Responses of Wild Norway Rats (Rattus norvegicus) to Predator Odors

If rats could be shown to avoid the odors of predators, then conservation managers could manipulate this behavior to exclude rats from important conservation sites. We evaluated the ability of six predator odors to elicit avoidance responses by wild-caught Norway rats (Rattus norvegicus) from two New Zealand populations (Kapiti Island and North Island). Kapiti Island is free of mammalian predators, while the North Island has established populations of felids, canids, and mustelids. Three of the predator odors were real and three were synthesized volatile ingredients of real animal feces or urine. We compared the rats' responses to predator odors with their responses to three natural herbivore odors. We used a Y maze, and rats were offered the choice of an odor in one arm of the maze and distilled water in the other arm. Each choice arm was ducted at the entrance to remove air and the odor. We recorded: (1) the time until the rat left the first arm of the maze, (2) the time until the rat visited each arm, (3) the number of visits to each arm, (4) the amount of time spent in each arm, and (5) a total activity score for each rat. Kapiti rats showed an aversion to five of the six predator odors, despite never having encountered them before. Kapiti rats visited herbivore odors more often than carnivore odors and were less active in the presence of carnivore odors than they were when tested with herbivore odors. In addition, Kapiti rats approached some herbivore odors more quickly than they approached carnivore odors. North Island rats appeared to avoid cat urine, but despite being predator experienced, did not show a consistent aversion to the carnivore odors we tested. Both samples of rats, but particularly the North Island group, showed high individual variation. We conclude that predator odors are unlikely to be an effective management tool for all populations of this species of rat because of this high individual variability and the likelihood that each island population will differ in its responses to a given odor.     

Morphology and chemistry of brown rat,Rattus norvegicus,preputial and clitoral glands

In contrast to previous results from laboratory rats, when sexual dimorphism occurred, clitoral glands from wild female rats were heavier and accounted for a greater proportion of body mass than preputial glands from wild males. Gland length and weight increased with body weight, but gland weight as a proportion of body weight did not. Preputial and clitoral glands showed seasonal differences in size: at one site glands were smaller in December than in April. Maturity, estrus, and pregnancy had no significant effect on clitoral gland size, but immature males had proportionally smaller preputial glands than mature males, and the absolute gland weight, but not gland weight as a proportion of body weight, increased with testes weight. There were no differences between the sexes in lipid production, which increased with preputial or clitoral gland weight. An homologous series of aliphatic acids and their methyl and ethyl esters, plus squalene, cholesterol and lanosterol, was revealed by GC-MS study of the trimethyl silyl derivatized lipid extract. Males and females could be distinguished by principal component analysis of chromatogram peaks.     

Taxon-specific differences in responsiveness to capsaicin and several analogues: Correlates between chemical structure and behavioral aversiveness

The present set of experiments was designed to explore avian insensitivity to capsaicin. Based upon a molecular model of avian chemosensory repellency, we hypothesized that structural modifications of the basic capsaicin molecule, which is itself not aversive to birds, might produce aversive analogues. To this end, European starlings (Sturnus vulgaris) and Norway rats (Rattus norvegicus) were given varied concentrations of synthetic capsaicin and four analogues (methyl capsaicin, veratryl amine, veratryl acetamide, vanillyl acetamide) in feeding and drinking tests. The results agreed with a model that we are developing to describe the chemical nature of avian repellents. Synthetic capsaicin and vanillyl acetamide were not repellent to birds, owing to the presence of an acidic phenolic OH group. Conversely, veratryl acetamide was aversive, due to the basic nature of this compound. For rats, repellent effectiveness among compounds was reversed: synthetic capsaicin was the best repellent while veratryl acetamide was the worst. We speculate that this taxonomic reversal may reflect basic differences in trigeminal chemoreception. In any case, it is clear that chemical correlates of mammalian repellents are opposite to those that predict avian repellency.     

Scent,sex, and the self-calibrating rat

We propose that one mechanism whereby male rats,Rattus norvegicus, might gauge the reproductive condition of a female is by calibrating a stable odor with an odor that fluctuates through her reproductive cycle. We provide behavioral and histological evidence in support of such a self-calibration model. Male rats sniffed frequently at various body zones of females, and the proportion of sniffs deployed to each zone varied with the females' reproductive condition and relatedness. The females' haunches received more sniffs than any other part of their bodies, irrespective of their relatedness or reproductive condition. Furthermore, males tended to sniff the haunch after sniffing the forequarters, as part of a sequence of sniffing along a female from forequarters to hindquarters. Histology of the skin sebaceous glands indicated that the secretory activity of glands in the haunch, but not those in the forequarters, changed during estrus. Therefore, male rats had the opportunity to judge a female's reproductive status by calibrating the odor of her haunch against that of her forequarters. Self-calibration could represent a means of accommodating differences in odor within individuals.     

Urine-marking and the response to fresh vs. aged urine in wild and domestic Norway rats

Wild and domestic Norway rats (Rattus norvegiens) were compared in regard to their tendency to investigate the odors of fresh vs. aged rat urine and to urine-mark metal rods and wooden blocks placed in their home cages. Castration, sex, and domestication had no effect on the tendency to investigate sources of fresh vs. aged urine odors, but the odor of aged urine was more attractive than fresh urine for most subjects tested. The frequency of urine marking was lower for females and castrated males but generally did not differ between wild and domestic stocks. The implications of these findings for the ecology of the species are discussed.     

Behavioral responses ofLittoraria irrorata (SAY) to water-borne odors

Behavioral responses of the gastropod molluscLittoraria (=Littorina)irrorata indicate that it can discriminate among environmental odors. Snails were assayed for responses to 11 odors from plants and animals potentially representing food, shelter, location in the environment, and predators. Crushed conspecifics were included as an alarm odor. Except for odor of crushed conspecifics, all odor sources were water-borne from living intact organisms. Behavioral responses were categorized as no response, positive response, or negative response. For some analyses, negative responses were subdivided into withdrawing and turning responses. Snails responded positively to several plant odors. They did not respond to odors of intact conspecifics, fiddler crabs, or grass shrimp. They responded negatively to odors of a plant found at the upper limit of their minimal habitat, predatory blue crabs, crushed conspecifics, predatory gastropods, and ribbed mussels. Odors of blue crabs on different diets affect the type of negative response the snails display.     

The role of chemosensory cues in discrimination of prey odors by the amphisbaenianBlanus cinereus

Responses of amphisbaenians (Blanus cinereus) to deionized water, a control for pungency (cologne), and integumental prey odors (coleopteran larvae and adult ants) on cotton swabs were studied in experiments with a randomized blocks design to discover whether amphisbaenians use chemical cues to detect and identify prey. No individual bit the applicators. Amphisbaenians tongue-flicked at lower rates than epigean saurians, which are active foragers. Tongue-flick rate differed among treatments, but responses to prey odors were not significantly different from those to cologne. The number of directed tongue-flicks emitted during the 60-sec trials was, however, lower in response to deionized water than in response to cologne or prey odors. Response details, the low rate of tongue-flick, and absence of biting are discussed in relation to the foraging behavior and fossoriality of amphisbaenians. Evidence from this study indicates that the vomeronasal sense is used by amphisbaenians to identify odors, but our experiments failed to demonstrate that amphisbaenians discriminate between prey and nonprey odors.     

Airborne Chemical Communication in the Wolf Spider Pardosa milvina

Most studies involving chemical communication in spiders focus on contact pheromones attached to spider silk. Here we tested if males of the wolf spider Pardosa milvina use airborne pheromones to identify, locate, and follow females. Using a two-choice olfactometer, we tested the response of adult male P. milvina to a number of potential chemical cues while controlling for concomitant visual and vibratory stimuli. An airborne chemical cue from adult virgin female P. milvina elicited a positive taxis response from the male. We also tested adult male responses to penultimate instar female P. milvina, one adult male P. milvina, and two adult males together. In each case, test males showed no attraction to the stimuli. Additional experiments were run with pitfall traps baited with adult virgin female P. milvina as attractants. Again, we controlled for visual and vibratory cues from females. Pitfall traps containing virgin females captured significantly more males than control traps. Collectively, these experiments demonstrate evidence of an airborne sex pheromone in P. milvina.     

Woodmice (Apodemus sylvaticus) can distinguish conspecific from heterospecific odors in the field

In order to eliminate a common source of bias from trap-choice experiments in the field, trapping data from a study on the olfactory biology of the woodmouse were screened, and only those in which a direct choice existed were analyzed further. Woodmice choose conspecific odor to no odor but make no distinction between heterospecific odor and no odor. When choosing between conspecific and heterospecific odors, a significant majority choose conspecific.     

Use of predator odors to protect chick-peas from predation by laboratory and wild mice

Synthetic stoat odor (3-propyl-1,2-dithiolane and 2-propylthietane) and fox fecal odor (2,5-dihydro-2,4,5-trimethylthiazoline) at various concentrations were applied to chick-peas (Cicer arietinum) at sowing in an investigation aimed at reducing damage caused by house mice (Mus musculus). Stoat odor at 10% concentration exerted a measure of protection, as did 1% fox odor against predation by laboratory mice. Wild mice were less affected by synthetic predator odor and appeared to have a shorter memory for it. Laboratory mice cannot be regarded as surrogate wild mice, when used in experimental situations such as those employed here.     

Trirhabda canadensis (Coleoptera: Chrysomelidae) responses to plant odors

The responses of the goldenrod leaf beetleTrirhabda canadensis to host and nonhost volatile odors were tested in a Y-tube olfactometer in the laboratory. Beetles preferred host to nonhost odors and were sensitive to concentrations of host odor. Beetles distinguished between host and nonhost volatiles of only one of the two nonhostSolidago species; host volatiles were preferred to all nonhost volatiles at the family and order levels. In other words, all nonhosts above the genus level had similar effects on beetle responses. Although the odors of most nonhosts were neutral (i.e., neither attractive nor repellent) to the beetles as tested against air, this neutrality disappeared if the odors of two or more nonhosts were added to the host odor and beetles were given a choice between this mixture and pure host odor. Given this choice, they strongly preferred pure host odor, which suggests that diversity of odors per se is unattractive to the beetles. Beetles walked rather than flew to locate their hosts in the field, and their movements suggest that they used olfactory cues to locate hosts.     

Behavioral and electrophysiological response of cabbage seed weevils (Ceutorhynchus assimilis) to conspecific odor

The responses ofCeutorhynchus assimilis Payk. (Coleoptera, Curculionidae) to the odor of overwintered and new generation weevils were studied using an olfactometer, choice tests in a laboratory cage, field tests using sticky traps baited with live weevils, and by electroantennograms (EAG's). Unmated male weevils and, to a lesser extent, female weevils of the overwintered generation were attracted to the odor of live unmated over-wintered female weevils. New generation weevils exhibited no behavioral response to conspecific odor. Male and female weevils of the overwintered generation exhibited positive EAGs to hexane extracts of overwintered female weevils, whereas EAGs of new-generation weevils of either sex were unresponsive to these extracts. This suggests that the unmated female weevils from the overwintered generation produce a volatile chemical or chemicals that attracts unmated male and female weevils. The new generation of female weevils does not produce this attractive chemical before overwintering, and male and female weevils of this generation can not detect the chemical(s) via their antennal chemoreceptors until they have undergone their overwintering period.     

Olfactory reception of potential pheromones and plant odors by tarnished plant bug,Lygus lineolaris (Hemiptera: Miridae)

Olfactory reception of potential pheromones and host-plant odors by male and female tarnished plant bugs (TPBs),Lygus lineolaris (Hemiptera: Miridae), was investigated by utilizing electroantennogram (EAG) techniques. In general, EAGs were similar between the sexes. Among 31 compounds of seven chemical groups tested, insect-produced butyrates and host-plant-containing green leaf volatiles (GLVs) were the most active. Hexyl butyrate and (E)-2-hexenyl butyrate elicited greater EAGs in males than in females. Females responded with significantly greater EAGs to alcohol and aldehyde GLVs than to their acetate derivatives. Among GLVs, sexual dimorphism was also observed in response to (E)-2-hexenol and (E)-2-hexenal. Females were more sensitive to the monoterpene geraniol than were males. While nonanal was the most stimulatory compound tested, no sexual differences in EAGs to this compound were observed. These studies reveal olfactory receptors on TPB antennae responsive to insect and host-plant volatiles that are likely to play a role in host finding and sexual attraction.     

Induced mimicry of colony odors in ants

The cuticular hydrocarbons ofFormica selysi (Formicinae) andMonica rubida (Myrmicinae) reared in single species and in mixed species colonies were determined using gas chromatography (GC) and GC-mass spectrometry. In colonies containing both species, each species modified its species-specific recognition odor. This odor is composed, at least partly, of cuticular hydrocarbons. The cuticular hydrocarbons ofM. rubida consist only of saturated alkanes (n-alkanes and branched alkanes). InF. selysi the mixture also contains unsaturated compounds (monoenes and dienes). In hetero-specific colonies, a new chemical signature developed. This signature resulted from qualitative and quantitative changes in the spectrum of hydrocarbons produced by each species and permitted the two species to inhabit the same nest without displaying interspecific aggression. The readjustment seemed to be more an active synthesis or an active transfer than simply a passive transfer from one species to the other. This may imply that the ants synthesized some components of the hydrocarbon signature of the other species. These synthesizing processes may be activated under particular social environmental conditions.     

Effect of predator odors on heart rate and metabolic rate of wapiti (Cervus elaphus canadensis)

We measured the heart rate (HR) and oxygen consumption ( ) of wapiti (Cervus elaphus canadensis) before, during, and after presentation of biologically irrelevant odors (pentane, thiophene, and a perfume), artificial predator odors (an ether extract of cougar feces, and PDT, a compound found in mustelid anal gland secretion), stale predator odors (dog feces and urine and fox urine, kept at ambient temperature for a few weeks), and fresh predator odors (wolf, coyote, and cougar feces and the odor of a dead coyote, kept frozen between collection and test). Overall, responses to odors were small compared to other stressful stimuli. Individual variability was high among scents and among wapiti, but two of the fresh predator odors (cougar and wolf feces) produced larger HR and responses than the other scents and were more often successful at producing responses. As a group, fresh predator odors produced larger tachycardias and elicited a larger number of significant HR responses than biologically irrelevant novel odors. although the two classes of odors did not differ in their effect on . Although several other studies have shown that ungulates have reduced feeding levels when their food is scented with predator odors, it is not clear if this is due to reduced palatability or antipredator behavior. This study is the first demonstration that a wild ungulate species reacted more strongly to predator odors than to other odors in a nonfeeding situation.     

Interpopulational variation in emitted pheromone blend of cabbage looper moth,Trichoplusia ni

Female cabbage looper moths,Trichoplusia ni, from laboratory colonies initiated from three locations across the United States emitted similar quantities and blend ratios of the six known pheromone components. In contrast, females from a long-established laboratory colony emitted a greater proportion of four of the five minor components relative to the major component, (Z)-7-dodecenyl acetate; only the relative proportion of 11-dodecenyl acetate was similar in all of the populations sampled. Females from this population emitted (Z)-7-dodecenyl acetate at a rate similar to that from females from field-collected colonies. Within each population there were highly significant correlations among the quantities of pheromone components of similar molecular weights. Correlations between components of different molecular weights were not as great, but often were significant. Similarities of blend ratios among field populations may indicate that the chemical signal in this species is conservative. The difference of the blend ratios in our laboratory population from the other populations may indicate a decrease in the intensity of selection pressure that usually would maintain these values.     

Kairomones Used by Trichogramma chilonis to Find Helicoverpa assulta Eggs

Chemically mediated interactions between an egg parasitoid, Trichogramma chilonis, and its host insect, Helicoverpa assulta, were studied in laboratory experiments. T. chilonis was attracted to the sex pheromone of H. assulta, and, among four components of its sex pheromone, (Z)-11-hexadecenyl acetate seemed to be most attractive. T. chilonis was also highly attracted to (E)-12-tetradecenyl acetate, a component of the sex pheromone of Ostrinia furnacalis, another host. H. assulta eggs were more parasitized by T. chilonis when the eggs were treated with male moth scale extract (MSE) of H. assulta. Parasitism was also affected by the age of the parasitoid, time of day, and MSE concentration. Silica gel chromatography and subsequent argentation chromatography for MSE fractionation indicated the activity was associated with the fraction of saturated hydrocarbons. A linear olfactometer experiment revealed that H. assulta eggs also contain a short-range attractant(s).     

Field response of Ips paraconfusus,Dendroctonus brevicomis,and their predators to 2-methyl-3-buten-2-ol,a novel alcohol emitted by ponderosa pine

Methylbutenol (MBO) is a major component of the aggregation pheromone of the European spruce beetle Ips typographus and also has been found to be emitted in large amounts by several species of pine native to western North America. This study investigates the influence this signal may have on the behavior of North American bark beetles and examines whether MBO functions as a defensive compound for emitting pines. The response of two North American bark beetles (Ips paraconfusus and Dendroctonus brevicomis) and their predaceous beetles (Trogositidae and Cleridae) to MBO, pheromone, and monoterpenes in varying release rates was investigated in the field using Lindgren funnel traps. MBO exhibited no repellent properties when tested alone, nor did MBO appear to have any effect on the aggregation response of these bark beetles and their predators to their pheromones. These results provide no support for a defensive function of MBO.     

Nonlinear response of an ideal gas bubble to ambient pressure change in a quiescent fluid

This paper is concerned with the small-amplitude oscillations of a bubble composed of an ideal gas in response to anabrupt change in the ambient pressure field. Specifically, we consider the bubble response to a pressure pulse and a pressure step in an otherwise quiescent fluid. The method of analysis employed in the present study is a standard two-timing expansion to eliminate a secular behavior encountered in the asymptotic expansion. In the impulse response the secularity is self-induced due solely to the nonlinearity of the problem whereas the secularity in the step response arises from the change in the equilibrium bubble volume caused by the ambient pressure change. The two-timing solution for each response shows that the secularity modifies the natural frequency of the radial oscillation. Further, the critical intensity of either the pressure pulse or the pressure step for existence of the steady-state bubble radius is determined from the frequency modulated solution and the stability of the bubble response is also discussed in terms of the bubble compressibility and heat transfer across the interface.