Morgan, J. A. T. | bioRxiv Science

bioRxiv2019

Transinfection of buffalo flies (Haematobia exigua) with Wolbachia and effect on host biology

A widespread insect endosymbiont Wolbachia is currently of much interest for use in novel strategies for the control of insect pests and blocking transmission of insect-vectored diseases. Wolbachia-induced effects can vary from beneficial to detrimental depending on host biology and the genetic background of the infecting strains. As a first step towards investigating the potential of Wolbachia for use in the biocontrol of buffalo flies (BF), embryos, pupae, and adult female BF were injected with three different Wolbachia strains (wAlbB, wMel and wMelPop). BF eggs were not easily injected because of their tough outer chorion and embryos were frequently damaged resulting in less than 1% hatch rate of microinjected eggs. No Wolbachia infection was recorded in flies successfully reared from injected eggs. Adult and pupal injection gave a much higher survival rate and resulted in somatic infection and germinal tissue infection in surviving flies with transmission to the succeeding generations on a number of occasions. Investigations of infection dynamics in flies from injected pupae confirmed that Wolbachia were increasing in numbers in BF somatic tissues and ovarian infections were confirmed with wMel and wMelPop in some instances, though not with wAlbB. Measurement of fitness traits indicated reduced longevity, decreased and delayed adult emergence, and reduced fecundity in Wolbachia-infected flies in comparison to mock-injected flies. Furthermore, fitness effects varied according to the Wolbachia strain injected with most marked reductions seen in the wMelPop-injected flies and least severe effects seen with the wAlbB strain.

microbiology↗

bioRxiv2019

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

BACKGROUNDHaematobia 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. RESULTSHere we report the successful establishment of a continuous HF cell line (HIE-18) from embryonic cells and its stable transinfection with Wolbachia strain wAlbB native to mosquitoes, and wMel and wMelPop 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. CONCLUSIONThe 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.

microbiology↗