Tachinidae
Encyclopedia
Tachinidae is a large and rather variable family of true flies
within the insect
order Diptera
, with more than 8,200 known species and many more to be discovered. There are over 1300 species in North America
. Insects in this family are commonly called tachina flies or simply tachinids. As far as is known, they all are Protelean
parasitoids, or occasionally parasites, of Arthropoda.
, Afrotropical, Palaearctic, Oriental, Australasia
n and Oceanic
.
.
Larva
e (maggot
s) of most members of this family are parasitoid
s (developing inside a living host, ultimately killing it). In contrast a few are parasitic
(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
and of host invasion. Typically, Tachinid larvae are endoparasites (internal parasites) of caterpillar
s of butterflies and moths, or the eruciform
larvae of sawflies
, but some species attack adult beetle
s and some attack beetle larvae. Others attack various types of true bugs, and others attack grasshopper
s; a few even attack centipede
s.
, Thrixion, Winthemia, and Eutachina as examples. In a closely related strategy some genera are effectively ovoviviparous (some authorities prefer the term ovolarviparous) and deposit a hatching larva onto the host. The free larvae immediately bore into the host's body. illustrative genera include: Exorista
, Voria
, and Plagia. 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
, sometimes called the oviscapt, which literally means something like "egg digger". Species in the genera Ocyptera, Alophora, and Compsilura
are examples. 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. Usually 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.
Many Tachinids are important natural enemies of major insect pests, and some species actually are used in biological pest control
; for example, many species of Tachinid flies have been introduced into North America from their native lands as biocontrol
s to suppress populations of alien pests. Conversely, certain tachinid flies are themselves pests; they can present troublesome problems in the sericulture
industry by attacking silkworm larvae. One particularly notorious silkworm pest is the Uzi fly (Exorista bombycis).
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
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".
usually is bare, though sometimes plumose. The calypter
s (small flaps above the halteres
) are usually very large. Their fourth long vein bends away sharply.
Adult flies feed on flower
s and nectar from aphid
s and scale insect
s. As many species typically feed on pollen
, they can be important pollinator
s of some plants, especially at higher elevations in mountains where bees are relatively few.
The taxonomy
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.
Fly
True flies are insects of the order Diptera . They possess a pair of wings on the mesothorax and a pair of halteres, derived from the hind wings, on the metathorax...
within the insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
order Diptera
Diptera
Diptera , or true flies, is the order of insects possessing only a single pair of wings on the mesothorax; the metathorax bears a pair of drumstick like structures called the halteres, the remnants of the hind wings. It is a large order, containing an estimated 240,000 species, although under half...
, with more than 8,200 known species and many more to be discovered. There are over 1300 species in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. Insects in this family are commonly called tachina flies or simply tachinids. As far as is known, they all are Protelean
Protelean
Protelean organisms are those that begin the growing phase of their lives as parasites, and in particular, typically as internal parasites. As a rule they end that phase of their lives parasitoidally by killing or consuming the host, and then they emerge as free-living adults.-Functional...
parasitoids, or occasionally parasites, of Arthropoda.
Occurrence
The family is cosmopolitan. Species occur in many habitats in many regions, including Neotropical, NearcticNearctic
The Nearctic is one of the eight terrestrial ecozones dividing the Earth's land surface.The Nearctic ecozone covers most of North America, including Greenland and the highlands of Mexico...
, Afrotropical, Palaearctic, Oriental, Australasia
Australasia
Australasia is a region of Oceania comprising Australia, New Zealand, the island of New Guinea, and neighbouring islands in the Pacific Ocean. The term was coined by Charles de Brosses in Histoire des navigations aux terres australes...
n and Oceanic
Oceania
Oceania is a region centered on the islands of the tropical Pacific Ocean. Conceptions of what constitutes Oceania range from the coral atolls and volcanic islands of the South Pacific to the entire insular region between Asia and the Americas, including Australasia and the Malay Archipelago...
.
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 HymenopteraHymenoptera
Hymenoptera is one of the largest orders of insects, comprising the sawflies, wasps, bees and ants. There are over 130,000 recognized species, with many more remaining to be described. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek ὑμήν : membrane and...
.
Larva
Larva
A larva 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...
e (maggot
Maggot
In everyday speech the word maggot means the larva of a fly ; it is applied in particular to the larvae of Brachyceran flies, such as houseflies, cheese flies, and blowflies, rather than larvae of the Nematocera, such as mosquitoes and Crane flies...
s) of most members of this family are parasitoid
Parasitoid
A parasitoid is an organism that spends a significant portion of its life history attached to or within a single host organism in a relationship that is in essence parasitic; unlike a true parasite, however, it ultimately sterilises or kills, and sometimes consumes, the host...
s (developing inside a living host, ultimately killing it). In contrast a few are parasitic
Parasitism
Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...
(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
Oviposition
Oviposition is the process of laying eggs by oviparous animals.Some arthropods, for example, lay their eggs with an organ called the ovipositor.Fish , amphibians, reptiles, birds and monetremata also lay eggs....
and of host invasion. Typically, Tachinid larvae are endoparasites (internal parasites) of caterpillar
Caterpillar
Caterpillars are the larval form of members of the order Lepidoptera . They are mostly herbivorous in food habit, although some species are insectivorous. Caterpillars are voracious feeders and many of them are considered to be pests in agriculture...
s of butterflies and moths, or the eruciform
Eruciform
Eruciform is the entomological term describing a certain class of shapes of insect larvae.-Origin and application:...
larvae of sawflies
Sawfly
Sawfly is the common name for insects belonging to suborder Symphyta of the order Hymenoptera. Sawflies are distinguishable from most other Hymenoptera by the broad connection between the abdomen and the thorax, and by their caterpillar-like larvae...
, but some species attack adult beetle
Beetle
Coleoptera is an order of insects commonly called beetles. The word "coleoptera" is from the Greek , koleos, "sheath"; and , pteron, "wing", thus "sheathed wing". Coleoptera contains more species than any other order, constituting almost 25% of all known life-forms...
s and some attack beetle larvae. Others attack various types of true bugs, and others attack grasshopper
Grasshopper
The grasshopper is an insect of the suborder Caelifera in the order Orthoptera. To distinguish it from bush crickets or katydids, it is sometimes referred to as the short-horned grasshopper...
s; a few even attack centipede
Centipede
Centipedes are arthropods belonging to the class Chilopoda of the subphylum Myriapoda. They are elongated metameric animals with one pair of legs per body segment. Despite the name, centipedes can have a varying number of legs from under 20 to over 300. Centipedes have an odd number of pairs of...
s.
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 GymnosomaGymnosoma
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 flies in the family Tachinidae.-Species:*G. acrosterni Kugler,...
, Thrixion, Winthemia, and Eutachina as examples. In a closely related strategy some genera are effectively ovoviviparous (some authorities prefer the term ovolarviparous) and deposit a hatching larva onto the host. The free larvae immediately bore into the host's body. illustrative genera include: Exorista
Exorista
Exorista is a genus of flies in the family Tachinidae..-Subgenera & Species:*SubgenusAdenia Robineau-Desvoidy, 1863*E. cuneata Herting, 1971*E. mimula *E. pseudorustica Chao, 1964*E. rustica...
, Voria
Voria
Voria is a genus of flies in the family Tachinidae.-Species:*V. ciliata d'Aguilar, 1957*V. micronychia Chao & Zhou, 1993*V. ruralis...
, and Plagia. 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
Embryonated
Embryonated, Unembryonated and De-embryonated are terms generally used in referring to eggs or, in botany, to seeds. Practitioners in various fields use the words confusingly in unconnected contexts, rather as professional jargon than as universally applicable terms or concepts...
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
Ovipositor
The ovipositor is an organ used by some animals for oviposition, i.e., the laying of eggs. It consists of a maximum of three pairs of appendages formed to transmit the egg, to prepare a place for it, and to place it properly...
, sometimes called the oviscapt, which literally means something like "egg digger". Species in the genera Ocyptera, Alophora, and Compsilura
Compsilura
Compsilura concinnata is a parasitoid native to Europe that was introduced to North America in 1906 to control the population of an exotic forest, univoltine, gypsy moth named Lymantria dispar. It is an endoparasitoid of larvae and lives with its host for most of its life. Eventually the...
are examples. 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
Gonia (fly)
Gonia is a genus of flies in the family Tachinidae.-Species:*G. albagenae Morrison, 1940*G. aldrichi Tothill, 1924*G. asiatica *G. atra Meigen, 1826*G. aturgida Brooks, 1944*G. bimaculata Wiedemann, 1819...
are such genera. Usually 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.
Many Tachinids are important natural enemies of major insect pests, and some species actually are used in biological pest control
Biological pest control
Biological control of pests in agriculture is a method of controlling pests that relies on predation, parasitism, herbivory, or other natural mechanisms...
; for example, many species of Tachinid flies have been introduced into North America from their native lands as biocontrol
BioControl
BioControl is a peer-reviewed scientific journal published by Springer Science+Business Media covering all aspects of basic and applied research in biological control of invertebrate, vertebrate, and weed pests, and plant diseases. The journal was established in 1956 as Entomophaga and published by...
s to suppress populations of alien pests. Conversely, certain tachinid flies are themselves pests; they can present troublesome problems in the sericulture
Sericulture
Sericulture, or silk farming, is the rearing of silkworms for the production of raw silk.Although there are several commercial species of silkworms, Bombyx mori is the most widely used and intensively studied. According to Confucian texts, the discovery of silk production by B...
industry by attacking silkworm larvae. One particularly notorious silkworm pest is the Uzi fly (Exorista bombycis).
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
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...
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".
Appearance
Tachinid flies are extremely varied in appearance. Some adult flies may be brilliantly colored and then resemble blow-flies (family Calliphoridae). Most however are rather drab, some resembling house flies. 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). They are aristate flies, and the aristaArista (biology)
In insect anatomy the arista is a simple or variously modified apical or subapical bristle, arising from the third antennal segment. It is the evolutionary remains of antennal segments, and may sometimes show signs of segmentation...
usually is bare, though sometimes plumose. The calypter
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, which covers the halteres....
s (small flaps above the halteres
Halteres
Halteres are small knobbed structures modified from the hind wings in some two-winged insects. They are flapped rapidly and function as gyroscopes, informing the insect about rotation of the body during flight....
) are usually very large. Their fourth long vein bends away sharply.
Adult flies feed on flower
Flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...
s and nectar from aphid
Aphid
Aphids, also known as plant lice and in Britain and the Commonwealth as greenflies, blackflies or whiteflies, are small sap sucking insects, and members of the superfamily Aphidoidea. Aphids are among the most destructive insect pests on cultivated plants in temperate regions...
s and scale insect
Scale insect
The scale insects are small insects of the order Hemiptera, generally classified as the superfamily Coccoidea. There are about 8,000 species of scale insects.-Ecology:...
s. As many species typically feed on pollen
Pollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...
, they can be important pollinator
Pollinator
A pollinator is the biotic agent that moves pollen from the male anthers of a flower to the female stigma of a flower to accomplish fertilization or syngamy of the female gamete in the ovule of the flower by the male gamete from the pollen grain...
s of some plants, especially at higher elevations in mountains where bees are relatively few.
The taxonomy
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
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.
External links
- Australasian/Oceanian Diptera Catalog
- British Insects: the Families of Diptera
- Bugguide.net: North American Tachinidae
- Diptera.info
- Diptera: Tachinidae - ENY 3005 Family Identification
- Key to the genera of Tachinidae in the eastern US
- NADS Homepage for Tachinidae Resources
- Rhinophorids - when a tachinid isn't a tachinid!
- Tachinid Flies - Family Tachinidae, diagnostic photographs of 8 species by Cirrus Digital Imaging
- Tachinid Morphology J. E. O'Hara, North American Dipterists Society
- The Siphonini (Diptera: Tachinidae) of Europe (preview), by Stig Andersen (1996)
- UK Tachinid Recording Scheme
- World Genera of the Tachinidae J. E. O'Hara, North American Dipterists Society