Warming climate is allowing tree-killing bark beetles to expand their ranges and access naïve and semi-naïve conifers. Conifers respond to attack using complex mixtures of chemical defences that can impede beetle success, but beetles exploit some compounds for host location and communication. Outcomes of changing relationships will depend on concentrations and compositions of multiple host compounds, which are largely unknown. We analysed constitutive and induced chemistries of Dendroctonus ponderosae's primary historical host, Pinus contorta, and Pinus albicaulis, a high-elevation species whose encounters with this beetle are transitioning from intermittent to continuous. We quantified multiple classes of terpenes, phenolics, carbohydrates and minerals. Pinus contorta had higher constitutive allocation to, and generally stronger inducibility of, compounds that resist these beetle-fungal complexes. Pinus albicaulis contained higher proportions of specific monoterpenes that enhance pheromone communication, and lower induction of pheromone inhibitors. Induced P. contorta increased insecticidal and fungicidal compounds simultaneously, whereas P. albicaulis responses against these agents were inverse. Induced terpene accumulation was accompanied by decreased non-structural carbohydrates, primarily sugars, in P. contorta, but not P. albicaulis, which contained primarily starches. These results show some host species with continuous exposure to bark beetles have more thoroughly integrated defence syndromes than less-continuously exposed host species.
Under laboratory conditions, Dendroctonus frontalis Zimmermann and Ips grandicollis (Eichhoff) adults became self-marked with fluorescent powders upon emergence from treated logs. The technique provided a reliable procedure for marking adult bark beetles without having to handle them. When the powder remained dry, nearly all of the emerged beetles were marked. However, the percentage of marked beetles decreased dramatically following simulated rain events. Once marked, the mark remains intact on beetles stored dry or in ethylene glycol or ethanol (95%). Marking did decrease the adult life span of both D. frontalis and I. grandicollis, but had no significant effect on flight initiation by either species or semiochemical perception by I. grandicollis. No semiochemical tests were conducted with D. frontalis. If beetles are recaptured shortly following emergence and self-marking, the technique should be useful for examining scolytid dispersal in the field.
The toxicity of four monoterpenes present in loblolly (Pinus taeda L.) and shortleaf (P. echinata Mill.) pine to Dendroctonus frontalis Zimmermann and Ips calligraphus (Germar) (Coleoptera: Scolytidae) was examined in the laboratory. The descending order of toxicity of the monoterpenes to D. frontalis was: limonene, β - pinene, α - pinene, camphene. No clearcut ordering in toxicity to I. calligraphus was observed.
Measurements of δ(13)C in CO(2) have traditionally relied on samples stored in sealed vessels and subsequently analyzed using magnetic sector isotope ratio mass spectrometry (IRMS), an accurate but expensive and high-maintenance analytical method. Recent developments in optical spectroscopy have yielded instruments that can measure δ(13)CO(2) in continuous streams of air with precision and accuracy approaching those of IRMS, but at a fraction of the cost. However, continuous sampling is unsuited for certain applications, creating a need for conversion of these instruments for batch operation. Here, we present a flask (syringe) adaptor that allows the collection and storage of small aliquots (20-30 mL air) for injection into the cavity ring-down spectroscopy (CRDS) instrument. We demonstrate that the adaptor's precision is similar to that of traditional IRMS (standard deviation of 0.3‰ for 385 ppm CO(2) standard gas). In addition, the concentration precision (±0.3% of sample concentration) was higher for CRDS than for IRMS (±7% of sample concentration). Using the adaptor in conjunction with CRDS, we sampled soil chambers and found that soil-respired δ(13)C varied between two different locations in a piñon-juniper woodland. In a second experiment, we found no significant discrimination between the respiration of a small beetle (~5 mm) and its diet. Our work shows that the CRDS system is flexible enough to be used for the analysis of batch samples as well as for continuous sampling. This flexibility broadens the range of applications for which CRDS has the potential to replace magnetic sector IRMS.
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