Characterization of Spodoptera litura Gut Bacteria and Their Role in Feeding and Growth of the Host

Abstract

Insect gut microbes play important roles in host feeding, digestion, immunity, growth and development. Spodoptera litura is an important agricultural pest distributed of global importance. In the present study, diversity and functions of the gut bacteria in S. litura are investigated based on the approaches of metagenomics and denaturing gradient gel electrophoresis (DGGE). The results showed that the gut bacterial diversity of S. litura reared on taro leaves or an artificial diet, were similar at the phylum level, as both were mainly composed of Proteobacteria, but differed significantly at the order level. Spodoptera litura reared on taro leaves (Sl-tar) had gut biota mainly comprised of Enterobacteriales and Lactobacillales, while those reared on artificial diet (Sl-art) predominantly contained Pseudomonadales and Enterobacteriales, suggesting that gut bacteria composition was closely related to the insect’s diet. We found that feeding and growth of S. litura were significantly reduced when individuals were treated with antibiotics, but could be both restored to a certain extent after reimporting gut bacteria, indicating that gut bacteria are important for feeding, digestion, and utilization of food in S. litura . Metagenomic sequencing of gut microbes revealed that the gut bacteria encode a large number of enzymes involved in digestion, detoxification, and nutrient supply, implying that the gut microbes may be essential for improving the efficiency of food utilization in S. litura .

A switch of microbial flora coupled with ontogenetic niche shift in Leptinotarsa decemlineata

“…In this study, we used a mixture of three antibiotics (ciprofloxacin, levofloxacin, and metronidazole) to remove the pupal bacteria according to the documented results in other insects (Campoli‐Richards et al, 1988; Löfmark et al, 2010; Xia et al, 2020), and to reduce soil bacteria by heating the soil sample. Our results displayed that soil sterilizing removed a major portion of bacteria in pupae.…”

“…In fact, insect bacteria possess the ability to quickly adapt to changes in food resources (Lü et al, 2019; Xu et al, 2020). For example, the strong correlations between symbiont communities and host plants or plant parts are revealed in hemipteran Acyrthosiphon pisum (Ferrari et al, 2012; Gauthier et al, 2015; Tsuchida et al, 2002), Aphis craccivora (Brady & White, 2013; Brady et al, 2014), Aphis gossypii (Najar‐Rodriguez et al, 2009), and Phylloxera notabilis (Medina et al, 2011), coleopteran L. decemlineata (Chung et al, 2017) and Henosepilachna vigintioctopunctata (Lü et al, 2019), dipteran B. tabaci (Santos‐Garcia et al, 2020), lepidopteran P. operculella (Zheng et al, 2020), and S. littoralis (Xia et al, 2020). In L. decemlineata , the same herbivory host plant (potato) and plant part (foliage) cause both larvae and adults to harbor similar bacteria, in contrast to the larvae and adults in H. erato (Hammer et al, 2014), B. dorsalis (Andongma et al, 2015), and Z. tau (Noman et al, 2021).…”

“…Conversely, some insects pupated in artificial substrates (i.e., in sterile sand) in a laboratory rather than in nature soil (Andongma et al, 2015;Malacrino et al, 2018;Noman et al, 2021), these insects did not acquire soil bacteria during ONS. As a result, the difference in bacterial flora between larvae and pupae of these insects (Andongma In this study, we used a mixture of three antibiotics (ciprofloxacin, levofloxacin, and metronidazole) to remove the pupal bacteria according to the documented results in other insects (Campoli-Richards et al, 1988;Löfmark et al, 2010;Xia et al, 2020), and to reduce soil bacteria by heating the soil sample. Our results displayed that soil sterilizing removed a major portion of bacteria in pupae.…”

“…To eliminate the bacteria in pupae, three antibiotics with different concentrations (1 mg/ml ciprofloxacin, 1 mg/ml levofloxacin, and 2 mg/ml metronidazole) were selected, according to the previous described method (Löfmark et al, 2010; Xia et al, 2020). The three antibiotics were mixed properly into sterile water, and then 1% Tween 20 was added.…”

“…For example, a higher microbial diversity associated with old larvae and pupae occurs in dipteran Zeugodacus tau (Noman et al, 2021), Ceratitis capitata (Malacrino et al, 2018), Bactrocera carambolae (Yong et al, 2017), Bactrocera dorsalis (Andongma et al, 2015), lepidopteran Heliconius erato (Hammer et al, 2014), and Spodoptera littoralis (Chen et al, 2016; Xia et al, 2020), hymenopteran Megalopta centralis and Megalopta genalis (Kwong & Moran, 2016; Mcfrederick et al, 2014). However, in a few above examples, such as those in lepidopterans and hymenopterans (Chen et al, 2016; Hammer et al, 2014; Kwong & Moran, 2016; Mcfrederick et al, 2014; Xia et al, 2020), no obvious ONS takes place during the larva–pupa transition. In other examples that perform ONS during metamorphosis, the wandering larvae are allowed to pupate in artificial substrates (i.e., in sterile sand) in a laboratory rather than in nature soil (Andongma et al, 2015; Malacrino et al, 2018; Noman et al, 2021).…”