June, 2004
Journal of Vector Ecology
Abundance and temporal distribution of Ornithonyssus sylviarum
Canestrini and Fanzago (Acarina: Mesostigmata) in gray catbird
(Dumatella carolinensis) nests
Mary C. Garvin, Lydia C. Scheidler, Dara G. Cantor, and Kristen E. Bell
Department of Biology, Oberlin College, Oberlin, OH 44074, U.S.A.
Received 6 March 2003; Accepted 21 October 2003
ABSTRACT: The northern fowl mite, Ornithonyssus sylviarum Canestrini and Fanzago, is a common ectoparasite
of wild birds. Despite its ability to transmit eastern equine encephalitis (EEE) virus under laboratory conditions
and potential for involvement in the natural EEE virus cycle, we know little about its abundance or temporal
distribution in nature. From June to August 2000, we studied the abundance of O. sylviarum in the nests of gray
catbirds (Dumatella carolinensis), a reservoir host for EEE virus, at Killbuck Marsh Wildlife Area (KMWA), a
known EEE virus focus in Wayne County, Ohio. A total of 7,883 O. sylviarum, including 1,910 adults and 5,973
protonymphs, were recovered from 23 of 26 gray catbird nests collected during various phases of the nesting cycle.
We found no association between mite abundance and number of catbird nestlings in successful nests. However,
mite abundance increased significantly with date of nest collection and peaked in late July when transmission of
EEE virus is likely to occur at KMWA. We therefore suggest that O. sylviarum may contribute to the transmission
of EEE virus among gray catbirds at KMWA. Journal of Vector Ecology 29 (1): 62-65. 2004.
Keyword Index: Dumatella carolinensis, gray catbird, Ornithonyssus sylviarum, eastern equine encephalitis virus,
arboviral transmission.
INTRODUCTION
Ornithonyssus sylviarum, the northern fowl mite,
is a common ectoparasite of wild and domestic birds.
Laboratory experiments with chickens have
demonstrated that it is capable of transmitting viral
pathogens, including eastern equine encephalitis (EEE)
virus (Chamberlain and Sikes 1955), for which wild
passerine birds serve as reservoir hosts. Furthermore,
heavy infestations in chickens have resulted in significant
blood loss (DeLoach and DeVaney 1981) and reduced
egg production (DeVaney 1979). Despite its potential
as a vector of EEE virus among wild birds, we understand
little about its abundance and temporal patterns in nature,
particularly relative to the breeding cycle of the avian
hosts (Masan 1997).
During a larger investigation of the gray catbird as
a reservoir host for EEE virus at Killbuck Marsh Wildlife
Area (KMWA), a known EEE virus focus in central Ohio
(Nasci et al. 1993), we conducted this study of O.
sylviarium in gray catbird nests. Wild bird nests provide
ideal habitats for free-living ornithophilic parasites, and
such species may be easily recovered from nest material.
The gray catbird (Dumatella carolinensis) is a
Neotropical-Nearctic migrant passerine bird that breeds
in brushy shrub-sapling successional habitat throughout
North America (Cimprich and Moore 1995). Catbirds
are especially abundant in bottomlands of KMWA where
wetlands with dense thickets provide optimal breeding
conditions. Here, we report on the incidence and
abundance of O. sylviarum in gray catbird nests at this
site in relation to the date of nest termination and brood
size.
MATERIALS AND METHODS
We collected mites from gray catbird nests from June
to August 2000 at KMWA (40°,41′N: 81°,58′W) in
Wayne County, OH. Nests were located by extensive
searches of woodland edges and thickets and by
following breeding adults to the nest site. Each nest was
monitored and nest contents were checked every 1-4 d,
depending on the phase of the nesting cycle. Within 24 h
of termination (fledging or failure) each nest was
collected, placed in a zip-lock bag, and returned to the
laboratory. To recover mites, within 24 h of collection
each nest was placed in a Berlesse Funnel for 24 h. All
specimens were stored in 70% ethyl alcohol and cleared
62
June, 2004
Journal of Vector Ecology
with either specimen clearing fluid (BioQuip., Gardena,
CA) or 55% lactic acid. They were then mounted on
microscope slides in euparal mounting medium (BioQuip
Products, Inc.), and identified.
Spearman’s rank correlation (SPSS, Inc, 2001) was
used to test for an association between Julian date and
number of mites per nest and between number of
nestlings and abundance of mites. To control for the
amount of time that the young had spent in the nest, for
both analyses we used only those nests that successfully
fledged young.
63
RESULTS
A total of 7,883 O. sylviarum, including 1,910 adults
and 5,973 protonymphs, was collected from 23 (88.5%)
of the 26 gray catbirds nests examined (Table 1). Mite
abundance per nest ranged from 0-3,401 and did not
appear to be influenced by number of nestlings in
successful nests (rs = 0.131, P = 0.642) which ranged
from 1-4 (Table 1). Mite abundance increased
significantly with Julian date in nests that fledged young
(rs = 0.616, P = 0.014, Figure 1). The greatest infestations
were detected in two nests that had recently fledged
young during the last week of July.
Table 1. Number of Ornithonyssus sylviarum in individual gray catbird nests relative to date of collection and
status of nest.
Date of
collection
8 August
8 August
7 August
6 August
4 August
29 July
27 July
25 July
23 July
21 July
18 July
18 July
18 July
14 July
14 July
12 July
11 July
10 July
10 July
6 July
3 July
1 July
30 June
19 June
15 June
13 June
TOTAL
Stage of nest at
collection
(no. of nestlings)
fledged (3)
eggs
fledged (1)
fledged (3)
eggs
fledged (2)
fledged (2)
fledged (4)
nestling (3)
fledged (1)
fledged (4)
nestling (2)
nestling (1)
fledged (2)
fledged (3)
nestling (3)
fledged (2)
nestling (2)
fledged (4)
eggs
fledged (3)
fledged (4)
nestling (3)
nestling (3)
fledged (3)
nestling (1)
No. of protonymphs
0
31
0
23
108
78
2,988
2,373
1
4
122
18
0
1
6
0
0
3
183
6
1
3
19
0
5
0
5,973
No. of adults
190
0
443
51
1
11
413
594
1
14
3
0
0
0
0
9
0
1
172
0
0
6
0
0
0
1
1,910
Total
190
31
443
74
109
89
3,401
2,967
2
18
125
18
0
1
6
9
0
4
355
6
1
9
19
0
5
1
7,883
64
Journal of Vector Ecology
June, 2004
Number of mites per nest
4000
3000
2000
1000
0
-1000
160
170
180
190
200
210
220
230
Julian Date
Figure 1. The association between Julian date and abundance of mites per successful gray catbird nest. Successful
nests are those that fledged young.
DISCUSSION
The increase in mite abundance during the course
of the breeding period is likely a result of the steady
increase in the total number of mites in the catbird habitat
(Masan 1997). Catbirds commonly make two nesting
attempts per breeding season, constructing a new nest
for each attempt (Cimprich and Moore 1995). Therefore,
nesting material from old nests is not reused and mites
from abandoned nests migrate to active nests in search
of new hosts (Sikes and Chamberlain 1954). Ambient
conditions and resulting nest microclimate were not
measured in this study and may also have contributed to
the observed temporal pattern of abundance.
The number of nestlings occupying the nest did not
appear to influence mite abundance. This result is
consistent with the work of Darolova et al. (1997) who
also found no relationship between abundance of O.
sylviarum and number of penduline tit (Remiz
pendulinus) nestlings. However, this is in contrast with
studies by Masan (1997) who found a positive correlation
between penduline tit clutch size and number of mites
per nest. Because the results of the current study could
be an artifact of sample size, a more extensive study of
gray catbirds could reveal a positive correlation as well.
The greatest abundance of mites per nest observed
later in the summer coincides with seasonal EEE activity
detected in gray catbirds at KMWA (Garvin et al. 2003).
Although Culiseta melanura Coquillett (Diptera:
Culicidae) is considered the primary enzootic vector of
EEE virus at inland EEE foci (Chamberlain et al. 1958),
Crans et al. (1994) suggested that ornithophilic mites
may also contribute to the natural transmission cycle.
Given that O. sylviarum feeds at least once every 24 h
(DeLoach and DeVaney 1981) and protonymphs require
at least two feedings at 1-2 d intervals (Sikes and
Chamberlain 1954), mites could acquire infection by
feeding on an infected brooding female and transmit the
infection to a nestling through a subsequent blood meal.
Thus, O. sylviarum could contribute to maintenance of
the virus in the avian reservoir host population, especially
during interepizootic years when epizootic mosquito
vectors are less abundant. Moreover, O. sylviarum could
also play a role in transmission of EEE and other
arboviruses to humans in light of its tendency to bite
mammals when present in large numbers and in the
absence of a suitable avian host (Cameron 1938, Schmidt
and Roberts 1989). Clearly, the positive correlation
reported here between number of mites per nest and
Julian date is due to the large number of mites in nests
collected in late July. Nonetheless, great variance and
large numbers of mites in late season broods have been
reported for the house sparrow, Passer domesticus
(Phillis 1972), and therefore may be an accurate
reflection of seasonal mite abundance in gray catbirds
as well.
June, 2004
Journal of Vector Ecology
Acknowledgments
This study was generously funded by Oberlin
College and a grant from the Howard Hughes Medical
Institute to Oberlin College. We thank Laura Vineyard
for assistance with lab work, Keith Tarvin for review of
this manuscript, and Hans Klompen, Acarology
Laboratory, Museum of Biological Diversity, Ohio State
University for guidance in mite identification. We also
thank the staff of KMWA, Ohio Department of Natural
Resources, especially Kevin Higgins, for assistance and
logistical support.
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