The Tachinidae are a large and variable family of true
flies
Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced ...
within the
insect
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of ...
order
Diptera
Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced ...
, with more than 8,200 known species and many more to be discovered. Over 1,300 species have been described in
North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the C ...
alone. Insects in this family commonly are called tachinid flies or simply tachinids. As far as is known, they all are
protelean parasitoids, or occasionally parasites, of
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chitin, o ...
s, usually other insects. The family is known from many habitats in all
zoogeographical regions and is especially diverse in South America.
Life cycle
Reproductive strategies vary greatly between Tachinid species, largely, but not always clearly, according to their respective life cycles. This means that they tend to be generalists rather than specialists. Comparatively few are restricted to a single host species, so there is little tendency towards the close co-evolution one finds in the adaptations of many specialist species to their hosts, such as are typical of protelean parasitoids among the
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 typic ...
.
Larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
Th ...
e (
maggot
A maggot is the larva of a fly (order Diptera); it is applied in particular to the larvae of Brachycera flies, such as houseflies, cheese flies, and blowflies, rather than larvae of the Nematocera, such as mosquitoes and crane flies.
Entom ...
s) of most members of this family are
parasitoid
In evolutionary ecology, a parasitoid is an organism that lives in close association with its host at the host's expense, eventually resulting in the death of the host. Parasitoidism is one of six major evolutionary strategies within parasitis ...
s (developing inside a living host, ultimately killing it). In contrast a few are
parasitic
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 ...
(not generally killing the host). Tachinid larvae feed on the host tissues, either after having been injected into the host by the parent, or penetrating the host from outside. Various species have different modes of
oviposition
The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typical ...
and of host invasion. Typically, Tachinid larvae are
endoparasite
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 ...
s (internal parasites) of
caterpillar
Caterpillars ( ) are the larval stage of members of the order Lepidoptera (the insect order comprising butterflies and moths).
As with most common names, the application of the word is arbitrary, since the larvae of sawflies (suborder Symph ...
s of butterflies and moths, or the
eruciform
Eruciform (literally: "caterpillar-shaped") is the entomological term describing a certain class of shapes of insect larvae.
Origin and application
The word ''eruciform'' literally means "caterpillar-shaped" (from Latin "eruca", a caterpilla ...
larvae of
sawflies
Sawflies are the insects of the suborder Symphyta within the order Hymenoptera, alongside ants, bees, and wasps. The common name comes from the saw-like appearance of the ovipositor, which the females use to cut into the plants where they lay ...
. For example, they have been found to lay eggs in
African sugarcane borer larva, a species of moth common in sub-Saharan Africa, as well as the more northerly
Arctic woolly bear moth. However, some species attack adult
beetle
Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...
s and some attack beetle larvae. Others attack various types of
true bug
Hemiptera (; ) is an order of insects, commonly called true bugs, comprising over 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, assassin bugs, bed bugs, and shield bugs. They range in size from to arou ...
s, and others attack
grasshopper
Grasshoppers are a group of insects belonging to the suborder Caelifera. They are among what is possibly the most ancient living group of chewing herbivorous insects, dating back to the early Triassic around 250 million years ago.
Grasshoppe ...
s; a few even attack
centipede
Centipedes (from New Latin , "hundred", and Latin , "foot") are predatory arthropods belonging to the class Chilopoda (Ancient Greek , ''kheilos'', lip, and New Latin suffix , "foot", describing the forcipules) of the subphylum Myriapoda, an a ...
s. Also parasitised are bees, wasps and sawflies.
Oviposition and ovoviviparity
Probably the majority of female Tachinids lay white, ovoid eggs with flat undersides onto the skin of the host insect. Imms
mentions the genera ''
Gymnosoma
''Gymnosoma'' is a genus of flies in the family Tachinidae.
The name ''"Gymnosoma"'' literally translates as "naked body", and presumably refers to the fact that some species in the genus are less conspicuously bristly than most species of flie ...
'', ''Thrixion'', ''Winthemia'', and ''Eutachina'' as examples. In a closely related strategy some genera are effectively
ovoviviparous
Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a term used as a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop insi ...
(some authorities prefer the term ''ovolarviparous''
[Wood, D. M. 1987. Chapter 110. Tachinidae. Pp. 1193-1269 in McAlpine, J.F., Peterson, B.V., Shewell, G.E., Teskey, H.J., Vockeroth, J.R. and D.M. Wood (eds.), Manual of Nearctic Diptera. Volume 2. Agriculture Canada Monograph 28: i-vi, 675-1332.]) and deposit a hatching larva onto the host. For example, this occurs in Tachinidae species which parasitize the butterfly ''
Danaus chrysippus
''Danaus chrysippus'', also known as the plain tiger, African queen, or African monarch, is a medium-sized butterfly widespread in Asia, Australia and Africa. It belongs to the Danainae subfamily of the brush-footed butterfly family Nymphalidae. ...
'' in Ghana. The free larvae immediately bore into the host's body. Illustrative genera include ''
Exorista'' and ''
Voria''. Many Tachinid eggs hatch quickly, having partly developed inside the mother's uterus, which is long and often coiled for retaining developing eggs. However, it is suggested that the primitive state probably is to stick
unembryonated eggs to the surface of the host.
[
Many other species inject eggs into the host's body, using the extensible, penetrating part of their ]ovipositor
The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typica ...
, sometimes called the oviscapt, which roughly translates to "egg digger". Species in the genera ''Ocyptera'', '' Alophora'', and ''Compsilura
''Compsilura'' is a genus of tachinid flies in the family Tachinidae from Mozambique, Malawi and South Africa
South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bound ...
'' are examples.
In many species only one egg is laid on or in any individual host, and accordingly such an egg tends to be large, as is typical for eggs laid in small numbers. They are large enough to be clearly visible if stuck onto the outside of the host, and they generally are so firmly stuck that eggs cannot be removed from the skin of the host without killing them. Furthermore, scientists have observed in studies with the host cabbage looper
The cabbage looper (''Trichoplusia ni'') is a medium-sized moth in the family Noctuidae, a family commonly referred to as owlet moths. Its common name comes from its preferred host plants and distinctive crawling behavior. Cruciferous vegetable ...
that being glued to the host insect helps maggots burrow into the larva, where they remain until fully developed.
Yet another strategy of oviposition among some Tachinidae is to lay large numbers of small, darkly coloured eggs on the food plants of the host species. ''Sturmia'', ''Zenillia'', and '' Gonia'' are such genera.
Many Tachinids are important natural enemies of major insect pests, and some species actually are used in biological pest control
Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also inv ...
; for example, some species of Tachinid flies have been introduced into North America from their native lands as biocontrol
Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also invo ...
s to suppress populations of alien pests. Conversely, certain tachinid flies that prey on useful insects are themselves considered as pests; they can present troublesome problems in the sericulture
Sericulture, or silk farming, is the cultivation of silkworms to produce silk. Although there are several commercial species of silkworms, ''Bombyx mori'' (the caterpillar of the domestic silkmoth) is the most widely used and intensively studi ...
industry by attacking silkworm larvae. One particularly notorious silkworm pest is the Uzi fly (''Exorista bombycis
''Exorista '' is a genus of flies in the family Tachinidae.
Subgenera & species
*Subgenus ''Adenia'' Robineau-Desvoidy, 1863
**'' E. cuneata'' Herting, 1971
**'' E. mimula'' ( Meigen, 1824)
**'' E. pseudorustica'' Chao, 1964
**'' E. rustica'' ...
'').
Another reproductive strategy is to leave the eggs in the host's environment; for example, the female might lay on leaves, where the host is likely to ingest them. Some tachinids that are parasitoids of stem-boring caterpillars deposit eggs outside the host's burrow, letting the first instar
An instar (, from the Latin '' īnstar'', "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (''ecdysis''), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or ass ...
larvae do the work of finding the host for themselves. In other species, the maggots use an ambush technique, waiting for the host to pass and then attacking it and burrowing into its body.
Adult Tachinids are not parasitic, but either do not feed at all or visit flowers, decaying matter, or similar sources of energy to sustain themselves until they have concluded their procreative activities. Their non-parasitic behaviour after eclosion from the pupa is what justifies the application of the term "protelean".
Description
Tachinid flies are extremely varied in appearance. Some adult flies may be brilliantly colored and resemble blow-flies (family Calliphoridae
The Calliphoridae (commonly known as blow flies, blow-flies, carrion flies, bluebottles, greenbottles, or cluster flies) are a family of insects in the order Diptera, with almost 1,900 known species. The maggot larvae, often used as fishing ba ...
). Most however are rather drab, some resembling house flies
The housefly (''Musca domestica'') is a fly of the suborder Cyclorrhapha. It is believed to have evolved in the Cenozoic Era, possibly in the Middle East, and has spread all over the world as a commensal of humans. It is the most common fl ...
. However, Tachinid flies commonly are more bristly and more robust. Also, they usually have a characteristic appearance. They have three-segmented antennae, a diagnostically prominent postscutellum bulging beneath the scutellum (a segment of the mesonotum
The mesothorax is the middle of the three segments of the thorax of hexapods, and bears the second pair of legs. Its principal sclerites (exoskeletal plates) are the mesonotum ( dorsal), the mesosternum (ventral), and the mesopleuron (lateral) on ...
). They are aristate flies, and the arista usually is bare, though sometimes plumose. The calypter
A calypter is either of two posterior lobes of the posterior margin of the forewing of flies between the extreme posterior wing base and the alula
The alula , or bastard wing, (plural ''alulae'') is a small projection on the anterior edge of ...
s (small flaps above the halteres
''Halteres'' (; singular ''halter'' or ''haltere'') (from grc, ἁλτῆρες, weights held in the hands to give an impetus in leaping) are a pair of small club-shaped organs on the body of two orders of flying insects that provide info ...
) are usually very large. Their fourth long vein bends away sharply.
Adult flies feed on flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechanis ...
s and nectar
Nectar is a sugar-rich liquid produced by plants in glands called nectaries or nectarines, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualis ...
from aphid
Aphids are small sap-sucking insects and members of the superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white woolly aphids. A t ...
s and scale insect
Scale insects are small insects of the order Hemiptera, suborder Sternorrhyncha. Of dramatically variable appearance and extreme sexual dimorphism, they comprise the infraorder Coccomorpha which is considered a more convenient grouping than the ...
s. As many species typically feed on pollen
Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophy ...
, they can be important pollinator
A pollinator is an animal that moves pollen from the male anther of a flower to the female stigma of a flower. This helps to bring about fertilization of the ovules in the flower by the male gametes from the pollen grains.
Insects are the maj ...
s of some plants, especially at higher elevations in mountains where bees are relatively few.
The taxonomy
Taxonomy is the practice and science of categorization or classification.
A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. A ...
of this family presents many difficulties. It is largely based on morphological characters of the adult flies, but also on reproductive habits and on the immature stage.
As biological pest control
Some tachinid flies parasitize pest species. This has allowed them to be used as biological control
Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also invo ...
agents by farmers. Some Tachinidae are generalists; for instance, ''Compsilura concinnata
''Compsilura concinnata'' (tachinid fly; order Diptera) is a parasitoid native to Europe that was introduced to North America in 1906 to control the population of an exotic forest, univoltine, spongy moth named ''Lymantria dispar''. It is an end ...
'' uses, at least, 200 different hosts, and they are not safe to be used as biological controls. Others are more specialized and are safer; for instance, '' Istocheta aldrichi'', which only attacks the Japanese beetle
The Japanese beetle (''Popillia japonica'') is a species of scarab beetle. The adult measures in length and in width, has iridescent copper-colored elytra and a green thorax and head. It is not very destructive in Japan (where it is controlle ...
.
Evolution
This clade appears to have originated in the middle Eocene
The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', "daw ...
. The oldest known putatively tachinid fossil ('' Lithexorista'') dates from the Eocene Green River Formation
The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes in three basins along the present-day Green River in Colorado, Wyoming, and Utah. The sediments are deposited in very fine ...
in Wyoming.[C. H. T. Townsend. 1921. Some new muscoid genera ancient and recent. ''Insectur Inscitiae Menstruus'' 9:132-134]
See also
* List of Tachinidae genera
*Parasitoid wasp
Parasitoid wasps are a large group of hymenopteran superfamilies, with all but the wood wasps ( Orussoidea) being in the wasp-waisted Apocrita. As parasitoids, they lay their eggs on or in the bodies of other arthropods, sooner or later causi ...
References
External links
Australasian/Oceanian Diptera Catalog
Bugguide.net: North American Tachinidae
Diptera.info
''Handbooks for the Identification of British Insects, Vol. X. Part 4(a): Diptera CyclorrhaphaCalyptrata (I) Section (a). Tachinidae and Calliphoridae'' (1st portion)(2nd portion)
by F.I. van Emden (1954), Royal Entomological Society of London
''Rhinophorids - when a tachinid isn't a tachinid!''
diagnostic photographs of 8 species by Cirrus Digital Imaging
J. E. O'Hara, North American Dipterists Society
''The Siphonini (Diptera: Tachinidae) of Europe'' (preview)
by Stig Andersen (1996)
UK Tachinid Recording Scheme
Stireman, J. TACHINIDAE: Evolution, Behavior, and Ecology
{{Taxonbar, from=Q235715
Insects used as insect pest control agents
Diptera used as pest control agents
Brachycera families