Molecular and cytogenetic differentiation within the Lariophagus distinguendus (Förster, 1841) species complex (Hymenoptera, Pteromalidae)

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.

Effects of High Temperatures on the Mortality of Stegobium paniceum (L.) (Coleoptera: Anobiidae)

ABSTRACT As an alternative to chemical fumigants, heat treatment has been a widely used physical method to successfully control stored-product insects in empty grain storage and food processing facilities. The drugstore beetle, Stegobium paniceum (L.) (Coleoptera: Anobiidae) is one of the most destructive stored-product insects in the world. The mortality of the eggs, larvae, pupae, and adults of S. paniceum was investigated when exposed to 43, 47, 51, and 55°C for different time intervals. The mortality rate of the S. paniceum eggs, larvae, pupae, and adults was found to significantly increase with increased exposure time and temperature, and the pupae were the most heat-tolerant stage. The mortality rate of the S. paniceum pupae was <43.3%, while the mortality rate of the S. paniceum eggs, larvae, and adults achieved nearly 100.0% when they were exposed to 43, 47, 51, and 55°C for 6 h, 17.5 min, 120 s, and 30 s, respectively. The current results favor designing a heat treatment protocol to successfully disinfest S. paniceum in practice.

Does early learning drive ecological divergence during speciation processes in parasitoid wasps?

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.