Encarsia of Australia

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Name

Introduction

Encarsia is a large, cosmopolitan genus of tiny parasitic wasps of the family Aphelinidae, currently containing about 400 described species[1]. The number of existing species is expected to be several times higher because many species are still undescribed[2]. The adult wasps, tiny insects with 1-2 mm in size, are primarily parasitoids of sessile stages of Sternorrhyncha, in particular whiteflies (Aleyrodidae) and scale insects (Diaspididae). A few species are known to parasitize aphids, eggs of shield-back bugs (Plataspidae), or eggs of Lepidoptera. Females are mostly developing as primary endoparasitoids whereas males are commonly hyperparasitoids of the same or other species[3][4].

Species of Encarsia have been considered as the most efficacious group of biocontrol agents of whitefly pests on a broad range of agricultural crops. Recently their economic importance has been recognized worldwide and more attention has been given to their taxonomy. This is especially true of the Encarsia species parasitic on whiteflies. New species are being continuously added and there is evidence for the presence of complexes of cryptic species within several of these described species.

Before 2006 the Australian Encarsia fauna was largely unknown and the few taxonomic treatments were almost exclusively based on the study of type specimens[5], most of which had been described by Alexandre Arsène Girault[6][7][8][9]. After Girault’s contribution, the genus Encarsia in Australia was largely ignored, and it was only after the establishment of the B-biotype of the silverleaf whitefly in 1994 that interest in Encarsia resurfaced. Australia has never before had a serious whitefly pest of outdoor crops and, as a consequence, there was very little research experience present in Australia capable of dealing with that pest. Subsequently a research programme was initiated because there were indications that agents capable of contributing significantly to the biological control of this pest may already be present in Australia. During this research project it became apparent that the genus Encarsia is particularly diverse in Australia. This observation was supported by the high species richness of host taxa, in particular whiteflies[10][11], and the high number of Australian species described by early authors: between 1913 and 1939 44 species of Encarsia were described, mostly by Girault. Nearly all of those species were insufficiently described and they are usually known only from the type specimen which is often in very poor condition.

For Australia 94 Encarsia species are treated as valid[12]. This is the highest number of species for any country, followed by China (76 species)[13] and India (52 species)[14]. Many Encarsia species have a wide or even cosmopolitan distribution, complicating taxonomic revisions on a local scale. However, in Australia three-quarters of the species seem to be restricted in their distribution to Australia, indicating a high level of endemism.

In Australia species richness of Encarsia is highest in Queensland with 65 species, followed by Western Australia with 31 species (33%) and New South Wales with 15 species (16%). The remaining states or territories (excluding external territories) have between three (Australian Capital Territory) and nine species (South Australia). It is estimated that the number of species occurring in Australia is about two to three times higher than currently known. This estimate is to some extent based on the relatively high species diversity of whiteflies in Australia, comprising about 110 described species with estimates of the total number of species being about three times as many[15]. About one-third of all Encarsia species with known host records parasitize armoured scale insects which are similarly diverse in Australia with about 240 species[16]. Species attacking armoured scale insects are still underrepresented because there has been more interest in parasitoids of whiteflies than in those species attacking diaspidids.

Diagnosis

For a positive diagnosis of Encarsia (females), the presence of the following character states is required:

  • Fore and hind tarsi with five tarsomeres
  • Antenna (excluding radicle) with eight antennomeres
  • Scutellum with two pairs of setae
  • Marginal vein longer than submarginal vein
  • Postmarginal vein absent
  • Stigmal vein very short, less than one-quarter of the length of the marginal vein

The closely related genus Coccophagus differs from Encarsia primarily in having six or more setae on the scutellum.

Preparation and identification

Slide mount with wings, antenna, body, and head under separate slides

The identification of Encarsia species is complicated because of their small size necessitating laborious slide-mounting. The taxonomy of Encarsia is primarily based on morphological characters that can only be examined in slide mounted specimens using contrast enhancing techniques like phase contrast or differential interference contrast (see detailed instructions for making slide preparations of Encarsia and other microhymenoptera).

Species pages

References

  1. ↑ Noyes, J.S. (2003) Universal Chalcidoidea database.
  2. ↑ Heraty, J.M., Polaszek, A. & Schauff, M.E. (2008) Systematics and Biology of Encarsia. Chapter 4, pp. 71-87 in: Gould, J., Hoelmer, K. & Goolsby, J. (Eds), In: Classical Biological Control of Bemisia tabaci in the United States. A review of interagency research and implementation. Progress in Biological Control 4. . Springer Science and Business Media B.V. 1-343.
  3. ↑ Williams, T. and Polaszek, A. (1996) A re-examination of host relations in the Aphelinidae (Hymenoptera: Chalcidoidea). Biological Journal of the Linnaean Society 57: 35-45. doi
  4. ↑ Hunter, M.S. and J.B. Woolley (2001) Evolution and behavioral ecology of heteronomous aphelinid parasitoids. Annual Review of Entomology 46: 251-290. PDF
  5. ↑ Viggiani G. 1985. Additional notes and illustrations on some species of aphelinids described by A. A. Girault and A. P. Dodd in the genera Coccophagus Westwood, Encarsia Först. and Prospaltella Ashm. (Hym.: Chalcidoidea). Bollettino del Laboratorio di Entomologia Agraria ‘‘Filippo Silvestri’’, Portici 42:233–255.
  6. ↑ Dahms EC. 1978. A checklist of the types of Australian Hymenoptera described by Alexandre Arsene Girault: I. Introduction, acknowledgments, biography, bibliography and localities. Memoirs of the Queensland Museum 19:127–190.
  7. ↑ Dahms EC. 1983. A checklist of the types of Australian Hymenoptera described by Alexandre Arsene Girault: II. Preamble and Chalcidoidea species A–E with advisory notes. Memoirs of the Queensland Museum 21:1–255.
  8. ↑ Dahms EC. 1984. A checklist of the types of Australian Hymenoptera described by Alexandre Arsene Girault: III. Chalcidoidea species F–M with advisory comments. Memoirs of the Queensland Museum 21:579–842.
  9. ↑ Dahms EC. 1986. A checklist of the types of Australian Hymenoptera described by Alexandre Arsene Girault: IV. Chalcidoidea species N–Z and genera with advisory notes plus addenda and corrigenda. Memoirs of the Queensland Museum 22:319–739.
  10. ↑ Carver M, Reid IA. 1996. Aleyrodidae (Hemiptera: Sternorrhyncha) of Australia. CSIRO Division of Entomology Technical Paper 37:1–55.
  11. ↑ Martin JH. 1999. The whitefly fauna of Australia (Sternorrhyncha: Aleyrodidae). A taxonomic account and identification guide. Commonwealth Scientific and Industrial Research Organization, Technical Paper 38:1–197.
  12. ↑ Schmidt, S. & Polaszek, A. (2007). The Australian species of Encarsia Förster (Hymenoptera, Chalcidoidea: Aphelinidae), parasitoids of whiteflies (Hemiptera, Sternorrhyncha: Aleyrodidae) and armoured scale insects (Hemiptera, Coccoidea: Diaspididae). Journal of Natural History 41(33-36): 2099–2265. doi
  13. ↑ Huang J, Polaszek A. 1998. A revision of the Chinese species of Encarsia Förster (Hymenoptera: Aphelinidae): parasitoids of whiteflies, scale insects and aphids (Hemiptera: Aleyrodidae, Diaspididae, Aphidoidea). Journal of Natural History 32:1825–1966.
  14. ↑ Hayat M. 1998. Aphelinidae of India (Hymenoptera: Chalcidoidea): a taxonomic revision. Memoirs on Entomology, International 13:1–416.
  15. ↑ Martin JH. 1999. The whitefly fauna of Australia (Sternorrhyncha: Aleyrodidae). A taxonomic account and identification guide. Commonwealth Scientific and Industrial Research Organization, Technical Paper 38:1–197.
  16. ↑ Carver M, Gross GF, Woodward TE. 1991. Hemiptera. In: CSIRO, editor. The insects of Australia. A textbook for students and research workers. Volume 1. 2nd ed. Melbourne: Melbourne University Press. p 429–509.

External links

Interactive key to Encarsia species of Australia and the Pacific Islands attacking Bemisia tabaci and Trialeurodes vaporariorum
Encarsia on Wikipedia

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