Abstract
Endoclita signifier Walker (Lepidoptera: Hepialidae), a polyphagous insect, has become a new wood-boring pest in Eucalyptus plantations in southern China since 2007, which represents a typical example of native insect adaptation to an exotic host. After the third instar, larvae move from soil to standing trees and damage the plants with a wormhole. Although females disperse to lay eggs, larvae can accurately find eucalyptus in a mingled forest of eight species, which leads us to hypothesize that the larval olfactory system contributes to its host selection. Herein, we investigated the transcriptomes of the head and tegument of E. signifer larvae and explored the expression profiles of olfactory proteins. We identified 15 odorant-binding proteins (OBPs), including seven general OBPs (GOPBs), six chemosensory proteins (CSPs), two odorant receptors (ORs), one gustatory receptor (GR), 14 ionotropic receptors (IRs), and one sensory neuron membrane protein (SNMP). Expression profiles indicated that all olfactory proteins, except for EsigCSP1, were expressed in the head, and most were also detected in non-olfactory tissues, especially thorax tegument. Furthermore, EsigOBP2, EsigOBP8, EsigGOBP1, EsigGOBP2, EsigGOBP5, EsigCSP3, EsigCSP5, and EsigOR1 were expressed most strongly in the head; moreover, EsigCSP3 expressed abundantly in the head. EsigGR1 exhibited the highest expression among all tissues. Besides phylogenetic analysis shows that EsigGOBP7 probably is the pheromone-binding protein (PBP) of E. signifier. This study provides the molecular basis for future study of chemosensation in E. signifier larvae. EsigCSP3 and EsigGR1, which have unique expression patterns, might be factors that govern the host choice of larvae and worth further exploration.
Highlights
The ghost moth Endoclita signifer Walker (Lepidoptera, Hepialidae) is a native polyphagous insect pest that is widely distributed in Japan, Korea, India, Thailand, Myanmar, and central, south, and southwest China (Yang et al, 2021)
This study investigated the transcriptomes in the head and tegument of E. signifer larvae to determine the expression profiles of olfactory proteins in E. signifer larvae and evaluated the phylogenetic relationships between E. signifer odorant-binding proteins (OBPs) and chemosensory proteins (CSPs) with those expressed in the larvae and adults of other species
The number of olfactory proteins in E. signifier is considerably fewer than the 26 OBPs and 21 CSPs identified in the transcriptomes of H. armigera larval antennae and mouthparts (Chang et al, 2017); the 20 OBPs, 11 CSPs, 9 odorant receptors (ORs), 11 ionotropic receptors (IRs), 7 gustatory receptor (GR), and 4 sensory neuron membrane protein (SNMP) in the transcriptomes of newly hatched Dastarcushelophoroides larvae (Li et al, 2020); and the 58 ORs, 20 GRs, and 21 IRs in the transcriptomes of the antennae of males and females and the head tissue of neonates of Cydia pomonella (Walker et al, 2016)
Summary
The ghost moth Endoclita signifer Walker (Lepidoptera, Hepialidae) is a native polyphagous insect pest that is widely distributed in Japan, Korea, India, Thailand, Myanmar, and central, south, and southwest China (Yang et al, 2021). After Eucalyptus was planted in the south of China, E. signifer was discovered to have infested Eucalyptus in Guangxi in 2007. This is an example of a native insect adapting to an exotic host, and it has resulted in great economic losses and major ecological impacts (Yang et al, 2016). In 2020, an infestation of E. signifier was found in 17.1% of the counties in Guangxi, where host plants included 51 species in 40 genera and 30 families (Yang et al, 2021). We hypothesized that the thoracic and abdominal tegument may have an olfactory function and help larvae to find their host
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