Multi-Omics Reveals the Effect of Population Density on the Phenotype, Transcriptome and Metabolome of Mythimna separata

Abstract

Population-density-dependent polymorphism is important in the biology of some agricultural pests. The oriental armyworm (Mythimna separata) is a lepidopteran pest (family Noctuidae). As the population density increases, its body color becomes darker, and the insect eats more and causes greater damage to crops. The molecular mechanisms underlying this phase change are not fully clear. Here, we used transcriptomic and metabolomic methods to study the effect of population density on the differentiation of second-day sixth instar M. separata larvae. The transcriptomic analysis identified 1148 differentially expressed genes (DEGs) in gregarious-type (i.e., high-population-density) armyworms compared with solitary-type (low-population-density) armyworms; 481 and 667 genes were up- and downregulated, respectively. The metabolomic analysis identified 137 differentially accumulated metabolites (DAMs), including 59 upregulated and 78 downregulated. The analysis of DEGs and DAMs showed that activation of the insulin-like signaling pathway promotes the melanization of gregarious armyworms and accelerates the decomposition of saccharides, which promotes the gregarious type to take in more food. The gregarious type is more capable of digesting and absorbing proteins and decreases energy consumption by inhibiting transcription and translation processes. The phase change traits of the armyworm are thus attributable to plasticity of its energy metabolism. These data broaden our understanding of the molecular mechanisms of insect-density-dependent polymorphism.

The diverse roles of insulin signaling in insect behavior

“…Future studies could investigate the mechanistic bases of this species-level variation, in terms of how both internal state and external information modulate IIS and cause behavioral change. Insects present some particularly interesting and economically relevant contexts where IIS is essential to feeding behavior, including grasshopper ( Oedaleus asiaticus ) plague activity resulting from sub-optimal diets ( 141 ) or changes in feeding behavior due to crowding in armyworms ( Mythimna separata 142 ). Examining IIS activation, including ILP production and modes of action in the brain across diverse taxa is critical to understanding the evolution of IIS and may also highlight new tools for pest control.…”

Gene expression responses to environmental cues shed light on components of the migratory syndrome in butterflies

“…High density during early developmental stages, for example, can lead to a predominant investment in migration, likely as a strategy to disperse from areas where competition with conspecifics is high. The desert locust (Schistocerca gregaria) is a notable example of this phenomenon, exhibiting a density-dependent phase polyphenism that triggers a transition from a benign, solitary phase to a more gregarious, highly migratory phase (12,28,29). In Lepidoptera, density-dependent migration has also been observed in the fall armyworm Spodoptera frugiperda; (30), and larval density has been associated with outbreaks in the agricultural pest, beet webworm (Loxostege sticticalis (20)).…”

The Maize Caterpillar Mythimna (= Leucania) loreyi (Duponchel, 1827) (Lepidoptera: Noctuidae): Identification, Distribution, Population Density and Damage in Tunisia

“…Also, these authors pointed out that changes in population densities and outbreaks of insects are mainly affected by biotic and abiotic constraints. Furthermore, Wang et al [25] showed that increases in population density of M. separata caused greater damage to crops. Similarly, these authors demonstrated that study of insect densities could extend our knowledge of the agricultural pest's biology and assist to develop appropriate management strategies.…”