These eggs, however, were sterile and unable to give rise to viable progeny, indicating the ultimate dependence of ticks on haem acquisition from host haemoglobin to sustain embryonic viability 11. Using an artificial feeding system implemented for the European Lyme disease vector Ixodes ricinus 10, we have recently demonstrated that ticks fed on red blood cell (RBC)-depleted serum can successfully engorge and lay eggs. This approach, however, does not reveal expression of novel transcripts induced by blood meal components. All these studies have been carried out using pooled samples of midgut preparations dissected from a number of ticks fed naturally on laboratory animals. Extensive characterisations of tick midguts have been conducted in various tick species, at both transcript 5, 6, 7, 8, 9 and protein 6, 9 levels, using massive parallel sequencing and mass spectrometry, respectively. As tick feeding progresses, tick digest cells develop along the tick gut epithelium 3, where nutrient endocytosis and lysosome maturation facilitate intracellular digestion 4. females feed on their hosts for 7‒9 days. Unlike blood-feeding mosquitoes, all tick life stages feed exclusively on host blood adult Ixodes spp. Ticks acquired the habit of blood feeding more than 100 million years ago and are the main vectors for pathogens of humans and livestock globally 1, 2. Our results broaden the current knowledge of tick digestive system and may lead to the discovery of potential molecular targets for efficient tick control. ricinus were deposited in public databases as an additional outcome of this study. Transcripts relevant to the processes associated with blood-meal digestion were analysed and involvement of selected encoded proteins in the tick midgut physiology discussed. In contrast, the number of transcripts significantly affected by the presence or absence of host red blood cells was low. We noted that tick gut transcriptomes are subject to substantial temporal-dependent expression changes between day 3 and day 8 of feeding. To address specific adaptations to the haemoglobin-rich diet, we compared the midgut transcriptomes of genetically homogenous female siblings fed either bovine blood or haemoglobin-depleted serum. Using RNA-seq, we aimed to characterise the midgut transcriptome composition in adult Ixodes ricinus females during early and late phase of engorgement. During this period, ticks internalise components of host blood by endocytic digest cells that line the tick midgut epithelium. Adult females of the genus Ixodes imbibe blood meals exceeding about 100 times their own weight within 7‒9 days.
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