Chalcidoidea: India
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Faunal Diversity in India: Chalcidoidea
This is an extract from FAUNAL DIVERSITY IN INDIA Edited by J. R. B. Alfred A. K. Das A. K. Sanyal. ENVIS Centre, Zoological Survey of India, Calcutta. 1998 ( J. R. B. Alfred was Director, Zoological Survey of India) |
Hymenoptera
Introduction
The superfamily Chalcidoidea, commonly called the Chalcidoid wasps or briefly chalcids is one of the largest groups of Parasitic Hymenoptera. They are taxonomically the most difficult, ecologically most complex and economically perhaps the most important group of insects. Most members of the group are parasitic, attacking major insect orders many of which are agricultural and forest pests of economic importance. By their parasitic mode of life they destroy populations of potential pest species in the field, regulating their numbers, thus playing an important role in biological control of serious pests. Chalcids are characterised by their minute size, ranging between 0.18 mm to almost 25 mm and readily distinguished from other groups of parasitic Hymenoptera by the reduced forewing venation without closed cells. From Proctotrupoidea, a closely resembling group, chalcids differ in the nature of pronotum which never touches tegulae, due to the presence of a sclerite called propectus. The other distinguishing characters of the group are geniculate antennae with 13 or fewer segments, biarticulate trochanters, sclerotised abdominal segments and the ovipositor issuing from the ventral surface far anteriorly to the anus.
Status Of The Taxon
Global and Indian Status
The number, definition and limits of Chalcidoid families have always been in a state of flux since the begining of 1800's. According to the recent classification by Boucek (1988) the superfamily is divided into 21 families to accommodate about 2000 genera and 19,000 described species.
Members of 19 families of Chalcidoidea are known from India. Among these Encyrtidae, Chalcididae, Eurytomidae, Aphelinidae, Trichogrammatidae and Agaonidae are well documented from the region. The families Tanaostigmatidae, Tetracampidae, Eulophidae, Pteromalidae, Perilampidae etc. are less studied from this part of the Oriental Region. The approximate number of valid genera and species of Indian Chalcidoidea is 528 and 1695 respectively. This forms only 27 % and 9 % respectively of the world genera and species. These figures are approximate and may go still high if the scattered publications on various families like Encyrtidae, Aphelinidae, Trichogrammatidae etc. are scrutinised.
Distribution
Eventhough chalcids have a wider distribution, they are poorly known from the colder parts of the country. The reason for the less common occurrence of chalcids at high altitudes may be attributed to the less availability of the host insects which in tum may be due to the decreased floral diversity. Low temperature may also be a limiting factor for the nonabundance of these insects in these areas.
The members of the families Trichogrammatidae, Mymaridae and Aphelinidae reached higher altitudes and this can be due to the probable wind dispersal by virtue of their smaller size. The families Chalcididae, Encyrtidae, Eurytomidae, Pteromalidae, Eupelmidae, Eulophidae, Aphelinidae and Trichogrammatidae, enjoy a wider distribution while Leucospidae, Tetracampidae, Eucharitidae, Perilampidae etc. appear less frequently in collections. Members of the family Agaonidae are widely distributed and are always associated with fig plants. Chalcids can be always collected in plenty around cultivated fields probably due to the presence of the insect pests in large numbers. Like all other animal groups species diversity of Chalcidoidea is also very high in tropical forest ecosystems though represented in low population densities. The Chalcid fauna of the peninsular part is better known in India.
Biological Diversity And Its Special Features
Chalcids show fascinating diversity in biology exhibiting both entomophagy and phytophagy. Adults are free living, feeding on nectar, honey dew and in some cases little water. The females (parasitic forms) insert the eggs into the body of the host with help of needle like ovipositor. The eggs develop inside the body of the host and the ensuing larva consume host tissue, pupate and emerge out as the adult. The term parasitoid is used to describe them as only the larval stages of Chalcidoieda are parasitic and they kill and consume the host during the development. ChaIcids attack a wide range of hosts that include 12 orders of insects and 2 of Arachnida. They attack the hosts in their various stages of development like eggs larvae, pupae or even adult.
The phytophagous species either cause galls on plants or are seed eaters. Some species feed on gall tissue but does not cause galls and are called inquilines as they co-exist with the gall causers. Members of Agaonidae (wasps) are obligatory phytophagous and develop inside the syconia of figs. They pollinate figs and cannot survive without figs and vice-versa. Some members of the family Eurytomidae and Torymidae exhibit both entomophagy and phytophagy.
In host selection parasitic Chalcidoidea are either specialists, generalists or opportunists. Mymaridae and Trichogrammatidae are speCialists being strictly internal parasites of insect eggs. Other examples of specialists can be found in Eucharitidae, parasitising ant larvae and pupae, Leucospidae parasitising bees and wasps and Tanaostigmatidae feeding on plant tissues. Chalcids are either solitary (one individual develops in a host) or gregarious. They are either monophagous, oligophagous or Polyphagous. They are primary (attacking only a phytophagous species), secondary or hyperparasitic (attacking a host already attacked by another primary parasite). Hyperparasitism may reach even tertiary or quarternary levels in some species. Chalcids are either ectoparasitic or endoparasitic.
Chalcids show several interesting behavioural patterns in their biology. Some Pteromalids oviposit into the body of the adult beetles and some species build straw like tubes on host's body to suck their body fluids. Eucharitids, parasitic on ants lay their eggs on the leaves and the emerging first instar larva (planidium) jumps and attack the ant when it passes by. The larvae complete development inside the ant's nest by attaching on the body of the ant larvae. One species of chalcid parasitic on ant lion larvae provokes the host into grabbing the parasite's legs with mandibles, at which time the parasite oviposits into the membrane between the larva's head and thorax. Some members of Eulophidae and Trichogrammatidae even dive into water in search of their host. The attacked host is often immediately prevented from further growth and feeding or in some cases the parasite larvae co-exist with the feeding host for some time. The former are called indiobionts and the latter koinobionts. Some members of family Aphelinidae show a very complex behavioural pattern known as adelphoparasitism, where males develop as parasites of females of their own species (obligate adelphoparasitism or autoparasitism) or of females of different species (facultative adelphoparasitism).
Sexual dimorphism is prominent in chalcids and sex ratio varies very much and in some species males are very rare. As generally in hymenoptera the males are haploid and females diploid. After copulation sperms are kept in spermathecae and the females lay either fertilised or unfertilised eggs, the former become females and the latter males (arrhenotoky). Thelytoky (female parthenogenesis) is also found in some species.
Endemicity
An analysis of the available data clearly indicates that Chalcidoidea exhibits a very low level of endemism at generic level in India. Among the various families, Encyrtidae and Agaonidae shows high level of endemism at generic level followed by Pteromalidae, Eurytomidae, Eulophidae, Aphelinidae, Eucharitidae etc. The families Leucospidae, Ormyridae, Perilampidae, Torymidae, Signiphoridae and Tetracampidae contain no endemic genera. At the species level, the range of endemism varies between 40 (Chalcididae) to 100% (Tetracampidae and Tanostigmatidae) among different families. Second to the Oriental species Palaearctic elements dominate in Indian fauna, followed by Australian and Ethiopian. Nearctic and Neotropical species are very poorly represented in India.
Threatened And Introduced Species
No species has so far been recorded extinct or any taxon categorised under the IUCN red data book. Several species of chalcids were however, introduced by man in diffemt parts of the world. Species introductions mainly occured in search of natural enemies for biocontrol programmes. Several species of Trichogramma (Trichogrammatidae) were introduced in different parts of India in biocontrol programmes against sugarcane and cotton pests. Several species of Encyrtidae also reached different parts of the country as coccid and mealybug parasites. Introduced species are also found In the families Aphellnidae, Eulophidae and Pteromalidae due to their greater utilisation in biocontrol programmes. Species introductions may also occur along with the dispersal of pest affected plant materials like fruits and seeds which are parasitised by chalcids.
Value
Chalcids play a significant role in the ecosystem as effective biocontrol agents and key stone species helping to maintain high diversity in other organisms and are directly beneficial to man in economic terms. Chalcids as Biocontrol Agents A large number of parasitic chalcids are proved to be of great value in biological control programmes. Most experiments and studies have been devoted to the egg parasite Trichogramma whose host range includes more than 150 species of insects. The species Trichogramma chilonis was effectively utilised in the biocontrol of sugarcane borers in Kamataka, Tamil Nadu and Gujarat. Trichospilus pupivorus (Eulophidae) has been proved a very effective control agent against the coconut black-headed caterpillar Nephantis serill0pa in different parts of South India. Many prospective parasites of scale insects are found in the family Aphelinidae. In the family Encyrtidae there are several effective parasites of coccids. Two species of encyrtids have been successfully used against two severe pests of agriculture in Africa, the Casava mealy bug and the mango mealy bug. Release of Tetrasticlllls hagerrowii (Eulophidae) proved effective in the control of cockroaches in USA and Pteromaills pllparllm (Pteromalidae) controlled Pieris brassicae (Cabbage butterfly) in Australia and New Zealand. An analysis of the literature dealing with the biological control programmes will reveal that no fewer than 16 % of references goes to chalcids and within the group the families Aphelinidae, Trichogrammatidae and Encyrtidae are most important. According to the summary given by Noyes (1985) in the utilisation of various parasites in biocontrol programmes a total of 406 species of chalcids involved in 1101 introductions achieved 233 instances of control of which 119 were of full economic control. The Chalcidoidea possesses a biocontrol index of 1657 which is next to the total of Hymenoptera Parasitica. In terms of numbers of introductions also chalcids come next to Hymenoptera Parasitica (1105 against 2053).
Fig wasps (Agaonidae) being the sole pollinators of fig plants act as key stone mutualists in nature. The fig plants can only be pollinated by these wasps and their existence in the nature depends only upon them and vice versa. Other chalcids playa major role in the balance of terrestrial ecosystems through their ability to control populations of phytophagous insects. By checking the populations of herbivorous insects chalcids not only maintain high species diversity in them but also prevent the herbivorous insects from decimating their plant hosts.
Phytophagous chalcids may assume another type of economic importance of man. Since they are gall inducers and seed eaters they become minor pests. Due to the formation of galls the plant stem become lignified and brittle, snapping easily in the wind. Seed eaters and fruit breeders cause damage to seeds and fruits.
Threat
The major threats faced by chalcids for survival are habitat destruction, excessive use of pesticides and pollution. Severe habitat destruction emanating from faulty agricultural practices and urbanisation lead to the loss of floral diversity which in tum affect chalcid population. Uncontrolled use of non selective pesticides will extirpate parasitoid populations from agroecosystems.
Secondary enemies or hyperparasites can disrupt the activity of chalcid parasites in nature. In general chalcids are also prone to species extinctions due to various factors.
Conservation Strategies And Future Studies
The importance of chalcids in nature makes urgent conservation measures imperative. As most of the decline in chalcid fauna is due to loss of floral diversity, large scale destruction of natural habitats (deforestation, monoculture) should be controlled. Increasing the adjacent vegetational diversity around cultivated fields will enhance the beneficial activity of Chalcidoid parasites. Minimising of the use of destructive pesticides is also very essential in order to boost the activity of useful parasitoids. The Integrated Pest Management strategies (IPM) adopted recently in the field of pest control may be of some help in protecting these useful insects in nature.
Chalcidoids being numerically rich, basic taxonomic research in the group has to be promoted much in order to utilise the beneficial species in biocontrol programmes. Detailed studies on the life history, ecology, behaviour, phylogeny or any other facet of chalcid life will be highly rewarding in entomological science.
Selective References
Ashmead, W. H. 1904. Classification of the Chalcid flies of the superfamily Chalcidoidea. Mem. Car. Mus., 1(4) : 225-551. Boucek, Z. et al. 1979.. A preliminary review of Pteromalidae (Hymenoptera) of India and adjacent countries. Oriental Ins., 12 : 433-468. Dalla Torre, K. W. von. 1898. Catalogus Hymenopterorum hucusque descriptorum systematicus et synonymicus. 5. Chalcididae et Proctotrupidae. 598 pp. Leipzig. Desantis, L. 1980. Cataloge de los Himenopteros Brasilenes de la Serie Parasitica induyendo Bethyloidea. 395 pp. Univ. Fed. do. Parana, Curityba. Gibson, G. A. P. et al. (eds.) 1997. Annotated keys to the genera of Nearctic Chalcidoidea. (Hymenoptera) NRC. Res. press. Ottawa. pp. 794. Mani, M. S. 1938. Chalcidoidea. Cataloglle Indian Ins. 23. ii & 170 pp. Delhi. Mani, M. S. 1989. The fauna of India and the adjacent countries. Chalcidoidea (Hymenoptera) part I & II. Zool. Surv. India. p. 1067. Narendran, T. C. 1994. Torymidae and Eurytomidae of Indian sub-continent (Hymenoptera: Chalcidoidea) Dept. Zool. Uni. of Calicut. pp. 500. Subba Rao, B. R. and Hayat, M., 1985 (eds.). The Chalcidoidea (Insecta: Hymenoptera) of India and the adjacent countries. Part 1. Review of families and keys to families and genera. Oriental Ins., 19 : 161-310. & 15pp. Subba Rao, B. R. and Hayal. M. 1986 (eds.). The Chalcidoidea (Insecta: Hymenoptera) of India and the adjacent countries. Part II. A catalogue. Oriental Ins., 20 :1¬ 430.
