There is growing evidence of a substantial decline in pollinators within Europe and North America, most likely caused by multiple factors such as diseases, poor nutrition, habitat loss, insecticides, ...and environmental pollution. Diesel exhaust could be a contributing factor to this decline, since we found that diesel exhaust rapidly degrades floral volatiles, which honey bees require for flower recognition. In this study, we exposed eight of the most common floral volatiles to diesel exhaust in order to investigate whether it can affect volatile mediated plant-pollinator interaction. Exposure to diesel exhaust altered the blend of common flower volatiles significantly: myrcene was considerably reduced, β-ocimene became undetectable, and β-caryophyllene was transformed into its cis-isomer isocaryophyllene. Proboscis extension response (PER) assays showed that the alterations of the blend reduced the ability of honey bees to recognize it. The chemically reactive nitrogen oxides fraction of diesel exhaust gas was identified as capable of causing degradation of floral volatiles.
If carbon (C) sinks withdraw carbohydrates as they are transported along tree
stems, carbohydrate availability may depend on local sink strength and distance
from sources. Defenses, including ...monoterpenes – a major component of
resin – limit the invasibility of pines. Since carbohydrate reserves
fund monoterpene synthesis, we hypothesized that monoterpene concentrations in
pine stems would decrease from the crown to the lower stem, and susceptibility
to fungal infection would increase.
Here, we measured carbohydrate and monoterpene concentrations along the stems of
lodgepole pine trees (Pinus contorta var.
latifolia) before inoculating with a blue-stain fungus at
different heights. After 6 wk, we assessed tree responses to fungal infection
based on lesion length and carbohydrate mobilization.
Concentrations of carbohydrates and monoterpenes in the phloem before inoculation
decreased with distance from the crown, whereas lesion lengths after inoculation
increased. However, trees mobilized sugars in response to fungal infection such
that carbohydrate reserves near lesions were similar at all heights.
Despite C mobilization, the lower stem was more vulnerable than the upper stem.
Consistent with predictions based on sink–source relationships,
vulnerability occurred where carbohydrates were less available, and likely
resulted from C withdrawal by sinks higher in the supply chain.
Historical data show that outbreaks of the tree killing mountain pine beetle are often preceded by periods of drought. Global climate change impacts drought frequency and severity and is implicated ...in the range expansion of the mountain pine beetle into formerly unsuitable habitats. Its expanded range has recently reached the lodgepole × jack pine hybrid zone in central Alberta, Canada, which could act as a transition from its historical lodgepole pine host to a jack pine host present in the boreal forest. This field study tested the effects of water limitation on chemical defenses of mature trees against mountain pine beetle-associated microorganisms and on beetle brood success in lodgepole × jack pine hybrid trees. Tree chemical defenses as measured by monoterpene emission from tree boles and monoterpene concentration in needles were greater in trees that experienced water deficit compared to well-watered trees. Myrcene was identified as specific defensive compound, since it significantly increased upon inoculation with dead mountain pine beetles. Beetles reared in bolts from trees that experienced water deficit emerged with a higher fat content, demonstrating for the first time experimentally that drought conditions benefit mountain pine beetles. Further, our study demonstrated that volatile chemical emission from tree boles and phloem chemistry place the hybrid tree chemotype in-between lodgepole pine and jack pine, which might facilitate the host shift from lodgepole pine to jack pine.
The mountain pine beetle (
Dendroctonus ponderosae,
MPB) has killed millions of lodgepole pine (
Pinus contorta
) trees in Western Canada, and recent range expansion has resulted in attack of jack ...pine (
Pinus banksiana
) in Alberta. Establishment of MPB in the Boreal forest will require use of jack pine under a suite of environmental conditions different from those it typically encounters in its native range. Lodgepole and jack pine seedlings were grown under controlled environment conditions and subjected to either water deficit or well watered conditions and inoculated with
Grosmannia clavigera
, a MPB fungal associate. Soil water content, photosynthesis, stomatal conductance, and emission of volatile organic compounds (VOCs) were monitored over the duration of the six-week study. Monoterpene content of bark and needle tissue was measured at the end of the experiment. β-Phellandrene, the major monoterpene in lodgepole pine, was almost completely lacking in the volatile emission profile of jack pine. The major compound in jack pine was α-pinene. The emission of both compounds was positively correlated with stomatal conductance. 3-Carene was emitted at a high concentration from jack pine seedlings, which is in contrast to monoterpene profiles of jack pine from more southern and eastern parts of its range. Fungal inoculation caused a significant increase in total monoterpene emission in water deficit lodgepole pine seedlings right after its application. By 4 weeks into the experiment, water deficit seedlings of both species released significantly lower levels of total monoterpenes than well watered seedlings. Needle tissue contained lower total monoterpene content than bark. Generally, monoterpene tissue content increased over time independent from any treatment. The results suggest that monoterpenes that play a role in pine-MPB interactions differ between lodgepole and jack pine, and also that they are affected by water availability.
The whitefly Aleyrodes proletella L. (Hemiptera: Aleyrodidae) has become a major agricultural pest on a broad range of Brassica crops in Europe and has spread to North and South America and ...Australia. In order to understand its present outbreak, information about its life history parameters in relationship to different host plants is needed. Therefore, we tested the reproduction potential of A. proletella on four different host plants under greenhouse conditions: Kohlrabi, kale, white cabbage, and winter oilseed rape. The influence of host plant on preoviposition period, fecundity, survival rate, and sex ratio was examined. Additionally the effect of mating scenario (45-d mated females and males; virgin females and males; 6-d mated females) on life history parameters of A. proletella adults was evaluated. The mating scenario did not significantly influence the survival rate of A. proletella females and males and did not impact female fecundity and preoviposition period. Fecundity of A. proletella was significantly affected by host plant species: the shortest preoviposition period and highest oviposition rate was observed on winter oilseed rape, while the longest and lowest was recorded on white cabbage. The survival rate on white cabbage was significantly lower compared with those reared on the other host plants. The sex ratio of A. proletella progeny was also significantly affected by the host plant species. Our research indicates that winter oilseed rape is a highly suitable host for A. proletella in terms of fecundity, survival rate, and sex ratio, which might explain the current outbreak of A. proletella.
The whitefly Aleyrodes proletella L. (Hemiptera: Aleyrodidae) has become a major agricultural pest on a broad range of Brassica crops in Europe and has spread to North and South America and ...Australia. In order to understand its present outbreak, information about its life history parameters in relationship to different host plants is needed. Therefore, we tested the reproduction potential of A. proletella on four different host plants under greenhouse conditions: Kohlrabi, kale, white cabbage, and winter oilseed rape. The influence of host plant on preoviposition period, fecundity, survival rate, and sex ratio was examined. Additionally the effect of mating scenario (45-d mated females and males; virgin females and males; 6-d mated females) on life history parameters of A. proletella adults was evaluated. The mating scenario did not significantly influence the survival rate of A. proletella females and males and did not impact female fecundity and preoviposition period. Fecundity of A. proletella was significantly affected by host plant species: the shortest preoviposition period and highest oviposition rate was observed on winter oilseed rape, while the longest and lowest was recorded on white cabbage. The survival rate on white cabbage was significantly lower compared with those reared on the other host plants. The sex ratio of A. proletella progeny was also significantly affected by the host plant species. Our research indicates that winter oilseed rape is a highly suitable host for A. proletella in terms of fecundity, survival rate, and sex ratio, which might explain the current outbreak of A. proletella. Key words: Brassica crop, host plant, mating scenario, life history parameter
Honeybees utilise floral odours when foraging for flowers; we investigated whether diesel exhaust pollution could interrupt these floral odour stimuli. A synthetic blend of eight floral chemicals, ...identified from oilseed rape, was exposed to diesel exhaust pollution. Within one minute of exposure the abundances of four of the chemicals were significantly lowered, with two components rendered undetectable. Honeybees were trained to recognise the full synthetic odour mix; altering the blend, by removing the two chemicals rendered undetectable, significantly reduced the ability of the trained honeybees to recognize the altered odour. Furthermore, we found that at environmentally relevant levels the mono-nitrogen oxide (NOx) fraction of the exhaust gases was a key facilitator of this odour degradation. Such changes in recognition may impact upon a honeybee's foraging efficiency and therefore the pollination services that they provide.
Bark beetles are important agents of tree mortality in conifer forests and their interaction with trees is influenced by host defense chemicals, such as monoterpenes and phenolics. Since mountain ...pine beetle (Dendroctonus ponderosae Hopkins) has expanded its host range from lodgepole pine (Pinus contorta Doug. ex Loud. (var. latifolia Engelm.))-dominated forests to the novel jack pine (Pinus banksiana Lamb.) forests in western Canada, studies investigating the jack pine suitability as a host for this beetle have exclusively focused on monoterpenes, and whether phenolics affect jack pine suitability to mountain pine beetle and its symbiotic fungus Grosmannia clavigera is unknown. We investigated the phenolic and monoterpene composition in phloem and foliage of jack and lodgepole pines, and their subsequent change in response to water deficit and G. clavigera inoculation treatments. In lodgepole pine phloem, water deficit treatment inhibited the accumulation of both the total and richness of phenolics, but had no effect on total monoterpene production or richness. Fungal infection also inhibited the total phenolic production and had no effect on phenolic or monoterpene richness, but increased total monoterpene synthesis by 71%. In jack pine phloem, water deficit treatment reduced phenolic production, but had no effect on phenolic or monoterpene richness or total monoterpenes. Fungal infection did not affect phenolic or monoterpene production. Lesions of both species contained lower phenolics but higher monoterpenes than non-infected phloem in the same tree. In both species, richness of monoterpenes and phenolics was greater in non-infected phloem than in lesions. We conclude that monoterpenes seem to be a critical component of induced defenses against G. clavigera in both jack and lodgepole pines; however, a lack of increased monoterpene response to fungal infection is an important evolutionary factor defining jack pine suitability to the mountain pine beetle invasion in western Canada.
We tested the hypotheses that responses to the mountain pine beetle fungal associate Grosmannia clavigera will differ between the evolutionarily co‐evolved host lodgepole pine (Pinus contorta var. ...latifolia) and the naïve host jack pine (Pinus banksiana) and that these responses will be influenced by water availability. G. clavigera inoculation resulted in more rapid stem lesion development in lodgepole than in jack pine; water deficit delayed lesion development in both species. Decreased hydraulic conductivity was observed in inoculated lodgepole pine seedlings, likely because of tracheid occlusion by fungal hyphae and/or metabolite accumulation. Drought but not inoculation significantly impacted bark abscisic acid levels. Jasmonic and salicylic acid were implicated in local and systemic responses of both species to G. clavigera, with salicylic acid appearing to play a greater role in jack pine response to G. clavigera than lodgepole pine. Water deficit increased constitutive levels and/or attenuated induced responses to G. clavigera for several monoterpenes in lodgepole but not jack pine. Instead, inoculation of well‐watered but not water deficit jack pine resulted in a greater number of xylem resin ducts. These findings reveal mechanisms underlying differences in G. clavigera‐induced responses between lodgepole and jack pine hosts, and how water availability modulates these responses.
Western North America is currently experiencing the largest mountain pine beetle epidemic in recorded history; in recent years, this destructive forest pest has undergone host range expansion to jack pine, a boreal forest species. We have examined the effect of water limitation on responses of the evolutionarily co‐evolved host lodgepole pine and the naïve host jack pine, focusing on delineating similarities and differences in responses to inoculation with a mountain pine beetle fungal associate, Grosmannia clavigera. These species show different physiological responses to water limitation and that water deficit alters both constitutive and induced defences. Hormone profiles correlate with treatment‐associated differences in induced defences, and hormone crosstalk may modulate the patterns of induced defences that we observed in this study.
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