Central to the concept of ecological speciation is the evolution of ecotypes, i.e. groups of individuals occupying different ecological niches. However, the mechanisms behind the first step of separation, the switch of individuals into new niches, are unclear. One long-standing hypothesis, which was proposed for insects but never tested, is that early learning causes new ecological preferences, leading to a switch into a new niche within one generation. Here, we show that a host switch occurred within a parasitoid wasp, which is associated with the ability for early learning and the splitting into separate lineages during speciation. Lariophagus distinguendus consists of two genetically distinct lineages, most likely representing different species. One attacks drugstore beetle larvae (Stegobium paniceum (L.)), which were probably the ancestral host of both lineages. The drugstore beetle lineage has an innate host preference that cannot be altered by experience. In contrast, the second lineage is found on Sitophilus weevils as hosts and changes its preference by early learning. We conclude that a host switch has occurred in the ancestor of the second lineage, which must have been enabled by early learning. Because early learning is widespread in insects, it might have facilitated ecological divergence and associated speciation in this hyperdiverse group.

Several strains of the apparently well-known cosmopolitan synanthropic parasitoid of coleopteran stored-product pests, Lariophagusdistinguendus (Förster, 1841) from Western Europe, were studied using DNA sequencing and chromosomal analysis. The presence of at least two cryptic species with different COI sequences and chromosome numbers (n = 5 and 6) was supported. The species with n = 6 is associated with the drugstore beetle Stegobiumpaniceum (Linnaeus, 1758), whereas the other one with n = 5 mostly develops on the granary weevil Sitophilusgranarius (Linnaeus, 1758). A phylogenetic study revealed that the karyotype with n = 6 represents an ancestral character state in this complex. Consequently, the chromosome set with n = 5 which is characteristic of a particular internal clade, apparently originated via chromosomal fusion which was probably preceded by a pericentric inversion. If this is true, inverted chromosome segments could accumulate a number of genetic loci responsible for certain interspecific differences.

The reproductive barriers that prevent gene flow between closely related species are a major topic in evolutionary research. Insect clades with parasitoid lifestyle are among the most species‐rich insects and new species are constantly described, indicating that speciation occurs frequently in this group. However, there are only very few studies on speciation in parasitoids. We studied reproductive barriers in two lineages of Lariophagus distinguendus (Chalcidoidea: Hymenoptera), a parasitoid wasp of pest beetle larvae that occur in human environments. One of the two lineages occurs in households preferably attacking larvae of the drugstore beetle Stegobium paniceum (“DB‐lineage”), the other in grain stores with larvae of the granary weevil Sitophilus granarius as main host (“GW‐lineage”). Between two populations of the DB‐lineage, we identified slight sexual isolation as intraspecific barrier. Between populations from both lineages, we found almost complete sexual isolation caused by female mate choice, and postzygotic isolation, which is partially caused by cytoplasmic incompatibility induced by so far undescribed endosymbionts which are not Wolbachia or Cardinium. Because separation between the two lineages is almost complete, they should be considered as separate species according to the biological species concept. This demonstrates that cryptic species within parasitoid Hymenoptera also occur in Central Europe in close contact to humans.

The click beetle Idolus picipennis represents the only species of its genus in Europe, where it is widely distributed but is rare and only occurs locally. In order to identify its sex pheromone we investigated gland extracts of females from populations in southern Germany. GC/MS analyses revealed two distinct types of gland compositions that correspond to slight but consistent morphological differences in the respective beetles. Extracts of one type contain four compounds, geranyl hexanoate (~ 40 %), (Z,E)-farnesyl hexanoate (~ 10 %), (E,E)-farnesyl hexanoate (~ 40 %), and (E,E)-farnesyl octanoate (~ 10 %), and this type belongs to the authentic I. picipennis (Bach 1852). Extracts of a second type contain neryl hexanoate (~10 %) and neryl octanoate (~ 90 %), and this type belongs to an Idolus species that apparently has been overlooked to date, presumably due to similarity with the authentic I. picipennis and insufficient material in collections. Synthetic blends of the identified compounds in their naturally-occurring ratios, as well as the main compounds alone, proved to be highly attractive to swarming males of the respective species in the field. A strong species-specific attraction also was observed in a locality where both species co-occur, thus confirming effective reproductive isolation. This study shows the potential of sex pheromones for monitoring rare and threatened insects as well as for detecting hitherto unknown cryptic species.