Elwood R. Hart

Cottonwood leaf beetle (Coleoptera: Chrysomelidae) defoliation impact on Populus growth and above-ground volume in a short-rotation woody crop plantation

Abstract 1 The impact of cottonwood leaf beetle Chrysomela scripta F. defoliation on four plantation‐grown Populus clones was examined over three growing seasons. We used a split‐plot design with two treatments: protected (by insecticides) and an unprotected control. Tree height and diameter at 1 m were measured annually and above‐ground volume was calculated. 2 Protected trees of most clones had grown over 2 m taller after three growing seasons. Diameter differences ranged from over 1–4 cm larger on protected trees. Insecticide protection increased above‐ground volume over 20 dm3 in one clone, and at least 4 dm3 in all others. Chrysomela scripta defoliation resulted in a 50–73% loss of above‐ground volume. Defoliation also resulted in increased lateral branching and forked terminals on unprotected trees. 3 Defoliation impact varied among clone. The pure Populus deltoides clone 91 × 04‐03 showed the greatest growth response to chemical protection, whereas clone NM2 (P. nigra × P. maximowiczii) responded the least. 4 Pest control is a key issue in short‐rotation plantation management. Until adequate pest‐resistant clones can be developed and natural enemy complexes better understood, chemical (biorational and organic) and cultural control may be used to reduce impacts of herbivorous pests.

Proteinase inhibitor II gene in transgenic poplar: Chemical and biological assays

Abstract Transgenic poplar lines were developed to investigate the role of a proteinase inhibitor in pest resistance of woody plants. Using an Agrobacterium binary vector system, the clone ‘Hansen’ ( Populus alba L. × P. grandidentata Michx.) was transformed with chimeric genes containing the coding region of potato proteinase inhibitor II ( PIN 2) linked to either a bacterial nopaline synthase ( nos ) or a cauliflower mosaic virus (35 S ) promoter. All transferred DNA also contained a selectable marker in the form of a nos promoter linked to a neomycin phosphotransferase II ( NPT II ) structural gene. The presence of the transferred PIN 2 and NPT II sequences in poplar was confirmed for nine transgenic lines using polymerase chain reaction (PCR). Expression of PIN 2 in leaves of transgenic poplar was demonstrated by enzyme-linked immunosorbent assays (ELISAs) and western blots. Two unique polypeptides from transgenic poplar, of ca 8 kDa and ca 12 kDa, indicate that PIN 2 was translated appropriately. Resistance to the imported willow leaf beetle was tested in laboratory bioassays. The untransformed clone ‘Hansen’ and 11 transgenic lines were submitted to freshly hatched larvae to determine effects on pupal weight, larval development time and leaf area consumed. A significant difference from the untransformed clone in leaf area consumed was detected in one transgenic line, Tr665. Trends were indicated for several other transgenic lines for the other parameters.

Laboratory and field evaluations of two Bacillus thuringiensis formulations, Novodor and Raven, for control of cottonwood leaf beetle (Coleoptera: Chrysomelidae).

Abstract Laboratory and field experiments were conducted to determine the efficacy of two Bacillus thuringiensis Berliner formulations, Novodor and Raven, for controlling cottonwood leaf beetle, Chrysomela scripta F. (Coleoptera: Chrysomelidae). In laboratory bioassays, larvae or adults were added to petri dishes containing Populus × euramericana Guinier ‘Eugenei’ foliage that had been treated with distilled water (control) or one of the commercial Bt formulations at either high or low label rates. Survival was recorded on a 24-h basis, and leaf area consumed was measured at the conclusion of all trials. Significant differences from the control in mortality and leaf area consumption resulted in the Novodor and Raven treatments for all life stages tested; however, adults were better able to withstand the effects of B. thuringiensis toxins than were the immatures. Early- and late instar C. scripta populations were monitored in the field (1998 and 1999) after treatment with either water or various concentrations of one of the commercial Bt formulations. Significant mortality resulted with all concentrations and for all life stages tested compared with the control (tap water). The commercial formulations also were tested under plantation conditions as part of a long-term defoliation study. Both Novodor and Raven reduced cottonwood leaf beetle defoliation damage after a single application, giving high efficacy for control of cottonwood leaf beetle under the conditions and concentrations evaluated.

Effect of Cottonwood Leaf Beetle (Coleoptera: Chrysomelidae) Larval Population Levels on Populus Terminal Damage

Abstract The cottonwood leaf beetle, Chrysomela scripta F., is a major defoliating pest of Populus in North America. We determined the relationship between larval population densities and defoliation levels in central Iowa, and related that to potential biomass loss. During the 1995 and 1996 growing seasons, egg mass surveys were performed: in 1995 for generation 2 and in 1996 for all 3 generations. Open and caged Populus trees were infested with different populations of freshly eclosed larvae on actively growing terminals. The 1996 observations from the open and caged trees in the 2nd generation and from the caged trees in generations 1 and 3 are consistent with those of the open and caged trees of the 1995 2nd generation. The results from the open trees during the 1st and 3rd generations in 1996 are much different from those of the 2nd generation in either year. The probability of reaching damage levels that cause biomass loss is greatest for the 2nd generation. Egg mass density may be useful in predicting damage levels. Damage rating is an accurate estimator of foliage loss.

Cottonwood Leaf Beetle (Coleoptera: Chrysomelidae) Larval Performance on Eight Populus Clones

Abstract The cottonwood leaf beetle, Chrysomela scripta F., is the most serious defoliator of young plantation-grown Populus in the eastern United States, yet there is a paucity of data on larval feeding performance across Populus clones used in tree breeding. Field experiments were conducted in 1998 and 1999 to determine the overall feeding performance of larval C. scripta on 8 Populus selections from a pedigree family. Using a randomized complete block design, entire trees were enclosed in mesh cages, and female C. scripta were allowed to oviposit in sleeve cages on each tree. Larval cohorts were culled to 10 upon hatch and allowed to develop to pupation within each sleeve cage. Larval survival, pupal weight, adult emergence, and total mortality were recorded as performance parameters. Significant but inconsistent performance differences were found among clones, suggesting that some clones were less suitable for C. scripta larval development in some insect generations. Larval performance was generally poorer on clones with higher P. trichocarpa parentage. C. scripta performance was significantly poorer in 1999 and showed a decline throughout the 1999 growing season, but it is not clear whether this was caused by conditions of the host plants, weather patterns, or changes made in the source of insects for infestation. Clones with foliar characteristics detrimental to larval C. scripta performance could be used for plantings or in developing C. scripta-resistant hybrid Populus selections for short-rotation woody crop systems.

Effects of Cottonwood Leaf Beetle (Coleoptera: Chrysomelidae) Larval Defoliation, Clone, and Season on Populus Foliar Phagostimulants

Abstract The cottonwood leaf beetle, Chrysomela scripta F., is a serious defoliator of plantation Populus in the United States. Current control methods include biorational and synthetic chemicals as well as selecting Populus clones resistant or tolerant to C. scripta defoliation. Specific ratios of long-chain fatty alcohols to alpha-tocopherylquinone (α-TQ) on the leaf surface of Populus spp. act as phagostimulants to adult C. scripta. The chemical concentrations and ratios vary among Populus clones; however, the effect of defoliation on the subsequent production of these chemicals is unknown. We investigated the effects of defoliation, clone, and season on Populus leaf surface chemical production. Chemical concentrations and ratios were monitored in 1998 and 1999 on eight Populus clones with and without larval C. scripta defoliation. Chemicals were extracted from the leaf surface and analyzed via gas chromatography. Larval C. scripta defoliation rarely caused changes in leaf surface chemistry at the defoliation levels tested; however, the production of these phagostimulants did vary by clone and season. Foliar alcohol and α-TQ concentrations and α-TQ:total alcohol ratios differed significantly among clones. Furthermore, α-TQ concentrations and α-TQ:total alcohol ratios varied temporally in some, but not all, clones. In general, foliar alcohol and α-TQ concentrations either did not vary or increased, but α-TQ:total alcohol ratios declined throughout the growing season. This research illustrates that the production of leaf surface phagostimulants is not a function of defoliation, but is most likely controlled by genetic and physiologic processes. Additionally, because Populus clones vary in their foliar chemistry, this variation could be exploited in tree breeding programs.

Deployment of Tree Resistance to Insects in Short-rotation Populus Plantations

Host plant resistance has been identified as a key component of integrated pest management (IPM) in agriculture and forestry. The topic of deploying and conserving host plant resistance to minimize economic damage caused by insect herbivores is not a new problem. For example, deployment strategies have been addressed in depth in traditional agricultural systems for several decades (see review by Gould 1998). In forestry, however, while the issues are recognized, little rigorous experimental work has been completed. Although theoretical models have been developed to predict the number of clones that are needed to minimize damage and to conserve resistant genes (Libby 1982), actual field tests of these conceptual models are lacking. To maintain the usefulness of host plant resistance mechanisms as a management tool while at the same time minimizing environmental risk, there are several critical factors to consider: 1) detennining and isolating multiple resistance mechanisms to insects, 2) maintaining the effectiveness of host plant resistance in plantation settings over time through adequate lines of resistance and planting designs, and 3) developing resistance to a complex of pests. These factors have even more importance when woody plant species are grown in systems similar to traditional

Economic Injury Level for Second-Generation Cottonwood Leaf Beetle (Coleoptera: Chrysomelidae) in Two-Year-Old Populus

Abstract The cottonwood leaf beetle, Chrysomela scripta F., is a major defoliating pest of Populus in North America. As the use of Populus in short-rotation woody crop plantations continues to increase, there are increasing economic and environmental needs to develop rational pest management programs to reduce the impact of this insect. Our objective was to determine the economic injury levels for the second generation of the cottonwood leaf beetle during plantation establishment. Integrating the cost of the management, market value, insect injury, and host response to the injury, the economic injury levels for second generation cottonwood leaf beetle on 2-yr-old Populus were determined to be from 0.2 to 0.9 egg masses per actively growing terminal.

Modifying Populus Environmental Responses: Impacts on Wood Quantity and Quality

ABSTRACT Natural selection for environmental fitness has led to a wide variety of wood properties between and within trees. In the redesign of trees to better serve industry needs, we believe that a focus on modifying genetic control of environmental responses can simultaneously improve total wood yield, tailor wood properties for different uses, and reduce the within tree variation in wood properties. To do that, we need much more understanding of environmental signals, the physiological processes they elicit, and the resulting changes in wood formation. We are studying two types of environmental interactions that we know have large impacts on wood yield, competition effects and responses to pest attack, to determine the corresponding impacts on wood properties. In wild trees, both of theses environmental factors cause a shift in allocation of photosynthate away from stem wood formation to stem height growth and/or replacement of shaded or damaged leaves. Concurrent changes in hormone levels within the tree may impact wood quality traits such as specific gravity and fiber length. We have started evaluating model systems to look at the magnitude of these effects. We discuss results from a spacing trial and an insect impact study in this paper.

Modeling developmental polymorphism in lepidopteran populations

Abstract The occurrence of supernumerary instars increases the length of time spent in the larval stage for many lepidopterans. This tends to increase the complexity of the biological system and the ability to predict events and manage the system. Using the yellowheaded fireworm, Acleris minuta (Robinson) (Lepidoptera: Tortricidae), as an example, a model was constructed to use environmental data to predict the mode of development and consequent effects upon population density and phenology. Calibration and validation data from the field are compared and evaluated.