D. M. Benjamin

Mechanism of feeding discrimination between matured and juvenile foliage by two species of pine sawflies

Two species of pine sawflies,Neodiprion rugifrons Midd. andN. swainei Midd., feed only on matured foliage of jack pine,Pinus banksiana Lamb., and leave juvenile or current-season foliage intact. This unique form of adaptation was studied from the viewpoint of the chemical ecology of this insect-host plant relationship. It was first determined that the differential larval feeding behavior reflects the presence of feeding deterrents. Two major biologically active substances were isolated and identified as 13-keto-8(14)-podocarpen-18-oic acid and dehydroabietic acid. These account for 63.5% and 24.6% of the total deterrency, respectively. The content of the former substance in current-year foliage decreases, as the foliage begins to mature, to the levels that become acceptable toN. swainei by August (60 days old) and to the second generationN. rugifrons by September (90 days old). The timing of their acceptance of juvenile foliage indicates the high levels of adaptation by these insects to allow oviposition for the on-coming adults and acceptable needles for the next generation of larvae. The level of dehydroabietic acid, on the other hand, does not change appreciably during the same time period: this indicates that the component does not play a significant role in the mechanism of differentiating juvenile from matured foliage by the sawfly larvae.

Influence of diterpene resin acids on feeding and growth of larch sawfly,Pristiphora erichsonii (Hartig)

Diterpene resin acids significantly affect consumption rates, feeding efficiencies, and growth rates of the larch sawfly,Pristiphora erichsonii (Hartig) when topically applied to their natural food, tamarackLarix laricina (DuRoi) K. Koch. Abietic acid, neoabietic acid, dehydroabietic acid, and isopimaric acid significantly reduced consumption rates, feeding efficiencies, and growth rates. Sandaracopimaric acid reduced growth and efficiency but did not influence consumption rate. Two-way analysis of variance indicates a significant interaction between chemical and concentration for growth rate, feeding efficiency, and consumption rate. This interaction indicates that increasing chemical concentrations do not influence the larch sawfly in a uniform manner, supporting the concept of concentration-dependent biological activity of allelochemics.

Chemical basis of differential feeding behavior of the larch sawfly,Pristiphora erichsonii (Hartig).

The machanisms by which the larvae of the larch sawfly,Pristiphora erichsonii (Hartig), are prevented from feeding on the single needles of the new shoot of tamarack,Larix laricina (DuRoi) K. Koch, were studied. As a result of extensive purification attempts, five deterrent chemicals were isolated and identified. They are: abietic, dehydroabietic, 12-methoxyabietic, sandaracopimaric, and isopimaric acid. These chemicals, particularly the first two, are abundant in mid-July to August in the single needles and, apparently, provide the basis for the deterrency against the larval feeding.

The chemical feeding ecology ofNeodiprion dubiosus schedl,N. rugifrons midd., andN. lecontei (Fitch) on jack pine (Pinus banksiana lamb.)

Two monophagous sawflies,Neodiprion dubiosus andN. rugifrons, actively avoid feeding on the current seasons needles of jack pine,Pinus banksiana, while the polyphagousN. lecontei feeds indiscriminately on foliage of all age classes. Bioassay studies with needle extracts indicate thatN. dubiosus andN. rugifrons larval feeding preference is governed by a group of tricyclic diterpene resin acids. Resin acids commonly occur in needles of all ages; however, levopimaric, palustric, dehydroabietic, and neoabietic acids were at higher concentrations in the new needles.N. dubiosus was significantly deterred from feeding on 1-year-old foliage when treated with the pure resin acids, palustric and levopimaric, at 0.5 and 1.0 mg/ml MeOH.N. rugifrons larvae were deterred from feeding by pure dehydroabietic, neoabietic, and palustric acids at 1.0 mg/ml MeOH.

Allelochemics and nutritional indices for larch sawfly,Pristiphora erichsonii (Hartig): A specialist feeding onLarix spp.

Nutritional indices for larch sawfly,Pristiphora erichsonii (Hartig), larvae fed single and tufted needles of fourLarix spp. are reported. Larvae offered only single needles ofL. lancina, L. russica, andL. decidua had lower relative growth rates than larvae fed tufted needles of the same species. There was no significant reduction in larval growth for larvae fedL.kaempferi single needles as compared to tufted needles. Abietic acid-treated foliage reduced consumption but did not lower relative growth rate. These findings are discussed with respect to the mechanism of preferential feeding of the larch sawfly and current hypotheses of host plant herbivore interaction.

Plasma-Generated OH Radical Production for Analyzing Three-Dimensional Structure in Protein Therapeutics

Protein three-dimensional structure dynamically changes in solution depending on the presence of ligands and interacting proteins. Methods for detecting these changes in protein conformation include ‘protein footprinting,’ using mass spectrometry. We describe herein a new technique, PLIMB (Plasma Induced Modification of Biomolecules), that generates µs bursts of hydroxyl radicals from water, to measure changes in protein structure via altered solvent accessibility of amino acid side chains. PLIMB was first benchmarked with model compounds, and then applied to a biological problem, i.e., ligand (EGF) induced changes in the conformation of the external (ecto) domain of Epidermal Growth Factor Receptor (EGFR). Regions in which oxidation decreased upon adding EGF fall along the dimerization interface, consistent with models derived from crystal structures. These results demonstrate that plasma-generated hydroxyl radicals from water can be used to map protein conformational changes, and provide a readily accessible means of studying protein structure in solution.

Diapause in the Swaine jack-pine sawfly, Neodiprion swainel, as influenced by temperature and photoperiod

Larvae of Neodiprion swainei Midd. were reared to the adult stage under temperatures of 15, 22 and 30°C and photoperiods of (LD): 1014, 1212, 1410, 168, 186hr. Diapause was prevented when the larvae were subjected to a long photoperiod. The higher the temperature the greater the number of individuals not entering diapause at a long photoperiod. A varying percentage of individuals may enter a short diapause similar to a summer diapause. Some cocooned larvae may also stay in prolonged diapause for an undetermined period, regardless of temperature-photoperiod conditions.

Effects of cesium ion implantation on the mechanical and electrical properties of porous SiCOH low-k dielectrics

In this work, the authors report an investigation of the effects of cesium (Cs) ion implantation on both porogen-embedded and ultraviolet (UV)-cured (porous) SiCOH films. For porogen-embedded SiCOH, it was found that Cs ion implantation can greatly improve the elastic modulus. It can also increase the time-zero dielectric breakdown (TZDB) strength. It also leads to an increase in the k-value for medium and high Cs doses, but for low Cs doses, the k-value decreased compared with its pristine counterpart. For UV-cured SiCOH, it was found that Cs-ion implantation does not improve the elastic modulus. It also leads to lower TZDB field strength and much higher k-values than its pristine counterpart. These effects can be understood by examining the changes in chemical bonds. This treatment is shown to have the potential to help solve the problem of the demand for lower k-values and the concomitant weak mechanical strength of SiCOH.