Olfactory Proteins and Their Expression Profiles in the Eucalyptus Pest Endoclita signifier Larvae

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.

De Novo Transcriptome Identifies Olfactory Genes in Diachasmimorpha longicaudata (Ashmead)

Diachasmimoorpha longicaudata (Ashmead, D. longicaudata) (Hymenoptera: Braconidae) is a solitary species of parasitoid wasp and widely used in integrated pest management (IPM) programs as a biological control agent in order to suppress tephritid fruit flies of economic importance. Although many studies have investigated the behaviors in the detection of their hosts, little is known of the molecular information of their chemosensory system. We assembled the first transcriptome of D. longgicaudata using transcriptome sequencing and identified 162,621 unigenes for the Ashmead insects in response to fruit flies fed with different fruits (guava, mango, and carambola). We annotated these transcripts on both the gene and protein levels by aligning them to databases (e.g., NR, NT, KEGG, GO, PFAM, UniProt/SwissProt) and prediction software (e.g., SignalP, RNAMMER, TMHMM Sever). CPC2 and MIREAP were used to predict the potential noncoding RNAs and microRNAs, respectively. Based on these annotations, we found 43, 69, 60, 689, 26 and 14 transcripts encoding odorant-binding protein (OBP), chemosensory proteins (CSPs), gustatory receptor (GR), odorant receptor (OR), odorant ionotropic receptor (IR), and sensory neuron membrane protein (SNMP), respectively. Sequence analysis identified the conserved six Cys in OBP sequences and phylogenetic analysis further supported the identification of OBPs and CSPs. Furthermore, 9 OBPs, 13 CSPs, 3 GRs, 4IRs, 25 ORs, and 4 SNMPs were differentially expressed in the insects in response to fruit flies with different scents. These results support that the olfactory genes of the parasitoid wasps were specifically expressed in response to their hosts with different scents. Our findings improve our understanding of the behaviors of insects in the detection of their hosts on the molecular level. More importantly, it provides a valuable resource for D. longicaudata research and will benefit the IPM programs and other researchers in this filed.

A Subset of Odorant Receptors from the Desert Locust Schistocerca gregaria Is Co-Expressed with the Sensory Neuron Membrane Protein 1

In the desert locust Schistocerca gregaria (S. gregaria), pheromones are considered to be crucial for governing important behaviors and processes, including phase transition, reproduction, aggregation and swarm formation. The receptors mediating pheromone detection in olfactory sensory neurons (OSNs) on the antenna of S. gregaria are unknown. Since pheromone receptors in other insects belong to the odorant receptor (OR) family and are typically co-expressed with the “sensory neuron membrane protein 1” (SNMP1), in our search for putative pheromone receptors of S. gregaria, we have screened the OR repertoire for receptor types that are expressed in SNMP1-positive OSNs. Based on phylogenetic analyses, we categorized the 119 ORs of S. gregaria into three groups (I–III) and analyzed a substantial number of ORs for co-expression with SNMP1 by two-color fluorescence in situ hybridization. We have identified 33 ORs that were co-expressed with SNMP1. In fact, the majority of ORs from group I and II were found to be expressed in SNMP1-positive OSNs, but only very few receptors from group III, which comprises approximately 60% of all ORs from S. gregaria, were co-expressed with SNMP1. These findings indicate that numerous ORs from group I and II could be important for pheromone communication. Collectively, we have identified a broad range of candidate pheromone receptors in S. gregaria that are not randomly distributed throughout the OR family but rather segregate into phylogenetically distinct receptor clades.