Haem as a maternal factor of ticks

Background Ticks are obligate blood-feeding parasites that lack de novo haem biosynthesis and must acquire haem from their hosts. Although host haem is essential for tick reproduction, the extent to which individual ticks rely on dietary haemoglobin-derived haem during immature development remains unclear. Results Here, we show that host-derived haem is maternally deposited in the midgut of newly emerged larvae as vitellin-bound haem. Using an ex vivo membrane feeding system, we fed larvae and the resulting nymphs on either blood or haemoglobin-depleted serum. Despite haemoglobin depletion, ticks engorged and moulted, indicating that immature development can proceed under reduced dietary haemoglobin input. By contrast, ticks failed to feed efficiently when dietary proteins were internalised but could not be proteolytically processed within midgut digest cells. Broad E-64 inhibition of lysosomal cysteine cathepsins prevented successful feeding of ticks. Gene-specific RNAi further resolved the contribution of individual cathepsins to tick feeding, moulting, and reproduction. Conclusions Together, these results show that immature ticks can tolerate limited dietary haemoglobin-derived haem during development, whereas successful blood-feeding requires lysosomal proteolytic throughput. This identifies cysteine cathepsins as a vulnerable node for anti-tick control.