Ixodiphagus Hookeri Research Articles

Molecular characterisation of Australasian Ixodiphagus (Hymenoptera; Encyrtidae; Encyrtinae) reveals unexpected diversity and a potential novel host switch

Ticks are important medical and veterinary parasites that represent a substantial health threat to humans, companion animals, and livestock. Ixodiphagus wasps (Hymenoptera; Encyrtidae) are known endoparasitoids of ixodid (hard) and argasid (soft) ticks, with potential utility as natural biocontrol agents. Two species, Ixodiphagus brunneus and Ixodiphagus mysorensis, are previously recorded from Australia, however, the genus lacks formal revisionary work in Australia, and the validity and host ranges of these species remain uncertain. This work aimed to investigate the diversity of Ixodiphagus in Australasia and provide a molecular data resource for future work on these understudied endoparasitoids. We extracted DNA from archival Ixodiphagus specimens from Australian and New Zealand insect collections and performed high-throughput sequencing which resulted in complete or mostly complete mitochondrial genome sequences from 11 specimens, including I. brunneus, Ixodiphagus taiaroaensis, and a novel Ixodiphagus sp. reared from Rhipicephalus linnaei from Townsville, Australia. In addition, approximately 70% of the genome of the Wolbachia endosymbiont of I. brunneus was recovered. Finally, we screened 178 recently collected pooled tick samples from southern New South Wales, Australia, for Ixodiphagus spp. using 28S rRNA and cytochrome c oxidase subunit 1(COI) gene PCR, and recovered 14 positive samples. Phylogenetic analysis of Australasian Ixodiphagus spp. based on 28S rRNA and complete mitochondrial genome sequences determined that members of the Australasian fauna are distinct from Ixodiphagus hookeri (the only other Ixodiphagus species for which genetic data exists), and that at least two distinct species are present in Australia; I. brunneus identified from Ixodes holocyclus and Haemaphysalis bancrofti ticks, and an uncharacterised Ixodiphagus sp. found in Rhipicephalus linnaei ticks from northern Queensland. Furthermore, there was substantial genetic diversity at the 28S rRNA loci among I. brunneus samples, which may represent normal genetic variability or a secondary cryptic species. The molecular data generated here represents the first known for the genus Ixodiphagus in Australasia, doubling that of the world fauna, and provides the first known complete mitochondrial genomes for these important tick parasitoids.

Ixodiphagus hookeri (Hymenoptera: Encyrtidae) and Tick-Borne Pathogens in Ticks with Sympatric Occurrence (and Different Activities) in the Slovak Karst National Park (Slovakia), Central Europe.

Ticks are involved in the transmission a plethora of pathogens. To effectively control ticks and mitigate the risks associated with tick-borne diseases, it is important to implement tick control measures. These may include the use of acaricides as well as the development and implementation of an alternative, environmentally friendly tick management program that include practices such as habitat modification or establishing biological control. Ixodiphagus hookeri Howard is a tick-specific parasitoid wasp that predates on several species of ixodid ticks and could contribute to the control of the tick population. This work aimed to detect the presence of parasitoid wasps in ticks (Ixodidae) using genetic approaches. Several tick species of the genera Ixodes, Haemaphysalis, and Dermacentor, with a sympatric occurrence in the Slovak Karst National Park in southeastern Slovakia, were screened for the presence of wasps of the genus Ixodiphagus. The DNA of the parasitoids was detected in four tick species from three genera. This work presents the first molecular detection of parasitoids in two Dermacentor tick species, as well as the first molecular identification of Ixodiphagus wasps in Ixodes ricinus and Haemaphysalis concinna ticks from the Karst area. In the given area, it was observed that I. ricinus and H. concinna ticks are hyper-parasitized by wasps. Moreover, it was observed that wasps here can parasitize several tick species, some of which are of less significance for human and animal health (as they transmit fewer pathogens).

Behavioral responses of Ixodiphagus hookeri (Hymenoptera; Encyrtidae) to Rhipicephalus sanguineus nymphs (Ixodida: Ixodidae) and dog hair volatiles

Abstract The wasp Ixodiphagus hookeri (Howard; Hymenoptera: Encyrtidae) parasitizes the larvae and nymphs of several tick species worldwide. In this study, we investigated whether I. hookeri females are attracted to Rhipicephalus sanguineus Latreille (Ixodida: Ixodidae) nymphs, hair samples from non-infested and infested Schnauzer dog volatiles, and a synthetic blend of compounds isolated from dog hair in a Y-tube glass olfactometer. We also studied the acceptance of fed and unfed R. sanguineus nymphs by female wasps. Our results showed that I. hookeri females were not attracted to R. sanguineus nymphs. In contrast, they were attracted to dog hair samples and extracts from non-infested and R. sanguineus-infested Schnauzer dog hair. Wasps were more attracted to hair samples from R. sanguineus-infested dogs than to those from non-infested dogs. In addition, I. hookeri females were attracted to a synthetic blend composed of hexanal, heptanal, and isovaleric acid, compounds previously isolated from dog hair. In contrast, I. hookeri females were not attracted to binary blends or individual compounds. Female wasps showed a higher acceptance of live-fed and live-unfed R. sanguineus nymphs than of dead fed nymphs washed with dichloromethane. Our results suggests that the host seeking behavior of I. hookeri females is attributable to a blend of volatiles from infested and non-infested schnauzer dogs, used to attack R. sanguineus nymphs.

The Role of Parasitoid Wasps, Ixodiphagus spp. (Hymenoptera: Encyrtidae), in Tick Control.

Species of Ixodiphagus (Hymenoptera: Encyrtidae) are parasitoid wasps whose immature forms develop inside ixodid and argasid ticks (Acari: Ixodida). Following oviposition by adult female wasps into the idiosoma of ticks, larvae hatch and start feeding on their internal contents, eventually emerging as adult wasps from the body of the dead ticks. Species of Ixodiphagus have been reported as parasitoids of 21 species of ticks distributed across 7 genera. There are at least ten species described in the genus, with Ixodiphagus hookeri being the most studied as an agent for biological control of ticks. Although attempts of tick control by means of this parasitoid largely failed, in a small-scale study 150,000 specimens of I. hookeri were released over a 1-year period in a pasture where a small cattle population was kept, resulting in an overall reduction in the number of Amblyomma variegatum ticks per animal. This review discusses current scientific information about Ixodiphagus spp., focusing on the role of this parasitoid in the control of ticks. The interactions between these wasps and the ticks' population are also discussed, focusing on the many biological and logistical challenges, with limitations of this control method for reducing tick populations under natural conditions.

First record of the parasitoid wasp Ixodiphagus hookeri (Hymenoptera: Encyrtidae) infesting the tick Amblyomma nodosum (Acari: Ixodidae)

Ticks (Ixodida) are ecologically important ectoparasites that may impact human health and economic activities. Parasitoid wasps are natural enemies of ticks and a potential option for its biological control. In the present study, we recorded parasitism of the nymphs of the tick Amblyomma nodosum by the parasitoid wasp Ixodiphagus hookeri. The ticks, in turn, were parasitizing white-bearded manakins, Manacus manacus (Passeriformes: Pipridae) in the União Biological Reserve, one of the last major remnants of lowland rainforest in Rio de Janeiro state, southeastern Brazil. During the collection of ectoparasites from two manakins in this reserve, 20-30 parasitoid wasps hatched spontaneously from two of the ticks collected. The species of the tick nymphs and adult wasps were identified using morphological traits and molecular analyses. This record is the first documented case of I. hookeri parasitizing A. nodosum and the first time that parasitoid wasps have been found in ticks parasitizing birds in Brazil. This is also the first record of Ixodiphagus from southeastern Brazil in more than a century, with the only other record dating back to 1914. The record presented here provides valuable new information on the biology of this tick and its parasitoids, and new insights into this interspecific interaction. Further research on these vertebrate-tick-wasp interactions will be necessary to better understand the respective roles of the organisms involved in these processes.

First detection of Ixodiphagus hookeri (Hymenoptera: Encyrtidae) in Ixodes ricinus ticks (Acari: Ixodidae) from multiple locations in Hungary

The parasitoid wasp, Ixodiphagus hookeri (Hymenoptera: Encyrtidae), is the natural enemy of a wide range of hard and soft tick species. While these encyrtid wasps are supposed to be distributed worldwide, only a few studies report on their actual distribution around the globe. Within a shotgun sequencing-based metagenome analysis, the occurrence of I. hookeri was screened at multiple Ixodes ricinus (Acari: Ixodidae) tick sampling points in Hungary to contribute to the assessment of the distribution patterns of the parasitoid wasps in Central Europe. To our knowledge, the first report of the species in Hungary and the description of the southernmost I. hookeri associated geoposition in Central Europe took place within our study. I. hookeri infested I. ricinus nymphs were detected at five sampling points in Hungary. The results show that the exact distribution range of I. hookeri is still barely studied. At the same time, unprecedented public health issues being brought about by climate change might require steps toward the exploitation of the tick biocontrol potential and as an ecological bioindicator role of the parasitoid wasp in the future.

Investigation of the parasitoid Ixodiphagus hookeri (Hymenoptera: Encyrtidae) in Amblyomma sculptum (Acari: Ixodidae) ticks in the municipality of Salto, São Paulo, Brazil

The presence of capybaras (Hydrochoerus hydrochaeris) in urban and periurban areas has caused increased numbers of cases of Brazilian spotted fever. With the aim of investigating the presence of the parasitoid Ixodiphagus hookeri in Amblyomma sculptum ticks in the municipality of Salto, state of São Paulo, samples were collected monthly from 14 sites. Thirty samples were placed in containers for observation of the emergence of microhymenopterans and 88 samples were subjected to molecular testing to identify the presence of I. hookeri DNA. Neither dissections nor observation of emergence indicated any presence of I. hookeri larvae in ticks. Samples subjected to polymerase chain reaction (PCR) amplification of the mCOX I region of I. hookeri did not reveal its presence, although fragments corresponding to mRNA 16S of Amblyomma sculptum ticks were amplified in all samples tested.

Temporal patterns in Ixodes ricinus microbial communities: an insight into tick-borne microbe interactions

BackgroundTicks transmit pathogens of medical and veterinary importance and are an increasing threat to human and animal health. Assessing disease risk and developing new control strategies requires identifying members of the tick-borne microbiota as well as their temporal dynamics and interactions.MethodsUsing high-throughput sequencing, we studied the Ixodes ricinus microbiota and its temporal dynamics. 371 nymphs were monthly collected during three consecutive years in a peri-urban forest. After a Poisson lognormal model was adjusted to our data set, a principal component analysis, sparse network reconstruction, and differential analysis allowed us to assess seasonal and monthly variability of I. ricinus microbiota and interactions within this community.ResultsAround 75% of the detected sequences belonged to five genera known to be maternally inherited bacteria in arthropods and to potentially circulate in ticks: Candidatus Midichloria, Rickettsia, Spiroplasma, Arsenophonus and Wolbachia. The structure of the I. ricinus microbiota varied over time with interannual recurrence and seemed to be mainly driven by OTUs commonly found in the environment. Total network analysis revealed a majority of positive partial correlations. We identified strong relationships between OTUs belonging to Wolbachia and Arsenophonus, evidence for the presence of the parasitoid wasp Ixodiphagus hookeri in ticks. Other associations were observed between the tick symbiont Candidatus Midichloria and pathogens belonging to Rickettsia. Finally, more specific network analyses were performed on TBP-infected samples and suggested that the presence of pathogens belonging to the genera Borrelia, Anaplasma and Rickettsia may disrupt microbial interactions in I. ricinus.ConclusionsWe identified the I. ricinus microbiota and documented marked shifts in tick microbiota dynamics over time. Statistically, we showed strong relationships between the presence of specific pathogens and the structure of the I. ricinus microbiota. We detected close links between some tick symbionts and the potential presence of either pathogenic Rickettsia or a parasitoid in ticks. These new findings pave the way for the development of new strategies for the control of ticks and tick-borne diseases.BH3gJgHYBsR7dGygrmQjw9Video abstract.

Bacterial Pathogens and Symbionts Harboured by Ixodes ricinus Ticks Parasitising Red Squirrels in the United Kingdom.

Red squirrels (Sciurus vulgaris) are native to most of Eurasia; in much of the United Kingdom, they have been supplanted by the non-native grey squirrel, and are considered an endangered species. Very little is known about the range of tick-borne pathogens to which UK red squirrels are exposed. As part of trap-and-release surveys examining prevalence of Mycobacterium spp. in red squirrel populations on two UK islands, Ixodes ricinus ticks were removed from squirrels and PCR screened for Borrelia spp., intracellular arthropod-borne bacteria and the parasitic wasp Ixodiphagus hookeri. At both sites, the most commonly encountered tick-transmitted bacterium was Borrelia burgdorferi sensu lato (overall minimum prevalence 12.7%), followed by Anaplasma phagocytophilum (overall minimum prevalence 1.6%). Single ticks infected with Spiroplasma were found at both sites, and single ticks infected with Borrelia miyamotoi or an Ehrlichia sp. at one site. Ticks harbouring Wolbachia (overall minimum prevalence 15.2%) were all positive for I. hookeri. Our study shows that UK red squirrels are potentially exposed to a variety of bacterial pathogens via feeding ticks. The effects on the health and survival of this already vulnerable wildlife species are unknown, and further studies are needed to evaluate the threat posed to red squirrels by Borrelia and other tick-borne pathogens.

Hymenopteran Parasitoids of Hard Ticks in Western Africa and the Russian Far East.

Some parasitoids of the genus Ixodiphagus (Hymenoptera, Chalcidoidea: Encyrtidae) are well-known natural enemies of ticks. In this study, we investigate the occurrence of parasitoid wasps in adult hard ticks from Western Africa (Côte d’Ivoire and Senegal) and Far Eastern Europe (Russia) using molecular methods. The morphological identification allowed the classification of 785 collected specimens of six species of ticks: Rhipicephalus (Boophilus) microplus (41%), Ixodes persulcatus (33%), Dermacentor silvarum (11%), Haemaphysalis concinna (7%), Amblyomma variegatum (5%), and Haemaphysalis japonica (3%). The newly developed MALDI-TOF MS protocol identified tick species in spite of their different storage (dried or in 70% ethanol) conditions for a long period. Molecular screening of ticks by a new standard PCR system developed in this study revealed the presence of parasitoid wasp DNA in 3% (28/785) of analyzed ticks. Ixodiphagus hookeri was detected in 86% (24/28) of infested ticks, including 13 I. persulcatus, 9 R (B) microplus, and one H. concinna and D. silvarum. While an unidentified parasitoid wasp species from the subfamily Aphidiinae and Braconidae family was detected in the remaining 14% (4/28) infested ticks. These infested ticks were identified as I. persulcatus. Our findings highlight the need for further studies to clarify the species diversity of parasitoid infesting ticks by combining molecular and morphological features. The novel molecular and MALDI-TOF MS protocols could be effective tools for the surveillance and characterization of these potential bio-control agents of ticks.

Tripartite Interactions among Ixodiphagus hookeri, Ixodes ricinus and Deer: Differential Interference with Transmission Cycles of Tick-Borne Pathogens

For the development of sustainable control of tick-borne diseases, insight is needed in biological factors that affect tick populations. Here, the ecological interactions among Ixodiphagus hookeri, Ixodes ricinus, and two vertebrate species groups were investigated in relation to their effects on tick-borne disease risk. In 1129 questing ticks, I. hookeri DNA was detected more often in I. ricinus nymphs (4.4%) than in larvae (0.5%) and not in adults. Therefore, we determined the infestation rate of I. hookeri in nymphs from 19 forest sites, where vertebrate, tick, and tick-borne pathogen communities had been previously quantified. We found higher than expected co-occurrence rates of I. hookeri with deer-associated Anaplasma phagocytophilum, and lower than expected rates with rodent-associated Borrelia afzelii and Neoehrlichia mikurensis. The prevalence of I. hookeri in nymphs varied between 0% and 16% and was positively correlated with the encounter probability of ungulates and the densities of all life stages of I. ricinus. Lastly, we investigated the emergence of I. hookeri from artificially fed, field-collected nymphs. Adult wasps emerged from seven of the 172 fed nymphs. From these observations, we inferred that I. hookeri is parasitizing I. ricinus larvae that are feeding on deer, rather than on rodents or in the vegetation. Since I. hookeri populations depend on deer abundance, the main propagation host of I. ricinus, these wasps have no apparent effect on tick populations. The presence of I. hookeri may directly interfere with the transmission cycle of A. phagocytophilum, but not with that of B. afzelii or N. mikurensis.

First evidence of Ixodiphagus hookeri (Hymenoptera: Encyrtidae) parasitization in Finnish castor bean ticks (Ixodes ricinus)

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.

Larvae of Ixodiphagus wasps (Hymenoptera: Encyrtidae) in Rhipicephalus sanguineus sensu lato ticks (Acari: Ixodidae) from Brazil

The biological control of ticks represents an alternative method to the chemical control, given its ecological-friendly approach. Amongst the alternatives, the use of parasitoids of the genus Ixodiphagus (Hymenoptera: Encyrtidae) has been largely investigated. The aim of this study was to document and molecularly characterize Ixodiphagus wasps in ticks from a tropical region of Brazil. From October 2015 to March 2016, Rhipicephalus sanguineus sensu lato ticks (n=1814) were collected from naturally infested dogs and Ixodiphagus larvae were detected by microscopic examination. In addition, adult wasps were obtained in the laboratory. Larvae and adults were molecularly identified as Ixodiphagus hookeri. These findings suggest that this type of parasitism deserves to be studied in local tick populations, in order to elucidate the role of these wasps as a potential alternative to chemical tick control.

Occurrence of Ixodiphagus hookeri (Hymenoptera: Encyrtidae) in Ixodes ricinus (Acari: Ixodidae) in Southern Italy

Natural enemies of ticks include the parasitoid wasp Ixodiphagus hookeri (Hymenoptera: Encyrtidae). The aim of this preliminary study was to investigate the occurrence of I. hookeri DNA in a community of ticks (Ixodes ricinus, Dermacentor marginatus, Hyalomma marginatum, Haemaphysalis inermis and Rhipicephalus turanicus). From May 2010 to March 2012, ticks were collected monthly by dragging and flagging, identified, and 481 adults and 305 nymphs screened molecularly for infection with I. hookeri. Of the samples tested (n=786), 3.1% (n=25) were positive for I. hookeri DNA, 7.2% (n=22) in nymphs and 0.6% (n=3) in adults. I. hookeri DNA was only detected in I. ricinus. This study shows that I. hookeri infests I. ricinus in southern Italy, with nymphs being the main developmental stage affected by this wasp.

Parasitism by <I>Ixodiphagus</I> Wasps (Hymenoptera: Encyrtidae) in <I>Rhipicephalus sanguineus</I> and <I>Amblyomma</I> Ticks (Acari: Ixodidae) in Three Regions of Brazil

Hymenopteran parasitoids have been shown to be of potential value in tick biocontrol. Tick parasitoids has been reported only once in Brazil, over 95 yr ago when Ixodiphagus hookeri (Howard) was reported parasitizing Rhipicephalus sanguineus (Latreille) nymphs in Rio de Janeiro. Herein, we report the occurrence of Ixodiphagus spp. in ticks from three different regions of Brazil. In the state of Maranhão, in northeastern Brazil, parasitoids were detected in R. sanguineus nymphs on three occasions, during August 2009 and September 2010 (dry season), and January 2011 (rainy season). All parasitoids found in northeastern Brazil were identified as I. hookeri. In the state of Mato Grosso do Sul (west-central Brazil), one Amblyomma sp. engorged nymph was shown to be parasitized by I. hookeri. In the state of Rondônia (northern Brazil), one Amblyomma sp. engorged nymph was parasitized by Ixodiphagus texanus (Howard). Because Ixodiphagus spp. are present in ecologically distinct and geographically distant areas of Brazil, they are of potential use for biocontrol in the country.

Detection of Wolbachia in the Tick Ixodes ricinus is Due to the Presence of the Hymenoptera Endoparasitoid Ixodiphagus hookeri

The identification of micro-organisms carried by ticks is an important issue for human and animal health. In addition to their role as pathogen vectors, ticks are also the hosts for symbiotic bacteria whose impact on tick biology is poorly known. Among these, the bacterium Wolbachia pipientis has already been reported associated with Ixodes ricinus and other tick species. However, the origins of Wolbachia in ticks and their consequences on tick biology (known to be very diverse in invertebrates, ranging from nutritional symbionts in nematodes to reproductive manipulators in insects) are unknown. Here we report that the endoparasitoid wasp Ixodiphagus hookeri (Hymenoptera, Chalcidoidea, Encyrtidae) – strictly associated with ticks for their development - is infested at almost 100% prevalence by a W. pipientis strain belonging to a Wolbachia supergroup that has already been reported as associated with other hymenopteran parasitoids. In a natural population of I. ricinus that suffers high parasitism rates due to I. hookeri, we used specific PCR primers for both hymenopteran and W. pipientis gene fragments to show that all unfed tick nymphs parasitized by I. hookeri also harbored Wolbachia, while unparasitized ticks were Wolbachia-free. We demonstrated experimentally that unfed nymphs obtained from larvae exposed to I. hookeri while gorging on their vertebrate host also harbor Wolbachia. We hypothesize that previous studies that have reported W. pipientis in ticks are due to the cryptic presence of the endoparasitoid wasp I. hookeri. This association has remained hidden until now because parasitoids within ticks cannot be detected until engorgement of the nymphs brings the wasp eggs out of diapause. Finally, we discuss the consequences of this finding for our understanding of the tick microbiome, and their possible role in horizontal gene transfer among pathogenic and symbiotic bacteria.

Parasites of vectors - Ixodiphagus hookeri and its Wolbachia symbionts in ticks in the Netherlands

BackgroundIxodiphagus hookeri is a parasitic wasp of ixodid ticks around the world. It has been studied as a potential bio-control agent for several tick species. We suspected that the presence of Wolbachia infected I. hookeri eggs in ticks is responsible for incidental detection of Wolbachia DNA in tick samples.MethodsThe 28S rRNA and 16S rRNA genes of a specimen of I. hookeri was amplified and sequenced. PCR on part of the 28S rRNA gene was used to detect parasitic wasp DNA in 349 questing Ixodes ricinus ticks from various sampling sites. Furthermore, the wsp gene of Wolbachia was sequenced from the I. hookeri specimen and a subset of ticks was tested using this marker.ResultsSeveral sequences from tick specimens were identical to the Wolbachia sequence of the I. hookeri specimen. Ixodiphagus hookeri was detected in 9.5% of all tested ticks, varying between 4% and 26% depending on geographic location. Ten out of eleven sampling sites throughout the Netherlands were positive for I. hookeri. Eighty-seven percent of I. hookeri-positive but only 1.6% of I. hookeri-negative ticks were Wolbachia positive. Detection of I. hookeri DNA was strongly associated with the detection of Wolbachia in ticks.ConclusionThis is the first reported case of I. hookeri in the Netherlands. Furthermore I. hookeri harbours Wolbachia species and is broadly distributed in the Netherlands. While detection of Wolbachia DNA in ticks might often be due to parasitism with this wasp, other sources of Wolbachia DNA in ticks might exist as well.

A hidden beneficial: biology of the tick-wasp Ixodiphagus hookeri in Germany

The parasitic wasp Ixodiphagus hookeri parasitizes hard ticks and is therefore considered as a potential candidate for biological control of ticks. However, there are still considerable gaps of knowledge about the biology of I. hookeri, especially for European populations. Thus, the present study was performed to assess important life-history parameters of the parasitoid in Germany. Field studies accomplished in three successive years revealed that unfed Ixodes ricinus nymphs are infested by the parasitoid at a low but constant rate of 1.9–3.8% and that adult wasps are present only during a short period in late summer. The mean developmental time of wasps in I. ricinus nymphs ranged from 28 to 70 days under constant laboratory conditions and was prolonged in the second half of the year. Bioassays on parasitization and host preference behaviour showed that unfed nymphs of the host species I. ricinus are significantly preferred in experiments, in which unfed and engorged larvae as well as fully engorged nymphs were offered as alternatives. The marsh tick Dermacentor reticulatus was not accepted as an alternative host. Our data show that the investigated I. hookeri populations differ markedly from populations in other regions of the world in many aspects. The adaptation of different strains to local conditions explains the limited success of imported strains in earlier biological control attempts and highlights the importance of doing research to enhance the control potential of native strains.

Being a parasitoid of parasites: host finding in the tick wasp Ixodiphagus hookeri by odours from mammals

AbstractThe parasitic wasp Ixodiphagus hookeri Howard (Hymenoptera: Encyrtidae) parasitizes larvae and nymphs of a number of tick species worldwide. Ticks themselves are parasitic on vertebrate hosts. To study the specificity and reliability of vertebrate odours used by I. hookeri for host location, we conducted bioassays in a four‐chamber olfactometer. Wasps were arrested by carbon dioxide and by odours from roe deer faeces and odours from hair of roe deer and wild boar. Odours from faeces of cattle, rabbit, and field mouse as well as odours from hair of cattle and field mouse had no effect. Odours from faeces of the host tick species Ixodes ricinus L. (Acari: Ixodidae) were attractive only up to a distance of 1 cm. Thus, I. hookeri reacts to general (carbon dioxide) and specific vertebrate odours from wild boar and deer. Examination of freshly shot specimens demonstrates that deer and wild boars are infested with a sufficient number of tick nymphs to tap the full reproductive potential of an I. hookeri female, which makes cues from these mammal species reliable. These results indicate that I. hookeri locates its hosts using specific and reliable mammal odours and that ticks are parasitized on their vertebrate hosts. The implications of this host‐finding strategy and its benefits for the parasitoid are discussed.

Life history of the tick parasitoid Ixodiphagus hookeri (Hymenoptera: Encyrtidae) in Kenya

We conducted laboratory and field experiments to elucidate the life history of Ixodiphagus hookeri, a parasitoid of the ixodid tick Amblyomma variegatum in Western Kenya. Ixodiphagus hookeri females oviposited in unfed host nymphs as well as engorged nymphs, but rarely in engorged larvae. While I. hookeri developed to adults in engorged nymphs, the eggs laid in unfed nymphs disappeared within 2 days after oviposition. As temperature increased, development time of I. hookeri from oviposition to adult emergence in engorged nymphs decreased from 46 days at 23 °C to 35 days at 28 °C, and their immature survival in engorged nymphs decreased from 67% at 23 °C to 22% at 28 °C. No parasitoid adult emerged from hosts at 30 °C. Individual hosts parasitized by single females produced 42–53 adult wasps, 73% of which were females. As a typical pro-ovigenic species, I. hookeri females had an average of 84 mature eggs at emergence and lived only for a few days. When laboratory-reared, unfed nymphs of A. variegatum were attached to cattle for 4–9 days in subsistence farmers’ fields in Western Kenya, 25% of the engorged nymphs and 4% of the unfed nymphs on cattle were parasitized by I. hookeri, demonstrating that I. hookeri females search for and oviposit in A. variegatum nymphs on cattle. Unlike other strains of I. hookeri that overwinter as eggs in unfed nymphs, I. hookeri could continuously reproduce throughout the year in Western Kenya.