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Taxon
Aphelinidae

Aphelinidae

Introduction:
Aphelinidae is a diverse family of insects and is poorly understood, both in terms of taxonomy, systematics, and biology. Yet, Aphelinidae are one of the most widely used and successful entomophagous biological control agents. Aphelinidae are small, soft-bodied insects, yellow or brown in color, and do not typically exceed 1.5mm in length. 

Genera & Species:

Aphelinidae once included more than 100 nominal genera and 860 to 11,200 described species.  The number of genera has varied: 44 (Hayat, 1983), 45 (Yasnosh, 1983) (excluded eriaporine genera), 49  (Hayat, 1985), 30 (Hayat, 1994), 32 (Hayat, 1998).  The number of subfamilies has also changed considerably, ranging in number from 3 to 7, with at least 10 family level classification schemes.

Characters Uniting the Family:
Characters uniting the family Aphelinidae are not apomorphic; i.e. they are not uniquely derived. Some of the more significant characters included in Hayat’s (1998) diagnosis of Aphelinidae are complete notaular lines of the mesoscutum; transverse or broad petiole (propodeum), long marginal, short stigmal, and short or absent postmarginal wing veins; and third valvula distinctly separated and articulated with third valvifer. While these character combinations might serve to differentiate Aphelinidae from other families of Chalcidoidea, they are, taken individually, not unique to Aphelinidae. Not surprisingly, Campbell et al. (2000) found their molecular analysis of 28S D2 rDNA to render Aphelinidae paraphyletic.

Biology:
With regard to their biology, Aphelinidae more closely resemble Encyrtidae. The majority of Aphelinidae are parasitoids of sternorrhynchous Hemiptera (Coccidae, Aleyrodidae, Aphidae), although some are know to be hyperparasitoids or primary parasitoids of Lepidoptera, Orthoptera, and Diptera eggs. Aphelinidae are thus considered economically important insects with regard to biological control. Success in biological control programs depends on the correct identification of both the biological control agent and the pest species. Consequently, our lack of understanding evolutionary relationships and diversity of Aphelinidae hampers progress with biological control.

Higher-level relationships:

Higher-level relationships of Aphelinidae have included placement within Eulophidae, Encyrtidae, Pteromalidae, or as a distinct family.  Rosen and DeBach (1990) noted that Aphelinidae share morphological affinities with both Encyrtidae (shape of the mesopleura and structure of the pro- and mesotibial spurs) and Eulophidae (thoracic sclerite morphology and antennal segmentation)

Relationships within Aphelinidae:
The most numerous classification (in terms of the number of subfamilies), was proposed by Yasnosh (1976) who proposed seven subfamilies; Aphelininae, Aphytinae (tribes Aphytini and Centrodorini), Coccophaginae, Azotinae, Physcinae, Prospaltellinae, and Calesinae. Shafee and Khan (1978) reduced the number of subfamilies to four; Aphelininae, (tribes Aphelinini and Mariettini), Coccophaginae (tribes Coccophagini and Prospaltellini), Pteroptricinae, and Eretmocerinae. Khan and Shafee (1980) maintained these subfamilies yet altered the tribes and added the subfamily Calesinae as follows; Aphelininae (tribes Aphelinini and Aphytini), Coccophaginae (tribes Coccophagini, Azotinae, and Prospaltellini), Pteroptricinae, Eretmocerinae, and Calesinae. 

The most recent treatment of Aphelinidae Hayat (1998) recognizes the following subfamilies and tribes: Aphelininae (tribes Aphelinini, Aphytini, Eretmocerini, and Eutrichosomellini)
Eriaphytinae
Azotinae
Coccophaginae (tribes Coccophagini, Azotinae, Physcini, and Pteroptricini)
Eriaporinae
Euryischiinae.

References:
Campbell, B., J. Heraty, J.-Y. Rasplus, K. Chan, J. Steffen-Campbell, and C. S. Babcock. 2000. Molecular
systematics of the Chalcidoidea using 28S-D2 rDNA in The Hymenoptera: Evolution, Biodiversity and
Biological Control
(A. D. Austin, and M. Dowton, eds.). CSIRO Publishing.
Hayat, M. 1983. The genera of Aphelinidae (Hymenoptera) of the world. Systematic Entomology 8:63-102.
Hayat, M. 1985. Family Aphelinidae. Pages 226-232 in The Chalcidoidea (Insecta: Hymenoptera) of India and     the Adjacent Countries. Part I. (B. R. Subba Rao, and M. Hayat, eds.).
Hayat, M. 1994. Notes on some genera of the Aphelinidae (Hymenoptera: Chalcidoidea), with comments on
the classification of the family. Oriental Insects 28:81-96.
Hayat, M. 1998. Aphelinidae of India (Hymenoptera: Chalcidoidea) a Taxonomic Revision. Associated
Publishers, Gainseville.
Khan, M. Y., and S. A. Shafee. 1980. Species of the genus Eretmocerus (Aphelinidae: Eretmocerinae) from
India. Oriental Insects 14:363-370.
Rosen, D., and P. DeBach. 1990. Conservation of natural enemies. Pages 461-472 in Armored Scale Insects:
Their Biology, Natural Enemies and Control
(D. Rosen, ed.) Elsevier, Amsterdam.
Shafee, S. A., and M. Y. Khan. 1978. Subfamilies and tribes of the family Aphelinidae (Hymenoptera:
Chalcidoidea). Journal of Zoological Research, Aligarh 2:42-45.
Yasnosh, V. A. 1976. Classification of the parasitic Hymenoptera of the family Aphelinidae (Chalcidoidea).
Entomological Review 55:114-120.
Yasnosh, V. A. 1983. Review of the world genera of Aphelinidae (Hymenoptera). 1. key to the genera.
Entomological Review 62:145-159.