Dastarcus helophoroides (Fairmaire) (Coleoptera: Bothrideridae) is an effective ectoparasitoid of pine sawyer beetle Monochamus alternatus Hope (Coleoptera: Cerambycidae) which is the major median insect for transmission of pine wood nematode, Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle (Aphelenchida: Parasitaphelenchidae). A sensitive and acute olfactory system is extremely essential for newly hatched larva of D. helophoroides to forage for a host. Therefore, we established the transcriptome of newly hatched D. helophoroides larvae and characterized the expression profiles of olfactory genes. We identified 20 transcripts encoding putative odorant binding proteins (OBPs), 11 putative chemosensory proteins (CSPs), 9 putative odorant receptors (ORs), 11 putative ionotropic receptors (IRs), 7 putative gustatory receptors (GRs) and 4 putative sensory neuron membrane proteins (SNMPs) olfactory genes from the transcriptome of newly hatched D. helophoroides larvae. According to the phylogenetic analysis, 3 OBPs (DhelOBP6, DhelOBP14 and DhelOBP19), 1 CSP (DhelCSP11), 1 OR (DhelOrco1), 3 IRs (DhelIR3, DhelIR6 and DhelIR8), 3 GRs (DhelGR2, DhelGR4 and DhelGR5) and 2 SNMPs (DhelSNMP1 and DhelSNMP3) had high similarities with reported Coleopteran species. The highest expressed olfactory gene was DhelCSP3, followed by DhelOBP8 and DhelCSP2. The expression levels of the majority of OR, IR, GR and SNMP genes were low. These results indicate that CSPs and OBPs may play important roles in the olfactory recognition process in newly hatched D. helophoroides larvae. The findings from the present study are helpful in unraveling the profound mystery between D. helophoroides and M. alternatus, as well as improving the parasitism efficiency of D. helophoroides larvae.

The pine sawyer beetle, Monochamus alternatus Hope, is a devastating wood borer of several species of pine trees, and the main transmitting vector of the pine wood nematode, Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle (Aphelenchida: Parasitaphelenchidae). To explore new techniques for prevention and control of this destructive beetle, a novel gene vacuolar ATPase subunit H (V-ATPase H) was chosen as RNA interference (RNAi) target gene. Relative expression of V-ATPase H in different tissues and silencing efficiency in an in vitro RNAi experiment was assayed by using reverse transcription–quantitative polymerase chain reaction. The results indicated that the mRNA abundance of V-ATPase H in the gut was significantly higher than that in fat body, residual body, and hemolymph. Double-stranded RNA (dsRNA) targeting V-ATPase H was able to silence the expression of target gene effectively at 24 h posttreatment. Expression of immunity-related genes was examined after treatment with dsRNA targeting V-ATPase H, and transcript levels were compared with the control. The results showed that RNAi suppression of V-ATPase H inhibited the expression of immunity-related genes. This is the first demonstration of an in vitro RNAi experiment in any insect hemolymph that provides a novel environment for evaluating RNAi in insects, as well as shows potential for developing RNAi-mediated strategy for the control of M. alternatus.