Germacrone defends labrador tea from browsing by snowshoe hares

Labrador tea (Ledum groenlandicum), a slow-growing late successional evergreen, is highly unpalatable to snowshoe hares (Lepus americanus). Germacrone, a sesquiterpene that is the major component of the essential oil ofL. groenlandicum, was shown by bioassay to be a potent antifeedant to hares. Its concentrations in leaves and intemodes of the plant are high enough to defendL. groenlandicum from hares. This chemical defense of Labrador tea from herbivory is consistent with the resource availability theory of antiherbivore defense.     

A comparison of the effectiveness of predator odor and plant antifeedant in deterring small mammal feeding damage on lodgepole pine seedlings

The influence of mustelid (weasel) anal-gland compounds (semiochemicals) and a plant antifeedant (pinosylvin) on snowshoe hare (Lepus americanus) and meadow vole (Microtus pennsylvanicus) feeding damage was investigated. This study has shown conclusively that when applied to spring-planted lodgepole pine seedlings, pinosylvin is effective in significantly reducing feeding damage. Seedlings treated with pinosylvin suffered damage levels of 2.3% and 21.2% compared to the controls with damage levels of 24.5% and 41.0%. Weasel scent was found to reduce damage levels, but the reduction was not statistically significant in all blocks.     

Use of predator odors as repellents to reduce feeding damage by herbivores

The effectiveness of predator odors (fecal, urine, and anal scent gland) in suppressing feeding damage by snowshoe hares was investigated in pen bioassays at the University of British Columbia Research Forest, Maple Ridge, British Columbia, Canada. A total of 28 bioassay trials tested the effects of these odors on hare consumption of willow browse and coniferous seedlings. Lynx and bobcat feces, weasel anal gland secretion, and lynx, bobcat, wolf, coyote, fox, and wolverine urines resulted in the most effective suppression of hare feeding damage. Novel odors of domestic dog urine and 2-methylbutyric acid did not reduce feeding. A field bioassay with lodgepole pine seedlings and weasel scent provided significant results comparable to the pen bioassays. The short-term (up to seven days) effectiveness of these treatments was more likely due to evaporative loss of the active repellent components of a given odor than habituation of hares to the stimulus. Predator odors as repellents have a biological basis compared with the anthropomorphic origins of commercial repellents. When encapsulated in weather-proof controlled-release devices, these odors could provide long-term protection for forestry plantations and agricultural crops which experience hare/rabbit feeding damage.     

Efficacy of pine oil as repellent to wildlife

Pine oil, a by-product of the pulp industry, is a feeding repellent to snowshoe hares and voles. In pen trials with snowshoe hares and field trials with voles, when given a choice between food in a pine oil-treated bowl and a control bowl, the animals fed preferentially from the control bowl. When the hares were presented with food only in a pine oil-treated bowl, two hares showed a reduced rate of food consumption and one hare did not feed at all. Pine oil contains monoterpenes which may inhibit microbial symbionts in the digestive tracts of hares and voles. The repellent action of pine oil is likely based on this interference of digestive processes, and it is of adaptive advantage for cecal digestors to avoid it. Pine oil has potential as a commercial repellent for snowshoe hares and voles.     

Camphor from juvenile white spruce as an antifeedant for snowshoe hares

One theory in plant antiherbivore defense predicts that slow growing late succession plants like white spruce (Picea glauca) make large investments in antiherbivore defenses. Juvenile stages of white spruce in the Yukon, Canada, are rarely browsed by snowshoe hares (Lepus americanus), an abundant herbivore, but mature spruce is a highly preferred food. The hexane-soluble fractions of the methanol extracts from juvenile and mature white spruce contain camphor and bomyl acetate. There is four times as much camphor in juvenile spruce as in mature spruce from GC analysis. Plant extracts were added to rabbit chow. Pairs of extracts were offered to hares in choice tests. These tests demonstrated that camphor in the juvenile spruce extracts deterred feeding. Bornyl acetate did not have a clear antifeeding effect.On leave from the Department of Chemistry, University of South Pacific, Fiji.     

Influence of the plant antifeedant,pinosylvin, on suppression of feeding by snowshoe hares

This study investigated the influence of the plant antifeedants, pinosylvin and pinosylvin methyl ether (PME), on suppression of feeding by snowshoe hares (Lepus americanus). Screening bioassays showed clearly that pinosylvin suppressed feeding by hares when sprayed directly on coniferous tree seedlings. Pinosylvin odor, when associated with food (but not mixed with it), also significantly reduced consumption of rabbit chow by hares. Large pen bioassays indicated that both pinosylvin and PME significantly reduced feeding on tree seedlings by hares when the antifeedants were sprayed directly on trees. In field bioassays near Prince George, British Columbia, Canada, pinosylvin sprayed on trees and encapsulated in controlled-release devices of PVC plastic, with an internal wire as a twist-tie for attachment to tree, significantly reduced feeding by hares. Thus, pinosylvin will generate an avoidance response in terms of feeding by snowshoe hares. This response is likely triggered by an olfactory pathway based on positive results with controlledrelease devices attached to seedlings. Our study reports the first practical utilization of plant antifeedants for forest crop protection and wildlife management.     

Trade-Off Between Chemical and Biotic Antiherbivore Defense in the South East Asian Plant Genus Macaranga

The plant genus Macaranga is known for its manifold mutualistic associations with ants. The plants provide food for the ants and in turn get protection from herbivores. Depending on the strength of the plant–ant interaction, the plant's investment in ants and the biotic defense derived from them is more or less effective. We conducted a comparative study on tannin content in 12 Macaranga species that were selected based on their associations with ants (three nonmyrmecophytes and nine myrmecophytes, three of which start their ontogeny as nonmyrmecophytes). Different developmental stages were investigated in three Macaranga species. Extracts of every individual plant analyzed for tannins were also tested for their effects on larval growth employing larvae of the common cutworm (Spodoptera littoralis). The studied Macaranga species differed significantly in their tannin contents as well as in the effects of their leaf extracts on the growth of S. littoralis larvae. A correlation analysis shows a connection between tannin contents and larval growth. High tannin contents and, thus more effective chemical defense, were observed in nonmyrmecophytic Macaranga species associated only facultatively with ants as compared to obligate myrmecophytes. Our study supports the hypothesis of a trade-off between chemical and biotic defense in the genus Macaranga.     

Chemical defense secretions of some species of Malaysian rhinotermitidae (Isoptera,Rhinotermitidae)

The defense secretions of the soldiers of the Malaysian rhinotermitid,Parrhinotermes aequalis (Havilandi) andP. pygmaeus (John),Termitogeton planus (Havilandi) andSchedorhinotermes malaccensis (Holmgren) consist mainly of vinyl ketones, whereas that ofProrhinotermes flavus (Bugnion & Popoff) gives (E)-1-nitropentadecene. The chemistry of the defense secretions ofParrhinotermes andTermitogeton is documented and based on their chemical relationships;Termitogeton shows a closer affinity to the Rhinotermitinae than Heterotermitinae.     

Influence of mustelid scent-gland compounds on suppression of feeding by snowshoe hares (Lepus americanus)

This study investigated the influence of mustelid anal-gland compounds in suppressing feeding by snowshoe hares on coniferous tree seedlings. Pen and field bioassays indicated that 3-propyl-1,2-dithiolane from the stoat (Mustela erminea), and secondarily, 2,2-dimethylthietane from the mink (M. vison) had a very negative effect on feeding behavior of hares. The major component of stoat anal gland secretions, 2-propylthietane, and the related compounds, thietane and 2-methylthietane, were not effective. 3,3-Dimethyl-1,2-dithiolane from the least weasel (M. nivalis) and ferret (M. putorius) and di-n-propyldisulfide (acyclic analog of 3-propyl-1,2-dithiolane) similarly did not affect hare feeding. 3-Propyl-1,2-dithiolane and 2,2-dimethylthietane (also found inM. erminea) may act as interspecific chemical signals which induce a fear or avoidance response in hares. Such compounds have outstanding potential as area repellents to reduce crop and livestock depredations. Our study reports one of the first practical utilizations of mammalian semiochemicals in crop protection and wildlife management.     

Prevalence of Chemical Defenses among Freshwater Plants

Although macrophyte–herbivore interactions in freshwater systems were generally disregarded for many years, recent data suggest that herbivory can be intense and important in structuring freshwater communities. This has led to the hypothesis that chemical defenses should be common among freshwater plants, but few studies have reported such chemical defenses, and no previous studies have assessed the frequency of chemical defenses among a substantial number of freshwater plant species. In a study of 21 macrophyte species co-occurring with the omnivorous crayfish Procambarus acutus in a southeastern USA wetland environment, we found that extracts of 11 species (52%) deterred feeding by P. acutus when tested in artificial foods at natural concentrations. Of these 11 chemically defended species, one species, Eupatorium capillifolium, consistently had a more unpalatable extract following mechanical damage to plant tissue, indicative of an activated chemical defense. Because herbivores are commonly nitrogen-limited and select food based on several plant traits, including plant nutritional value, it might be expected that chemical defenses would be especially important for protein-rich plants. However, we found no relationship between soluble protein concentration and deterrence of plant extracts.     

Effects of birch phenolics on a grazing and a browsing mammal: A comparison of hares

Mountain hares (Lepus timidus L.) commonly have high proportions of birch (Betula spp.) in their winter diets, whereas European hares (Lepus europaeus) do not. The effects of a birch extract added to laboratory diets offered to mountain hares and European hares on the digestibility and sodium balance were measured. The extract added contained total phenolics equivalent in amount to that occurring in diets containing 0, 40, 60 and 80% dry matter of birch twigs. Increasing dietary phenolic concentration led to reduced voluntary food intake and apparent protein digestibility in both hare species. No effects on apparent dry matter digestibility were observed. The highest concentration of birch extract caused severe sodium losses via the urine by European hares but not by mountain hares. The effects of the birch extract within the digestive system appear to be similar in the two hare species, whereas the mountain hare appears to be better adapted to the toxic effects that disrupted sodium balance in the European hare. These preliminary results suggest that detoxification rather than digestive abilityper se may contribute to different mammalian herbivores' feeding strategies.     

Watercress and amphipods Potential chemical defense in a spring stream macrophyte

We investigated the potential role of defensive chemicals in the avoidance of watercress (Nasturtium officinale) by the cooccurring amphipod,Gammarus pseudolimnaeus at two spring brooks: Carp Creek, Michigan and Squabble Brook, Connecticut. We conducted observations and laboratory experiments on the consumption of watercress, the toxicity of damaged (frozen) watercress, and the toxicity of damage-released secondary chemicals. Field-collected yellowed watercress typically lacked the bite and odor characteristic of green watercress and was consumed byG. pseudolimnaeus. G. pseudolimnaeus strongly preferred yellowed watercress to green watercress despite the higher nitrogen content of the latter (2.7 vs 5.4%), and usually consumed five times more yellowed watercress (>50% of yellowed leaf area vs. <8% of green leaf area presented). Fresh green watercress contained seven times more phenylethyl glucosinolate than yellowed watercress (8.9 mg/g wet vs. 1.2 mg/g). Cell-damaged (frozen) watercress was toxic toG. pseudolimnaeus (48-hr LC₅₀s: ca. 1 g wet/liter), and the primary volatile secondary chemicals released by damage were highly toxic. The predominant glucosinolate hydrolysis product, 2-phenylethyl isothiocyanate had 48-hr LC₅₀s between 0.96 and 3.62 mg/liter, whereas 3-phenylpropionitrile was less toxic, with 48-hr LC₅₀s between 130 and 211 mg/liter. These results suggest that live watercress is chemically defended against consumption. The glucosinolate-myrosinase system, recognized as the principle deterrent system of terrestrial crucifers, is also possessed byN. officinale and may contribute to defense from herbivory by aquatic crustaceans. This system may be just one of many examples of the use of defensive chemicals by stream and lake macrophytes.     

Chemical defense in birch. Platyphylloside: A phenol fromBetula pendula inhibiting digestibility

Extracts of Scandinavian birch (Betula pendula Roth) buds and internodes of varying twig diameters have been investigated for their inhibitory effect on ruminant digestibility in vitro. The predominant inhibitory effect was observed in extracts containing the phenol platyphylloside, 5-hydroxy-1,7-bis-(4-hydroxy-phenyl)-3-heptan-one-3-O--d-glucopyranoside. Isolation of the pure compound and incubation with rumen inocula showed that digestibility was negatively related to the concentration. Significant effect was measured below the concentration naturally occurring in birch (0.8% of dry matter). Another isolated compound, the closely related rhododendrin, 4-(4-hydroxyphenyl)-2-butanol-2-O--d-glucopyranoside, did not depress digestibility within the concentrations found in birch. An important phenol of buds, apigenin-4,7-dimethylether, did not have any measurable effect on digestibility, while a nonphenolic fraction of bud extract had a slight inhibitory effect on digestibility. Implications for browsers feeding on birch are briefly discussed.     

Feeding responses of snowshoe hares (Lepus americanus) to volatile constituents of red fox (Vulpes vulpes) urine

This study investigated the influence of the volatile constituents of red fox (Vulpes vulpes) urine in suppressing feeding by snowshoe hares (Lepus americanus) on coniferous tree seedlings. Pen and field bioassays indicated that the odor of fox urine and its principal component, 3-methyl-3-butenyl methyl sulfide, had a negative effect on feeding behavior of hares. The other sulfur-containing compounds, 2-phenylethyl methyl sulfide and 3-methylbutyl methyl sulfide, as well as six other constituents, were not effective. Synthetic urine mixtures composed of eight and nine volatile constituents, respectively, did not suppress feeding in pen bioassays. However, the mixture of eight compounds in a field bioassay did result in significantly fewer seedlings being eaten by hares than in the control. 3-Methyl-3-butenyl methyl sulfide may act as an interspecific chemical signal which induces a fear or avoidance response in hares. Additional work is required to determine the optimum concentration and release system for 3-methyl-3-butenyl methyl sulfide to be used as a mammalian semiochemical in crop protection.     

Soldier defense secretions ofTrinervitermes bettonianus (Isoptera,Nasutitermitinae): Chemical variation in allopatric populations

The soldier defense secretions of major and minor soldiers of the East African nasute termiteTrinervitermes bettonianus were analyzed chromatographically and spectrometrically, and the diterpene and monoterpene constituents were determined for three allopatric populations. Incipient colonies from one population raised on food from a second population produced their population-specific terpene pattern independent of food source. Secretion compositions are thus genetically rather than nutritionally determined, in agreement with biosynthetic studies in other nasutes. A minor volatile constitutent, previously proposed to be 3-ethyl-2-octanol was re-identified as (R)-2-decanol.     

Chemical defense of a dorid nudibranch,Glossodoris quadricolor,from the red sea

The nudibranch,Glossodoris quadricolor (Doridacea) feeds on the red spongeLatrunculia magnifica, which grows in the reefs of the Gulf of Aqaba, Red Sea. The ichthyotoxic substance from the sponge, latrunculin B, was also indentified in the mucous secretion of the mollusk by TLC, indicating the use of this substance as defense allomone.     

Caffeine Does Not Protect Coffee Against the Leaf Miner Perileucoptera coffeella

The larvae of Perileucoptera coffeella, a leaf miner, is one of the main pests attacking coffee plantations. Caffeine is the major alkaloid in this crop and may have a role in insect resistance. Since there is genetic variability in both resistance to the coffee leaf miner and in caffeine content among different coffee species, we investigated the role of this alkaloid as an antiherbivory compound. Coffee plants containing different levels of caffeine were exposed to oviposition of the insect, and the caffeine content and damaged leaf area were evaluated. The same procedure was carried out with interspecific hybrids between C. arabica and C. racemosa, varying in resistance against the leaf miner. In addition, plants were exposed to the insect, but one leaf of each pair was protected from oviposition with paper bags. In another experiment, leaf disks from plants with known susceptibility to attack by the leaf miner were infiltrated with 0–2% aqueous caffeine solutions and exposed to oviposition. When one leaf of a pair was protected from the insect, there was an increase in caffeine in the infested leaves, particularly in younger leaves. None of the experiments established a significant correlation between reduction of leaf damage and caffeine content of the tissue. The results indicate that P. coffeella is well adapted to coffee, and it has evolved a mechanism to tolerate the potentially toxic effects of caffeine.     

Chemical contents of stinging trichomes ofCnidoscolus texanus

Plants known as nettles bear trichomes that deliver a painful sting when touched. Studies of members of the Urticaceae have suggested that their trichomes may contain histamine, acetylcholine, and serotonin. We report investigations using TLC, HPLC, and UV-VIS spectrophotometry to analyze the hair fluids ofCnidoscolus texanus, a member of the Euphorbiaceae, along with standards of known histamine, acetylcholine, and serotonin. Of these, only serotonin was detected in hair extracts. Up to four other compounds were detected and partially characterized, but they have not been identified.     

Homarine as a feeding deterrent in common shallow-water antarctic lamellarian gastropodMarseniopsis mollis: A rare example of chemical defense in a marine prosobranch

The common bright yellow antarctic lamellarian gastropodMarseniopsis mollis was examined for the presence of defensive chemistry. Proton nuclear magnetic resonance (NMR) spectroscopy indicated that a major component of ethanolic extracts purified by reversed-phase column chromatography was homarine. Further high-performance liquid chromatography (HPLC) analysis of the mantle, foot, and viscera verified the presence of homarine in all body tissues at concentrations ranging from 6 to 24 mg/g dry tissue. A conspicuous macroinvertebrate predator of the shallow antarctic benthos, the sea starOdontaster validus, always rejected live individuals ofM. mollis, while readily feeding on pieces of fish tail muscle. Filter paper disks treated with shrimp elicited a broad range of feeding behaviors in the sea starO. validus (movement of disc to mouth, extrusion of cardiac stomach, humped feeding posture). Shrimp disks treated with homarine (0.4 and 4 mg/disk) were rejected byO. validus significantly more frequently than control disks treated with solvent carrier and shrimp or shrimp alone. The highest concentration of homarine tested not only caused feeding deterrence, but in several sea stars a flight response was noted. Homarine was not detected in the tunic of the antarctic ascidianCnemidocarpa verrucosa, a presumed primary prey ofM. mollis. Nonetheless, crude extracts of the epizooites that foul the tunic (primarily the bryozoans and hydroids) contain homarine, suggestingM. mollis may ingest and derive its chemistry from these organisms. This appears to be only the third example of chemical defense in a member of the Order Mesogastropoda. As the vestigial internalized shell ofM. mollis is considered a primitive condition, the findings of this study lend support to the hypothesis that chemical defense evolved prior to shell loss in shell-less gastropods.     

Chemical defense of giant springtailTetrodontophora bielanensis (Waga) (Insecta: Collembola)

The giant springtail,Tetrodontophora bielanensis (Waga), is characterized by integumental openings (pseudocells) from which small droplets of a sticky defensive fluid are secreted after molestation. The secretion originates initially from secretory cells below the pseudocellae; subsequent irritations result in release of hemolymph, which was identified by both chemical and microscopical methods as well as by scanning electron microscopy. Bioassays with topically treated ground beetlesNebria brevicollis showed that the pseudocellular fluid evokes a total disorientation and cleansing behavior of the beetle. The main constituents were identified as the following pyridopyrazines: 2,3-dimethoxpyrido[2,3-b]pyrazine (1), 3-isopropyl-2-methoxypyrido[2,3-b]pyrazine (2), and 2-methoxy-4H-pyrido[2,3-b]pyrazine-3-one (3). These alkaloids are mainly present in the pseudocellar fluids of female and male springtails but are absent in their food or feces. Minor amounts are found in the hemolymph of adults, while larvae contain traces of2 only. All compounds were synthesized and tested for activity. In natural concentrations, the synthetic alkaloids elicited the same effects from the ground beetles as the pseudocellar fluid.