Effect of birch (Betula pendula) bark and food protein level on root voles (Microtus oeconomus): I. food consumption,growth, and mortality

The effect of protein and birch bark powder (BBP) content of forage on food consumption and growth of root voles (Microtus oeconomus) was studied by feeding young voles with eight different diets for two weeks. Voles ate more when the protein content of forage was moderate (6%) or low (3%), and when BBP was added to the diets, as compared to a high (12%) protein diet without BBP addition. On high and moderate protein diets voles gained weight, whereas on low protein diets they lost weight. Addition of BBP caused reduced growth or weight loss. Consuming a diet with moderate (6%) protein and high BBP (20%) resulted in high mortality (9 of 10 died). These results show that root voles need at least 6% protein for growth and that the effect of birch bark depends on the protein content of the forage.     

Lespedeza phenolics andPenstemon alkaloids: Effects on digestion efficiencies and growth of voles

Lespedeza cuneata contains high levels of phenolics and is a common food plant of the meadow vole (Microtus pennsylvanicus);Penstemon digitalis contains substantial quantities of alkaloids and is a common food plant of meadow voles and prairie voles (M. ochrogaster). We investigated the palatability of these plants and the effects of their secondary compounds on the digestion efficiencies and growth of both species of voles. Voles ate very little of either plant when alternative food was present. Phenolics and alkaloids were extracted from the plants, incorporated into separate artificial diets, and fed to weanling voles for three weeks.Lespedeza phenolics reduced the growth of meadow voles but not prairie voles throughout the feeding trial. These compounds disrupted digestion, reducing protein digestibility by more than half.Penstemon alkaloids lowered only the initial growth rates of prairie voles and had no significant effect on meadow voles. Prairie voles tended to increase food consumption rates on bothLespedeza andPenstemon diets. This response offset some of the decrease in digested protein intake in the first case, and offset the increased metabolic cost of processing the diet in the latter case. Our results indicate that althoughLespedeza phenolics andPenstemon alkaloids do influence consumption and digestibility of artificial diets, they do not greatly reduce the performance (i.e., growth or survival) of voles when consumed at levels generally observed for wild voles. However, these compounds probably do place an upper limit on the amount of freshLespedeza andPenstemon that can be consumed and contribute to the generalist feeding strategy of voles.     

Bark beetle pheromones: Production of verbenone by a mycangial fungus ofDendroctonus frontalis

A mycangial symbiotic fungus ofDendroctonus frontalis is capable of oxidizingtrans-verbenol to verbenone. Both of these compounds are known to be important behavioral chemicals for this species, and it is suggested that development of the fungus in the plant host may play a role in influencing the behavior of the beetle to a successfully colonized tree.Supported in part by a cooperative agreement with the USDA Forest Service, Southern Forest Experiment Station, Pineville, Louisiana 71360.The use of a trade name in this paper does not constitute an official endorsement or approval by the USDA.     

Disruption by Conophthorin of the Kairomonal Response of Sawyer Beetles to Bark Beetle Pheromones

Antennally active nonhost angiosperm bark volatiles were tested for their ability to reduce the response of three common species of coniferophagous wood-boring Cerambycidae to attractant-baited multiple funnel traps in the southern interior of British Columbia. Of the nonhost volatiles tested, only conophthorin was behaviorally active, disrupting the attraction of sawyer beetles, Monochamus spp., to traps baited with the host volatiles -pinene and ethanol and the bark beetle pheromones ipsenol and ipsdienol. Conophthorin did not affect the attraction of sawyer beetles to the host kairomones -pinene and ethanol in the absence of bark beetle pheromones, nor did it have any behavioral effect on adults of Xylotrechus longitarsis, which were not attracted to bark beetle pheromones. These results indicate that conophthorin does not act as a general repellent for coniferophagous Cerambycidae, as it seems to do for many species of Scolytidae, but has the specific activity of disrupting the kairomonal response of sawyer beetles to bark beetle pheromones.     

Susceptibility to vole attacks due to bark phenols and terpenes inPinus contorta provenances introduced into Sweden

Seedlings of North AmericanPinus contorta introduced to Sweden and Finland are severely gnawed by voles, e.g.,Microtus agrestis. The level of damage varies between provenances. Chemical analyses of various phenolic compounds, monoterpenes, and resin acids of different provenances and of damaged and undamaged stems showed that some phenolic substances in the bark increased after damage without deterring the animals, that monoterpene differences between provenances were not related to vole damage, and that certain resin acids occurred in larger amounts in lightly than in severely damaged provenances. Levopimaric and neoabietic acid, and possibly abietic acid, may be important for a partial resistance to vole browsing.     

Branch-cutting behavior by the vole (Microtus pennsylvanicus)

While investigating the preferences of meadow voles (Microtus pennsylvanicus) toward various coniferous species, we noted they often cut the branches of young trees, and then left them lying on the snow for two days or more before eating them completely. We tested whether this behavioral manipulation of a potential food resource resulted in a decrease in the level of secondary metabolites in branches. We found that after being cut for more than three days, the branches of young conifers had significantly less phenolics and condensed tannins. These postmanipulation levels of secondary metabolites were similar to those found in preferred summer food resources. Voles were thus capable of transforming a low-quality resource into one that was more compatible with their feeding patterns and detoxification mechanisms.     

Electrophysiological and Olfactometer Responses of Two Histerid Predators to Three Pine Bark Beetle Pheromones

We measured electrophysiological responses in the antennae of two predaceous hister beetles, Platysoma parallelum and Plegaderus transversus, exposed to racemic mixtures of primary aggregation pheromones of scolytid bark beetle prey, ipsenol, ipsdienol, and frontalin. No significant differences were found for either histerid species between male and female antennal responses to any of the three pheromones. Measurement of antennal threshold responses indicated that Pla. parallelum has increasing antennal sensitivity to ipsdienol, ipsenol, and frontalin. In contrast, Ple. transversus exhibited similar detection thresholds to all three pheromones. Pla. parallelum antennae exhibited different response amplitudes to the three pheromones at quantities above the detection threshold, while Ple. transversus had similar responses to each. Behavioral responses to the same three pheromones were evaluated for both histerid species using pedestrian olfactometer bioassays. Both species were attracted to frontalin and ipsenol, but not ipsdienol. Pla. parallelum was significantly more attracted to frontalin than ipsenol, while Ple. transversus showed no significant preference for either compound. Our results suggest that histerids that prey upon pine bark beetles may have different host or host habitat preferences, which could reduce interspecific competition.     

Odor Perception in the Bark Beetle Parasitoid Roptrocerus xylophagorum Exposed to Host Associated Volatiles

Y-tube olfactometer bioassays and combined gas chromatography–electroantennographic detector (GC-EAD) analyses were performed to investigate the specific odors utilized as host location cues by the bark beetle parasitoid, Roptrocerus xylophagorum, originating from the southeastern United States. R. xylophagorum parasitizes several economically important holarctic bark beetle species and females oviposit preferentially on late larval stages. Both female and male parasitoids were tested with volatiles derived from host infestations of either Dendroctonus frontalis, the southern pine beetle, or Ips grandicollis, the southern pine engraver. Tested volatiles were steam distillates from the bark of loblolly pine, Pinus taeda, infested with larvae of the respective bark beetle species. Combined gas chromatography–mass spectrometry (GC-MS) was employed for identification and quantification of the compounds in the steam distillates. To confirm the EAD activity of identified compounds, GC-EAD analyses were repeated with a synthetic blend composed predominantly of compounds in the crude extracts that had revealed apparent electrophysiological activity. In Y-olfactometer bioassays, female parasitoids were attracted to both of the above-mentioned distillates. Male parasitoids were tested with one of the distillates but failed to respond. In GC-EAD analyses, the sexes displayed similar relative sensitivities to the components of the blends. Males exhibited generally higher amplitudes of response to the tested compounds than females. Monoterpene hydrocarbons associated with the constitutive resin of the host tree did not elicit significant EAD responses. Compounds known to be associated specifically with the host–tree complex, such as certain oxygenated monoterpenes, generated the greatest EAD responses. Female parasitoids were attracted by a synthetic blend composed of several of the EAD active oxygenated monoterpenes.     

Demonstration of an odorous intramale primer effect in short-tailed vole,Microtus agrestis L.

Anal (proctodeal) glands of maleMicrotus agrestis housed in social isolation undergo severe atrophy. Their weight and volume is significantly lower than those of the stock control males. The atrophied glands can be revived by subjecting deprived voles to various social odors. Atrophied glands of isolated males do not respond to the odors of male and female urine, voided feces of females, and unvoided feces of males. Atrophied anal glands of males exposed to voided male feces (which have passed the orifice of the anal gland) and soiled bedding from adult males show strong recrudescence. The mean weight and volume of the glands and plasma testosterone level are significantly higher than of males maintained in complete social isolation, although they are significantly less than those of stock control males. Atrophied glands of socially deprived males strongly respond to the odor of ethereal extract of gland secretion. In males exposed daily to anal gland secretion extract, the weight and volume of the gland and plasma testosterone level increase and are not significantly different from those of stock controls. They enjoy higher plasma testosterone levels and consequently larger and more active anal glands than complete isolates.     

Nitrogen fixation by trees in relation to soil nitrogen economy

The N₂-fixing potential (NFP) (i.e. the amount of fixed N₂ in a constraint-free environment) of N₂-fixing trees (NFTs) varies with the genotype. The NFP can be higher than 30-50 g N₂ fixed tree^–1 year^–1 in the most active species, be they leguminous trees such asAlbizia lebbeck, Gliricidia sepium andLeucaena leucocephala, or actinorhizal trees such asCasuarina equisetifolia. The actual amount of nitrogen fixed (ANF) (i.e. the amount of N₂ fixed in the field) is lower than the NFP or even nil because of various constraints, especially drought, nutrient deficiencies, excess of available N and pathogenic nematodes. As tree litters are mineralized, the amount of available N in the soil increases with time, this process leading to the cessation of N₂ fixation in aging plantations. When the mineralization rate is slowed down or inhibited, N₂ fixation can continue. NFTs improve the N status of soils, but the transfer of fixed N to associated plants is not always ensured. Three main approaches are appropriate to increase N₂ fixation: clonal selection of trees combined with vegetative propagation, inoculation with effective rhizobium orFrankia strains, and proper fertilization (especially P). In the absence of major environmental constraints, a positive response to inoculation is expected only when specific (non-promiscuous) NFTs are grown in sites where the density of compatible rhizobia is low or nil. The potentialities of NFTs are far from being fully exploited. Further investigations are proposed and the economics of NFT management is briefly discussed.     

Role of phenolics of coniferous trees as deterrents against debarking behavior of meadow voles (Microtus pennsylvanicus)

Preferences of meadow voles (Microtus pennsylvanicus) toward various coniferous species were tested under winter conditions. Cafeteria tests showed preferences for Norway spruce (Picea abies) and Norway pine (Pinus resinosa) and rejection of white pine (Pinus strobus) and white spruce (Picea glauca). When phenolic extracts of these species were prepared and added to a low 8% protein diet, food intake of voles and preferences by rank followed the same patterns. Determination of the concentration of phenolics in branch samples using the Singleton and Rossi procedure showed that Norway pines contained the smallest amount (2.15%/g dry matter) while spruces yielded the most (2.76%/g dry matter). These experiments lead us to expect high losses of Norway pine and Norway spruce in habitats harboring high vole densities.     

Volatiles from Potential Hosts of Rhopalicus tutela a Bark Beetle Parasitoid

Host location cues for parasitic wasps that attack bark beetle larvae concealed under the bark of spruce trees were analyzed by collecting odor samples from entrance holes into the bark beetle galleries, isolated larvae, and pupal chambers with or without bark beetle larvae. Odor samples were collected by dynamic headspace adsorptions on Porapak Q or static adsorptions by using solid-phase microextraction (SPME) with Carbowax–divinylbenzene as the adsorbing phase. Samples were analyzed by coupled gas chromatographic–electroantennographic detection (GC-EAD) and GC-mass spectrometry (GC-MS). The antennae of Rhopalicus tutela females responded primarily to oxygenated monoterpenes that are typical for damaged host trees. These compounds are attractive to bark beetle parasitoids in long-range host location, suggesting that they are used in both long- and short-range host location. No differences could be detected between samples collected from pupal chambers with or without mature larvae. Larvae outside pupal chambers emitted low quantities of the same compounds present in empty pupal chambers. The data support the hypothesis that volatiles used by host foraging parasitoids arise from the interaction between introduced microorganisms and the bark and/or vascular tissue of the host tree rather than from the bark beetle larvae.     

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.     

Marking urine and preputial gland secretion of male bank voles (Clethrionomys glareolus L.) chemical analyses and behavioral tests

Urine and preputial gland secretion of male bank voles were analyzed by gas chromatography (GC) and mass spectrometry (MS) (selected ion monitoring, SIM). GC-MS analyses showed the presence of hexadecyl acetate in preputial gland secretion and in marking urine but not in metabolic urine. Female bank voles responded more strongly to marking urine of males than to metabolic urine, and they responded more to preputial gland secretion (pure or added to urine) than to metabolic urine. Dominant males spent more time and marked more frequently in response to hexadecyl acetate-enriched urine than to urine alone. The opposite reaction was shown by subordinate males. The results suggest that the acetate functions in the bank voles' dominance interactions.     

Cover and efficacy of predator-based repellents for Townsend's voleMicrotus townsendii

Predator-based repellents have been used experimentally to control wildlife damage in both agriculture and forestry, but they have not always been effective. We examined the relative importance of cover and predator odors in forage patch selection by Townsend's vole,Microtus townsendii, and its behavior related to cover and predator cues. Experiments were conducted in which forage patch and area choices were related to available habitat alternatives. Outdoor enclosures were divided into halves: one side was treated and the other used as a control. Treatments consisting of cover, repellent, and cover plus repellent were compared to controls (no cover, no repellent). In the absence of cover, voles preferred to feed on the side without repellents. When cover was present, voles preferred to feed on the side with cover, regardless of whether or not repellents were present. Voles visited more feeding stations on the side without cover when repellents and cover were present than they visited during cover-only treatments. These additional feeding stations, visited outside of cover, were used only lightly as food sources. The amounts of oats eaten by voles decreased with increasing distance from cover. This inverse relationship had a steeper slope in coveronly treatments compared to cover plus repellent treatments. A selection model based on forage patch selection and a habitat preference hierarchy is proposed. We conclude that predator odors are effective as repellents, but their efficacy depends on habitat conditions. Managers intending to use predator-based repellents must ensure that alternative sites available to pests are better quality habitat than in areas to be protected.     

Preference of meadow voles (Microtus pennsylvanicus) for conifer seedlings: Chemical components and nutritional quality of bark of damaged and undamaged trees

Meadow voles (Microtus pennsylvanicus Ord.) of the 1987–1988 population density peak left several seedling plantations of Norway spruce (Picea abies) and Norway pine (Pinus resinosa) severely damaged in southern Quebec, Canada, while white spruce (Picea glauca) and white pine (Pinus strobus) suffered no damage. We compared levels of crude protein, total nonstructural carbohydrates (TNC), total phenols, and monoterpenes in the bark to detect differences between damaged and undamaged seedlings within and between plantations. There were no significant differences in levels of nutritional components between both types of seedlings within the same plantation. However, differences were noted among tree plantations for protein, TNC, and phenolics content but these differences could not be assigned to the voles' selection for particular species. Quantitative and qualitative differences also were registered in monoterpene levels between species. -Myrcene and bornyl acetate were found only in seedlings of undamaged species. Moreover, the latter contained higher levels of limonene. We conclude that the presence of specific monoterpenes is more important in defense mechanisms of conifer seedlings than relative levels of nutrients (protein or TNC) or total phenolics.     

Effect of birch (Betula pendula) bark and food protein level on root voles (Microtus oeconomus): II. detoxification capacity

The effect of protein and birch bark powder (BBP) content of forage on detoxification capacity of root voles (Microtus oeconomus) was studied. Young voles were fed with eight different diets for two weeks. Individuals on low (3%) protein diets had significantly lighter livers and kidneys than those on moderate (6%) or high (12%) protein diets. Birch bark powder addition did not have significant effect on organ weight. Detoxification was significantly induced, apparently due to secondary compounds in BBP. The activity of ethoxyresorufin-O-dealkylase (EROD) was high when protein content or BBP concentration in forage was high as compared to low protein diets or diets containing no BBP. Glucuronidation, on the other hand, was not induced by BBP. High BBP content caused serious physiological stress to the voles. The only individuals surviving were those capable of sufficiently allocating energy and protein to detoxification.     

Response of ensete (Ensete ventricosum W.) to mineral fertilizers in southwest Ethiopia

Ensete (Ensete ventricosum W. Cheesm.) is a root crop which stores starch in the root and in the lower part of the stem. It is grown in the southwest of Ethiopia and due to its drought resistance, it is of outstanding importance for the supply of food to the local population. Until now virtually nothing is known about the response of Ensete to fertilizer application. Field trials carried out on three representative soils in Ethiopia showed that Ensete biomass yields were increased significantly on all three soils by nitrogen and phosphorus application. Potassium had only marginal effect on biomass growth but favourably influenced starch production. Sulfate application had no major impact on growth and starch yield. The yield response was well related to the level of available nutrients in the soil, as determined by electroultrafiltration (EUF). Leaf analysis provided preliminary evidence that optimum levels of N, P, and K may be 3.8%, 0.3%, and 4.8%, respectively.     

Opposing Effects of Host Monoterpenes on Responses by Two Sympatric Species of Bark Beetles to Their Aggregation Pheromones

The effects of host tree monoterpenes on primary and secondary attraction of the bark beetles, Ips pini and Ips grandicollis, and their associated phloeophagous insects were investigated. Monoterpenes alone were not attractive to I. pini. However, monoterpenes mediated the attraction of I. pini to its aggregation pheromones. With the exception of 3–carene, the effect of monoterpenes on I. pini's response to its pheromone, ipsdienol plus lanierone, was inhibitory. In contrast, (–)--pinene both attracted I. grandicollis and enhanced the attraction of I. grandicollis to its pheromone, ipsenol. No monoterpene inhibited the response of I. grandicollis to its pheromone. The inhibitory effect of host monoterpenes on I. pini response to its aggregation pheromone differs from previous work, in which monoterpenes either synergized responses or had no effect. In addition to possible geographic differences, the concentrations used in our study simulated trees that had begun to respond to attack, whereas previous studies deployed lower concentrations, which simulated constitutive phloem from unattacked trees. These results support the view that trees that undergo induced responses to bark beetles sometimes inhibit attraction of additional beetles, despite the beetles' production of aggregation pheromones. Neither species displayed cross-attraction to the pheromone of the other. The red turpentine beetle, Dendroctonus valens, showed weak and consistent attraction to (+)--pinene and in some cases to (–)--pinene. Attraction to (–)--pinene was usually enhanced by Ips spp. pheromones. The absence of strong attraction to (+)--pinene and partial attraction to (–)--pinene suggest that the effects of different stereoisomers of -pinene on D. valens vary throughout its geographical range. Hylastes porculus was also attracted to some monoterpenes, particularly (–)--pinene. An additional 10 species of phloeophagous insects were caught in response to monoterpenes and/or pheromones, including the pine root weevils, Hylobius pales and Pachylobius picivorus, and the longhorned beetle, Monochamus carolinensis.