Abiotic parameters and diel and seasonal activity of Borrelia-infected anduninfected Ixodes persulcatus (Acarina : Ixodidae)

During the 1997 season of Ixodes persulcatus Schulze rick activity, 579 spe cimens were collected by nagging in the vicinity of St. Petersburg (Morskaj a, Lisy Nos). Collections were made from April to July, and at each collect ion time the following measurements were recorded: light intensity (in lux) ; temperature of soil 1-1.5 cm below leaf litter, at the soil surface, and in the air 1.5 m above the soil surface; and relative humidity. The gradien t between soil at a depth of 1-1.5 cm and soil surface temperatures appeare d to be the main physical parameter that initiated tick migration out of th e leaf litter. At soil temperature intervals of 5-10 degrees C and 21-26 de grees C, ticks were found only when the soil temperature 1-1.5 cm below the soil surface was colder than at its surface. When temperature ranged from 11 to 20 degrees C, 24% of the ticks were collected when the surface temper ature was colder than that below the soil surface. Sixty percent of the tic ks, especially nymphs, were collected when the soil surface and subsoil tem perature difference ranged from 0 to 2.0 degrees C. The gradient between so il temperature and relative humidity appeared to increase the importance of the gradient between the soil and surface temperature at which time the ma ximum number of ticks were caught. Borrelia burgdorferi sensu lato infected ticks were collected only after 1100 hours. Prior to and just after 1100 h the mean difference between soil temperatures was 4.7 degrees C, whereas t he mean difference between soil and surface temperatures was 6.4 degrees C at this time. The most important factors that influenced the appearance of Borrelia-infected ticks were the temperature gradients that existed between the surface and soil temperatures and the soil and air relative humidity. Greater numbers of infected nymphs were collected when temperature interval s ranged from 10 to 14 degrees C and lower numbers were collected between 1 5 and 20 degrees C. No Borrelia-infected nymphs were captured when the temp erature interval ranged from 21 to 26 degrees C. Infected adults appeared t o be more tolerant of higher temperatures than Borrelia-infected nymphs. A significant relationship was found between the activity of Borrelia-infecte d I. persulcatus and the temperature of the air, soil below the surface, at the soil surface, and relative humidity.