Influence of pre-existing eggs and larval rearing water on ovipositional responses of Culicoides peregrinus Kieffer and Culicoides oxystoma Kieffer (Diptera: Ceratopogonidae), vectors of bluetongue virus.

内容摘要

Oviposition site selection by gravid females depends on the interaction of a complex array of chemical and physical factors. This study aimed to investigate ovipositional responses of two vector species, Culicoides peregrinus Kieffer (Diptera: Ceratopogonidae) and Culicoides oxystoma Kieffer, when exposed to conspecific and heterospecific pre-existing eggs and larval-rearing water. We performed both choice and no-choice-based assays to detect their oviposition responses. In these experiments, females of both species laid a higher number of eggs in response to conspecific pre-existing eggs and larval rearing water than heterospecific. The following choice-based assay was conducted as follows: (i) in the presence of conspecific pre-existing eggs and larval rearing water, females of C. peregrinus oviposited 60.1% and 50.7%, whereas in the presence of heterospecific pre-existing eggs and larval rearing water, oviposited eggs were 59.6% and 48.2%, respectively (ii) in the presence of conspecific pre-existing eggs and larval rearing water, females of C. oxystoma oviposited 42.6% and 52.9%, whereas in the presence of heterospecific pre-existing eggs and larval rearing water, oviposited eggs were 41.6% and 37.3%, respectively. The no-choice-based assay was conducted as follows: (iii) in the presence of conspecific pre-existing eggs and larval rearing water, females of C. peregrinus oviposited 92.8% and 84.5%, whereas in the presence of heterospecific pre-existing eggs and larval rearing water, oviposited eggs were 82.0% and 75.9%, respectively (iv) in the presence of conspecific pre-existing eggs and larval rearing water, females of C. oxystoma oviposited 79.6% and 58.2%, whereas in the presence of heterospecific pre-existing eggs and larval rearing water, oviposited eggs were 78.4% and 46.3%, respectively. To determine a possible explanation, bacteria and semiochemicals from oviposited egg's surface area and larval-reared water were identified. Fourteen culturable bacteria isolated and identified by Sanger sequencing of 16S rRNA gene, of which 12 bacteria belong to the phylum Firmicutes and class Bacilli. The other two bacteria belong to the phylum Proteobacteria. Ten semiochemicals from the egg surface of both species were detected by GC-MS and HRMS. Semiochemicals like 3-methylbutanoic acid, skatole, indole and octanoic acid from C. peregrinus and dodecanoic acid from C. oxystoma were specifically identified. These semiochemicals may have a role on the selection of the oviposition site, and these can be utilised in the fabrication of a baited ovitrap. The bacterial communities and semiochemicals of the conspecific eggs influenced gravid females in selecting the suitability of the oviposition sites. This acquired information can guide the development of more effective management strategies to reduce the burden of vector-borne diseases.