Anderson, N. L., R. F. Wack, L. Calloway, T. E. Hetherington, and J. B. Williams.
1999. Cardiopulmonary effect and efficacy of propofol as an anesthetic agent in
Brown Tree Snakes, Boiga irregularis. Bulletin of the Association of Reptile and
Amphibian Veterinarian 9:9-15.
Nine wild-caught brown tree snakes, Boiga irregularis
, were anesthetized with 5
mg/kg of propofol. Mean duration of anesthesia was 24 minutes. Eight of nine snakes
experienced 30 to 60 seconds of self-limiting apnea immediately following propofol injection.
Two of the nine snakes failed to achieve a surgical level of anesthesia, as assessed by positive
response to tail and vent pinch. Only mild ranges of heart rate, cardiac blood gases, ETCO2, and
SpO2 were observed. The magnitude of these changes was small, which correlates with smooth,
uncomplicated anesthesia experienced by all study snakes. Propofol appears to be a safe and
effective anesthetic for restraint or minor procedures in brown tree snakes. Standard techniques
used to monitor heart and respiratory rates should be adequate to assess cardiopulmonary status
of healthy brown tree snakes anesthetized with a single 5-mg/kg bolus of propofol. Brooks, J. E., P. J. Savarie, and J. J. Johnston. 1995. Acute oral toxicity of
selected chemicals to Brown Tree Snakes. Unpublished progress report for project
No. 1281. United States Department of Agriculture – APHIS. Denver, CO.
We tested seven chemicals for their oral toxicity to brown tree snakes: natural
pyrethrins, warfarin, diphacinone, aspirin, propoxur, carbaryl, and rotenone. The materials were
toxic to brown tree snakes at doses as low as 1.25 mg/kg, with death occurring in 37-55 min.
Natural pyrethrins and propoxur were approximately equal in toxicity, killing snakes in doses of
10-40 mg/kg. Propoxur was fast-acting, with death occurring in 39-46 min. Diphacionone killed
snakes at does of 20-80 mg/kg within 24 hr. Warfarin failed to kill any snakes at doses of 20-40
mg/kg. Carbaryl cause poisoning symptoms at doses of 80-160 mg/kg but killed only 2 of 10
snakes. Aspirin was found to be lethal at doses of 640 mg/kg and greater. These results agree
with earlier research. It also appears that the ethanol used as the gavaging carrier previously may
have enhanced mortality with some chemicals.
Brooks, J. E., P. J. Savarie, and J. J. Johnston. 1998. The oral and dermal toxicity of
selected chemicals to Brown Tree Snakes (Boiga irregularis). Wildlife Research
We evaluated the oral and dermal toxicity of 18 chemicals to brown tree snakes (Boiga
). Chemicals that produced mortality when dosed orally were rotenone, propoxur,
natural pyrethrins, allethrin, resmethrin, diphacinone, warfarin, and aspirin. The lowest oral
doses that gave 100% mortality were: rotenone, 2.5 mg kg–1; pyrethrins, 40 mg kg–1,
diphacinone, 80 mg kg–1, and aspirin, 1280 mg kg–1. Allethrin, resmethrin, and warfarin
produced 80% mortality at 40 mg kg–1, the highest dose tested. Materials given orally that
produced little mortality were permethrin, fenvalerate, and carbaryl; those given no mortality
were phenothrin, tetramethrin, piperonyl butoxide, propylene glycol, and cholecalciferol.
Chemicals that produced mortality when applied dermally at doses of 40 mg kg-1 were rotenone,
nicotine, propoxur, natural pyrethrins, allethrin, and resmethrin; those that gave more mortality
were permethrin, fenvalerate, phenothrin, tetramethrin, piperonyl butoxide, and diphacinone.
Retenone, at 10 mg kg-1, and nicotine, at 40 mg kg-1, were the most toxic dermally, killing all
tested snakes. Piperonyl butoxide enhanced the oral toxicity of allethrin and resmethrin and the
dermal activity of resmethrin; it did not enhance the activity of natural pyrethrins either orally or
dermally. Brooks, J. E., P. J. Savarie, and R. L. Bruggers. 1998. The toxicity of commercial
insecticide aerosol formulations to Brown Tree Snakes. The Snake 28:23-27.
A study was conducted in which brown tree snakes (Boiga irregularis) were treated
dermally with 10 commercially available insecticides containing natural pyrethrins or synthetic
pyrethroids, sometimes in combination with other insecticides or synergists. Snakes received 2
seconds of spray delivered from the aerosol containers. The results indicated that a
concentration-effect relationship existed for at least pyrethrins. Synergists appeared to enhance
the activity of the compounds, and at least one carbamate insecticide (propoxur) in one of the
commercial formulations was potentially toxic to brown tree snakes.
Brooks, J. E., P. J. Savarie, J. J. Johnston, and R. L. Bruggers. 1998. Toxicity of
pyrethrin/pyrethroid fogger products to Brown Tree Snakes, Boiga
irregularis, in cargo containers. The Snake 28:33-36.
We tested 3 insect fogger products as fumigation devices for toxicity to brown tree
snakes (Boiga irregularis
) in cargo containers on Guam. These insecticide fogger products are
registered with the U. S. Environmental Protection Agency (EPA) for use in homes, garages,
attics, basements, hospitals, hotels, railroad cars, truck trailers, warehouses, and zoos for the
control of cockroaches, ticks, crickets, earwigs, spiders, mosquitoes, and wasps. We found that
smoke-fumigators containing 12.6% permethrin failed to kill snakes, whether they were exposed
or semi-protected (in cloth bags). A fogger containing 0.5% pyrethrin and 0.1% cyfluthrin (a
synthetic pyrethroid) and the synergist 1% piperonyl butoxide, killed 6 of the 18 exposed snakes
in 3 hr exposure period but killed none of the 18 semi-protected snakes. A fogger containing
0.535% pyrethrin with two synergists (1.05% piperonyl butoxide and 0.71% n-octyl
bicycloheptene dicarboximide) killed 4 of the exposed snakes; none of the 18 bagged snakes
died. All snakes that were killed died within 24 hr after treatment; survivors showed no overt
symptoms of intoxication. Johnston, J. J., P. J. Savarie, T. M. Primus, J. D. Eisemann, J. C. Hurley, and D. J. Kohler.
2002. Rick assessment of an acetaminophen baiting program for chemical control
of Brown Tree Snakes on Guam: evaluation of baits, snake residues, and potential
primary and secondary hazards. Environmental Science Technology 36:3827-3833.
The brown tree snake (Boiga irregularis
) is a significant ecological, agricultural, and
economic pest on Guam. Acetaminophen has recently been identified as a promising snake
toxicant. Subsequent experimentation has shown that acetaminophen-mouse baits are readily
consumed by and acutely toxic to brown tree snakes. Before implementing an island-wide
acetaminophen-mouse baiting program for the reduction of brown tree snake populations, the
potential risks to non-target wildlife must be evaluated. Quantification of nontarget hazards by
comparing potential exposure levels of toxicity values suggested a significant level of concern
for rodents, cats, pigs, and birds. For these species, subsequent calculations and field and
laboratory experiments, which quantified acetaminophen consumption under field conditions,
indicated that acetaminophen consumption was minimal. These results indicate that the
advantages of using acetaminophen to reduce brown tree snake populations on Guam outweigh
the minimal risks to non-target feral and wildlife species.
McMoid, M. J., E. W. Campbell, III, and B. C. Alokoa. 1993. Efficacy of a chemical
repellent for the Brown Tree Snake (Boiga irregularis). The Snake 25:115-119.
The brown tree snake, Boiga irregularis
, has been on Guam since the late 1940’s.
Since then, this species has been responsible for considerable damages on many different levels
of Guam. This species has also, been observed using both aircraft and surface traffic to move to
neighboring islands in the Pacific Basin. Considerable effort has been expanded on control and
contaminant. In late 1990, a commercially available product was introduced on Guam for
localizing snake control. Subsequent testing indicated that this product was not effective in
repelling B. irregularis
. Savarie, P. J., D. L. York, J. C. Hurley, S. A. Volz, and J. E. Brooks. 2000. Testing the dermal
and oral toxicity of selected chemicals to Brown Treesnakes. Pages 139-145 in T. P.
Salmon and A. C. Crabb, editors., Vol.19, Proceedings of the 19th Vertebrate Pest
Conference, University of Calififornia, Davis, CA.
Dermal and oral toxicity tests were conducted on brown treesnakes (Boiga irregularis
with active ingredients and insecticide formulated products registered with the U.S. Environmental
Protection Agency (EPA). Over-the-counter drugs approved by U.S. Food and Drug Administration
(FDA) were evaluated for oral toxicity. Dermal applications of pyrethrin and pyrethroid
commercially formulated aerosol insecticides containing the synergists piperonyl butoxide and n-
octyl bicyloheptene dicarboximide were toxic to the snakes. The lowest oral average dose that
resulted in 100% mortality for rotenone, pyrethrins, propoxur, and aspirin was 2.5, 40, 40 and 1,280
mg/kg, respectively; but, when these chemicals were consumed by snakes in bait matrices at doses
several times higher tan the gavage doses, mortality was greatly reduced. Uncoated tablets of aspirin
(150 and 300 mg), ibuprofen (100 and 200 mg), acetaminophen (100 and 200 mg), and commercial
over-the-counter tablets formulations of 80 mg and 325 mg acetaminophen were offered to snakes in
a dead mouse bait matrix. The mortality with aspirin ranged from 67% to 100%. No mortality was
observed with ibuprofen. Acetaminophen resulted in 100% mortality for each of the doses tested.
Overall, these dermal and oral toxicity results indicate that some EPA-registered pesticides and drugs
approved by FDA may have use as toxicants for brown treesnakes.
Savarie, P. J., J. A. Shivik, G. C. White, J. C. Hurley, and L. Clark. 2001. Use of
acetaminophen for large-scale control of Brown Treesnakes. Journal of Wildlife
Because the brown treesnake (Boiga irregularis
) has virtually extripated the avifauna on
Guam and is a threat to other Pacific islands, the development of alternative and efficient control
methods is required. Therefore, we performed a large-scale field experiment to determine whether
the acetaminophen baits we developed could be used to reduce population levels of brown treesnakes
on Guam. Toxic baits were made by inserting 80 mg of acetaminophen into dead neonatal mice, and
these mouse baits were used to treat plots. Reference plots were baited with unadulterated baits. We
used mark-recapture methods to estimate snake abundance on plots before treatment, monitored bait-
take rates on treated plots for 30 days, and used mark-recapture to estimate snake populations post-
treatment. Bait-take rates were reduced on treated plots by 83% relative to reference plots after 14
days, when they reached an asymptote. Usina a robust design model in program MARK, snakes on
reference plots had higher apparent survival rates (x = 0.3505) than those on treated plots (x =
0.0072) for the duration of the study, but estimates were influenced by snake movement between
plots. When we accounted for movement using a multi-strata model, survival on treated plots was
estimated as zero. High mobility of brown treesnakes presents difficulty for complete removal of
snakes from large areas, but we conclude that acetaminophen baits may provide an effective and
selective management tool for quickly and efficiently reducing populations of brown treesnakes on
Guam. Shivik, J. A., and L. Clark. 1999b. The development of chemosensory attractants for
Brown Tree Snakes. Pages 649-654 in R. E. Johnson, D. Muller-Schwarze, and P.
W. Sorensen, editors. Advances in chemical signals in vertebrates. Kluwer
Academic/Plenum Publishers, New York.
Concern that the brown treesnake (Boiga irregularis
) may be inadvertently transported
in cargo shipments from Guam has resulted in management programs aimed at limiting the
likelihood of snake stowaways. A primary tool used to capture snakes is a trap within which is a
live mouse lure. Because using live mouse presents logistical problems and concerns about
animal care and use, it is desirable to develop an effective inanimate lure. Previous studies
indicate that brown tree snakes are attracted to carrion odors. Here, we present the results of
several pilot studies examining the attractiveness of cadaverine, dimethylamine, dimethyl
disulfide, dimethyl sulfide, ethanethiol, trimethylamine, and putrescine (all components of
carrion odor) to brown tree snakes. Results indicate that the major components of carrion odor,
as defined by human perception, are not necessarily salient odors to brown tree snakes. We
encourage a more systematic approach to the isolation of specific brown tree snake attractants by
testing serial fractions of carrion odor for bioactivity.
Shivik, J. A., W. G. Wright, and L. Clark. 2000a. Seasonal variability in Brown Tree
(Boiga irregularis) response to lures. Canadian Journal of Zoology 78:1-6.
In continuing investigations of brown treesnake attraction to carrion odor, we
hypothesize that the attractiveness of live or dead and visually apparent or concealed lures varies
seasonally. We determined that lure type (live or dead mouse lures) and sensory cues (visual
apparent or concealed lure) interact among wet and dry seasons. Concealed carrion lures were
more effective during the dry season than the wet season, but the effectiveness of other lures
showed less seasonal variability. We identified whether variables that covary with observed
seasonal trends in capture rates and investigated the influence of recent feeding on snake
response to lures. Data suggest that live mouse lure capture rates correlate with wind, and dead
mouse capture rates correlate with rainfall. Recently fed and satisfied snakes were not less
responsive to lures, but were less active than unfed snakes. Snakes held for over two years were
less responsive than recently captured snakes. More intensive studies will be required to
determine cause and affect relationships between lure types, seasonality, and snake behavior. Shivik, J.A., P.J. Savarie, and L. Clark. 2002. Aerial delivery of baits to brown treesnakes.
Wildlife Society Bulletin 30(4):1062-1067.
The exotic brown treesnake (Boiga irregularis
) has been implicated in the
extermination of endemic species from Guam, and fears that it will be transported elsewhere
have resulted in an intensive trapping and containment program. Current management methods
do not depopulate large areas, a presumed prerequisite for the effective reintroduction of
endangered native species, and logistically tenable techniques for removing snakes from remote
forests are needed. Bait stations containing dead neonatal mice (Mus musculus) implanted with
acetaminophen have been effective for depopulating areas of brown treesnakes, but a bait
delivery system for effective use of toxicants on a large scale and in remote areas has yet to be
developed, and the selectively of air-dropped baits requires assessment. We developed and
tested aerial delivery methods of distributing baits in forest canopy on Guam by implanting baits
with radio transmitters. We recorded bait uptake by snakes and other species and measured
morphology and movements of snakes that consumed baits. Bait take by snakes was high (63%)
using parachuted baits designed to entangle in forest canopy, and snakes moved 1-70m after
consuming baits. Snakes that consumed baits were of similar size, weight, and body condition to
snakes captured in traps on the drop areas. Implanting transmitters in carcass baits was a useful
method for monitoring brown treesnake movement for 5-11 days post-consumption.
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