Family Tachinidae - Parasitic Flies

current taxonomy in (1)

Tachinidae Robineau-Desvoidy 1830

Second largest dipteran family (after Tipulidae), with ~1350 spp. in >300 genera of 4 subfamilies in our area(1) and ~8600 spp. in almost 1500 genera total; it is possible that only half of the species have been described(2)(3)

* –taxa not yet in the guide; classification adapted from (1)(4)

Family Tachinidae

SUBFAMILY DEXIINAE

SUBFAMILY EXORISTINAE

SUBFAMILY PHASIINAE

SUBFAMILY TACHININAE

Many tachinids are similar in general appearance to muscids and flesh flies; many are large, bristly, and beelike or wasplike in appearance. Presence of a subscutellum is a useful character:

  

Bristle pattern, facial conformation, and antennal shapes all help identify genera; images that show these features have a better chance of being identified.

Key to e. US genera(5)

worldwide and throughout NA

larval hosts: insects and a few other arthropods (millipedes, spiders, scorpions)(2)(7); adults may take nectar

Current knowledge summarized in(2)

Larval stages are parasitoids of other arthropods; hosts include members of 11 insect orders, centipedes, spiders, and scorpions. Some tachinids are very host-specific, others parasitize a wide variety of hosts. The most common hosts are caterpillars. Some tachinids deposit their eggs directly on the body of their host, and it is not uncommon to see caterpillars with several tachinid eggs on them. Upon hatching the larva usually burrows into its host and feeds internally. Full-grown larva leaves the host and pupates nearby. Some tachinids lay their eggs on foliage; the larvae are flattened and are called planidia; they remain on the foliage until they find a suitable host.

Tachinid flies have a wide variety of ways they can lay eggs -- they can carefully place a few on hosts, scatter many in an area frequented by hosts or lay them on leaves by host larvae. The eggs have a tough outer shell and can remain viable for weeks until the host ingests them. Then they hatch inside the host's gut.(8)

Some tachinid flies deposit newly hatched larvae on leaves, logs, or soil where they are left to search for their host. These larvae have thick cuticles to prevent desiccation and they have 2 false legs and 2 long cerci to expedite their search. Once inside the host they mold to sedentary, legless larvae.(9)

Tachinid who use beetles as hosts have elaborate abdominal segments that enable them to snatch beetles in flight and pierce the beetle's cuticle. The piercing spine guides the short ovipositor.(9)

For the larvae to survive inside the host, they rely on the insect's immune system and use the blood cells that would normally fight off intruders to encapsulate them, sealing off the body, leaving only the mouth free to access nutrients. Oxygen is obtained from the read end via a snorkel-like connection to the exterior.(9)

Eggs larvae puparium

Most hibernate in the pupal stage.

Examples of eggs on hosts

At least 16 species have been introduced as biological controls (Grenier 1988)

(10)