Abstract
Ixodiphagus hookeri (Hymenoptera: Encyrtidae) is a parasitoid wasp specialized in parasitizing the larvae and nymphs of ticks (Acari: Ixodidae). As parasitized ticks die prior to reproduction, I. hookeri is seen as a prime biological control agent candidate. Despite this, little is known of their occurrence or ecology in northern Europe. The main aim of the current study was to determine whether adult wasps or parasitized ticks can be found from a tick-infested island in southwestern Finland, using field collections and molecular methods. Following the initial discovery of an adult I. hookeri female on Seili Island, we set out to collect further specimens via sweep netting and Malaise trappings between May and October 2017. Furthermore, 1310 Ixodes ricinus (1220 nymphs, 90 adults) collected from the island during 2012–2014 were screened for I. hookeri DNA using qPCR. Whereas no further wasp specimens could be collected via sweep netting or Malaise trappings, I. hookeri DNA was consistently detected in I. ricinus nymphs (annual minimum infection rates in 2012, 2013, and 2014: 2.3, 0.4, and 0.5%, respectively), whereas all adult samples were negative. Although the annually repeated detections of parasitized ticks suggest that the wasp inhabits the island, further field and molecular surveys are needed to more comprehensively determine the status and stability of the population.
Highlights
Ticks (Acari: Ixodidae) and tick-borne diseases, Lyme borreliosis and tickborne encephalitis (TBE), have become a growing problem in Europe and Russia in the twenty first century
Whereas no further wasp specimens could be collected via sweep netting or Malaise trappings, I. hookeri DNA was consistently detected in I. ricinus nymphs, whereas all adult samples were negative
I. persulcatus has recently been found across Estonia and Finland, and in 2016 the species was reported for the first time from Sweden as well (Geller et al 2012; Jaenson et al 2016; Laaksonen et al 2017)
Summary
Ticks (Acari: Ixodidae) and tick-borne diseases, Lyme borreliosis and tickborne encephalitis (TBE), have become a growing problem in Europe and Russia in the twenty first century. In Fennoscandia—the region encompassing Finland, Norway, Sweden and regions of Russia in the Kola Peninsula and Karelia—the geographical distribution of I. ricinus has shifted northwards in recent decades (Jore et al 2011; Jaenson et al 2012; Hvidsten et al 2014; Laaksonen et al 2017) Their abundance seems to be increasing, in the more southern parts of this region (Jaenson et al 2012; Sormunen et al 2016b). In Finland, changes in the geographical range and abundance of ticks are reflected in cases of tick-borne diseases: the annual numbers of microbiologically confirmed cases of Lyme borreliosis have been increasing since the mid 1990s (Sajanti et al 2017) This has sparked public concern regarding the safety of outdoor activities, and highlighted the need for developing novel control methods against the growing tick populations. Only a few of these studies have focused on I. ricinus
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