Joel D. McMillin

Influence of Elevation on Bark Beetle (Coleoptera: Curculionidae, Scolytinae) Community Structure and Flight Periodicity in Ponderosa Pine Forests of Arizona

Abstract We examined abundance and flight periodicity of five Ips and six Dendroctonus species (Coleoptera: Curculionidae, Scolytinae) among three different elevation bands in ponderosa pine (Pinus ponderosa Douglas ex. Lawson) forests of northcentral Arizona. Bark beetle populations were monitored at 10 sites in each of three elevation bands (low: 1,600–1,736 m; middle: 2,058–2,230 m; high: 2,505–2,651 m) for 3 yr (2004–2006) using pheromone-baited Lindgren funnel traps. Trap contents were collected weekly from March to December. We also studied temperature differences among the elevation bands and what role this may play in beetle flight behavior. Bark beetles, regardless of species, showed no consistent elevational trend in abundance among the three bands. The higher abundances of Ips lecontei Swaine, I. calligraphus ponderosae Swaine, Dendroctonus frontalis Zimmerman, and D. brevicomis LeConte at low and middle elevations offset the greater abundance of I. knausi Swaine, D. adjunctus Blandford, D. approximatus Dietz, and D. valens LeConte at high elevations. I. pini (Say) and I. latidens LeConte were found in similar numbers across the three bands. Flight periodicity of several species varied among elevation bands. In general, the flight period shortened as elevation increased; flight initiated later and terminated earlier in the year. The timing, number, and magnitude of peaks in flight activity also varied among the elevation bands. These results suggest that abundance and flight seasonality of several bark beetles are related to elevation and the associated temperature differences. The implications of these results are discussed in relation to bark beetle management and population dynamics.

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.

Synergistic effects of α-pinene and exo-brevicomin on pine bark beetles and associated insects in Arizona

The southern pine beetle (Dendroctonus frontalis) and western pine beetle (Dendroctonus brevicomis) cause significant mortality to pines in the southern and western United States. The effectiveness of commercial lures at capturing these bark beetles in Arizona has not been tested and may vary from other regions of their distribution. We conducted experiments using baited Lindgren funnel traps to investigate (i) if D. frontalis is more attracted to the standard commercial lure for D. brevicomis (frontalin + exo‐brevicomin + myrcene) than the D. frontalis lure (frontalin + terpene blend), (ii) whether replacement of myrcene with α‐pinene changes trap catches of Dendroctonus and associated insects, and (iii) whether the attraction to these lures varies across the geographical range of ponderosa pine forests throughout Arizona. In 2005, we tested various combinations of frontalin, exo‐brevicomin, myrcene and α‐pinene to D. frontalis, D. brevicomis and associated species. Dendroctonus frontalis, D. brevicomis and the predator Temnochila chlorodia were most attracted to lures with exo‐brevicomin. The replacement of the myrcene component with α‐pinene in the D. brevicomis lure resulted in the capture of twice as many bark beetles and Elacatis beetles. However, T. chlorodia did not differentiate between monoterpenes. In 2006, traps were set up in 11 locations around Arizona to test the relative attraction of lure combinations. In 9 out 11 locations, the D. brevicomis lure with α‐pinene was more attractive than the lure with myrcene or a terpene blend. These results suggest that the D. brevicomis lure with α‐pinene rather than myrcene is more effective lure to capture D. brevicomis and D. frontalis in Arizona. However, geographical variation in attractiveness to lures is evident even within this region of the beetles’ distributions. Differential attraction of Dendroctonus and their predators to these lures suggests potential use in field trapping and control programmes.

Influence of temperature on spring flight initiation for southwestern ponderosa pine bark beetles (Coleoptera: Curculionidae, Scolytinae).

Abstract Determination of temperature requirements for many economically important insects is a cornerstone of pest management. For bark beetles (Coleoptera: Curculionidae, Scolytinae), this information can facilitate timing of management strategies. Our goals were to determine temperature predictors for flight initiation of three species of Ips bark beetles, five species of Dendroctonus bark beetles, and two genera of bark beetle predators, Enoclerus spp. (Coleoptera: Cleridae) and Temnochila chlorodia (Mannerheim) (Coleoptera: Ostomidae), in ponderosa pine forests of northcentral Arizona. We quantified beetle flight activity using data loggers and pheromone-baited funnel traps at 18 sites over 4 yr. Ambient air temperature was monitored using temperature data loggers located in close proximity to funnel traps. We analyzed degree-day accumulation and differences between minimum, average, and maximum ambient temperature for the week before and week of first beetle capture to calculate flight temperature thresholds. Degree-day accumulation was not a good predictor for initiation of beetle flight. For all species analyzed other than D. adjunctus Blandford, beetles were captured in traps only when springtime temperatures exceeded 15.0°C. D. adjunctus was collected when maximum temperatures reached only 14.5°C. Once initial flights had begun, beetles were often captured when maximum ambient air temperatures were below initial threshold temperatures. Maximum and average air temperatures were a better predictor for beetle flight initiation than minimum temperature. We establish a temperature range for effective monitoring of bark beetles and their predators, and we discuss the implications of our results under climate change scenarios.

Chronic defoliation impacts pine sawfly (Hymenoptera : Diprionidae) performance and host plant quality

We assessed the effects of chronic defoliation on host plant quality and larval performance of a pine sawfly. Neodiprion autumnalis larvae were reared on ponderosa pine (Pinus ponderosa) that had experienced moderate to severe defoliation (>50%) of mature foliage for at least 15 yr and on trees sustaining no observable defoliation during the same time interval. N. autumnalis performance was 23% (total instar survival) to 12% (potential fecundity) higher on chronically defoliated trees compared with non-defoliated trees. Perennially attacked trees had reduced dry matter (an estimate of total carbon) content of mature needles, higher foliar nitrogen, and a 10% lower carbon/nitrogen balance compared with non-defoliated trees. No differences were detected in foliar toughness. Based on these findings, we maintain that chronic defoliation of evergreen conifers reduces the production of carbon-based secondary compounds in foliage and increases plant nutrition resulting in a positive feedback loop.

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.

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.

Evaluation of Funnel Traps for Characterizing the Bark Beetle (Coleoptera: Scolytidae) Communities in Ponderosa Pine Forests of North-Central Arizona

Abstract Lindgren funnel traps baited with aggregation pheromones are widely used to monitor and manage populations of economically important bark beetles (Coleoptera: Scolytidae). This study was designed to advance our understanding of how funnel trap catches assess bark beetle communities and relative abundance of individual species. In the second year (2005) of a 3-yr study of the bark beetle community structure in north-central Arizona pine (Pinus spp.) forests, we collected data on stand structure, site conditions, and local bark beetle-induced tree mortality at each trap site. We also collected samples of bark from infested (brood) trees near trap sites to identify and determine the population density of bark beetles that were attacking ponderosa pine, Pinus ponderosa Douglas ex Lawson, in the area surrounding the traps. Multiple regression models indicated that the number of Dendroctonus and Ips beetles captured in 2005 was inversely related to elevation of the trap site, and positively associated with the amount of ponderosa pine in the stand surrounding the site. Traps located closer to brood trees also captured more beetles. The relationship between trap catches and host tree mortality was weak and inconsistent in forest stands surrounding the funnel traps, suggesting that trap catches do not provide a good estimate of local beetle-induced tree mortality. However, pheromone-baited funnel trap data and data from gallery identification in bark samples produced statistically similar relative abundance profiles for the five species of bark beetles that we examined, indicating that funnel trap data provided a good assessment of species presence and relative abundance.

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