Common salvinia (Salvinia minima

Baker) is an exotic floating fern that has been in the U.S. from at least 1928(Small 1931). Its pest status in Florida is less clear perhaps due to the presence of the specialized herbivore Cyrtobagous salviniae (Coleoptera: Curculionidae). Our objective was to sample populations of adult

C. salviniae

in south Florida in order to assess temporal abundance

and estimate density on common salvinia. (PDF has 4 pages.

Center, T.D.

Tipping, Philip W.

English

Aquatic Commons

 J. Aquat. Plant Manage.
 
 43: 2005. 47
 
J. Aquat. Plant Manage.
 
 43: 47-50
NOTES
Population Dynamics of 
 
Cyrtobagous salviniae
 
on Common Salvinia
 
 
 
in South Florida
 
PHILIP W. TIPPING AND T. D. CENTER
 
1
 
INTRODUCTION
 
Common salvinia (
 
Salvinia minima 
 
Baker) is an exotic
floating fern that has been in the U.S. from at least 1928
(Small 1931). It colonizes lentic or slow moving, fresh water
bodies like ponds, lake, swamps, and marshes. The native
range of this species encompasses Central and South Ameri-
ca (Mickel and Beitel 1988, Stoltze 1983, Palacios-Rios and
Cortes 1990). It is adventive in Bermuda (Weatherby 1937),
Puerto Rico (Proctor 1989), and Spain (Lawalree 1964). Ja-
cono et al. (2001) documented multiple introductions of
this species in North America where it now occurs in at least
7 states and 69 drainages. Madeira et al. (2003) analyzed the
genetic variation of common salvinia and found relatively
close similarity among North American populations with the
exception of a recent introduction in Mississippi.
This species has become an increasing problem in parts of
the United States, especially Texas and Louisiana. It often
dominates fresh water systems, replacing native vegetation
like duckweed (
 
Lemna
 
 sp.), which is valued as waterfowl
food. The pest status is less clear in Florida where it seems
less aggressive and unable to form persistent mats, in con-
trast to its status in Texas and Louisiana. The less aggressive
nature of this plant in Florida may be due to the presence of
the specialized herbivore 
 
Cyrtobagous salviniae 
 
(Coleoptera:
Curculionidae) which did not occur in the mid-South until
its recent introduction (P. W. T., unpubl. data). This weevil
was found widely distributed throughout Florida in 68% of
all drainages containing common salvinia (Jacono 2001).
This species has been used worldwide as an effective biologi-
cal control agent for giant salvinia (
 
Salvinia molesta
 
 Mitchell),
a close relative of common salvinia
 
 
 
(Room et al. 1981). The
 
C. salviniae 
 
widely used to control giant salvinia
 
 
 
originated in
Brazil, so we refer to them as the Brazil population while we
refer to those naturalized in Florida as the Florida popula-
tion. There has been some question of the identity of the
Florida population because of minor genetic differences be-
tween the two populations (Goolsby et al. 2000). However,
the most recent molecular work indicates that Brazil and
Florida populations of 
 
C. salviniae 
 
are very similar when com-
pared to the closely related 
 
C. singularis
 
 (P. Madeira, unpubl.
data).
Our objective was to sample populations of adult 
 
C. salvin-
iae
 
 in south Florida in order to assess temporal abundance
and estimate density on common salvinia.
 
MATERIALS AND METHODS
 
Sampling Method. 
 
We sampled six sites in south Florida ev-
ery 2 to 3 weeks from October 1999 through October 2001
for the presence of 
 
C. salviniae 
 
adults. We used a stratified
sampling approach to identify suitable locations within a site
which were then sampled with a fine mesh net to collect com-
mon salvinia. In preliminary studies, we collected separate
samples from three locations within the site and processed
them using a Berlese funnel. Our initial results found ex-
tremely large variability in the number of weevils among loca-
tions from within a site leading us to increase the number of
locations to five and then twenty with no appreciable reduc-
tion in variances. In order to reduce sampling and processing
costs while maximizing our chances of detecting this species,
we elected to take a composite sample from 5 locations within
each site and to sample more frequently. Plant material was
bulked within site and date and returned to the lab where it
was placed in a Berlese funnel to extract adults. The collec-
tion vial was filled with tap water and 1 to 2 plants of common
salvinia were placed inside as ‘trap plants’ to attract and pro-
vide food for adults. The samples were held in the Berlese
funnels for 72 h and vials were changed every 24 h. The plant
material was removed from the Berlese funnels, dried at 32 C
for 7 d then weighed to obtain dry weight biomass.
The data were examined in two ways: 1) the number of
 
C. salviniae 
 
per g of dry weight biomass of common salvinia
and, 2) the estimated mean number of 
 
C. salviniae 
 
per
square meter of common salvinia on the water. The first
number was generated by dividing the number of weevils in
each sample by the dry weight biomass of common salvinia.
This value corrected for sample differences in the weight of
plant material collected in the field.
The same dry weight biomass of each sample was used to
estimate the area occupied by common salvinia on the sur-
face of the water. The first step was obtain an representative
estimate of fresh weight biomass per square meter by floating
five 0.1 m
 
2
 
 pvc frames in a water-filled tank. Living primary
and secondary growth form, common salvinia plants were
placed in a frame until it was completely filled without
crowding, i.e. fronds laid flat and completely covering water
surface. This is the most typical condition for the plants in
 
1
 
USDA-ARS Invasive Plant Research Laboratory, Fort Lauderdale, FL; e-
mail: ptipping@saa.ars.usda.gov. Received for publication September 13,
2004 and in revised form February 3, 2005.
 48
 
J. Aquat. Plant Manage.
 
 43: 2005.
south Florida where the larger growth form (tertiary)
formed by crowding is rarely if ever present. Although mats
are very dynamic and irregular, this estimate targeted a solid
mat of a square meter which does exist regularly, if tempo-
rarily, at many sites. Plants were then removed, blotted dry
with paper towels and weighed. Through extrapolation, the
mean of these measurements provided a realistic estimate of
the average fresh biomass of common salvinia per square
meter at sites in south Florida. We compared these values
with numerous field collected samples of contiguous mats of
common salvinia in the primary and secondary growth form
from another study and found them not significantly differ-
ent. We determined the area sampled by converting dry
weight to fresh weight biomass (divide dry weight by mean
percent moisture [4%]), then dividing the estimated fresh
weight of the sample by the estimate (mean ± SE) for mean
fresh weight per square meter (1010.7 ± 9.51 g). The mean
number of 
 
C. salviniae 
 
adults per square meter of common
salvinia was estimated by multiplying the area of the sample
by the number of weevils collected in that sample. This esti-
mate was generated to provide some context for relative
comparison to other studies.
 
Site Descriptions
 
. Sample sites differed in water and light
conditions, as well as associated vegetation, and included
river, canal, slough, and ditch habitats. The Hiatus site
(N26°05.101, W81°17.663) was a ditch in a residential area in
full sun that also contained populations of giant duckweed
(
 
Spirodela polyrhiza
 
 [L.] Schleiden), water penny (
 
Hydrocotyle
umbellata 
 
L.), and cattail (
 
Typha latifolia 
 
L). The Keri Rd.
(N26°35.826, W81°24.774) site was situated in a canal in full
sun in Glades County with waterhyacinth (
 
Eichhornia crassipes
 
[Mart.] Solms), water lettuce (
 
Pistia stratiotes 
 
L.), and mos-
quito fern (
 
Azolla caroliniana 
 
Willdenow) growing within. Rt.
29 (N26°48.956, W81°24.596) was a full sun site in a slough
in Hendry County colonized with torpedo grass (
 
Panicum lit-
torale 
 
Morhr ex Vasey), primrose willow (
 
Ludwigia peruviana
 
[L.]) Hara, and various sedges. Fish Eating Creek
(N26°55.845, W81°18.877) was a shaded site in an oxbow in
Glades County with waterhyacinth as the predominate vege-
tation besides common salvinia. Fakahatchee Strand
(N25°58.941, W81°24.213) was a roadside drainage ditch in
partial shade in a cypress swamp in Collier County with a va-
riety of emergent vegetation in close association. The Turner
river site (N25°53.265, W81°16.254) was located on the Turn-
er River just south of the Tamiami Trail bridge in Collier
County. Sampling at this site was conducted from boats
around emergent vegetation on both banks. These last two
sites were not sampled as often as the first four sites.
 
RESULTS AND DISCUSSION
 
A floating plant like common salvinia is completely de-
pendent on water conditions, especially water levels, and
there were multiple occasions where sites dried up or were
flushed out by high water levels (Figure 1). Despite these
perturbations, 
 
C. salviniae 
 
populations were present through-
out the course of the study as long as common salvinia was
present. Although the relationship between common salvinia
density and 
 
C. salviniae 
 
populations at the site level was not
quantified implicitly in this study, it was rare that weevils were
not collected from the plants. The most intensively sampled
site, Hiatus, showed somewhat regular peaks in 
 
C. salviniae
 
densities that generally corresponded with fall and winter
seasons in the first two years. However, during 2001, a peak
in population density was evident during the spring and sum-
mer. Similar trends were visible at the Keri Rd., Rt. 29, and
Fish Eating creek sites (Figure 1).
Populations of 
 
C. salviniae 
 
rebounded quickly following
drought events when the site dried up and later rehydrated.
This indicates that local extinction events can be ameliorated
by the metapopulation dynamics of this species, which is ca-
pable of flight dispersal to new sites. Sites like Keri Road,
Fakahatchee Strand, and Fish Eating Creek experienced reg-
ular local extinctions of the host plant because of drought,
yet were quickly recolonized by weevils after water levels rose
and common salvinia reappeared (Fakahatchee Strand data
not shown). A site like Turner River, which was less stagnant
than the other sites and experienced regular flushing events,
supported smaller and more fugitive populations of com-
mon salvinia. Despite this, 
 
C. salviniae 
 
was found regularly as
long as the plant was present, albeit at lower densities (data
not shown).
During the course of this survey there appeared to be a
least one major peak of adult density each year at the less dy-
namic sites, with the highest numbers occurring more often
during late fall and early winter, but sometimes during the
summer. Populations of 
 
C. salviniae 
 
can
 
 
 
build up to high lev-
els on common salvinia mats and such densities may have a
suppressive effect on populations of the plant, rendering it
less aggressive as suggested by Jacono (2001). It is notewor-
thy that during this survey we never saw common salvinia in
the tertiary growth stage. This growth form typifies sites in
Texas and Louisiana where unrestricted growth by the plant
occurs (P. W. T., pers. observ.). This may be a result of nutrifi-
cation or other environmental factors but may also reflect
the absence of herbivory by 
 
C. salviniae
 
. The overall mean (±
SE) for the estimate of weevils per square meter of common
salvinia ranged from 40.6 ± 5.0 at Keri Rd. to 11.0 ± 3.1 at
Turner River. This estimate approached or exceeded 100 at
some dates and sites in this study. Although Room (1988)
and Room and Thomas (1985) estimated that 300 adults and
900 larvae of 
 
C. salviniae 
 
per square meter were necessary to
control giant salvinia, a larger plant, recent work in the U.S.
on giant salvinia found that less than 100 adults of 
 
C. salvini-
ae 
 
per square meter would suffice (P. W. T., unpubl. data).
Accordingly, a lesser number would presumably be sufficient
to control the smaller common salvinia.
Two additional herbivores were commonly found during
this survey: 
 
Samea multiplicalis 
 
(Guenée) (Lepidoptera: Pyral-
idae) and 
 
Synclita obliteralis 
 
(Walker) (Lepidoptera: Pyral-
idae)
 
.
 
 Both species are generalists and feed on a variety of
aquatic plants throughout the southeastern U.S. (Knopf and
Habeck 1976, Habeck et al. 1986). 
 
Samea multiplicalis 
 
was re-
leased in Australia on giant salvinia with no significant effect
(Forno 1987). It is present in both common and giant salvin-
ia infestations in Texas and Louisiana where the impact ap-
pears to be negligible (P. W. Tipping, unpubl. data).
These data indicate that 
 
C. salviniae 
 
is present throughout
the year in south Florida on common salvinia. It can build up
to densities estimated to exceed 100 adults per square meter
 J. Aquat. Plant Manage.
 
 43: 2005. 49
 
Figure 1. Mean number of 
 
C. salviniae 
 
adults collected per g of common salvinia
 
 
 
in various sites in south Florida during 1999 to 2001.
 50
 
J. Aquat. Plant Manage.
 
 43: 2005.
at sites where common salvinia populations are relatively sta-
ble. At these higher densities, we suggest that 
 
C. salviniae
 
 may
regulate populations of common salvinia in south Florida.
 
ACKNOWLEDGMENTS
 
We thank L. Bauer, T. Davern, A. Forrestal, E. Porkorny,
and A. Strong for their assistance in collecting and process-
ing samples.
 
LITERATURE CITED
 
Forno, I. W. 1987. Biological control of the floating fern 
 
Salvinia molesta 
 
in
north-eastern Australia: plant-herbivore interaction. Bull. Entomol. Res.
77:9-17.
Goolsby, J. A., P. W. Tipping, T. D. Center and F. Driver. Evidence of a new
 
Cyrtobagous 
 
species (Coleoptera: Curculionidae) on 
 
Salvinia minima
 
Baker in Florida. Southwest. Entomol. 25:299-301.
Habeck, D. H., K. Haag and G. Buckingham. 1986. Native insect enemies of
aquatic macrophytes-moths. Aquatics 8:17-19, 22.
Jacono, C. C., T. R. Davern and T. D. Center. 2001. The adventive status of 
 
Sal-
vinia minima 
 
and 
 
S. molesta 
 
in the southern United States and the related
distribution of the weevil 
 
Cyrtobagous salviniae
 
. Castanea 66:214-226.
Knopf, K. W. and D. H. Habeck. 1976. Life history and biology of 
 
Samea multi-
plicalis
 
. Envir. Entomol. 5:539-542.
Lawalree, A. 1964. Salviniaceae, pp. 24-25. 
 
In:
 
 T. G. Tutin and others (eds.)
with the assistance of P. W. Ball and A. O. Chater. Flora Europaea. Vol. 1.
University Press, Cambridge.
Madeira, P. T., C. C. Jacono, P. W. Tipping, T. K. Van and T. D. Center. 2003.
A genetic survey of 
 
Salvinia minima 
 
in the southern United States.
Aquatic Bot. 76:127-139.
Mickel, J. T. and J. M. Beitel. 1988. Pteridophyte flora of Oaxaca, Mexico.
Mem. New York Bot. Gard. 46:328-329.
Palacios-Rios, M. and G. Cortes. 1990. New pteridophyte records for the
state of Quintana Roo, Mexico. Brittonia 42:241-243.
Proctor, G. R. 1989. Ferns of Puerto Rico and the Virgin Island. Mem. New
York Bot. Gar. 53. Bronx, New York.
Room, P. M. 1988. Effects of temperature, nutrients and a beetle on branch
architecture of the floating weed 
 
Salvinia molesta 
 
and simulations of bio-
logical control. J. Ecology 76:826-848.
Room, P. M., K. L. S. Harley, I. W. Forno and D. P. A. Sands. 1981. Successful
biological control of the floating weed 
 
salvinia
 
. Nature 294:78-80.
Room, P. M. and P. A. Thomas. 1985. Nitrogen and establishment of a beetle
for biological control of the floating weed salvinia in Papua New Guinea.
J. Applied Ecology 22:139-156.
Small, J. K. 1931. Ferns of Florida: being descriptions of an notes on the
fern-plants growing naturally in Florida (illustrated). The Science Press,
New York. pp. 190-193.
Stoltze, R. G. 1983. Ferns and fern allies of Guatemala. Part III. Mar-
sileaceae, Salviniaceae, and the fern allies. Fieldiana Bot. 12:10-13.
Weatherby, C. A. 1937. A further note on 
 
Salvinia
 
. Am. Fern J. 27:98-102.
Manual Control of 
 
Phragmites australis
 
in Freshwater Ponds of Cape Cod
National Seashore, Massachusetts, USA
 
STEPHEN M. SMITH
 
1
 
INTRODUCTION
 
The non-native, invasive genotype of the common reed
(
 
Phragmites
 
 
 
australis
 
 (Cav.) Trin. ex Steudel) has become a
problem of significant proportions throughout wetlands of
North America (Saltonstall 2001). Although attempts to sup-
press or eradicate 
 
Phragmites
 
 have utilized a wide variety of
techniques, herbicides have generally been most effective
(Marks et al. 1994). However, their use may be infeasible due
to policy, political, or ecological concerns and alternative
techniques are often sought.
In non-tidal, freshwater environments, 
 
Phragmites
 
 may oc-
casionally experience lengthy periods of flooding. Although
well-adapted for growth in anaerobic substrates, extreme
flooding results in increased metabolic demands associated
with the transport of oxygen from aerial parts to the roots
(McKee et al. 1989). In 2003, Cape Cod experienced record
amounts of rainfall that resulted in extremely high water lev-
els. In the spring, mid-summer, and late summer of that year
we attempted to opportunistically control 
 
Phragmites
 
 in five
freshwater ponds within Cape Cod National Seashore
(CCNS) by repeatedly severing stems underwater, at ground
level. Based on previous studies on the effects of underwater
cutting (Husak 1978, Weisner and Graneli 1989, Hellings
and Gallagher 1992, Rolletschek et al. 1998, 1999, Rollet-
schek and Hartzendorf 2000, Asaeda et al. 2003), we hypoth-
esized that the stress of root oxygen deprivation and forced
depletion of carbohydrate reserves during re-growth might
be sufficient to induce substantial mortality in this particular
setting.
 
MATERIALS AND METHODS
 
Five freshwater ponds within CCNS that had been invaded
by 
 
Phragmites
 
 (Long, Round, Snow, Ryder, and Great) were
randomly selected for treatment. Since there were no other
spatially discrete stands of 
 
Phragmites
 
 that could serve as within-
 
1
 
National Park Service, Cape Cod National Seashore, 99 Marconi Site
Road, Wellfleet, MA 02667; (508) 487-3262 x104; stephen_m_smith@nps.gov.
Received for publication September 13, 2004 and in revised form December
17, 2004.
 
J. Aquat. Plant Manage.
 
 43: 50-53


Population Dynamics of Cyrtobagous salviniae on Common Salvinia in South Florida

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Population Dynamics of Cyrtobagous salviniae on Common Salvinia in South Florida

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