Study of egg laying pattern and hatching line formation of Culicoides peregrinus Kieffer and C. oxystoma Kieffer (Diptera, Ceratopogonidae), vector of bluetongue virus

Abstract

Gravid Culicoides females play an effective role in the propagation of the midge population which is ultimately associated with the outbreak of the disease. The high abundance of the vectors Culicoides peregrinus Kieffer and C. oxystoma Kieffer (Diptera, Ceratopogonidae) has been recorded in West Bengal, followed by C. fulvus Sen and Das Gupta, C. innoxius Sen and Das Gupta and C. anophelis Edwards. The habitat of these vector species was reported from semi-aquatic muddy areas mixed with dung, but the species-specific micro-habitat remains unknown. The gravid females influenced by various cues like physicochemical parameter of habitat (i.e., pH, salinity, bacterial influence) to assess suitable oviposition site to optimize survival of progeny. To avoid competition, gravid female can express different oviposition strategies. The study focused on the timing and differences in egg laying pattern with initiation of hatching line in both species in laboratory condition. Oviposited eggs and the hatched eggs were examined by scanning electron microscope (SEM) to observe the changes in exochorion. The results revealed that both species showed crepuscular oviposition activity but C. peregrinus laid eggs in cluster and C. oxystoma oviposited singly. The arrangement of ansulae on egg surface and hatching pattern of eggs in both species was different. The egg laying and hatching pattern seems to be species specific which may be used as taxonomic marker.