Sääksjärvi, I. E. | bioRxiv Science

bioRxiv2026

First record of the subfamily Eucerotinae (Hymenoptera: Ichneumonidae) from the mainland Afrotropics, with a description of a new species

The ichneumonid subfamily Eucerotinae has been thought to be almost absent from the tropics, with the only known Afrotropical species found in Madagascar. We report the subfamily to be present in the mainland Afrotropics, and describe a new species, Euceros species 1 from Uganda and Cameroon (name not yet shown in preprint). The subfamily had likely not been observed in the mainland Afrotropics before due to low abundances and insufficient sampling. More Eucerotinae likely remain to be discovered in tropical Africa and Asia, although tropical America may genuinely have few eucerotine species. Much more extensive sampling will be needed before it is possible to make confident estimates of how eucerotine diversity is distributed globally.

zoology↗

bioRxiv2026

Temporal variation and drivers of Ixodiphagus hookeri parasitisation in Ixodes ricinus ticks in northern Europe

Ixodiphagus hookeri (Hymenoptera: Encyrtidae) is a highly specialized koinobiont endoparasitoid of hard ticks (Acari: Ixodidae). While it is considered a prime target for biological control of ticks, longitudinal data on natural parasitisation of tick populations is scarce, consequently leading to a lack of understanding regarding the effects of global warming on wasp populations and factors impacting natural parasitisation rates of ticks. To fill in these gaps, we present a longitudinal time series on natural I. hookeri parasitisation of Ixodes ricinus from the northernmost limits of their occurrence. In total, 2,111 I. ricinus nymphs collected between 2014-2021 from Seili Island in southwestern Finland were screened for I. hookeri DNA utilizing an in-house qPCR assay. Samples had previously been screened for several tick-borne pathogens and larval blood meal sources. Generalized linear mixed models were fitted to determine factors influencing the probability of parasitisation of questing nymphs, whether parasitisation influences tick densities, and if differences in parasitisation can be identified between early (May to mid-July) and late (mid-July to October) season. Log odds ratios were calculated to assess parasitisation-pathogen and parasitisation-host associations. An artificial tick feeding system was used to feed nymphs collected from the island. An increase in I. hookeri parasitisation was observed on the island between 2014-2021. The overall parasitisation prevalence was 8.2 %, with year and study site specific values ranging from 0 to 38 %. Larvae densities, July mean temperatures and parasitisation rates at t-1 were observed to increase probability of parasitisation. Parasitisation was more likely if the nymphs had fed on deer as larvae or carried Babesia spp. protozoa, and less likely if they carried Borrelia spp. Twelve wasps emerged from an artificially fed nymph, immediately starting oviposition and expiring within seven days. We present here the longest time series of natural I. hookeri parasitisation of I. ricinus ticks. An increasing trend in parasitisation was observed, indicating increases in the wasp population likely linked to global warming. Our results regarding associations between parasitisation and tick-borne pathogens - and directly linking parasitisation events to deer - support findings from previous research, which have indicated that parasitisation of ticks is more likely to occur on large host animals than on small hosts or ticks questing on the ground. The results suggest that larvae may be more important parasitisation targets for the wasps than previously accredited.

ecology↗

bioRxiv2023

A comparison of the parasitoid wasp species richness of tropical forest sites in Peru and Uganda - subfamily Rhyssinae (Hymenoptera: Ichneumonidae)

The global distribution of parasitoid wasp species richness is poorly known. Past attempts to compare data from different sites have been hampered by small sample sizes and lack of standardisation. During the past decades, we have carried out long-term Malaise trapping using a standardised approach in the tropical forests of Peru (western Amazonia) and Uganda (eastern Africa). Here, we test how well such data can be used for global comparisons, by comparing the results for the subfamily Rhyssinae (Hymenoptera: Ichneumonidae). We found that more rhyssine species were caught in Peru than in Uganda, despite the Ugandan samples containing many more individuals both in absolute terms and per unit time. The difference in the number of individuals caught may largely be due to more rainfall in Peru, since rain reduces Malaise trap catches. Peruvian traps caught species at a faster rate (per individual caught) than Ugandan traps. We interpret this as a sign that the Peruvian sites have more species than the Ugandan site. Long-term, standardised Malaise trapping showed promise for global comparisons of species richness. Sampling more sites on both continents, and analysing all subfamilies, would give an estimate of which continent has more parasitoid wasp species. We suggest some refinements to the sampling design that would further improve sampling efficiency for future studies.

zoology↗