Invasive Snake Activity Before and After Automated Aerial Baiting

Aerially delivered toxic baits have proven effective for landscape-level control of numerous invasive vertebrate populations with major benefits for conservation and ecosystem function, but this technique has not been broadly adapted for control of invasive reptiles. Nonnative brown treesnakes (Boiga irregularis) on the Pacific island of Guam have caused severe ecological and economic damage and pose an invasion risk on other islands, making them a high-profile candidate for application of aerial baiting methods. Although terrestrial applications of traps, toxicants, and hand-removal are standard brown treesnake management practices, these methods are not cost-effective for control in the island's large tracts of remote, rugged forest. In 2016, the first major in situ evaluation of a helicopter-borne automated aerial bait delivery system applied snake-targeted toxic baits at an effective rate of approximately 120 baits/ha over a 110-ha forested test plot on Guam. We evaluated the extent and duration of the suppressive effect of this toxic bait application on brown treesnakes by measuring nontoxic bait take rates as a proxy index of relative snake abundance before and after toxic bait application in a treatment plot and surrounding reference area. We placed 4,420 nontoxic baits in random transects at georeferenced locations, from 1 month before until nearly 12 months after toxic bait application, allowing temporal analysis of the suppressive effect and spatial analysis of treatment plot reinvasion. Over the first 30 days after toxic bait application, average nontoxic bait take rate in the treatment plot was 41.2% lower than the pre-application rate, and there was no immediate decrease in bait take in the reference area. Reduced snake activity was still evident nearly 12 months after bait application. Roads forming a portion of the treatment boundary appeared to slow snake movement between treated area and surrounding untreated area. Trail cameras monitoring a subset of bait tubes showed that 97.5% of baits removed were taken by snakes rather than nontarget species. We indexed rodent abundance in the treatment plot and reference area, and found no indication of a rodent population increase following toxic bait application. Our results show that automated aerial bait applications can suppress brown treesnake abundance over a large area and that reinvasion from surrounding untreated habitat occurs over several months. We anticipate that repeated bait applications could achieve and maintain greatly reduced brown treesnake abundance on a landscape scale, potentially improving biosecurity and enabling experimental reintroduction of native birds extirpated by brown treesnake predation. Published 2019. This article is a U.S. Government work and is in the public domain in the USA. The Journal of Wildlife Management published by Wiley Periodicals, Inc. on behalf of The Wildlife Society.     

Demographic response of brown treesnakes to extended population suppression

From a management perspective, reptiles are relatively novel invasive taxa. Few methods for reptile control have been developed and very little is known about their effectiveness for reducing reptile populations, particularly when the goal is eradication. Many reptiles, and especially snakes, are cryptic, secretive, and undergo extended periods of inactivity, traits that decrease detection probabilities and create challenges in estimating population size or evaluating management effects. The brown treesnake (Boiga irregularis) is a notorious invasive species that continues to cause major ecological and economic harm following their introduction to the island of Guam after World War II. They have been the subject of intensive research on the effectiveness of various techniques to control snakes, including the first ever aerial system for the distribution of toxic acetaminophen baits for reptile control. We provide a cohort-based life table for a cryptic and invasive reptile undergoing extended population control using toxic baits from March 2017–2020. We also evaluated the effects of single (toxic bait) versus multi-tool (toxic bait and live trapping) management efforts on population trajectories, and estimated which population vital rates are most important for influencing population growth or decline in a treated landscape. Treatment of the population with acetaminophen-laced baits resulted in an immediate reduction followed by a gradual population decline that suggested that eradication was the probable outcome given sufficient treatment time but that the period of treatment was decades in magnitude. Inclusion of live trapping reduced the predicted time required to achieve eradication by more than half. Preventing the transition of 1,000-mm snout-vent length (SVL) females to larger sizes was predicted to have the greatest effect on population reduction based on integral projection modeling. Our results suggest that toxic baits are capable of eradicating brown treesnakes in an enclosure, although inclusion of trapping reduced overall treatment time required. Tools that effectively target females >1,000 mm SVL may have the greatest effect on reducing overall treatment timelines.     

Brown Treesnake Mortality After Aerial Application of Toxic Baits

Quantitative evaluation of control tools for managing invasive species is necessary to assess overall effectiveness and individual variation in treatment susceptibility. Invasive brown treesnakes (Boiga irregularis) on Guam have caused severe ecological and economic effects, pose a risk of accidental introduction to other islands, and are the greatest impediment to the reestablishment of extirpated native fauna. An aerial delivery system for rodent-based toxic baits can reduce brown treesnake abundance and heterogeneity among individuals may influence bait attraction or toxicant susceptibility. Previous baiting trials have either been simulated aerial treatments or relied on slightly different bait capsule compositions and the results of aerial delivery of toxic baits under operational conditions may not be directly comparable. We monitored 30 radio-tagged adult snakes (990–1,265 mm snout-vent length) during an aerial baiting operation in a 55-ha area using transmitters equipped with accelerometers and receivers programed to display a status code indicating mortality if a snake failed to move for >24 hours. We used known-fate models to estimate mortality and evaluate a priori hypotheses explaining differences in mortality based on size, sex, and treatment effects. Eleven radio-tagged snakes died in the aerial baiting treatment period (0.37, 95% CI = 0.21–0.55) and no individuals (0.00, 95% CI = 0.00–0.04) died during the non-treatment period. Our data provide strong evidence for an additive size-based treatment effect on mortality, with smaller adults (0.59, 95% CI = 0.35–0.80) exhibiting higher mortality than larger snakes (0.14, 95% CI = 0.02–0.37) but did not support a sex effect on mortality. The high mortality of snakes during the treatment period indicates that aerial baiting can reduce brown treesnake abundance, but further refinement or use in combination with other removal tools may be necessary to overcome size-based differences in susceptibility and achieve eradication. © 2021 The Authors. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society.     

Size Bias in Visual Searches and Trapping of Brown Treesnakes on Guam

ABSTRACT The accidental introduction of the brown treesnake (BTS; Boiga irregularis) to the island of Guam after World War II set off a chain of bird, bat, and lizard extirpations. Fortunately, many of the eliminated species have the potential to be restored following population reduction or eradication of the snake. The primary operational tool for population reduction is an effective snake trap, but areas subjected to long-term trapping continue to support BTS, suggesting that some adult snakes are refractory to trapping. We closed a 5-ha area to BTS emigration and immigration and surveyed the population using trapping and visual surveys to determine whether a refractory stratum of adult snakes existed and if trapping was effective for snakes of all sizes. Our surveys included 101 trapping occasions and 109 visual surveys over 309 days, resulting in 2,522 detections of 122 individuals. We detected 44 of 45 supplemented snakes by this intensive sampling effort, which also revealed that trapping was fully effective for snakes >900 mm in snout—vent length (SVL), partially effective for snakes 700–900 mm SVL, and totally ineffective for smaller juveniles (350–700 mm SVL). Visual searching was effective for snakes of all sizes. As BTS mature at approximately 950-1, 050 mm SVL, continuous trapping should suffice to eliminate recruitment in the absence of immigration. Immigration or inadequate effort is most likely responsible for the persistence of BTS in areas subject to long-term trapping. Thus, current efforts to capture trap-refractory adult snakes with alternate control tools are less likely to be successful than immigration barriers alone or in combination with elevated capture effort.     

Bait delivery for oral rabies vaccine to gray foxes

Rabies is a widespread zoonotic disease that has reached epizootic proportions in gray foxes (Urocyon cinereoargenteus) in central Texas. Because each species of carnivore has different food preferences and foraging strategies, it is essential that the efficacy of a bait delivery program be examined for gray foxes prior to an oral vaccination program being attempted. Field trials were conducted to determine bait preferences of free-ranging gray foxes to selected baits and odor attractants. Baits consisted of polymer cubes made of either dog food meal or fish meal, and a wax-lard cake that was enhanced with marshmallow flavoring. Attractants added to baits exuded sulfurous, fatty, cheesy, or sweet odors and flavors. During 3,589 operable bait station nights, gray fox visitation and bait uptake rates were 9.2% and 8.3%, respectively. Gray foxes exhibited no preference in bait uptake rates between bait and odor attractant combinations. Gray foxes exhibited no difference in cumulative bait uptake rates between onroad and offroad sites; however, the uptake rate by raccoons was significantly greater for baits placed on roads than for baits randomly placed. Raccoons were the major non-target species competing for baits, being attributed with 73% of the total uptake. Visitation and bait uptake rates by raccoons significantly increased after a 7-day lethal removal of raccoons (n = 37) from the study area. Random distribution of baits is recommended; it reduced bait uptake by non-target species without adversely affecting uptake by gray foxes.     

Response of Brown Treesnakes to Reduction of Their Rodent Prey

ABSTRACT Trapping brown treesnakes (Boiga irregularis; BTS) with live-mouse (Mus domesticus) lures is the principal control technique for this invasive species on Guam. Lure-based trapping is also used on other islands as a precaution against undetected arrivals and in response to verified BTS sightings. However, the effectiveness of lure-based trapping on other islands is questionable, as it has yielded no BTS despite other evidence of their presence. Some evidence suggests that high rodent numbers may interfere with BTS control. To test the relationship between rodent abundance and snake trappability, we conducted a controlled, replicated field experiment incorporating a rodenticide treatment during a BTS mark-recapture study. Using open population modeling in Program MARK, we estimated BTS apparent survival and recapture probabilities. Rodent reduction increased BTS recapture probabilities by 52–65% in 2002 and 22–36% in 2003, and it decreased apparent survival by < 1% both years. This appears to be the first published instance of manipulating wild prey to influence snake behavior. Rodent reduction may enhance detection and control of BTS with traps on Guam and other islands. It may also amplify the effectiveness of oral toxicants against BTS.     

A new flavor-coated sachet bait for delivering oral rabies vaccine to raccoons and coyotes

Research was conducted during 1996-2000 to develop baits for delivering an oral rabies vaccine to raccoons (Procyon lotor) and coyotes (Canis latrans). A bait was sought that: (1) was attractive to the target species, (2) could be distributed by aircraft, (3) was as effective (or more so) than the currently used fish meal polymer bait, and (4) could be produced in large numbers by automated procedures and could be purchased by user groups at substantially lower cost. Ten field trials were conducted to document raccoons' bait flavor preferences, evaluate a new vaccine sachet bait coated with various attractants, and determine if the sachet bait would effectively deliver Raboral V-RG oral rabies vaccine (Merial Limited, Athens, Georgia, USA) to this species. Raccoons preferred fish and crustacean-based flavors over those derived from plant materials. Raccoon visits to tracking stations, frequency of bait removals, and percent of sachets discarded by this species that were emptied of placebo vaccine indicated efficacy of the new bait was equal or superior to the currently used fish meal polymer bait. A field trial conducted in fall 1998 compared aerially distributed vaccine-laden sachet and polymer baits and showed there was no difference between the percent of raccoons from the test and reference areas subsequently found positive for rabies antibody. Four bait trials to determine coyote response to sachet baits were conducted in 1997-98. The propensity for canids to gulp or bolt smaller food items is well known. Thus, a first trial involved offering fish-flavored sachet baits of different sizes to 30 captive coyotes to determine if smaller size baits were more frequently swallowed intact. Two field trials were also conducted in fall 1997 to determine if free-ranging coyotes discriminated among sachet baits coated with different attractants. Finally, Raboral V-RG-laden poultry-flavored sachet baits were aerially dropped and the percent of seropositive coyotes was compared with coyotes from surrounding areas where fish meal polymer vaccine baits had been distributed. Captive coyotes did not swallow sachet baits intact, regardless of size. Bait preference field trials indicated that coyotes preferred poultry, cheese/beef tallow, and fish-flavored sachet baits and that such baits were taken at the same rate as polymer baits. A sample of coyotes from the area baited with vaccine-laden sachet baits had a markedly higher (P = 0.01) seropositivity rate than coyotes from areas where vaccine was distributed in polymer baits. Sachet bait production could be facilitated by automated technology and sachet baits used either as an alternative vaccine delivery device or in combination with the fish meal polymer bait.     

Selection of carrion by the Australasian harrier (Circus approximate) in New Zealand

Abstract

The selection of carrion by Australasian harriers was studied by offering a choice of baits in the field. These trials tested preferences for carrion species, amount of flesh exposed, body posture, and colour of the carrion. Domestic hen pullets and Norway rats were chosen significantly more often than rabbits, opossums, or eels. Skinned rabbits were preferred to unskinned ones. Body posture of rabbit carcasses did not appear to affect a harrier's choice. White and blue baits were preferred to red, brown, or green baits. The most important factors involved in the selection of carrion by harriers appear to be the ease of handling of the carrion, and the colour of the bait.     

The bioinvasion of Guam: inferring geographic origin,pace, pattern and process of an invasive lizard (<Emphasis Type="Italic">Carlia</Emphasis>) in the Pacific using multi-locus genomic data

Invasive species often have dramatic negative effects that lead to the deterioration and loss of biodiversity frequently coupled with the burden of expensive biocontrol programs and subversion of socioeconomic stability. The fauna and flora of oceanic islands are particularly susceptible to invasive species and the increase of global movements of humans and their products since WW II has caused numerous anthropogenic translocations and increased the ills of human-mediated invasions. We use a multi-locus genomic dataset to identify geographic origin, pace, pattern and historical process of an invasive scincid lizard (Carlia) that has been inadvertently introduced to Guam, the Northern Marianas, and Palau. This lizard is of major importance as its introduction is thought to have assisted in the establishment of the invasive brown treesnake (Boiga irregularis) on Guam by providing a food resource. Our findings demonstrate multiple waves of introductions that appear to be concordant with movements of Allied and Imperial Japanese forces in the Pacific during World War II.     

Species-specific visitation and removal of baits for delivery of pharmaceuticals to feral swine

Within the domestic swine industry there is growing trepidation about the role feral swine (Sus scrofa) play in the maintenance and transmission of important swine diseases. Innovative disease management tools for feral swine are needed. We used field trials conducted in southern Texas from February to March 2006 to compare species-specific visitation and removal rates of fish-flavored and vegetable-flavored baits with and without commercially available raccoon (Procyon lotor) repellent (trial 1) and removal rates of baits deployed in a systematic and cluster arrangement (trial 2). During trial 1, 1) cumulative bait removal rates after four nights ranged from 93% to 98%; 2) bait removal rates by feral swine, raccoons, and collared peccaries (Pecari tajacu) did not differ by treatment; and 3) coyotes (Canis latrans) removed more fish-flavored baits without raccoon repellent and white-tailed deer removed more vegetable-flavored baits without raccoon repellent than expected. During trial 2, feral swine removed fish-flavored baits distributed in a cluster arrangement (eight baits within 5 m2) at a rate greater than expected. Our observed bait removal rates illustrate bait attractiveness to feral swine. However, the diverse assemblage of omnivores in the United States compared with Australia where the baits were manufactured adds complexity to the development of a feral swine-specific baiting system for pharmaceutical delivery.     

The response of German cockroaches to toxic baits:strain differences and the effects of selection pressure

Strain differences in the response of German cockroaches to toxic baits and their potential to evolve resistance to them was evaluated in choice tests. Percentage bait consumption (amount of bait consumed divided by total food consumed) was used to estimate relative attractancy/repellency of the baits. One strain apparently had low level resistance to abamectin, but no evidence of resistance was found in other strains tested with either Roach Ender or a gel bait (abamectin-based baits). Incipient behavioral resistance occurred in two strains selected for three generations with Roach Ender; a stronger response in a strain selected with the gel bait is attributed to the development of behavioral resistance. Baygon bait was highly repellent. Low level resistance to propoxur caused a large decrease in mortality compared with susceptible strains. Strong behavioral resistance developed in strains selected with Stapleton's Magnetic Roach Food.     

Canine detection of radio-telemetered brown treesnakes

We are investigating canine teams (dogs and their handlers) on Guam as a potential tool for finding brown treesnakes (BTS) (Boiga iregularis), especially incipient populations on other islands. Canine teams have demonstrated proficiency at finding captive snakes in hidden tubes. Teams also find free-ranging BTS in various habitats, but detection rates for the latter are unknown. Dog handlers usually rely on visual searchers to locate BTS once a dog has signalled snake presence. At times, dogs signal but the visual search team cannot locate the snake; this complicates attempts to quantify detection rates. Our research aimed to estimate detection rate of free-ranging BTS by canine teams as a function of snake attributes, characteristics of snake refugia, and environmental conditions. Canine teams searched a defined 40m × 40m forested area with a snake that had consumed a dead mouse containing a radio-transmitter. Trials were conducted during the morning, when snakes were usually hidden in refugia. A tracker knew the snake’s location, but dog handlers and data recorders did not. We recorded data on dog alerts and on-scent behaviour during trials. Out of 86 trials, the two canine teams had an average success rate of 36%. This study provides initial estimates of canine team efficacy when searching in complex habitats in information on optimizing visual search strategy after dog signals snake presence (defining size of area to search, identifying preferred refugia, etc.). We discuss experimental design, challenges and initial results.     

Efficacy of commercial baits and new active ingredients against firebrats and silverfish (Zygentoma: Lepismatidae)

Commercial baits containing boric acid, hydramethynon, and indoxacarb were tested against the firebrat, Thermobia domestica (Packard), and silverfish, Lepisma saccharina L. (both Zygentoma: Lepismatidae), under laboratory conditions. Three boric acid baits were consumed in significantly smaller amounts than untreated control food and did not effectively control either species. Baits containing hydramethylnon and indoxacarb were consumed in greater amounts than boric acid baits, but were relatively ineffective, with LT50 values >9 d. Presence or absence of competitive untreated food did not consistently affect bait efficacy. A ground oat matrix was used to evaluate the potential effectiveness of abamectin, chlorfenapyr, dinotefuran, fipronil, hydramethylnon, metaflumizone, and novaluron baits. The most effective compound was chlorfenapyr. At 0.05 and 0.20% (wt:wt) rates, chlorfenapyr baits produced LT50 values, for both species, ranging from 2 to 4 d. All other compounds had LT50 values >7 d.     

Increasing Attractiveness of Baits with Venom Gland Extract for Atta sexdens rubropilosa (Forel) (Hymenoptera: Formicidae)

The effect of larval cuticle extract (larval pheromone) and venom gland extract (trail pheromone) on transport of formulated baits by Atta sexdens rubropilosa (Forel) was studied in the field and under laboratory conditions. In the laboratory, we observed the transport to the nest of baits impregnated with 10???L of venom gland extract (0.01 gland/bait) or 10???L of larval cuticle extract (0.05 larva/bait). The most transported impregnated bait was then tested in the field placing rubber septa impregnated with 100?mL of extract or with 100?mL of solvent with the baits at 0.2, 1.0, 5.0, and 10.0?m away from the trail and from the nest entrance. Baits impregnated with venom gland extract were transported more often than baits formulated with larval cuticle extract. In field tests, the venom gland extract reduced the time required for ants to detect baits and increased the transport of baits displayed at 0.2?m from the foraging trail or nest entrance. The increase in the transport of impregnated baits and the lower time to be transported might help to reduce the loss of bait in the field and decrease the risk of active ingredient contacts with non-target species.     

Evaluating seasonal bait delivery to badgers using rhodamine B

In the UK and Ireland, research on the control of bovine tuberculosis in badgers includes the development of a palatable bait for oral delivery of a vaccine and a means of its deployment in the field. In the present study, we carried out field deployment of bait according to the established method of bait marking in early spring and early summer to compare the effects of seasonality on bait uptake rates. All baits contained rhodamine B (RhB) which was subsequently detected in the hair and whiskers of captured badgers. During the 8 days of bait feeding at 14 badger setts, 99% of baits deployed in spring, and 100% of those deployed in summer were removed. The presence of RhB in captured badgers indicated high rates of uptake amongst adult badgers in spring (93%) and summer (98%). Only cubs captured in summer showed evidence of having taken bait (91%). Between 67% and 100% of each social group was estimated to have taken bait. The detection of RhB in 96% of badgers captured at outlier setts, where bait was not fed, suggested that deployment at main setts alone may be sufficient to target a relatively high proportion of the badger population. The number of baits deployed per marked badger suggested that a similar level of uptake might be achievable using fewer baits. The results clearly demonstrate the potential value of the bait-marking methodology for delivering vaccine baits to badgers during spring and summer, but that deployment in early summer is necessary to target cubs.     

The effect of bait design on bait consumption in termites (Isoptera: Rhinotermitidae)

The efficacy of baiting as a pest control method relies on the bait appealing to the pest species. In the case of wood-eating termites, bait stations should be designed to encourage termite presence and to maximize their consumption of bait matrix in order to expedite control in minimal time. A field experiment examined the effect of bait size (one large bait or four small baits of equivalent total size, with commensurate inspection and replacement schedules), compaction (tightly rolled or loosely folded) and composition (paper only or paper plus wood) on termite presence and on untreated bait paper removal rates over four months. All three factors were significant, with bait size the most important factor, followed by compaction and then composition. The least effective baits were small, compacted (rolled) paper-only baits with monthly inspections; these had the highest abandonment rate (70%) and had the least paper removed (mean of 24 g). The most effective baits were large, folded paper-plus-wood baits with inspections at two months; these had the lowest abandonment rate (20%) and had the highest paper removal (mean of 112 g). The more than four-fold difference between these baits types demonstrates that bait efficacy can be altered considerably merely by changing bait design without adding new ingredients to the bait matrix.     

The effects of food presentation and microhabitat upon resource monopoly in a ground-foraging ant (Hymenoptera: Formicidae) community

In Neotropical wet forests several species of omnivorous, resource-defending ants, live and forage in close proximity to one another. Although the forest floor is heterogeneous in microhabitat and food quantity, little is known about the impact of microhabitat and food variation upon resource monopoly among ants. We investigated how food type and microhabitat influence food monopoly in resource-defending ants in old-growth tropical wet forest in the Caribbean lowlands of Costa Rica. We measured several microhabitat characteristics at 66 points in a 0.5 hectare plot, and baited each point with two categories of tuna bait. These baits were presented in "split" and "clumped" arrangements. We measured the frequency of bait monopoly by a single species, as well as the number of recruited ant foragers at a bait. Out of five common species, two (Wasmannia auropunctata and Pheidole simonsi) more frequently monopolized one bait type over the other, and one (P. simonsi) recruited more ants to the split baits. We then considered the recruitment response by all ant species in the community. We found that the frequency of monopoly, sharing, and the absence of ants at a given point in the rainforest differed with bait type. The frequency of monopoly was associated with microhabitat type in two out of eight microhabitat variables (leaf litter depth and palms); variation in two other types (canopy tree distance and leafcutter ant trails) was associated with changes in forager number. In at least two ant species, food presentation affected monopoly at baits; among all resource-defending ants, the microhabitats where ants foraged for food and the type of food located determined in part the frequency of monopoly and the number of foragers at the food item. These results suggest that the location and presentation of food items determines in part which ant species will utilize the resource.     

Wild carnivore acceptance of baits for delivery of liquid rabies vaccine

A series of experiments are described on the acceptance, by red foxes (Vulpes vulpes) and other species, of two types of vaccine-baits intended to deliver liquid rabies vaccine. The baits consisted of a cube of sponge coated in a mixture of tallow and wax, or a plastic blister-pack embedded in tallow. All baits contained tetracycline as a biological marking agent: examination of thin sections of carnivore canines under an ultraviolet microscope revealed a fluorescent line of tetracycline if an individual had eaten baits. Baits were dropped from fixed-wing aircraft flying about 100 m above ground at approximately 130 km/h. Flight lines followed the edges of woodlots midway between parallel roads. Baits were dropped at one/sec, resulting in one bait/36 m on the ground, or 17 to 25 baits per km2. Crows (Corvus brachyrhynchos) removed many baits, but did not appear to lower the percent of the fox population which took bait. Dropping baits only into corn and woodland to conceal baits, to reduce depredation by crows, reduced acceptance by foxes. Acceptance by foxes ranged between 37 and 68%. Meat added as an attractant did not raise acceptance. Presence, absence, color and perforations of plastic bags did not alter bait acceptance. Dispersal by juvenile foxes probably lowered the estimates of bait acceptance. It took 7 to 17 days for 80% (n = 330) of foxes to eat their first bait. The rapidity with which foxes picked up their first bait appeared more affected by unknown characteristics of years or study areas than by experimental variables. Skunks (Mephitis mephitis) and raccoons (Procyon lotor) also ate these baits, but acceptance was lower. Small mammals contacted baits, but rarely contacted the vaccine, which had the potential for vaccine-induced rabies in some species. Aerial distribution of baits was more cost-effective than ground distribution as practiced in Europe. This system has potential for field control of rabies, although higher acceptance will be desirable.     

A baiting system for delivery of an oral plague vaccine to black-tailed prairie dogs

Laboratory and field studies were conducted between July and October 1999 to identify bait preference, biomarker efficacy, and bait acceptance rates for delivering an oral plague vaccine to black-tailed prairie dogs (Cynomys ludovicianus). Twenty juvenile captive prairie dogs were offered alfalfa baits containing either alfalfa, alfalfa and 5% molasses, or alfalfa, 5% molasses and 4% salt. Based on the results of these trials we selected a bait containing alfalfa, 7% molasses, and 1% salt for field trials to determine bait acceptance rates by free-ranging animals. The biomarkers DuPont Blue dye, iophenoxic acid, and tetracycline hydrochloride were orally administered to captive prairie dogs to determine their efficacy. Only tetracycline proved effective as a biomarker. Two field trials were conducted at separate prairie dog colonies located at the Buffalo Gap National Grassland (Pennington County, South Dakota, USA). In Trial 1, three baits containing tetracycline were distributed around each active burrow entrance and an additional bait was placed inside the burrow (1,276 baits total). In Trial 2, baits were distributed at the same density per burrow as Trial 1, but along transects spaced 10 m apart (1,744 baits total). Trapping began 3 days after bait distribution, and 30 prairie dogs then were captured at each site to determine the percentage of animals marked. In Trial 1, 67% of the prairie dogs captured had tetracycline deposits indicative of bait consumption. In Trial 2, 83% of the prairie dogs had ingested a bait. Approximately 15% of the animals in both trials ate more than one bait. Fleas (Opisocrostis hirsutus) were found on 64 of 70 (91%) of the prairie dogs captured during this study.     

马尾松毛虫性信息素在不同类型诱芯中的稳定性

顺5,反7-十二碳二烯醇、顺5,反7-十二碳二烯乙酸酯和顺5,反7-十二碳二烯丙酸酯是马尾松毛虫Dendrolimus punctatus性信息素的主要成分。为研究如何减少上述共轭二烯信息素成分中的几何构型异构化和氧化的发生,作者制备了几种不同剂型的诱芯并进行了田间诱蛾试验。与常用的天然橡胶诱芯相比,诱芯中加入抗氧化剂（topanol CA）、提高性信息素的纯度、每5天重新更换诱芯及将载体换为硅橡胶等处理均不能明显提高诱芯的诱蛾效果,然而载体为复合橡胶（氯化丁基橡胶和天然橡胶的混合体）的诱芯诱蛾效率比天然橡胶诱芯提高了1倍以上。田间试验后,用毛细柱气相色谱对不同类型诱芯中残留的信息素及其异构体的分析结果显示：复合橡胶诱芯中只有12%～16%的不同信息素成分发生了异构化,而在天然橡胶诱芯中此值高达69%～87%。而且前者中信息素及其异构体的剩余量是后者的4倍。这些结果表明,复合橡胶诱芯之所以具有较高的诱效,主要由于在这种诱芯中,共轭二烯信息素更稳定,释放速率较为缓慢且均匀。