Parasitism is one of the most successful and ancient strategies. Due to the specialized lifestyle of parasites, they are usually affected by reductions and changes in their body plan in comparison with nonparasitic sister groups. Extreme environmental conditions may impose restraints on behavioural or physiological adaptations to a specific host and limit morphological changes associated with speciation. Such morphological homogeneity has led to the diversity of parasites being underestimated in morphological studies. By contrast, the species concept has dramatically changed in many parasitic groups during recent decades of study using DNA sequence data. Here we tested the phenomenon of cryptic species diversity in the twisted‐wing parasite family Xenidae (Strepsiptera) using nuclear and mitochondrial DNA sequence data for a broad sample of Xenidae. We used three quantitative methods of species delimitation from the molecular phylogenetic data – one distance‐based (ABGD) and two tree‐based (GMYC, bPTP). We found 77–96 putative species in our data and suggested the number of Xenidae species to be more diverse than expected. We identified 67 hosts to species level and almost half of them were not previously known as hosts of Xenidae. The mean number of host species per putative species varied between 1.39 and 1.55. The constant rate in net diversification can be explained by the flexibility of this parasitic group, represented by their ability to colonize new host lineages combined with passive long‐range dispersal by hosts.

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1. Maternal investment can be influenced by several factors, especially maternal quality and possibilities for future reproduction. Mass provisioning Hymenoptera are an excellent group for measuring maternal investment because mothers distribute food sources to each brood cell for each offspring separately. Generally in aculeate Hymenoptera, larger females produce larger offspring and invest more in female offspring than in male offspring. 2. This study investigated patterns of maternal investment in Ceratina chalcites, which has an uncommon type of sexual size dimorphism in Hymenoptera: on average, males are heavier than females. It was found that larger females produce a significantly higher proportion of male offspring, as males are the costlier sex in this species. 3. Facultative nest guarding by females was observed. Females can guard offspring until adulthood, as is typical for bees of genus Ceratina (34.43% of nests); however, in the majority of cases (65.56% of nests), females plug and abandon the nest. Significant differences were found in the amount of investment between guarded and unguarded nests. Guarded nests had a greater number of provisioned brood cells and a higher proportion of male offspring. It is suggested that mothers have two facultative strategies – either she makes a large investment in the offspring of one nest or she abandons the first nest and carries out a second nesting elsewhere.

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Mimicry is usually understood to be an adaptive resemblance between phylogenetically distant groups of species. In this study, we focus on Batesian and Müllerian mimicry, which are often viewed as a continuum rather than distinct phenomena, forming so-called Batesian-Müllerian mimicry rings. Despite potent defence and wide environmental niche of hornets, little attention has been paid to them as potential models in mimicry research. We propose a Batesian-Müllerian mimicry ring of the Oriental hornet (Vespa orientalis, Hymenoptera: Vespidae) consisting of eight species that coexist in the Mediterranean region. To reveal general ecological patterns, we reviewed their geographical distribution, phenology, and natural history. In accordance with the ‘model-first’ theory, Batesian mimics of this ring occurred later during a season than the Müllerian mimics. In the case of Batesian mimic Volucella zonaria (Diptera: Syrphidae), we presume that temperature-driven range expansion could lead to allopatry with its model, and, potentially, less accurate resemblance to an alternative model, the European hornet (Vespa crabro: Hymenoptera: Vespidae). Colour morphs of polymorphic species Cryptocheilus alternatus (Hymenoptera: Vespidae), Delta unguiculatum (Hymenoptera: Vespidae), Rhynchium oculatum (Hymenoptera: Vespidae), and Scolia erythrocephala (Hymenoptera: Scoliidae) appear to display distinct geographical distribution patterns, and this is possibly driven by sympatry with alternative models from the European hornet (Vespa crabro) complex. General coevolution patterns of models and mimics in heterogenous and temporally dynamic environments are discussed, based on observations of the proposed Oriental hornet mimicry ring.