POLYMORPHIC
LARVAL RETREATS IN THE NET-SPINNING
CADDISFLY
MACROSTEMUM CAROLINA (TRICHOPTERA:
HYDROPSYCHIDAE):
FORM AND PUTATIVE FUNCTION
GORDON
R. PLAGUE AND J VAUN McARTHUR Savannah
River Ecology Laboratory, University of Georgia,
PO Drawer E, Aiken, SC 29802
Larval net-spinning caddisflies of the genus
Macrostemum Kolenati (Trichoptera:
Hydropsychidae) construct their catchnets within protective retreats.This genus is
composed of 88 species and is distributed worldwide
(Morse 1999).However, the retreat architecture has only been described for
three North American species (Wallace
& Sberberger 1974, 1975, Wallace 1975) and one
South American species (Sattler
1963).The
described retreats share a general, rather elaborate architecture (Fig. la)
with the following characteristics: (i) two chambers,
one housing the catchnet and one
housing the insect, and (ii) the water entrance hole is
at the end of a silken or sand
grain tube that leads into the two-chamber area.Here we report an alternate retreat
design constructed by some Macrosteinum Carolina
(Banks) individuals in the Savannah River, Georgia and South Carolina.
Macrostemum Carolina is widely distributed
throughout the southeastern United
States, and has been recorded west to Texas (Moulton
& Stewart 1997) and north to
New York (Ross 1944).In coastal plain streams with shifting sand streambeds, M.
Carolina primarily inhabits submerged snags (i.e. fallen trees or branches),
gouging
the base of their retreats out of the wood and covering the top of the
structure with
silk.In
their original description, Wallace & Sherberger (1974) noted that some M.
Carolina individuals in the Apalachicola River construct a second, slightly
different
retreat than the one described above.This alternate retreat lacks a silken tube and
simply has the entrance hole open into the chamber area
(Fig. lb) (some Macrostemu zebratum (Hagen) individuals construct a
similar alternate retreat(seeWallace
1975)).In
the Savannah River, M. Carolina individuals construct the two retreats
described above as well as a third type with yet a different entrance hole
configuration.The entrance hole of this third retreat also lacks a
silken tube and instead has a ~180° silken backstop, with the other ~180°
essentially flush with the top of the retreat (Fig.1c).These
backstops vary in size, from 3-8 mm in height, though some of this variation
is positively correlated with instar (G.R.
P., personal observation).Macrostemum
carolina
is common in the Savannah River (Cudney
& Wallace 1980), and each retreat
morph is regularly encountered.Individuals of a single morph are often clustered on
snags, although the "flush" phenotype is
generally the most prevalent (G.R.
P., personal observation).
SREL
Reprint #2492
Plague, G. R., and J. V. McArthur. 2000.
Polymorphic larval retreats in the net-spinning caddishfly Macrostemum
carolina (Trichoptera: Hydropsychidae): form and putative function. Florida
Entomologist 83:497-500.
