Biology of Rhipicephalus appendiculatus and R. zambeziensis and production of a fertile hybrid under laboratory conditions.

In some areas of Eastern and Southern provinces of Zambia Rhipicephalus appendiculatus and R. zambeziensis are sympatric, and numerous intermediate forms as well as typical R. appendiculatus and R. zambeziensis are found. Experiments were carried out in order to clarify the taxonomic status of the intermediate forms. Biology and hybridization capacities of two strains of R. appendiculatus (A and D) and one strain of R. zambeziensis (H) were studied. Infestations on rabbits and calves were performed at the beginning and at the end of the Zambian rainy season. The adults of both species showed preference for the bovine host and performed better at the end of the rainy season. A recently isolated strain of R. appendiculatus had notably higher larval production per unit engorgement weight than the strain that had been maintained for prolonged periods under laboratory conditions. R. zambeziensis produces fewer larvae and had longer development periods than R. appendiculatus. The two species cross-breed under laboratory conditions. A fertile hybrid is produced by R. zambeziensis females and R. appendiculatus males, whereas a sterile hybrid is a result of a reciprocal cross. Morphology of adults of the fertile hybrid (H/A) is indistinguishable from the maternal species, whereas adults of the sterile hybrid (A/H) are of maternal, paternal and intermediate forms. Larval production indices (LPI) vary from 0.4 to 3.7 for the H (females) X A (males) cross, approximately three-fold less than in the maternal species. For the reciprocal cross, LPI ranges from 0.1 to 2.7, five- to thirty-fold less than in the maternal species. The fertile hybrid has a higher LPI than both first crosses, and under the most favourable climatic conditions LPI is even higher than for the maternal species. Adults of the sterile hybrid rarely formed pairs. Only partially engorged female ticks detached, which produced no viable eggs. Both hybrids may occur in areas where the two species are sympatric. However, detailed field studies will have to be performed in order to gain knowledge on population dynamics, interbreeding and the vector role of the two species and their hybrids under field conditions.