Where to find questing Ixodes frontalis ticks? Under bamboo bushes!

Tick-borne diseases have a complex epidemiology that depends on different ecological communities, associating several species of vertebrate hosts, vectors and pathogens. While most studies in Europe are focused on Ixodes ricinus, other Ixodes species may also be involved in the transmission or maintenance of pathogens. This is the case of Ixodes frontalis, a poorly known species associated with different bird species such as blackbirds, thrushes and robins, with a wide distribution covering most European countries. In a previous study, high densities of questing I. frontalis larvae were found during autumn-winter at a site close to Nantes (western France) where a long-term survey focused on I. ricinus was conducted. These I. frontalis were mostly observed under bamboo bushes. In the present study, we investigated the presence of I. frontalis under bamboo bushes at various locations. With that aim in mind, a systematic search for questing I. frontalis was undertaken by the flagging method in public urban parks and private gardens presenting bamboo bushes (32 sites). This survey was carried out during autumn-winter to maximize the probability of finding the most abundant stage, i.e. larvae. We searched for I. frontalis first in the area of Nantes (10 sites), then in other regions of France (21 sites) and at one site in northern Italy. A single visit to each site revealed the presence of I. frontalis at 29 out of 32 sites: larvae were always present, nymphs were frequent (59 % of the positive sites), while adults were found at only 14 % of the sites. Questing stages of this understudied species are thus easy to find, by dragging or flagging under bamboo bushes in autumn or winter. We make the assumption that bamboo offers a favourable place for birds to roost overnight outside their breeding period (i.e. spring), sheltered from both predators and wind. This would explain higher densities of I. frontalis under bamboo, relative to other biotopes. As I. frontalis is known to harbour zoonotic pathogens, the consequences of this discovery on the epidemiology of tick-borne diseases are discussed.