Stomach-content analyses of pitfall-trapped amphibians and small mammals showed that the eastern American toad, Bujo americanus americanus, and the wood frog, Rana sylvatica, preyed on late instars and moths of the spruce budworm, Choristoneura fumiferana. The spotted salamander, Ambystoma maculatum, and the masked shrew, Sorex cinereus, also preyed on late instars of the spruce budworm

Crawford, Hewlette S, Jr.

Hunter, Malcolm L, Jr.

Jennings, Daniel T

English

ValpoScholar

The Great Lakes Entomologist 
Volume 24 
Number 2 - Summer 1991 Number 2 - Summer 
1991 
Article 2 
June 1991 
Predation by Amphibians and Small Mammals on the Spruce 
Budworm (Lepidoptera: Tortricidae) 
Daniel T. Jennings 
Northeastern Forest Experiment Station 
Hewlette S. Crawford Jr. 
Northeastern Forest Experiment Station 
Malcolm L. Hunter Jr. 
University of Maine 
Follow this and additional works at: https://scholar.valpo.edu/tgle 
 Part of the Entomology Commons 
Recommended Citation 
Jennings, Daniel T.; Crawford, Hewlette S. Jr.; and Hunter, Malcolm L. Jr. 1991. "Predation by Amphibians 
and Small Mammals on the Spruce Budworm (Lepidoptera: Tortricidae)," The Great Lakes Entomologist, 
vol 24 (2) 
Available at: https://scholar.valpo.edu/tgle/vol24/iss2/2 
This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. 
It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. 
For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. 
1991 THE GREAT LAKES ENTOMOLOGIST 69 
PREDATION BY AMPHIBIANS AND SMALL MAMMALS ON 

THE SPRUCE BUDWORM (LEPIDOPTERA: TORTRICIDAE) 

Daniel T. Jenningsl Hewlette S. Crawford, Jr.2 and Malcolm L. Hunter, Jr.3 
ABSTRACT 
Stomach-content analyses of pitfall-trapped amphibians and small mammals 
showed that the eastern American toad, Bujo american us american us, and the wood 
frog, Rana sylvatica, preyed on late ins tars and moths of the spruce budworm, 
Choristoneura jumijerana. The spotted salamander, Ambystoma maculatum, and 
the masked shrew, Sorex cinereus, also preyed on late instars of the spruce 
budworm. 
Known predators of the spruce budworm, Choristoneura jumijerana (Clem.), 
include both invertebrates and vertebrates (Jennings and Crawford 1985). Of the 
vertebrate predators, birds are the best known and most extensively studied (Dow­
den et al. 1953, Morris 1963, Crawford et al. 1983, Crawford and Jennings 1989). 
Although small mammals have long been implicated as potential predators of the 
spruce budworm (Morris et al. 1958, Morris 1963, Otvos 1981, Kelly and Regniere 
1985), definitive evidence of such predation generally has been lacking, except for 
the red squirrel, Tamiasciurus hudsonicus (Bangs), (Dowden et al. 1953, Jennings 
and Crawford 1989). Because of their dependence on fresh water, amphibians gener­
ally are considered unimportant predators of forest insects (Buckner 1966). Never­
theless, budworm larvae and pupae are susceptible to predation by terrestrial verte­
brates, such as amphibians and small, insectivorous mammals, when the large larvae 
drop from host-tree crowns to the forest floor (Morris and Mott 1963, Kelly and 
Regniere 1985). Amphibian populations were monitored during budworm­
suppression projects in Maine (Banasiak 1974, Peterson 1976, Sassaman 1978), but 
predation on the spruce budworm was not determined. 
Here we describe for the first time predation by amphibians (both anurans and 
caudates) on late instars and moths f the spruce budworm. We also provide defini­
tive evidence of predation by small mammals (insectivores) on late instars of C. 
jumijerana. 
MATERIALS AND METHODS 
Study Sites. We pitfall-trapped amphibians and small mammals for two years 
(1977, 1978) in a spruce-fir (Picea-Abies) forest that was heavily infested with the 
spruce budworm. Individual study sites were 48-61 km northwest of Millinocket, 
lNortheastern Forest Experiment Station, 180 Canfield St., Morgantown, WV 26505. 
2Northeastern Forest Experiment Station, USDA Building, University of Maine, Orono, 
ME 04469. 
3Department of Wildlife, College of Forest Resources, University of Maine, Orono, ME 
04469. 
1
Jennings et al.: Predation by Amphibians and Small Mammals on the Spruce Budworm (
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70 THE GREAT LAKES ENTOMOLOGIST Vol. 24, No.2 
Piscataquis County, Maine (45 0 45' -460 10' N, 68°55' -69"20' W). Portions of the 
forest had been strip clearcut, resulting in alternating clearcut and uncut residual 
strips. We investigated 5 strip-clear cut stands and 5 nearby dense (uncut) stands in 
1977; 
7 strip-clearcut stands and 3 dense stands were investigated in 
1978. For details 
of 
study-site vegetation, sampling design, and associated invertebrates, 
see Jennings 
et al. (1984, 1986a, 1986b, 1988). 
Pitfall Traps. For both study years, we used40 large-capacity pitfall traps (House­
weart et al. 1979) to capture terrestrial amphibians and small mammals. Each trap 
bottle (I liter) contained ca. 300 ml of a 1:1 mixture of ethylene glycol (antifreeze) 
and 700/0 ethanol as a killing-preservative agent. Four traps were placed in each 
strip-clearcut stand (5 replications, 1977; 7 replications, 1978); one trap each in two 
clearcut strips and in two adjacent uncut residual strips (see Fig. 1, Jennings et al. 
1984). 
Correspondingly, four traps were placed in each nearby dense (uncut) stand 
investigated 
(5 replications, 1977, 3 replications, 1978). Traps were open continu­
ously and their contents collected weekly for 10 weeks (26 May-4 August) in 1977, 
and for 11 weeks (18 May-3 August) in 1978. Total sampling effort was 5580 trap 
nights. 
Identifications. Pitfall-trap contents were transferred to small jars and trans­
ported to the laboratory where collections were sorted and identified. Amphibian 
identifications follow Conant (1975); small mammal identifications follow Burt and 
Grossenheider (1976) and Godin (1977). All vertebrate identifications were verified 
by comparison with museum specimens retained in the Department of Wildlife, and 
Department of Zoology, University of Maine, Orono. Voucher specimens of col­
lected amphibians and small mammals have been deposited in the collections of the 
Department of Wildlife, College of Forest Resources, University of Maine, Orono. 
Stomach-Content Analyses. Digestive tracts of captured amphibians (n = 134; 5 
desiccated specimens not dissected) and of small mammals (Insectivora only; n = 
41) were removed and their contents examined with a stereomicroscope. Larval 
mandibles, pupal cremasters, and moth genitalia were compared with a reference 
collection of the spruce budworm and associated insects. The chitinized mandibles, 
cremasters, and genitalic parts are the most reliable diagnostic structures for identi­
fying remains of C. jumiferana in predator stomachs (Crawford and Jennings 
1982). For amphibian stomach contents, larval instars of the spruce budworm were 
determined by head-capsule size (McGugan 1954). Because larval head capsules are 
seldom found intact in small mammal stomachs, we estimated instars based on 
relative mandible size, i.e., ocular estimates of mandible size compared with refer­
ence material. 
RESULTS 
Amphibian Nnmbers and Species. One hundred thirty-nine amphibians represent­
ing two orders, five families, five genera, and six species were pitfall-trapped in 
spruce-fir forests of northern Maine. The species and total numbers trapped were: 
eastern American toad, Bujo americanus american us Holbrook, (n = 64); wood 
frog, Rana sylvatica LeConte, (n = 62); redback salamander, Plethodon cinereus 
(Green), (n = 9); red-spotted newt, Nofopthalmus viridescens viridescens (Rafines­
que), (n = 1); spotted salamander, Ambystoma maculatum (Shaw), (n = 1); and 
blue-spotted salamander, Ambystoma laterale Hallowell, (n = 2). Anura (toads, 
frogs) were found in all three forest conditions studied; Caudata (salamanders, 
newts) were found mostly in uncut residual strips and in dense (uncut) stands. 
Amphibian Predation on Spruce Budworm. For both study years, amphibians fed 
on larvae and moths of the spruce budworm (Table 1). However, the percentage of 
pitfall-trapped amphibians that had eaten budworm prey was low « 7.5Ofo, n 
134). 
Numbers 
of spruce budworm prey per stomach ranged from 1 to 6; most 
2
The Great Lakes Entomologist, Vol. 24, No. 2 [1991], Art. 2
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1991 THE GREAT LAKES ENTOMOLOGIST 71 
(70010) 
were late instars (Ls• 
L6), the keyage interval th t influences generation 
survival of the spruce budworm (Morris 1963). 
Small Mammal Numbers and Species. Forty-six small mammals representing two 
families, four genera, and five species were pitfall-trapped in strip-clearcut and 
dense (uncut) spruce-fir stands of northern Maine. The species and total numbers 
trapped were: masked shrew, Sorex cinereus Kerr, (n = 33); smoky shrew, Sorex 
fumeus Miller, (n = I); pygmy shrew, Mierosorex hoyt (Baird), (n = 7); red-backed 
vole, Clethrionomys gapperi (Vigors), (n 2); and southern bog lemming, Synapto­
mys 
eooperi Baird, (n 
= 3). Most (90.2%) of the Insectivora were trapped in strip­
clearcut stands, both in residual (uncut) strips and in strip clearcuts. Although few 
Rodentia were caught, they were trapped in all three forest conditions studied. 
Small Mammal Predation on Spruce Budworm. Digestive tracts of 16 (48%, n 
33) masked shrews and 3 (44010, n = 7) pygmy shrews contained insect larval 
mandibles (range 1 - 8). One tract of a masked shrew had an insect pupal cremaster. 
However, only two of these insect parts could be positively identified as remains of 
C. 
fumiferana. One distinctive spruce budworm 
mandible was found in each diges­
tive tract of 2 masked shrews, both captured on 30 June 1977 in residual strips. A 
possible mandible of the spruce budworm also was found in the digestive tract of 1 
pygmy shrew, but positive identification was impossible because distinctive features 
(mandibular teeth and condyle) were missing. 
DISCUSSION 
OUf 
stomach-content analyses 
of amphibian foods provides the first evidence that 
Ambystoma 
maculatum preys on larvae 
of the spruce budworm. The results of this 
study also indicate that both spruce budworm larvae and moths are included in the 
diets of Bufo a. american us and Rana sylvattea. All three species of amphibians 
should be added to the list of known predators of the spruce budworm (Jennings 
and Crawford 1985). 
We 
suspect that amphibian predation on the spruce budworm 
is opportunistic, 
and is influenced by prey availability and prey activity. Only the more active life 
stages (Le., larvae and moths) of the spruce budworm were eaten by amphibians. 
Although pre-pupae and pupae of the spruce bud worm also may drop from host­
tree crowns to the forest floor (Morris and Mott 1963, Kelly and Regniere 1985), 
none were eaten by the pitfall-trapped amphibians (Table I). Hence, these less 
active, generally immobile life stages may escape detection by amphibians. 
Because some amphibians frequently eat ants (Hamilton 1954. LeClair and Val­
lieres 1981), and most budworm life stages are susceptible to predation by ants 
(Finnegan 1978, McNeil et al. 1978), secondary predation may occur when ants 
transport budworm prey back to the nest. At least four of the eastern American 
toads examined during this study contained both budworm and ant prey in their 
stomachs. 
Our stomach-content analyses of small mammals confirms previously suspected 
but unsubstantiated predation by S. cinereus on large larvae of the spruce budworm. 
Otvos (1981) included the masked shrew among three small mammals suspected to 
feed on the spruce budworm in Newfoundland; however, stomach-content analyses 
were not made. Our study indicates that the masked shrew, and possibly the pygmy 
shrew, should be added to the list of vertebrate predators of the spruce budworm 
(Jennings and Crawford 1985). 
The extent and relative importance of predation by amphibians and small mam­
mals on the spruce budworm generally are unknown. Kelly and Regniere (1985) 
concluded that predation on spruce budworm pupae on the forest floor was high 
(72.5% per day). and w s largely attributable to vertebrate predators. No doubt the 
susceptibilities o predation by terrestrial vertebrates varies among the different 
3
Jennings et al.: Predation by Amphibians and Small Mammals on the Spruce Budworm (
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72 THE GREAT LAKES ENTOMOLOGIST Vol. 24, No.2 
Table 1. Predation by amphibians on the spruce budworm based on stomach-content analyses (N 
134) 
of pitfall-trap collections, Piscataquis County. Maine. 
Spruce budworm number and 
Date Predator 
species Habitat" life stage" 
1977 
30 June 
30 June 
30 
June 21 
July 4 Aug. 
Bujo a. americanus 
Rana sylvatica 
Rana sytvatica 
Bujo a. 
american us 
Rana sylvatica 
D 
R 
R 
C 
D 
3 - L6 
1- Ls 
1- L6 
1- L? 
I ~ 'moth 
1978 
1 June 
15 
June 15 
June 22 June 
20 
July 
Bujo a. americanus 
Bujo a. american us 
Ambystoma maculatum 
Bujo a. 
american us 
Bujo 
a. americanus 
D 
D 
D 
D 
R 
1 Ls 
1 - L3• 3 - L4• I - Ls. I 
I - L4• 1 Ls. I - L6 
I - Ls. 1 - L6 
1 ­ c moth 
L6 
°D 
= dense (uncut) stand; R uncut residual strip; C = c1earcut strip. 
"*L3 . . . L6 instar. 
budworm life stages (eggs, larvae, pre-pupae, pupae, moths). Such predation also 
may be influenced by budworm behavior (e.g., larval-pupal droppage from host­
tree crowns; increased mobility of starved larvae; moth-flight activity) and popula­
tion density (i.e., potential-prey abundance). Predator abundance and feeding 
behavior (generalist vs. specialist) also are factors. 
The large-capacity pitfall trap used in this study was primarily designed to capture 
terrestrial invertebrates such as ants, carabid beetles, phalangids, and spiders 
(Houseweart et al. 1979). Because this trap ha a plastic funnel (15 cm) that tapers to 
a 2.54-cm diameter spout, it no doubt was selectively biased toward capture of 
small-sized amphibians and insectivores. For future studies, larger-diameter traps 
with drift fences may yield substantially greater catches. 
LITERATURE CITED 
Banasiak, C. F. 1974. Population structure and reproductive ecology of the red-backed sala­
mander in DDT-treated forests f northern Maine. Ph.D. Diss. Univ. Maine, Orono Maine. 
127 
pp. 
Buckner, 
C. H. 1966. The role of vertebrate predators in the biological control of forest 
insects. Ann. Rev. Entomol. 11;449-470. 
Burt, W. H., and R. P. Orossenheider. 1976. A field guide to the mammals. Houghton Mifflin, 
Boston. 289 pp. 
Conant, R. 1975. A field guide to reptiles and amphibians of eastern and central North 
America. 2nd ed. The Peterson Field Guide Series. Houghton Mifflin Co., Boston. 429 pp. 
Crawford, H. S., Jr., and D. T. Jennings. 1982. Relationships of birds and spruce 
budworms-Literature 
review 
and annotated bibliography. USDA, For. Serv  Bibliogra­
phies and Literature of Agriculture No. 23. 38 pp. 
1989. Predation by birds on spruce bud worm Choristoneurafumiferana; functional, 
numerical, and total responses. Ecology 70:152-163. 
4
The Great Lakes Entomologist, Vol. 24, No. 2 [1991], Art. 2
https://scholar.valpo.edu/tgle/vol24/iss2/2
1991 THE GREAT LAKES ENTOMOLOGIST 73 
Crawford, H. S., R. W. Titterington, and D. T. Jennings. 1983. Bird predation and spruce 
budworm populations. J. Forestry 81:433-435, 478. 
Dowden, P. B., H. A. Jaynes, and V. M. Carolin. 1953. The role of birds in a spruce budworm 
outbreak in Maine. J. Econ. Entomo!. 46:307-312. 
Finnegan, R. J. 1978. Predation by Farmica lugubris (Hymenoptera: Formicidae) on Charista­
neura fumi/erana (Lepidoptera: Tortricidae). Can. For. Servo Bi-Mon. Res. Notes 
34(1):3-4. 
Godin, A. J. 1977. Wild mammals of New England. John Hopkins University Press, Balti­
more. 304 pp. 
Hamilton, W. J., Jr. 1954. The economic status of the toad. Herpetologica 10: 37-40. 
Houseweart, M. W., D. T. Jennings, and J. C. Rea. 1979. Large capacity pitfall trap. Ento­
mol. News 90:51-54. 
Jennings, D. T., and H. S. Crawford, JI. 1985. Predators of the spruce budworm. USDA, 
Agric. Handb. 644. 77 pp. 
Jennings, D. T. and H. S. Crawford, Jr. 1989. Predation by red squirrels on the spruce 
budworm Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae). Can. Entomol. 
121 
:827-828. 
Jennings, 
D. T., M. W. Houseweart, and J. C. Cokendolpher. 1984. Phalangids (Arachnida: 
Opiliones) associated with strip dearcut and dense spruce-fir forests in Maine. Environ. 
Entomol. 13: 1306-1311. 
Jennings, D. T., M. W. Houseweart, and A. Francoeur. 1986a. Ants (Hymenoptera: Formici­
dae) associated with strip cIearcut and dense spruce-fir forests of Maine. Can. Entomol. 
118:43-50. 
Jennings, D. T., M. W. Houseweart, and G. A. Dunn. 1986b. Carabid beetles (Coleoptera: 
Carabidae) associated with strip clearcut and dense spruce-fir forests of Maine. Coleopt. 
Bull. 40:251-263. 
Jennings, D. T., M. W. Houseweart, C. D. Dondale, and J. H. Redner. 1988. Spiders (Ara­
neae) associated with stripclearcut and dense spruce-fir forests of Maine. J. Arachno!. 
16:55-70. 
Jennings, D. T., and H. S. Crawford, Jr. 1989. Predation by red squirrels on the spruce 
budworm Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae). Can. EntomoL 
121:827-828. 
Kelly, 
B., and 
J. Regniere. 1985. Predation on pupae of the spruce budworm (Lepidoptera: 
Tortricidae) on the forest floor. Can. Entomol. 117:33-38. 
LeClair, R., JI., and L. Vallieres. 1981. Regimes alimentaires de Bufa am ricanus (Holbrook) 
et Rana sylvatica LeConte (Amphibia: Anura) nouvellement metamorphoses. Naturaliste 
Canada 108:325-329. 
McGugan, B. M. 1954. Needle-mining habits and larval instars of the spruce budworm. Can. 
Entomol. 86:439-454. 
McNeil, J. N., J. Delisle, and R. J. Finnegan. 1978. Seasonal predatory activity of the intro­
duced red wood ant, Formica lugubris (Hymenoptera: Formicidae) at Valcartier, Quebec, in 
1976. 
Can. Entomol. 110:85-90. 
Morris, 
R. F. 1963. Predation and the spruce budworm, pp. 244-248 In: R. F. Morris, Ed. The 
dynamics of epidemic spruce budworm populations. Mem. Entomol. Soc. Can. 31. 332 pp. 
Morris, R. F., W. F. Cheshire, C. A. Miller, and D. G. Mott. 1958. The numerical response of 
avian and mammalian predators during a gradation of the spruce budworm. Ecology 
39:487-494. 
Morris, R. F., and D. G. Mott. 1963. Dispersal and the spruce budworm, Pp. 180-189. In: R
F. 
Morris, Ed. The dynamics of epidemic spruce budworm populations. Mem. Entomol. 
Soc. 
Can. 31. 332 pp. 
Otvos, I. S. 1981. Predators. pp. 103-104. In: J. Hudak and A. G. Raske, Eds. Review of the 
spruce budworm outbreak in Newfoundland-its control and forest management implica­
tions. Information Report N-X-205. Can. For. Servo Environment Canada, St. John's, 
Newfoundland. 280 pp. 
Peterson, J. W. 1976. Effects of Dylox, Matacil, and Sumithion on birds, small mammals and 
amphibians, pp. 2-10. In: 1975 Cooperative Pilot Control Project of Dylox, Matacil, and 
5
Jennings et al.: Predation by Amphibians and Small Mammals on the Spruce Budworm (
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74 THE GREAT LAKES ENTOMOLOGIST Vol. 24, No.2 
Sumithion for spruce budworm control in Maine. USDA, For. Servo Northeastern Area 
State and Private Forestry. 92 pp.
Sassaman, J. F. 1978. Post-spray monitoring of amphibians (Orthene: Acephate) pp. 192-206. 
In: Environmental Monitoring of Cooperative Spruce Budworm Control Projects, Maine 
1976 and 1977. Maine Dept. Conserv. Bur. For., Augusta. 242 pp. 
6
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Predation by Amphibians and Small Mammals on the Spruce Budworm (Lepidoptera: Tortricidae)

Valparaiso University

The Great Lakes Entomologist Volume 24 Number 2 - Summer 1991 Number 2 - Summer 1991 Article 2 June 1991 Predation by Amphibians and Small Mammals on the Spruce Budworm (Lepidoptera: Tortricidae) Daniel T. Jennings Northeastern Forest Experiment Station Hewlette S. Crawford Jr. Northeastern Forest Experiment Station Malcolm L. Hunter Jr. University of Maine Follow this and additional works at: https://scholar.valpo.edu/tgle  Part of the Entomology Commons Recommended Citation Jennings, Daniel T.; Crawford, Hewlette S. Jr.; and Hunter, Malcolm L. Jr. 1991. "Predation by Amphibians and Small Mammals on the Spruce Budworm (Lepidoptera: Tortricidae)," The Great Lakes Entomologist, vol 24 (2) Available at: https://scholar.valpo.edu/tgle/vol24/iss2/2 This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. 1991 THE GREAT LAKES ENTOMOLOGIST 69 PREDATION BY AMPHIBIANS AND SMALL MAMMALS ON THE SPRUCE BUDWORM (LEPIDOPTERA: TORTRICIDAE) Daniel T. Jenningsl Hewlette S. Crawford, Jr.2 and Malcolm L. Hunter, Jr.3 ABSTRACT Stomach-content analyses of pitfall-trapped amphibians and small mammals showed that the eastern American toad, Bujo american us american us, and the wood frog, Rana sylvatica, preyed on late ins tars and moths of the spruce budworm, Choristoneura jumijerana. The spotted salamander, Ambystoma maculatum, and the masked shrew, Sorex cinereus, also preyed on late instars of the spruce budworm. Known predators of the spruce budworm, Choristoneura jumijerana (Clem.), include both invertebrates and vertebrates (Jennings and Crawford 1985). Of the vertebrate predators, birds are the best known and most extensively studied (Dow­den et al. 1953, Morris 1963, Crawford et al. 1983, Crawford and Jennings 1989). Although small mammals have long been implicated as potential predators of the spruce budworm (Morris et al. 1958, Morris 1963, Otvos 1981, Kelly and Regniere 1985), definitive evidence of such predation generally has been lacking, except for the red squirrel, Tamiasciurus hudsonicus (Bangs), (Dowden et al. 1953, Jennings and Crawford 1989). Because of their dependence on fresh water, amphibians gener­ally are considered unimportant predators of forest insects (Buckner 1966). Never­theless, budworm larvae and pupae are susceptible to predation by terrestrial verte­brates, such as amphibians and small, insectivorous mammals, when the large larvae drop from host-tree crowns to the forest floor (Morris and Mott 1963, Kelly and Regniere 1985). Amphibian populations were monitored during budworm­suppression projects in Maine (Banasiak 1974, Peterson 1976, Sassaman 1978), but predation on the spruce budworm was not determined. Here we describe for the first time predation by amphibians (both anurans and caudates) on late instars and moths f the spruce budworm. We also provide defini­tive evidence of predation by small mammals (insectivores) on late instars of C. jumijerana. MATERIALS AND METHODS Study Sites. We pitfall-trapped amphibians and small mammals for two years (1977, 1978) in a spruce-fir (Picea-Abies) forest that was heavily infested with the spruce budworm. Individual study sites were 48-61 km northwest of Millinocket, lNortheastern Forest Experiment Station, 180 Canfield St., Morgantown, WV 26505. 2Northeastern Forest Experiment Station, USDA Building, University of Maine, Orono, ME 04469. 3Department of Wildlife, College of Forest Resources, University of Maine, Orono, ME 04469. 1Jennings et al.: Predation by Amphibians and Small Mammals on the Spruce Budworm (Published by ValpoScholar, 199170 THE GREAT LAKES ENTOMOLOGIST Vol. 24, No.2 Piscataquis County, Maine (45 0 45' -460 10' N, 68°55' -69"20' W). Portions of the forest had been strip clearcut, resulting in alternating clearcut and uncut residual strips. We investigated 5 strip-clear cut stands and 5 nearby dense (uncut) stands in 1977; 7 strip-clearcut stands and 3 dense stands were investigated in 1978. For details of study-site vegetation, sampling design, and associated invertebrates, see Jennings et al. (1984, 1986a, 1986b, 1988). Pitfall Traps. For both study years, we used40 large-capacity pitfall traps (House­weart et al. 1979) to capture terrestrial amphibians and small mammals. Each trap bottle (I liter) contained ca. 300 ml of a 1:1 mixture of ethylene glycol (antifreeze) and 700/0 ethanol as a killing-preservative agent. Four traps were placed in each strip-clearcut stand (5 replications, 1977; 7 replications, 1978); one trap each in two clearcut strips and in two adjacent uncut residual strips (see Fig. 1, Jennings et al. 1984). Correspondingly, four traps were placed in each nearby dense (uncut) stand investigated (5 replications, 1977, 3 replications, 1978). Traps were open continu­ously and their contents collected weekly for 10 weeks (26 May-4 August) in 1977, and for 11 weeks (18 May-3 August) in 1978. Total sampling effort was 5580 trap nights. Identifications. Pitfall-trap contents were transferred to small jars and trans­ported to the laboratory where collections were sorted and identified. Amphibian identifications follow Conant (1975); small mammal identifications follow Burt and Grossenheider (1976) and Godin (1977). All vertebrate identifications were verified by comparison with museum specimens retained in the Department of Wildlife, and Department of Zoology, University of Maine, Orono. Voucher specimens of col­lected amphibians and small mammals have been deposited in the collections of the Department of Wildlife, College of Forest Resources, University of Maine, Orono. Stomach-Content Analyses. Digestive tracts of captured amphibians (n = 134; 5 desiccated specimens not dissected) and of small mammals (Insectivora only; n = 41) were removed and their contents examined with a stereomicroscope. Larval mandibles, pupal cremasters, and moth genitalia were compared with a reference collection of the spruce budworm and associated insects. The chitinized mandibles, cremasters, and genitalic parts are the most reliable diagnostic structures for identi­fying remains of C. jumiferana in predator stomachs (Crawford and Jennings 1982). For amphibian stomach contents, larval instars of the spruce budworm were determined by head-capsule size (McGugan 1954). Because larval head capsules are seldom found intact in small mammal stomachs, we estimated instars based on relative mandible size, i.e., ocular estimates of mandible size compared with refer­ence material. RESULTS Amphibian Nnmbers and Species. One hundred thirty-nine amphibians represent­ing two orders, five families, five genera, and six species were pitfall-trapped in spruce-fir forests of northern Maine. The species and total numbers trapped were: eastern American toad, Bujo americanus american us Holbrook, (n = 64); wood frog, Rana sylvatica LeConte, (n = 62); redback salamander, Plethodon cinereus (Green), (n = 9); red-spotted newt, Nofopthalmus viridescens viridescens (Rafines­que), (n = 1); spotted salamander, Ambystoma maculatum (Shaw), (n = 1); and blue-spotted salamander, Ambystoma laterale Hallowell, (n = 2). Anura (toads, frogs) were found in all three forest conditions studied; Caudata (salamanders, newts) were found mostly in uncut residual strips and in dense (uncut) stands. Amphibian Predation on Spruce Budworm. For both study years, amphibians fed on larvae and moths of the spruce budworm (Table 1). However, the percentage of pitfall-trapped amphibians that had eaten budworm prey was low « 7.5Ofo, n 134). Numbers of spruce budworm prey per stomach ranged from 1 to 6; most 2The Great Lakes Entomologist, Vol. 24, No. 2 [1991], Art. 2https://scholar.valpo.edu/tgle/vol24/iss2/21991 THE GREAT LAKES ENTOMOLOGIST 71 (70010) were late instars (Ls• L6), the keyage interval th t influences generation survival of the spruce budworm (Morris 1963). Small Mammal Numbers and Species. Forty-six small mammals representing two families, four genera, and five species were pitfall-trapped in strip-clearcut and dense (uncut) spruce-fir stands of northern Maine. The species and total numbers trapped were: masked shrew, Sorex cinereus Kerr, (n = 33); smoky shrew, Sorex fumeus Miller, (n = I); pygmy shrew, Mierosorex hoyt (Baird), (n = 7); red-backed vole, Clethrionomys gapperi (Vigors), (n 2); and southern bog lemming, Synapto­mys eooperi Baird, (n = 3). Most (90.2%) of the Insectivora were trapped in strip­clearcut stands, both in residual (uncut) strips and in strip clearcuts. Although few Rodentia were caught, they were trapped in all three forest conditions studied. Small Mammal Predation on Spruce Budworm. Digestive tracts of 16 (48%, n 33) masked shrews and 3 (44010, n = 7) pygmy shrews contained insect larval mandibles (range 1 - 8). One tract of a masked shrew had an insect pupal cremaster. However, only two of these insect parts could be positively identified as remains of C. fumiferana. One distinctive spruce budworm mandible was found in each diges­tive tract of 2 masked shrews, both captured on 30 June 1977 in residual strips. A possible mandible of the spruce budworm also was found in the digestive tract of 1 pygmy shrew, but positive identification was impossible because distinctive features (mandibular teeth and condyle) were missing. DISCUSSION OUf stomach-content analyses of amphibian foods provides the first evidence that Ambystoma maculatum preys on larvae of the spruce budworm. The results of this study also indicate that both spruce budworm larvae and moths are included in the diets of Bufo a. american us and Rana sylvattea. All three species of amphibians should be added to the list of known predators of the spruce budworm (Jennings and Crawford 1985). We suspect that amphibian predation on the spruce budworm is opportunistic, and is influenced by prey availability and prey activity. Only the more active life stages (Le., larvae and moths) of the spruce budworm were eaten by amphibians. Although pre-pupae and pupae of the spruce bud worm also may drop from host­tree crowns to the forest floor (Morris and Mott 1963, Kelly and Regniere 1985), none were eaten by the pitfall-trapped amphibians (Table I). Hence, these less active, generally immobile life stages may escape detection by amphibians. Because some amphibians frequently eat ants (Hamilton 1954. LeClair and Val­lieres 1981), and most budworm life stages are susceptible to predation by ants (Finnegan 1978, McNeil et al. 1978), secondary predation may occur when ants transport budworm prey back to the nest. At least four of the eastern American toads examined during this study contained both budworm and ant prey in their stomachs. Our stomach-content analyses of small mammals confirms previously suspected but unsubstantiated predation by S. cinereus on large larvae of the spruce budworm. Otvos (1981) included the masked shrew among three small mammals suspected to feed on the spruce budworm in Newfoundland; however, stomach-content analyses were not made. Our study indicates that the masked shrew, and possibly the pygmy shrew, should be added to the list of vertebrate predators of the spruce budworm (Jennings and Crawford 1985). The extent and relative importance of predation by amphibians and small mam­mals on the spruce budworm generally are unknown. Kelly and Regniere (1985) concluded that predation on spruce budworm pupae on the forest floor was high (72.5% per day). and w s largely attributable to vertebrate predators. No doubt the susceptibilities o predation by terrestrial vertebrates varies among the different 3Jennings et al.: Predation by Amphibians and Small Mammals on the Spruce Budworm (Published by ValpoScholar, 1991------------------------------------------72 THE GREAT LAKES ENTOMOLOGIST Vol. 24, No.2 Table 1. Predation by amphibians on the spruce budworm based on stomach-content analyses (N 134) of pitfall-trap collections, Piscataquis County. Maine. Spruce budworm number and Date Predator species Habitat" life stage" 1977 30 June 30 June 30 June 21 July 4 Aug. Bujo a. americanus Rana sylvatica Rana sytvatica Bujo a. american us Rana sylvatica D R R C D 3 - L6 1- Ls 1- L6 1- L? I ~ 'moth 1978 1 June 15 June 15 June 22 June 20 July Bujo a. americanus Bujo a. american us Ambystoma maculatum Bujo a. american us Bujo a. americanus D D D D R 1 Ls 1 - L3• 3 - L4• I - Ls. I I - L4• 1 Ls. I - L6 I - Ls. 1 - L6 1 ­ c moth L6 °D = dense (uncut) stand; R uncut residual strip; C = c1earcut strip. "*L3 . . . L6 instar. budworm life stages (eggs, larvae, pre-pupae, pupae, moths). Such predation also may be influenced by budworm behavior (e.g., larval-pupal droppage from host­tree crowns; increased mobility of starved larvae; moth-flight activity) and popula­tion density (i.e., potential-prey abundance). Predator abundance and feeding behavior (generalist vs. specialist) also are factors. The large-capacity pitfall trap used in this study was primarily designed to capture terrestrial invertebrates such as ants, carabid beetles, phalangids, and spiders (Houseweart et al. 1979). Because this trap ha a plastic funnel (15 cm) that tapers to a 2.54-cm diameter spout, it no doubt was selectively biased toward capture of small-sized amphibians and insectivores. For future studies, larger-diameter traps with drift fences may yield substantially greater catches. LITERATURE CITED Banasiak, C. F. 1974. Population structure and reproductive ecology of the red-backed sala­mander in DDT-treated forests f northern Maine. Ph.D. Diss. Univ. Maine, Orono Maine. 127 pp. Buckner, C. H. 1966. The role of vertebrate predators in the biological control of forest insects. Ann. Rev. Entomol. 11;449-470. Burt, W. H., and R. P. Orossenheider. 1976. A field guide to the mammals. Houghton Mifflin, Boston. 289 pp. Conant, R. 1975. A field guide to reptiles and amphibians of eastern and central North America. 2nd ed. The Peterson Field Guide Series. Houghton Mifflin Co., Boston. 429 pp. Crawford, H. S., Jr., and D. T. Jennings. 1982. Relationships of birds and spruce budworms-Literature review and annotated bibliography. USDA, For. Serv  Bibliogra­phies and Literature of Agriculture No. 23. 38 pp. 1989. Predation by birds on spruce bud worm Choristoneurafumiferana; functional, numerical, and total responses. Ecology 70:152-163. 4The Great Lakes Entomologist, Vol. 24, No. 2 [1991], Art. 2https://scholar.valpo.edu/tgle/vol24/iss2/21991 THE GREAT LAKES ENTOMOLOGIST 73 Crawford, H. S., R. W. Titterington, and D. T. Jennings. 1983. Bird predation and spruce budworm populations. J. Forestry 81:433-435, 478. Dowden, P. B., H. A. Jaynes, and V. M. Carolin. 1953. The role of birds in a spruce budworm outbreak in Maine. J. Econ. Entomo!. 46:307-312. Finnegan, R. J. 1978. Predation by Farmica lugubris (Hymenoptera: Formicidae) on Charista­neura fumi/erana (Lepidoptera: Tortricidae). Can. For. Servo Bi-Mon. Res. Notes 34(1):3-4. Godin, A. J. 1977. Wild mammals of New England. John Hopkins University Press, Balti­more. 304 pp. Hamilton, W. J., Jr. 1954. The economic status of the toad. Herpetologica 10: 37-40. Houseweart, M. W., D. T. Jennings, and J. C. Rea. 1979. Large capacity pitfall trap. Ento­mol. News 90:51-54. Jennings, D. T., and H. S. Crawford, JI. 1985. Predators of the spruce budworm. USDA, Agric. Handb. 644. 77 pp. Jennings, D. T. and H. S. Crawford, Jr. 1989. Predation by red squirrels on the spruce budworm Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae). Can. Entomol. 121 :827-828. Jennings, D. T., M. W. Houseweart, and J. C. Cokendolpher. 1984. Phalangids (Arachnida: Opiliones) associated with strip dearcut and dense spruce-fir forests in Maine. Environ. Entomol. 13: 1306-1311. Jennings, D. T., M. W. Houseweart, and A. Francoeur. 1986a. Ants (Hymenoptera: Formici­dae) associated with strip cIearcut and dense spruce-fir forests of Maine. Can. Entomol. 118:43-50. Jennings, D. T., M. W. Houseweart, and G. A. Dunn. 1986b. Carabid beetles (Coleoptera: Carabidae) associated with strip clearcut and dense spruce-fir forests of Maine. Coleopt. Bull. 40:251-263. Jennings, D. T., M. W. Houseweart, C. D. Dondale, and J. H. Redner. 1988. Spiders (Ara­neae) associated with stripclearcut and dense spruce-fir forests of Maine. J. Arachno!. 16:55-70. Jennings, D. T., and H. S. Crawford, Jr. 1989. Predation by red squirrels on the spruce budworm Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae). Can. EntomoL 121:827-828. Kelly, B., and J. Regniere. 1985. Predation on pupae of the spruce budworm (Lepidoptera: Tortricidae) on the forest floor. Can. Entomol. 117:33-38. LeClair, R., JI., and L. Vallieres. 1981. Regimes alimentaires de Bufa am ricanus (Holbrook) et Rana sylvatica LeConte (Amphibia: Anura) nouvellement metamorphoses. Naturaliste Canada 108:325-329. McGugan, B. M. 1954. Needle-mining habits and larval instars of the spruce budworm. Can. Entomol. 86:439-454. McNeil, J. N., J. Delisle, and R. J. Finnegan. 1978. Seasonal predatory activity of the intro­duced red wood ant, Formica lugubris (Hymenoptera: Formicidae) at Valcartier, Quebec, in 1976. Can. Entomol. 110:85-90. Morris, R. F. 1963. Predation and the spruce budworm, pp. 244-248 In: R. F. Morris, Ed. The dynamics of epidemic spruce budworm populations. Mem. Entomol. Soc. Can. 31. 332 pp. Morris, R. F., W. F. Cheshire, C. A. Miller, and D. G. Mott. 1958. The numerical response of avian and mammalian predators during a gradation of the spruce budworm. Ecology 39:487-494. Morris, R. F., and D. G. Mott. 1963. Dispersal and the spruce budworm, Pp. 180-189. In: RF. Morris, Ed. The dynamics of epidemic spruce budworm populations. Mem. Entomol. Soc. Can. 31. 332 pp. Otvos, I. S. 1981. Predators. pp. 103-104. In: J. Hudak and A. G. Raske, Eds. Review of the spruce budworm outbreak in Newfoundland-its control and forest management implica­tions. Information Report N-X-205. Can. For. Servo Environment Canada, St. John's, Newfoundland. 280 pp. Peterson, J. W. 1976. Effects of Dylox, Matacil, and Sumithion on birds, small mammals and amphibians, pp. 2-10. In: 1975 Cooperative Pilot Control Project of Dylox, Matacil, and 5Jennings et al.: Predation by Amphibians and Small Mammals on the Spruce Budworm (Published by ValpoScholar, 199174 THE GREAT LAKES ENTOMOLOGIST Vol. 24, No.2 Sumithion for spruce budworm control in Maine. USDA, For. Servo Northeastern Area State and Private Forestry. 92 pp.Sassaman, J. F. 1978. Post-spray monitoring of amphibians (Orthene: Acephate) pp. 192-206. In: Environmental Monitoring of Cooperative Spruce Budworm Control Projects, Maine 1976 and 1977. Maine Dept. Conserv. Bur. For., Augusta. 242 pp. 6The Great Lakes Entomologist, Vol. 24, No. 2 [1991], Art. 2https://scholar.valpo.edu/tgle/vol24/iss2/2

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Predation by Amphibians and Small Mammals on the Spruce Budworm (Lepidoptera: Tortricidae)

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