Now here's a topic I can sink my teeth into since I spent my
dissertation looking at these critters, and am still working on this
fascinating system. There are three species of dipterans (flies and their
relatives) that form a symbiotic partnership with S. purpurea. The pitcher
plant mosquito (Wyeomyia smithii), a small, black midge (Metriocnemus
knabi) and a sarcophagid fly (Blaesoxipha fletcher - I think the name on
this one was recently changed) all lay their eggs in pitchers and, to the
best of anyone's knowledge, nowhere else. The fly larvae are big, white
maggots and hang suspended from the water surface feeding on recently
captured prey before they sink to the bottom. Usually only one will be
found per pitcher since they are highly cannibalistic and the biggest
larvae eats its smaller kin. The midge larvae are thin, white "worms" and
range from tiny 1 mm long beasties at hatching to about 1 cm long or a
little more just before they pupate. They feed on the dead prey as well
and are normally found, often in very large numbers, down in the bottom of
the pitcher. Finally, the mosquito larvae are often very numerous at all
levels in the pitchers, and feed by filtering bacteria, protozoa, algae,
and rotifers, as well as fine particles of detritus produced by the
activities of the fly and midge larvae. There are also protozoa, algae,
rotifers, cladocerans, several species of mites, and occasional nematodes
that can be found in the pitcher fluid. None are used by the pitcher
directly for food. Insects that fall into S. purpurea pitchers simply
drown, and since these critters are all aquatic species, theyare not harmed
and live quite happily in the pitcher fluid. Some like the midge larvae
and the mites also appear to migrate from old pitchers to new ones. The
mosquito larvae and fly larvae do not.
Most of the controlled experiments indicate that the activities of
these insect larvae benefit the plant by speeding up physical breakdown of
prey and increasing bacterial degradation rates. This then helps get the
nitrogen and phosphorous to the plant more efficiently. While there is
good evidence to support an obligate relationship on the part of the
insects, it is not known however, just how strong the mutualism is from the
plant's point of view. Plants whose leaves contain these insect larvae do
appear to grow bigger and produce more pitchers, and there does appear to
be an ether-soluble chemical attractant that the female mosquitoes home in
on, but no one has really done the definitive studies to show co-evolution
between the plants and its inhabitants.
To answer your question, just leave them alone. They are part of the
natural pitcher food web that helps the plant get its nutrients from its
prey. They're also really neat to observe. Oh, BTW, if your plants came
from a northern population, the adult female mosquitoes do not bite so
don't worry about itching and scratching. However, females from south
populations do take a blood meal before they lay their second and
subsequent clutches of eggs, so you might want to remove the pupae (little,
brown, comma-shaped, wiggly things that float near the top) as they form.
There are some really good papers on this system. I could send you a
bibliography if you're interested.
Liane
>Hi everyone,
>
> I was recently sent some mature plants of S.purpurea and
>D.rotundifolia. The Drosera are growing like a weed :-) and the S.
>purpurea are just starting to show signs of new pitcher formation.
>The question I had is this, in the S.purpurea pitchers there are
>small, white worms swimming along the sides in the water. They are,
>I believe, hatching into small black flies, the same kind that
>accumulate on rotting fruit. The worms are immune to the pitcher
>plant and most of the flies escape although some have drowned (:-)).
>When the flies do escape, they usually end up being caught by my
>Drosera (another :-)!).
>
> My question is, are these worms or flies harmful to my pitcher plant?
>With new pitchers being formed, should I just cut off the old, infested
>ones if they are harmful? Finally, does anyone have any idea what these
>might be? I haven't had time to like at them under the dissecting scope,
>but will if it's helpful in their identification. Please let me know if
>more information is needed or if cutting off the pitchers is a drastic
>measure (ie: maybe insecticides should be used?). Thanks in advance.
>
>Regards,
>
>Chris Teichreb
>Department of Biology
>University of Regina
>Regina, Saskatchewan, CANADA
>
>E-mail: teichrch@Meena.CC.URegina.CA
Liane Cochran-Stafira
Dept. of Ecology and Evolution
The University of Chicago
1101 East 57th Street
Chicago, Illinois 60637-5415
phone: 312-702-1930
e-mail: lcochran@midway.uchicago.edu