J S Noyes
Department of Entomology
The Natural History Museum
© Not to be reproduced without the author's permission. Revised June 2003
The superfamily Chalcidoidea belongs to the insect order Hymenoptera (bees, ants and wasps). Currently about 22,000 species have been described and catalogued. Most species are less than 3mm in length, averaging 1.5mm with the smallest about 0.11mm (Mymaridae: Dicopomorpha echmepterygis Male). Their small size can make them extremely difficult to collect and study and, as a result, they have received comparatively little attention from taxonomists. Had it not been for their importance as parasitoids of insect pests, the group would have received even less attention. Yet evidence from the British fauna and detailed work in tropical America suggests that perhaps up to 10% of all insect species may belong to the Chalcidoidea. Equating this to well-studied insect groups such as beetles, moths and butterflies would suggest that had the Chalcidoidea been as popular with collectors and taxonomists of these groups in the past, the current number could well be in excess of 100,000 species. Recent estimates suggest that there may be more than 500,000 species in existence.
The superfamily is presently divided into 19 separate families with more than 90 subfamilies recognised. Currently the largest family is the Eulophidae with nearly 4,500 included species followed closely by the Encyrtidae and Pteromalidae. The phylogenetic relationships between the various groups are poorly understood and this is subject to investigation using a combination of molecular and morphological methods. The superfamily Mymarommatoidea is also dealt with here. This group was included initially within the chalcidoid family Mymaridae, but in recent years it has been treated as a superfamily and regarded as a sister group to the Chalcidoidea. There are now some suggestions that it may be more closely related to the proctotrupoid family Diapriidae.
Chalcidoids probably have a greater range of biological diversity than species of any other parasitican superfamily and, to a much greater extent than in other groups, considerable diversity often occurs within genera. Most species are parasitoids, but groups of species in several families are phytophagous. Species of the family Agaonidae develop only in figs, and other phytophages occur in the Eurytomidae, Eulophidae, Pteromalidae, Tanaostigmatidae and Torymidae. Phytophagous chalcids are associated with 44 different plant families. Other chalcids have predaceous larvae. For example, some encyrtid larvae develop by feeding on coccid eggs and certain eurytomids are predators of cynipid larvae. Parasitoid biology reaches its most elaborate development in the Chalcidoidea. There are solitary and gregarious species; ectoparasitoids and endoparasitoids; primary, secondary and tertiary parasitoids; polyembryonic species; and species with planidial larvae. Some species are extremely polyphagous whilst others may be very host specific. All stages of hosts are attacked, from the egg (which may be parasitized by species of Mymaridae, Trichogrammatidae, Eulophidae, Encyrtidae, Aphelinidae) to the pupa (attacked by several groups of Pteromalidae in particular). Chalcids attack insects in 339 families representing 15 different orders, including all endopterygote orders, many exopterygotes and also some arachnids (including pseudoscorpions, ticks and mites). Homoptera (especially Coccoidea and Aphidoidea) are attacked as eggs, nymphs or adults by a variety of chalcids, but especially species of the Encyrtidae and Aphelinidae. The eggs of Psocoptera are parasitized by mymarids and the eggs of Thysanoptera by trichogrammatids. Nymphal Thysanoptera are parasitized by some Eulophidae, and immature Acari are attacked by encyrtids. A few species of Eulophidae, Encyrtidae and Pteromalidae are associated with spider egg sacs.
Chalcidoids are important both as biological control agents of agricultural pests and as pests themselves.
Chalcidoidea as biological control agents
The Chalcidoidea is the most important successful group used in applied biological control. Over 800 different species have been associated with biocontrol programmes in one way or another. Two families in particular, Aphelinidae and Encyrtidae, have proven extremely successful in the biological control of insects pests, although species of most other chalcidoid families have also been successfully utilised. The beneficial effects of chalcidoids is often revealed only when the injudicious use of pesticides leads to their eradication, and a consequent explosion of the pest population.
Among the Aphelinidae, the genus Encarsia is one of the most important parasitoid groups exploited for biological control. Many species have demonstrated their importance in the biological control of whiteflies (Aleyrodidae) and armoured scale insects (Diaspididae). Examples include E . perplexa Huang & Polaszek against citrus blackfly (Aleurocanthus woglumi) in the southern US and Caribbean (Clausen 1978), E. smithi (Silvestri) against spiny blackfly Aleurocanthus spiniferus (Kuwana 1934) and E. inaron (Walker) against ash whitefly in California The best-known example of an Encarsia species, and probably the most well-known parasitoid used for biocontrol world-wide, is E. formosa, used for 80 years against the greenhouse whitefly Trialeurodes vaporariorum and widely available commercially. Encarsia species used successfully against scale insects include E. berlesei on white peach scale Pseudaulacaspis pentagona, and E. perniciosi on San Jose scale, Quadraspidiotus perniciosus. As with many other chalcidoids, Encarsia species also exert a controlling effect against pest species without being deliberately exploited to do so. Other aphelinid genera that include a number of species that have been used for classical biocontrol purposes are Eretmocerus for control of whiteflies and Aphytis for the control of diaspidids.
A large number of species belonging to the family Encyrtidae have been associated with classical biological control programmes throughout the world, but most successfully in warmer climates. Some of the most spectacular successes have been achieved in the control of mealybug pests using encyrtids as natural enemies. Perhaps the best known of these is the recent extremely successful use of Anagyrus lopezi from South America for the control of cassava mealybug (Phenacoccus manihoti) throughout subsaharan Africa. This mealybug was first noted in Congo in 1973 and by the mid 1980's had spread to virtually the whole of subsaharan Africa threatening to destroy the main carbohydrate source of at least 200 million people. A search for natural enemies in Central and South America eventually located Anagyrus lopezi in Paraguay. This encyrtid was released in Nigeria in the early 1980's and by 1990 it had completely controlled the mealybug throughout most of its range in Africa. The total expenditure on this programme by 1988 had reached nearly $15m but has been estimated to save more than $250m per annum. Perhaps even more successful, but less well known, is the use of Neodusmetia sangwani to control rhodesgrass mealybug in the southern USA. The success of this project was estimated to be worth at least about $200m per annum to the Texas cattle and turf industry in 1979 for an initial outlay of not more than $0.2m. The mealybug is now controlled over the whole of its range in the New World, from Texas and Florida to southern Brazil, by this parasitoid, with an appropriate saving to the cattle industries of all the countries where it occurs. A species that has been used successfully for biocontrol purposes in Europe is Psyllaephagus pilosus. Since 1993, it has been released in Ireland, Wales, France and California (USA) for the control of eucalyptus psyllid. It successfully controlled the pest in these countries and has more recently been introduced (probably accidentally) into a number of South American countries including Peru and Argentina.
Several species of phytophagous chalcidoid have been used for controlling plant pests. The best known of these is the gall-forming pteromalid Trichilogaster acaciaelongifoliae. This species was introduced into southern Africa from Australia in 1982 for the control of Acacia longifolia, a rapidly spreading weed, and successfully controlled the plant.
Chalcidoids as pests
Although chalcidoids are mainly beneficial more than 80 species are known to be pests of agriculture. Most of these belong to the families Eurytomidae and Torymidae. Of the eurytomids Bruchophagus and Systole are perhaps the best known. Species of Bruchophagus are found in seeds of a number of leguminous crops such as lucerne (Medicago sativa) and species of Systole are fequently pests of seeds of various Apiaceae used as spices such as coriander (Coriandrum sativum). Several species of Megastigmus (Torymidae) are serious pests of Pinaceae as they attack the seeds of plantation species.
Barnard, 1999 (annotated bibliography of key works for identifying British Chalcidoidea); Boucek, 1988 (key to familes and Australasian genera); Gauld & Bolton, 1988 (key to families occurring in British Isles); Gibson, et al., 1997 (Keys to families and genera occurring in North America); Goulet & Huber, 1993 (key to families); Hanson & Gauld, 1995 (keys to families occurring in Costa Rica); Noyes, 1998 (complete world catalogue with references to identification keys to families, genera and species); Noyes & Valentine, 1989 (key to families occurring in New Zealand); Peck, Boucek & Hoffer, 1964 (Key to families and genera occurring in Czechoslovakia); Trjapitzin, 1978 (keys to families, genera and species occurring in European Russia).
Barnard, P.C. (Ed.) 1999. Identifying British Insects and Arachnids. An annotated bibliography of key works. xii+353pp. Cambridge University Press.
Boucek, Z. 1988. Australasian Chalcidoidea (Hymenoptera). A biosystematic revision of genera of fourteen families, with a reclassification of species. :832pp.. CAB International, Wallingford, Oxon, U.K., Cambrian News Ltd; Aberystwyth, Wales.
Gauld, I.D. & Bolton, B. (Eds) 1988. The Hymenoptera. Xi+332pp. Oxford University Press, Oxford, UK (Reprinted and revised, 1996; ISBN 0-19-858521-7).
Gibson, G.A.P., Huber, J.T. & Woolley, J.B. (Eds) 1993. Annotated keys to the genera of Nearctic Chalcidoidea (Hymenoptera) xi+794pp. National Research Council of Canada, Ottawa, Canada (ISBN 0-660-16669-0).
Goulet, H. & Huber, J.T. (Eds) 1993. Hymenoptera of the World: an identification guide to families. vii+668pp. Research Branch, Agriculture Canada.
Hanson, P. & Gauld, I.D., 1995. The Hymenoptera of Costa Rica. xx+893pp. Oxford University Press, Oxford, UK (ISBN 0-19-854906-9)
Noyes, J.S. 1998. Catalogue of Chalcidoidea of the World. CD-ROM Series, ETI, Amsterdam, Netherlands (ISBN 3-540-14675-X).
Noyes, J.S. & Valentine, E.W. 1989. Chalcidoidea (Insecta: Hymenoptera) - introduction, and review of genera in smaller families. Fauna of New Zealand 18:1-91.
Peck, O., Boucek, Z. & Hoffer, A. 1964. Keys to the Chalcidoidea of Czechoslovakia (Insecta: Hymenoptera). Memoirs of the Entomological Society of Canada No 34:170pp, 289 figs.
Trjapitzin, V.A. 1978. Oprediteli Nasekomikh Evreopeyskoy Chasti SSR. Tom III. Pereponchatokriliye Vtoraya Chasti. 759pp. Nauka, Leningrad, USSR (English Translation:
Sharma, B.R., 1988. Keys to the insects of the European part of the USSR. Volume III Hymenoptera Part II. Oxonian Press Pvt. Ltd., New Delhi, India; ISBN 90-04-08806-7).Last updated 22-Sep-2003