Wolbachia successfully replicate in a newly established horn fly, Haematobia irritans irritans (L.) (Diptera: Muscidae) cell line

BACKGROUND Haematobia spp., horn flies (HF) and buffalo flies (BF), are economically important ectoparasites of dairy and beef cattle. Control of these flies relies mainly on the treatment of cattle with chemical insecticides. However, the development of resistance to commonly used compounds is compromising the effectiveness of these treatments and alternative methods of control are required. Wolbachia are maternally transmitted endosymbiotic bacteria of arthropods that cause various reproductive distortions and fitness effects, making them a potential candidate for use in the biological control of pests. RESULTS Here we report the successful establishment of a continuous HF cell line (HIE-18) from embryonic cells and its stable transinfection with Wolbachia strain w AlbB native to mosquitoes, and w Mel and w MelPop native to Drosophila melanogaster . The established HIE-18 cells are typically round and diploid with ten chromosomes (2n = 10) or tetraploid with 20 chromosomes (4n=20) having a doubling time of 67.2 hours. Wolbachia density decreased significantly in the HIE-18 cells in the first 48 hours of infection, possibly due to overexpression of antimicrobial peptides through the Imd immune signalling pathway. However, density recovered after this time and stably Wolbachia -infected HIE-18 cell lines have now all been subcultured more than 50 times as persistently infected lines. CONCLUSION The amenability of HF to infection with different strains of Wolbachia suggests the potential for use of Wolbachia in novel approaches for the control of Haematobia spp. Further, the availability of the HIE-18 cell line will provide an important resource for the study of genetics, host-parasite interactions and chemical resistance in Haematobia populations.