In 1909, the entomologist

Carlo Emery Carlo Emery (25 October 1848, Naples – 11 May 1925) was an Italian entomologist. He is remembered for Emery's rule, which states that insect social parasites are often closely related to their hosts. Early in his career Carlo Emery pursued ...

noted that social parasites among insects (e.g.,

kleptoparasite Kleptoparasitism (etymologically, parasitism by theft) is a form of feeding in which one animal deliberately takes food from another. The strategy is evolutionarily stable when stealing is less costly than direct feeding, which can mean when foo ...

s) tend to be

parasites Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...

of species or genera to which they are closely related.Emery, C. "Über den Ursprung der dulotischen, parasitischen und myrmekophilen Ameisen". ''Biologisches Centralblatt'' 29, 352–362 (1909) Over time, this pattern has been recognized in many additional cases, and generalized to what is now known as Emery's rule. The pattern is best known for various

taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

Hymenoptera Hymenoptera is a large order of insects, comprising the sawflies, wasps, bees, and ants. Over 150,000 living species of Hymenoptera have been described, in addition to over 2,000 extinct ones. Many of the species are parasitic. Females typi ...

. For example, the

social wasp A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder. ...

'' Dolichovespula adulterina ''parasitizes other members of its genus such as '' Dolichovespula norwegica'' and '' Dolichovespula arenaria''. Emery's rule is also applicable to members of other kingdoms such as

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

red algae Red algae, or Rhodophyta (, ; ), are one of the oldest groups of eukaryotic algae. The Rhodophyta also comprises one of the largest phyla of algae, containing over 7,000 currently recognized species with taxonomic revisions ongoing. The majority ...

, and

mistletoe Mistletoe is the common name for obligate hemiparasitic plants in the order Santalales. They are attached to their host tree or shrub by a structure called the haustorium, through which they extract water and nutrients from the host plan ...

. The significance and general relevance of this pattern are still a matter of some debate, as a great many exceptions exist, though a common explanation for the phenomenon when it occurs is that the parasites may have started as

facultative parasite A facultative parasite is an organism that may resort to parasitic activity, but does not absolutely rely on any host for completion of its life cycle. Examples of facultative parasitism occur among many species of fungi, such as family members ...

s within the host species itself (such forms of intraspecific parasitism are well-known, even in some species of

bee Bees are winged insects closely related to wasps and ants, known for their roles in pollination and, in the case of the best-known bee species, the western honey bee, for producing honey. Bees are a monophyletic lineage within the superfa ...

s), but later became reproductively isolated and split off from the ancestral species, a form of

sympatric speciation Sympatric speciation is the evolution of a new species from a surviving ancestral species while both continue to inhabit the same geographic region. In evolutionary biology and biogeography, sympatric and sympatry are terms referring to organis ...

. When a parasitic species is a sister taxon to its host in a

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

sense, the relationship is considered to be in "strict" adherence to Emery's rule. When the parasite is a close relative of the host but not its sister species, the relationship is in "loose" adherence to the rule.Hines, H. M., & Cameron, S. A. (2010)
The phylogenetic position of the bumble bee inquiline ''Bombus inexspectatus'' and implications for the evolution of social parasitism.
''Insectes Sociaux'', 57(4), 379–383.

References

{{Biological rules Parasitology 1909 introductions Biological rules 1909 in biology