Morphological features of Ixodes persulcatus and I. ricinus hybrids: nymphs and adults.

Our aim was to reveal morphological features of first-generation Ixodes persulcatus and I. ricinus hybrids (nymphs and adults) obtained under laboratory conditions for further study of natural populations of these species in sympatry foci. In 65 nymphs of three groups I. ricinus (23 specimens), I. persulcatus (21 specimens), and hybrids (21 specimens), 16 parameters were evaluated (length/width of the scutum and capitulum, length of the hypostome, palp, tarsus I, coxa I, sternal setae, and various scutal and alloscutal setae) and discrimination analysis was performed allowing differentiation of hybrid nymphs from original species. General effectiveness of classification of I. ricinus, I. persulcatus, and hybrids was >95 %. Discriminant functions are presented allowing classification of I. persulcatus, I. ricinus, and hybrid nymphs. For description of morphology, 27 adult hybrids (13 males and 14 females) were examined under a stereo microscope at 14-28× (without preparation of permanent mounts). The following morphological distinctions of hybrids from original species were described: posterior marginal groove is not clear (as in I. ricinus) and absence of syncoxa on coxa I (as in I persulcatus). In hybrid males, simultaneous absence of syncoxa on coxa I (as in I. persulcatus) and a long internal spur on coxa I (as in I. ricinus) can be used as a diagnostic feature. Based on the detected characteristics, 10 of 157 ticks collected in Karelia in I. ricinus and I. persulcatus sympatry area were classified as hybrids.

Morphological differentiation of Ixodes persulcatus and I. ricinus hybrid larvae in experiment and under natural conditions.

The objective of the study was detection of hybrid larvae in Ixodes persulcatus and Ixodes ricinus cohabitation sites. To this end, the following three tasks were solved: interspecies crossing of ticks, evaluation of typical morphological signs of the hybrid larvae, and analysis of collected specimens from sites of sympatry. Under experimental conditions, hybrid larvae of I. persulcatus (female) and I. ricinus (male) were obtained that differed from the parental species by the size of setae on the scutum and alloscutum. Discriminant analysis yielded 87.5% classification accuracy for the priory set groups of I. persulcatus, I. ricinus, and hybrids. Of 88 hybrid larvae, 13 (15%) were classified as I. persulcatus and 4 (5%) as I. ricinus. We measured larvae of Ixodes ticks (n=141) collected from small mammals in 1950-1970 in Karelia in cohabitation sites of these species that were previously classified as I. persulcatus or I. ricinus. According to the results of discriminant analysis, 31 larvae (22%) were classified as hybrids with probability p≥0.52; for 10 larvae (7%), the probability of placement to the hybrid group was >0.95.

Distribution of Ixodes ricinus and I. persulcatus ticks in southern Karelia (Russia).

The northern boundary of the sympatric zone of Ixodes persulcatus and I. ricinus (Acari: Ixodidae) passes through Karelia. Studies carried out in the 1950s showed that these Ixodes species were mostly found in southern Karelia. I. ricinus inhabited the west of the region, I. persulcatus the east, with a zone of sympatry in the centre. Here, we describe the present distribution of these species in southern Karelia and provide a retrospective assessment of potential changes in the sympatric zone. Tick distribution and abundance were investigated during transect samplings, conducted in May-June 2006-2010. Additional information was obtained during examination of pet dogs and cats. Overall, 4561 adult ticks were collected. Since the 1950s, there has been a significant increase in the abundance of I. persulcatus, and a decrease in I. ricinus. Currently, southern Karelia can be considered as a zone of sympatry for I. ricinus and I. persulcatus, without a clear geographic boundary between the 2 species. In most areas, except to the west of Lake Ladoga, I. persulcatus is more abundant. Possible reasons for this trend are discussed.