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Tachinid Fly: Trichopoda pennipes
Diptera
Family Tachinidae
Trichopoda pennipes is a parasite of
several species of Hemiptera (true bugs), most notably
squash bugs and
stink bugs.
Live adult Tachinid flies photographed in the wild at Winfield,
Illinois, USA.
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Trichopoda pennipes |
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Trichopoda pennipes is about the
size of a large housefly, and is primarily a parasite of
insects in the families
Coreidae (squash bugs and leaf-footed bugs) and the
Pentatomidae
(stinkbugs). Although several species of Tachinid flies have
been imported as biological control agents of agricultural
pests, this distinctively colored fly is native throughout
much of the United States.
T. pennipes appears to have different
biotypes across the country, preying on very specific hosts
in different regions. In California, a population of the fly
was reported attacking the bordered plant bug (Largus
succinctus fig. 1), but the same flies never
attacked the squash bug.
[1]
Recently, T. pennipes were collected from fields of squash
in New York state and released near farms growing squash in
northern California. They have now established permanent
populations, and now nearly 50% of the squash bugs preying
on the plants are found with fly eggs deposited on them.
However, it is not known how effective is this control, or
whether the flies have managed to reduce populations of the
voracious crop pests. (I'm privately wondering what other
"unintended consequences" have arisen from this experiment,
and gone undetected). In Nezara
viridula (figure 2), a species of stinkbug originating
in Ethiopia that has spread worldwide and become a pest of
crops in many regions, the defensive secretions (what puts
the "stink" in stinkbug) are effective deterent to many
predators, but T.pennipes appears to be tolerant of the
chemicals. Indeed, T. pennipes appears attracted to
N. viridula's pheromones which mediate sex attraction in the
bug. [2]
Chemical warfare amongst the insects is an extremely complex
and highly evolved adaptation. |
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Trichopoda pennipes is commonly called the "fringe-legged" fly.
T. pennipes overwinters as a larva in its host
and emerges in late spring or early summer. The female fly lays one
to many small, white or gray, oval eggs on large numphs or adult
bugs. The larvae burrow from the egg directly into the bug's body.
Only one larva survives within each pest bug. A large, cream-colored
maggot exits from the body of the bug, drops to the ground, and
pupates in a dark reddish-brown, capsule-like puparium. The bug soon
dies. A new generation of adult flies emerges to lay eggs about two
weeks later. Each female fly may lay several hundred eggs, and there
may be three generations each year, depending on location. The
parasitoid overwinters as a larva within the body of the
overwintering bug, emerging in late spring or early summer.
[1]
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Figure 2. Nezara viridula
Photo: © Sean McCann
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The southern green stinkbug, Nezara
viridula, emits foul-smelling secretions
from a single thoracic gland. The
exudate appears to be only marginally
effective against birds, and the pheromones
produced by this bug appear to attract their
chief parasites: T. Pennipes.
[2]
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References
1. Weeden, C.R., A. M. Shelton, and M. P. Hoffman. Biological
Control:
A Guide to Natural Enemies in North America
2. Thomas Eisner, Maria Eisner, and Melody Siegler,
Secret Weapons: Defenses of
Insects, Spiders, Scorpions, and Other Many-Legged Creatures
(Belknap Press, 2005).
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