbionts are microorganisms that establish enduring and sustained associations with insect hosts. These microorganisms inhabit the body surface, gut, hemocoel, or intracellular cells of insects, participating in the regulation of various physiological functions of their host insects. Research on insect-symbiont interactions involves multidisciplinary collaboration. In-depth exploration of the functions of insect symbionts and their interactions with hosts not only advances our understanding of fundamental mechanisms in the life sciences but also introduces innovative perspectives and methods for pest management, vector-borne disease control, and optimal utilization of beneficial insects. In recent years, Chinese researchers have made noteworthy progress in the insect microbiome and got significant achievements in many research directions. In this article, we provided an overview of the most recent research progress in insect symbionts, introduced the main contents of this special issue, and proposed three noteworthy research directions: (1) the functions of insect intracellular symbionts; (2) the mechanisms by which insects regulate the abundance and transmission of symbionts; and (3) genetic modification and application of insect symbionts.

Isolation and identification of actinomycete strain BYC-18 and its antimicrobial metabolites from the gut of Odontotermes formosanus (Isoptera: Termitidae)

YIN Cai-Ping, BAI Xue-Yan, Naeem ABBAS, SUN Lu-Lu, YIN Xin-Ran, ZHANG Ying-Lao

2023, 66(10): 1282-1288. doi:10.16380/j.kcxb.2023.10.002

Abstract ( 22 )

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【Aim】To determine the antimicrobial activities of the fermentation products of actinomycetes from the gut of Odontotermes formosanus and analyze their antimicrobial components, so as to find novel antimicrobial lead compounds.【Methods】 The gut actinomycetes of O. formosanus were isolated by spread plate method. The antimicrobial activities of the fermentation broth extracts against four pathogens (Staphylococcus aureus, Escherichia coli, Bacillus subtilis and Candida albicans) were tested by the Oxford cup method, and the active strain BYC-18 was screened. The taxonomic status of BYC-18 was determined according to its morphological features and 16S rRNA sequence analysis. The antimicrobial activities of different polar solvent extracts of BYC-18 fermentation solution were determined by filter paper method. Active compounds were isolated and purified from ethyl acetate crude extract by various chromatographic methods, and the chemical structure of the isolated compound was identified by mass spectrometry and nuclear magnetic resonance spectroscopy. The antimicrobial activities of the isolated compound were determined by filter paper method and minimum inhibitory concentration method. 【Results】 BYC-18 was identified as a strain of Streptomyces sp. The fermentation broth of BYC-18 had antimicrobial activities against all the four pathogens, and its ethyl acetate extract had an obvious inhibitory effect on S. aureus, with an inhibition zone diameter of 11.1 mm. A monomer compound BYC-18-1 was isolated from the ethyl acetate extract and identified as β-rubromycin. The antimicrobial activity test showed that β-rubromycin had a strong inhibitory effect on S. aureus at the test concentration of 30 μg/6 mm filter paper, and its inhibition zone diameter was 13.2 mm, which was close to that of the positive gentamicin sulfate (inhibition zone diameter: 16.6 mm). 【Conclusion】The Streptomyces strain BYC-18 has the potential to be developed as a new bactericide.

Effects of introduction of Bacillus spp. on the microbiota and growth and development of the brown planthopper, Nilaparvata lugens (Hemiptera: Delphacidae)

WANG Wei-Xia, ZHU Ting-Heng, LAI Feng-Xiang, WEI Qi, WAN Pin-Jun, HE Jia-Chun, FU Qiang

2023, 66(10): 1289-1301. doi:10.16380/j.kcxb.2023.10.003

Abstract ( 16 )

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【Aim】To identify the species of culturable symbiotic bacteria in the brown planthopper, Nilaparvata lugens, explore the effects of the symbiotic Bacillus spp. on the microbiota and growth and development of N. lugens. 【Methods】 The culturable symbiotic bacteria were isolated from two different virulent populations of N. lugens (the susceptible population TN1 and the virulent population IR56) by in vitro culture. The obtained cuttural symbiotic bacteria were identified by 16S rDNA sequencing technology. On this basis, the distribution of symbiotic bacteria in N. lugens was studied by in situ hybridization. The effects of reducing symbionts and supplementation of Bacillus spp. on the growth and development of N. lugens, as well as the abundance of symbionts, were studied using artificial diet added with antibiotics or symbiotic Bacillus spp. The effects of introducing symbiotic Bacillus spp. through feeding and microinjection methods were compared, and the correlation between Bacillus spp. colonization and the virulence of TN1 population was investigated. 【Results】 In total 15 strains of different symbiotic bacteria were obtained from N. lugens by in vitro culture, including 2 strains of the symbiotic Bacillus spp. (BPH-S36 and BPH-S33) from the highly virulent population IR56. The result of in situ hybridization showed that symbiotic bacteria were distributed in the salivary glands, gut, fat body and female internal genitalia of N. lugens, but rarely in the male internal genitalia. Symbionts are crucial for the growth and development of N. lugens. The reduction of symbiotic bacteria led to a significant decrease in the survival rate of N. lugens on the 3rd and 6th day, while supplementing the symbiotic Bacillus BPH-S33 or BPH-S36 resulted in a significant increase in the survival rate of N. lugens on the 6th day. The relative abundance of Bacillus spp.in N. lugens increased by 23.2-24.5-fold by feeding on the artificial diet supplemented with the symbiotic Bacillus spp., but not increased through microinjection into nymphs. With the increase of the symbiotic Bacillus spp., the relative abundance of yeast-like symbiont (YLS) also significantly increased by 5-12-fold. Introduction of Bacillus strain BPH-S36 significantly increased the survival rate of N. lugens TN1 population on the resistant rice IR56 from 52.1%±1.5% to 64.2%±3.0%. 【Conclusion】Symbiotic bacteria are widely distributed in the salivary glands, gut and ovaries of N. lugens. Antibiotic treatment can significantly reduce the abundance of symbiotic bacteria in their bodies and result in a decline in survival rate. The exogenous symbiotic bacteria colonize successfully in N. lugens through artificial feeding. Bacillus strain BPH-S36 derived from the IR56 population can improve the population virulence to the resistant rice variety IR56.
Key words: Nilaparvata lugens; symbiotic bacteria; yeast-like symbiont; virulence; Bacillus spp.; adundance

Vitellogenin determines the abundance of the symbiotic bacterium Rickettsia in Bemisia tabaci (Hemiptera: Aleyrodidae) by regulating autophagy

SUN Xiang, LIU Bing-Qi, CHEN Zhan-Bo, LI Huan, LI Chu-Qiao, HONG Ji-Sheng, LUAN Jun-Bo

2023, 66(10): 1302-1310. doi:10.16380/j.kcxb.2023.10.004

Abstract ( 14 )

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【Aim】 To explore the molecular mechanism by which vitellogenin (Vg) regulates the abundance of the symbiotic bacterium Rickettsia in Bemisia tabaci. 【Methods】 Female adult of B. tabaci MEAM1 was microinjected with dsRNA to conduct RNAi of BtVg, the expression levels of BtVg and the autophagy gene BtAtg8 in the female adult were detected by qRT-PCR, the mortality rate of female adults was recorded, and the abundance of Rickettsia in the female adult was quantified by qPCR. The localization and expression of BtVg and BtAtg8 in ovarioles and the abundance of Rickettsia in the ovarioles and midguts of the female adult were examined by immunofluorescence microscopy. After the autophagy induction by feeding the female adult of B. tabaci MEAM1 with the artificial diet containing rapamycin (10 μmol/L), the expression and localization of BtAtg8 in ovarioles were investigated by immunofluorescence microscopy and the abundance of Rickettsia in ovaries was detected by qPCR. 【Results】 The expression levels of BtVg and BtAtg8 in the female adult of B. tabaci MEAM1 were significantly decreased and significantly increased, respectively, the mortality rate of female adults of B. tabaci MEAM1 was significantly increased, the abundance of Rickettsia in the female adult of B. tabaci MEAM1 was significantly decreased, the expression levels of BtVg and BtAtg8 in ovarioles were obviously decreased and obviously increased, respectively, and the abundance of Rickettsia in the ovarioles and midgut obviously decreased at 3 d after microinjection of dsBtVg compared to the control (microinjected with dsGFP). The expression level of BtAtg8 in the ovarioles of the female adult of B. tabaci MEAM1 was increased significantly at 5 d after feeding with the artificial diet containing rapamycin (10 μmol/L), and the abundance of Rickettsia in the ovarioles of the female adult of B. tabaci MEAM1 was significantly decreased at 3 and 5 d after feeding with the artificial diet containing rapamycin (10 μmol/L) compared with the control fed with the artificial diet containing DMSO. 【Conclusion】 These results suggest that BtVg can protect Rickettsia from degradation by autophagy, and demonstrate the role of BtVg in regulating the abundance of Rickettsia in B. tabaci.

Effects of the symbiont Serratia symbiotica on the development and reproduction of the pea aphid, Acyrthosiphon pisum (Hemiptera: Aphididae)

LI Yue-Ming, ZHANG Yong-Dong, GONG Hou-Yan, LÜ Zhi-Qiang

2023, 66(10): 1311-1318. doi:10.16380/j.kcxb.2023.10.005

Abstract ( 16 )

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【Aim】 To clarify the effects of antibiotics on the obligate symbiont in the pea aphid, Acyrthosiphon pisum and investigate the impacts of the symbiont Serratia symbiotica on the growth, development and reproduction of A. pisum. 【Methods】 The type of facultative symbionts in adults of the green morph of A. pisum used in this study was detected by diagnostic PCR. The facultative symbionts were removed by injecting and feeding antibiotics to establish A. pisum line without facultative symbionts. The copy numbers of specific gene fragment of the obligate symbiont Buchnera aphidicola in A. pisum adults with and without S. symbiotica were determined by quantitative PCR. The body weight, rates of ecdysis, mortality rates and fecundity of A. pisum with and without S. symbiotica were recorded. 【Results】The A. pisum adults used in this study harbored only one facultative symbiont, S. symbiotica. The facultative S. symbiotica in A. pisum adults could be removed by injecting antibiotics, while the injection of antibiotics had no effect on the content of the obligate symbiont B. aphidicola. Compared with S. symbiotica-harboring A. pisum adults, S. symbiotica-removed A. pisum adults gained weight very slowly, and had less than one-third of the weight of S. symbiotica-harboring A. pisum adults at 9 d after birth. S. symbiotica-removed A. pisum adults had longer 1st instar nymphal duration, higher mortality rate and fewer offspring produced by per adult. 【Conclusion】The laboratory green A. pisum line carries the symbiont S. symbiotica. The removal of the symbiont S. symbiotica from A. pisum does not affect the content of the obligate symbiont B. aphidicola but has a negative effect on the growth, development and reproduction of A. pisum.

Effects of carrying Bursaphelenchus xylophilus on the bacteria in the gut and trachea of adult Monochamus alternatus (Coleoptera: Cerambycidae)

GU Yu-Tong, ZHU Hao-Cheng, CHANG Yue, ZHOU Jiao, FAN Jian-Ting, ZHAO Li-Lin

2023, 66(10): 1319-1328. doi:10.16380/j.kcxb.2023.11.006

Abstract ( 13 )

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【Aim】 To investigate the effects of Bursaphelenchus xylophilus in Monochamus alternatus on the bacteria in the gut and trachea of M. alternatus.【Methods】The whole gut and trachea were isolated from the collected M. alternatus adults carrying B. xylophilus in the field to extract DNA for sequencing and splicing of the 16S rDNA gene. The composition, structure, abundance and diversity of bacteria in the gut and trachea of M. alternatus adults carrying B. xylophilus were analyzed by bioinformatics methods. 【Results】A total of 15 phyla, 26 classes, 66 orders, 110 families, 201 genera, 296 species and 444 operational taxonomic units (OTUs) of bacterial flora in the gut and trachea of M. alternatus adults carrying B. xylophilus were detected. There was no significant change in the dominant bacterial flora in the gut between M. alternatus adults carrying B. xylophilus and M. alternatus adults without carrying B. xylophilus, and their dominant bacterial flora were Proteobacteria and Enterobacterales. Proteobacteria and Enterobacterales were the dominant bacterial flora in the trachea of M. alternatus adults carrying B. xylophilus, while Firmicutes and Lactobacillales were the dominant bacterial flora in the trachea of M. alternatus adults without carrying B. xylophilus. The diversity and abundance of bacteria in the trachea of M. alternatus adults carrying B. xylophilus were higher than those of M. alternatus adults without carrying B. xylophilus, and the bacterial community structure in the trachea of M. alternatus adults carrying B. xylophilus was significantly different from that of M. alternatus adults without carrying B. xylophilus. Serratia and Enterobacter were enriched in the gut and trachea of M. alternatus adults carrying B. xylophilus. 【Conclusion】The introduction of B. xylophilus has significant effects on the composition, structure, abundance and diversity of bacterial flora in the trachea of M. alternatus adults. Serratia and Enterobacter in the trachea of M. alternatus adults may be closely related to the B. xylophilus-M. alternatus complex. The increase of Serratia in the trachea of M. alternatus adults carrying B. xylophilus may be associated with the suppressed tracheal immunity of M. alternatus. This study provides a theoretical basis for the study of bacterial diversity in the gut and trachea of M. alternatus, and a new direction for the prevention and control of B. xylophilus.

Community composition and functional gene annotation of the symbiotic microbes in Ips nitidus (Coleoptera: Scolytinae)

LIU Cai-Xia, LI Gang, LIANG Ling-Yu, HAN Fu-Zhong, WANG Zheng, WANG Hui-Min, LÜ Quan

2023, 66(10): 1329-1342. doi:10.16380/j.kcxb.2023.11.007

Abstract ( 12 )

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【Aim】To reveal the community composition and functional characteristics of the symbiotic microbes in Ips nitidus. 【Methods】Metagenomics and correlation network analysis were conducted on the symbiotic fungi and bacteria in the gut and other tissues of I. nitidus from Maixiu Nature Reserve in Qinghai Province, Northwest China to compare the community composition of the symbiotic fungi and bacteria in the gut and other tissues of I. nitidus, to analyze the interrelationships of the microbial communities and to annotate the functional genes of the symbiotic microbes by non-redundant protein sequence alignment method. 【Results】A total of 3 520 species of symbiotic microbes were found in the gut and other tissues of I. nitidus. Fungi and bacteria possessed the highest numbers of species (accounting for 23.21% and 69.01% of all species, respectively), with the average relative abundance of 9.69% and 13.79%, respectively. For fungal symbionts, Erysiphales showed higher relative abundance and species diversity in other tissues than in the gut, and Saccharomycetales showed lower relative abundance and species diversity in other tissues than in the gut. Ophiostomatoid fungi in other tissues showed higher species diversity than those in the gut (16 species of 6 genera, and 13 species of 5 genera, respectively). The average relative abundance of ophiostomatoid fungi in other tissues and gut occupied 0.016% and 0.013%, respectively. The relative abundance and species diversity of Enterobacterales in other tissues were higher than those in the gut. Enterobacter, Erysiphe, Rhizophagus and Wolbachia were the core genera in the gut and other tissues. Some communities of fungi and bacteria showed opposite interrelationships in the gut and other tissues, suggesting that there may be complex interactions between the symbionts in I. nitidus. A total of 7 010 and 6 483 functional genes were identified from symbiotic fungi and bacteria, respectively. The number of functional genes related to xenobiotics biodegradation and metabolism in bacteria was higher than that in fungi. However, 11 pathways such as mRNA surveillance pathway, propanoate metabolism, ubiquitin-mediated proteolysis and so on had more significant differential genes in the gut than in other tissues. The annotation results for functional genes related to limonene degradation and sterol synthesis showed that bacteria may degrade limonene significantly compared with fungi, but fungi may play a more crucial role in promoting sterol biosynthesis than bacteria. A total of 74 functional genes of ophiostomatoid fungi are mainly involved in oxidative phosphorylation, metabolic pathway and amino acid metabolism. Moreover, ophiostomatoid fungi were of higher diversity in other tissues and mainly distributed in Ophiostoma, etc. 【Conclusion】There are some differences in the community composition, diversity and function of the symbiotic microbes in the gut and other tissues of I. nitidus. Enterobacter, Erysiphe, Rhizophagus and Wolbachia are the most important core flora, and they might play an important role in the community assembly.

Isolation and identification of Pantoea agglomerans PxG45 from Plutella xylostella (Lepidoptera: Plutellidae) gut and its antifungal activities

FU Dong-Ran, XU Xiao-Xia, FENG Shu-Jie, JIN Feng-Liang

2023, 66(10): 1343-1353. doi:10.16380/j.kcxb.2023.10.008

Abstract ( 14 )

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【Aim】 Gut symbiotic bacteria in insects, the main members of the gut microbial community, play important roles in the growth and development, nutrient absorption, and immune system of insects. In this study, a gut symbiotic bacterium of Plutella xylostella was isolated and cultured, and its function was identified to explore the influence of the gut symbiotic bacteria on the adaptability of P. xylostella and the broad-spectrum inhibitory activities against fungi. 【Methods】 The gut bacterium, PxG45, was isolated and purified from the 3rd instar larva of P. xylostella by plate culture in vitro. Morphological characterization, 16S rDNA gene sequencing, and physiological and biochemical characterization were used to identify the bacterial species. The effects of PxG45 on the survival rate of the 3rd instar larva of P. xylostella and the effects of the Beauveria bassiana infection on the survival rate of the 3rd instar larva of P. xylostella were detected by bioassay. The inhibition of PxG45 on B. bassiana was defined by plate confrontation method to further detect the broad-spectrum resistance of PxG45 to the plant pathogenic fungi Colletotrichum higginsianum, C. camelliae, Fusarium oxysporum f. sp. cubense race 4, Alternaria solani, Magnaporthe oryzae and Pseudomonas syringae pv. myricae. 【Results】 PxG45 in the gut of the 3rd instar larva of P. xylostella was identified as Pantoea agglomerans. Compared with the control group which was not fed with PxG45, supplemental PxG45 not only significantly increased the survival rate of the healthy 3rd instar larva of P. xylostella, but also improved the survival rate of the 3rd instar larva infected by B. bassiana. The colonial diameters of B. bassiana and six plant pathogenic fungi in antagonistic culture with PxG45 were significantly smaller than those cultured alone of B. bassiana and six plant pathogenic fungi, and the growth of fungi was inhibited after antagonistic culture with PxG45. 【Conclusion】 PxG45 affects the adaptability of P. xylostella by direct and broad-spectrum antibacterial effects, and can significantly inhibit the growth of plant pathogenic fungi. This study demonstrates that PxG45 possesses the potential as a biocontrol bacterium and provides a new way to use the gut symbionts of pest.
Key words: Plutella xylostella; Pantoea agglomerans PxG45; improved survival rate; antifungal activity

Degradation regulation of chlortetracycline residue by the black soldier fly, Hermetia illucens (Diptera: Stratiomyidae)

WANG Hui, ZHENG Chao-Zhong, CHEN Yu-Liang, WANG Fei, WANG Lei-Yu, ZHANG Qi-Hui, HUANG Jun-Kui, ZHAO Jun-Cheng

2023, 66(10): 1354-1361. doi:10.16380/j.kcxb.2023.10.009

Abstract ( 12 )

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【Aim】 To clarify the degradation regulation of chlortetracycline residue by the black soldier fly, Hermetia illucens. 【Methods】 The eggs of H. illucens collected on the same day were cultured to the 3-day-old larvae, then transferred to the mixed diets of wheat bran and chlortetracycline residue in different mass ratios (wheat bran∶chlortetracycline residue=1∶0, 1∶1, 2∶1, 5∶1, 10∶1 and 20∶1), and the body length and body weight of different day-old larvae were measured, meanwhile, the degradation rate of chlortetracycline by different day-old larvae were calculated based on the chlortetracycline contents in H. illucens larvae and diet residues.【Results】 The content of chlortetracycline residue in the mixed diets exhibited significant effects on the biological characteristics such as body length and body weight of H. illucens larvae, and the degradation rate of chlortetracycline by different day-old larvae of H. illucens. The body length and body weight of H. illucens larvae reared with the mixed diets of wheat bran and chlortetracycline residue in different mass ratios were increased with the day-old age of larvae until 11-day-old, and then decreased at the 13-day-old larval stage. The body length and body weight of H. illucens larvae reared with the mixed diets of wheat bran and chlortetracycline residue in the mass ratios of 5∶1, 10∶1 and 20∶1 were bigger than those of the control group cultured with the pure wheat bran. The initial content of chlortetracycline had a significant effect on the degradation rate of chlortetracycline by different day-old larvae of H. illucens through the comparison of degradation rates of chlortetracycline by different day-old larvae of H. illucens reared with the mixed diets of wheat bran and chlortetracycline residue in different mass ratios. The degradation rates of chlortetracycline by the 7-, 9-, 11- and 13-day-old larvae reared with the mixed diets of wheat bran and chlortetracycline residue in the mass ratio of 5∶1 were 39.21%, 68.94%, 66.53% and 68.26%, respectively, significantly higher than those by the larvae reared with the mixed diets of wheat bran and chlortetracycline residue in the mass ratios of 10∶1 and 20∶1.【Conclusion】 H. illucens is able to reduce the content of chlortetracycline residue, and the initial content of chlortetracycline in diets has a significant effect on the biological characteristics of H. illucens and degradation rate of chlortetracycline.

Effects of adding glucose to foods on the development and gut bacterial community structure of Drosophila suzukii (Diptera: Drosophilidae)

GAO Huan-Huan, ZHAO Meng, LIU Li, LONG Shi-Ying, ZHANG An-Sheng, ZHOU Xian-Hong, ZHUANG Qian-Ying

2023, 66(10): 1362-1373. doi:10.16380/j.kcxb.2023.10.010

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【Aim】 To clarify the effects of adding glucose to foods on the development and gut bacterial community structure of Drosophila suzukii, and select the gut bacteria related to glycometabolism of D. suzulii. 【Methods】 After being fed with the artificial diets added with different concentrations of glucose (0, 5% and 10%), the growth and development of axenic (gut microbiota-free) and conventionally reared strains of D. suzukii, and the changes in the glucose content were observed, and the diversity of gut bacteria of conventionally reared D. suzukii adults was analyzed by PacBio sequencing platform. 【Results】 In the 5% glucose treatment group, the larval survival rate and adult eclosion rate of conventionally reared D. suzukii increased by 60.44% and 123.79%, respectively, and in the 10% glucose treatment group, the larval survival rate of conventionally reared D. suzukii increased by 87.87%, as compared to those in the control group. However, the development of axenic D. suzukii was not significantly affected by the addition of glucose. Axenic D. suzukii adults could not utilize glucose, leading to their higher glucose content than conventionally reared adults. The diversity analysis of gut bacteria revealed that Gluconobacter and Acetobacter were the dominant genera of gut bacteria in conventionally reared D. suzukii adults. Glucose added in foods significantly increased the diversity indexes of gut bacteria and the abundance of Acetobacter, Providencia and Morganella. The dominant species in the gut of conventionally reared D. suzukii adults were L. lactis, G. frateurii, A. thailandicus and P. alcalifaciens, and their relative abundance in D. suzukii adults exposed to different concentrations of glucose was significantly different. 【Conclusion】 Axenic D. suzukii can not utilize glucose directly. Gut bacteria (mainly Acetobacter) can promote the utilization of glucose in D. suzukii. These results provide an important basis for studying the mechanism of gut bacteria involved in nutritional metabolism in D. suzukii.

Effects of pure water culture on the diversity and potential function of bacterial communities in the larval gut of Propsilocerus akamusi (Diptera: Chironomidae) in heavy metal polluted areas

MA Wei-Wei, XU Hai-Xuan, CAO Wei, YAN Chun-Cai, SUN Ze-Yang

2023, 66(10): 1374-1384. doi:10.16380/j.kcxb.2023.10.011

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【Aim】To understand the effects of habitat changes on the bacterial communities in the larval gut of chironomids by studying the diversity and potential function of bacterial communities in the gut of Propsilocerus akamusi, a pollution-resistant chironomid identified in the freshwater area of the heavy metal polluted Bohai Bay of Tianjin City. 【Methods】The 4th instar larvae of P. akamusi identified in the freshwater area of the heavy metal polluted Bohai Bay of Tianjin City were raised with distilled water in laboratory for 7 d as the laboratory-cultured group, and the bacterial genomic DNA in the 4th instar larval gut of P. akamusi from the laboratory-cultured group and the wild-captured group was extracted. The high-throughput sequencing of the V3-V4 region of 16S rRNA gene was carried out, and the sequencing results were subjected to data quality control, sequence alignment and filtering, the changes in the species composition of gut bacterial communities were analyzed and the potential functions of gut bacteria were predicted. 【Results】Based on the 16S rRNA sequencing results of the gut bacteria in the 4th instar larvae of P. akamusi, 11 phyla, 13 classes, 33 orders, 54 families, 71 genera, 90 species and 105 operational taxonomic units (OTUs) were annotated. The diversity and abundance of bacterial communities in the 4th instar larval gut of P. akamusi in the laboratory-cultured group were lower than those in the wild-captured group. The dominant bacterial phyla in the 4th instar larval gut of the two groups were similar, including Firmicutes, Proteobacteria, Bacteroidota and Desulfobacterota. The abundance of Proteobacteria in the 4th instar larval gut of the wild-captured group was significantly higher than that in the laboratory-cultured group. The average abundance of Aeromonas, Shewanella, Serratia, Pseudomonas and Yersinia in the 4th instar larval gut in the laboratory-cultured group was significantly lower than that in the wild-captured group. The results of linear discriminant analysis revealed that there were bacterial species with significantly different abundance in the 4th instar larval gut of P. akamusi between the wild-captured group and the laboratory-cultured group. The KEGG analysis results showed that the relative abundance of metabolism-related genes in the bacterial genome of the 4th instar larval gut of P. akamusi was extremely high. The relative abundance of genes related to environmental information processing and cellular processes in the gut bacterial genome of the 4th instar larva of P. akamusi in the laboratory-cultured group significantly decreased as compared to that in the wild-captured group.【Conclusion】The results of this study indicate that there are significant differences in the diversity of the gut bacterial communities and gene functions between P. akamusi larvae living in adverse field environments and those reared in laboratory pure water environments. This helps to study the individual resistance mechanisms of chironomids from an environmental perspective, provides a new idea for further exploring the mechanism of the symbiotic microorganisms in the gut of chironomid larvae to cope with environmental stress, and also lays a foundation for the study of the tolerance mechanism of insects in adverse environmental conditions and the regulatory mechanism of homeostasis of their gut microbial communities.

Intergenerational effects of the entomopathogen Beauveria bassiana on the mortality and parasitism of the ectoparasitoid Sclerodermus guani (Hymenoptera: Bethylidae)

WEI Yun, LI Li, ZHANG Meng-Meng, PAN Shu-Mei

2023, 66(10): 1385-1403. doi:10.16380/j.kcxb.2023.10.012

Abstract ( 8 )

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【Aim】 Based on the complex relationship of competition and parasitism between two parasitic natural enemies, Beauveria bassiana and Sclerodermus guani in natural microhabitats, the adaptive reproductive strategies of parasitoids under the stress of B. bassiana were investigated, and the lethal and parasitic effects of the parental parasitoid carrying B. bassiana on itself and its offspring were comprehensively evaluated. 【Methods】 After the female adults of the parent (F₄₈ generation) of S. guani were treated with the spore suspension of B. bassiana at different concentrations (1×10⁴, 1×10⁵ and 1×10⁶ conidia/mL) by the immersion method, and put into the test tubes containing the host Monochamus alternatus larvae, the mortality, cumulative mortality and corrected mortality, pre-oviposition period, oviposition period, total fecundity (total number of eggs laid) and number of eggs laid per female of the adults of the parent (F₄₈ generation), and the mean developmental duration, survival rates, body weight per female and proportion of males of the corresponding offspring (F₄₉ and F₅₀ generations) were tested, and the dose and time effects of B. bassiana on the female adults of F₄₈ and F₄₉generations during the lethal process were also determined by using the time-dose-mortality model (TDM). 【Results】 The pathogen load of S. guani female adults of the parent (F₄₈ generation) increased with increasing concentration of B. bassiana spore suspension, with the average initial pathogen load of about 0.91×10⁴, 1.73×10⁴ and 1.95×10⁴ conidia/female, respectively, under the concentrations of 1×10⁴, 1×10⁵ and 1×10⁶ conidia/mL. Subsequently, B. bassiana was passed from the female adults of the parent (F₄₈ generation) to the offspring (F₄₉ generation) of S. guani, with an average initial pathogen load of 0.78×10⁴, 1.40×10⁴ and 1.51×10⁴ conidia/female, respectively, under the concentrations of 1×10⁴, 1×10⁵ and 1×10⁶ conidia/mL. This phenomenon of carrying B. bassiana by S. guani (F₄₈ generation) not only affected the longevity and reproduction of the female adults of F₄₈ and F₄₉ generations of S. guani, but also affected the fitness of their corresponding offspring (F₄₉ and F₅₀ generations). Compared with the control (non-inoculation with B. bassiana), the stress of different concentrations of B. bassiana spore suspension resulted in a series of significant changes in the performance of the female adults of the parent (F₄₈ generation) and the corresponding offspring (F₄₉ generation), including the mean pre-oviposition period was shortened (F₄₈: shortened by 1.03, 1.43 and 2.03 d, respectively; F₄₉: shorted by 0.30, 0.80 and 1.00 d, respectively), the mean oviposition period was extended (F₄₈: extended by 0.30, 1.00 and 1.30 d, respectively; F₄₉: extended by 0.43, 0.73 and 1.43 d, respectively), the total number of eggs laid increased (F₄₈: increased by 4.80, 17.16 and 10.33 grains, respectively; F₄₉: increased by 11.57, 25.04 and 9.14 grains), and the number of eggs laid per female decreased (F₄₈: decreased by 4.07, 7.06 and 15.98 grains, respectively; F₄₉: decreased by 5.30, 9.37 and 20.47 grains, respectively). Similarly, the fitness of the corresponding offspring (F₄₉ and F₅₀ generations) of S. guani showed the same change trend. Overall, due to the transmission of B. bassiana at different concentrations (1×10⁴, 1×10⁵ and 1×10⁶ conidia/mL) carried by the female adults of the parent (F₄₈ generation) of S. guani, the developmental process of its offspring (F₄₉ and F₅₀ generations) was obviously accelerated. After B. bassiana carried by the parent female adults of S. guani (F₄₈ generation) was passed to the offspring, the generation time of the F₅₀ generation was shortened by 3.00, 3.00 and 4.00 d, respectively, the survival rate and emergence rate of the F₅₀ generation were decreased by 16.21% and 19.40%, respectively, the body weight per female actually increased by 0.09 and 0.94 mg, respectively, and the proportion of male offspring significantly decreased by 1.95% and 0.22%, respectively, as compared to those in the control. The TDM model showed that after inoculation with a high concentration (1×10⁶ conidia/mL) of B. bassiana spore suspension, the female adults of the parent (F₄₈ generation) of S. guani reached 50.83% mortality at 20 d after inoculation, while their corresponding offspring (F₄₉ generation) reached 50.00% mortality at 18 d after emergence. The LT₅₀value of 1×10⁶ conidia/mL of B. bassiana spore suspension against the parent female adults of S. guani was 22.72 d, and that against the female adults of the F₄₉generation was 24.352 d. Simultaneously, under other concentrations (1×10⁴ and 1×10⁵ conidia/mL) of B. bassiana spore suspension, the mortality of the female adults of F₄₈ and F₄₉ generations was less than 40.00%. 【Conclusion】 In response to B. bassiana stress, the parent female adults of S. guani not only reduce their fertility, but also indirectly affect the survival and development of their offspring. The concentrations of B. bassiana carried by the parent female adults of S. guani have a direct effect on the cumulative mortality of themselves and the female adults of the offspring, which increase with the increase in the concentration of B. bassiana spore suspension and test time. The dose and time effects of B. bassiana on the lethal process of S. guani show a significant interactive relationship.

Regulatory mechanism of intestinal microbial homeostasis in insects

SONG Yang, FAN Lin-Lin, SHENTU Xu-Ping, YU Xiao-Ping

2023, 66(10): 1404-1414. doi:10.16380/j.kcxb.2023.10.013

Abstract ( 13 )

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A stable intestinal microbial internal environment is the result of the interaction between intestinal microbes and intestinal immune response. During the continuous feeding, the species and number of insect intestinal microbes constantly change, so a complex and dynamic homeostatic mechanism is formed between intestinal microbes and intestinal epithelial cells. Insect intestinal epithelial cells can sense beneficial and harmful conditions and use immunoregulatory pathways for dynamic regulation of microbial population homeostasis, such as the dual oxidase-reactive oxygen species (Duox-ROS) system and immunodeficiency (Imd) signaling pathways, which can sense the changes in the number of intestinal microbies and participate in the regulation of intestinal microbial homeostasis. In addition, the intestinal microbes can also indirectly play a role in homeostatic regulation by releasing corresponding effectors to regulate the behavior of the flora through quorum sensing (QS). Thus, in this article, we reviewed the roles of physical defense, immune signaling pathways and QS in the maintenance of insect intestinal microbial homeostasis, which will deepen the understanding of the interactions between intestinal tissues and intestinal microbes. In the future, we will continue to reveal the regulatory mechanisms of microbial homeostasis in more species of insects and the relationship between the regulatory mechanisms. In addition, new pesticides will be designed and developed to alter the homeostasis of intestinal microbes based on the regulatory mechanisms, which will provide new targets and ideas for the pest control.

Research progress in insect gut microbes and the methods for studying their functions

MA Ling, CAO Jing-Yu, BAI Jian-Yang, XU Zhe, LI Lu, ZHANG Yue, MIN Meng-Ru

2023, 66(10): 1415-1424. doi:10.16380/j.kcxb.2023.10.014

Abstract ( 12 )

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Insects are the most abundant and widespread group of animals in the world that harbor complex and diverse gut microbes. Different insects differ in gut structure, gut environment, edibility, age and external environment, and the composition and abundance of gut microbes also show difference. Insect gut microbes are mainly transferred vertically and horizontally between populations and individuals, and play a vital role in nutrient metabolism, physiological behaviour, defence, detoxification and many other functions in insect hosts. Insect gut microbes can be isolated from culture media by in vitro culture methods and rapidly identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and sequencing technologies such as 16S rRNA gene sequencing. The combination of metagenomics, proteomics, metabolomics and other omics technologies makes the identification and functional prediction of gut microbes more efficient. Microbial functions can be more accurately verified by in vitro experiments, microbial supplementation, microbiota transplantation and silencing of genes associated with microbial members. Sterile insects can be obtained by high temperature treatment, lysozyme treatment, sterile feeding and antibiotic treatment for functional verification experiments. However, the most widely used antibiotic method still has limitations in application. By exploiting the characteristics of gut microbes, genetic engineering of symbiotic bacteria can be used to control pests and insect-borne infectious diseases. At present, insect gut microbes play an important role in the fields of ecology, economy, energy and environmental protection. With the development and integration of new technologies, more insect-microbe interaction mechanisms will be revealed, and pest control methods through insect gut microbes will become more diverse, environmentally friendly and efficient.

Contents of Vol. 66 Issue 10

2023, 66(10): 1425-1425.

Abstract ( 10 )

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