Pupal and Adult Parameters as Potential Indicators of Cottonwood Leaf Beetle (Coleoptera: Chrysomelidae) Fecundity and Longevity

Cottonwood leaf beetle, Chrysomela scripta, pupae from a laboratory colony were weighed and monitored through adult emergence, oviposition, and mortality to determine if correlations existed between various pupal or adult parameters and fecundity or longevity. Forty-three female cottonwood leaf beetles were monitored. Pupal weight was not a good indicator of fecundity, total oviposition events, number of eggs/beetle/day, or adult longevity. In addition, adult weight showed very low correlation with fecundity, adult longevity, total oviposition events, or number of eggs/beetle/day. However, adult weight was a marginal indicator of the number of eggs/beetle/day, and correlated well with adult body length. Adult longevity could be used to predict fecundity

Pupal and Adult Parameters as Potential Indicators of Cottonwood Leaf Beetle (Coleoptera: Chrysomelidae) Fecundity and Longevity

Cottonwood leaf beetle, Chrysomela scripta, pupae from a laboratory colony were weighed and monitored through adult emergence, oviposition, and mortality to determine if correlations existed between various pupal or adult parameters and fecundity or longevity. Forty-three female cottonwood leaf beetles were monitored. Pupal weight was not a good indicator of fecundity, total oviposition events, number of eggs/beetle/day, or adult longevity. In addition, adult weight showed very low correlation with fecundity, adult longevity, total oviposition events, or number of eggs/beetle/day. However, adult weight was a marginal indicator of the number of eggs/beetle/day, and correlated well with adult body length. Adult longevity could be used to predict fecundity

Phenology and Infestation Patterns of the Cottonwood Twig Borer (Lepidoptera: Tortricidae) in Iowa

Cottonwood twig borer, Gypsonoma haimbachiana (Lepidoptera: Totricidae), phenology and infestation patterns on Populus spp. were examined over a 2-year period in Iowa. Weekly sampling of infested shoots during the host growing season verified the existence of five instars. Head capsule size increased nonlinearly from the first to the fifth instar and corresponded to a concomitant geometric increase in the volume of larval feeding galleries. The sampling indicated that the cottonwood twig borer had two generations per year in Iowa. Corresponding with the two generations, two peaks of larval abundance were observed; one in the second week of June and the other in the first week of August. Greater volume of feeding galleries occurred in the early season generation compared with the late season generation. Sampling of infested shoots revealed that more than 80% of infested terminals contained only one active attack (freshly bored hole in tree terminal with frass present); more than 88% of feeding galleries contained only one larva; and more than 80% of the larvae were found in the first active attack nearest the terminal apex. These data were compared with results published on the phenology and attack patterns of the cottonwood twig borer in the southern United States

Stand-scale tree mortality factors differ by site and species following drought in southwestern mixed conifer forests

Impacts of drought on tree mortality in high-elevation mixed-conifer forests of southwestern U.S. are poorly understood. A recent extended and severe drought in the region provided an opportunity to investigate the patterns and factors associated with tree mortality in this forest type. Specifically, we quantified mortality that occurred between 1995 and 2008 of four tree species, white fir (Abies concolor), limber pine (Pinus flexilis), trembling aspen (Populus tremuloides), and Douglas-fir (Pseudotsuga menziesii), in mixed-conifer forests over three sites in northern Arizona within 84, 0.02 ha plots. We found: (1) varied but substantial tree mortality (4–56% by basal area) in most species between 1996 and 2006 in association with recent severe and prolonged drought; (2) tree mortality differed among sites and species with aspen and white fir having the most mortality (\u3e30% by basal area); (3) relationships between tree mortality and most climatic factors (e.g. temperature, precipitation, Palmer Drought Severity Index) were lagged 1–4 yr; (4) bark beetle attack and intraspecific tree basal area were consistently and positively related to tree mortality for most species and sites, whereas topographic and other stand characteristics were less consistently related to mortality. Results show that aspen, Douglas-fir, and white fir were more vulnerable to recent drought-associated mortality than limber pine. Associations between tree mortality and intraspecific basal area support further evaluation of treatments that reduce intraspecific competition within stands to lower risks of tree mortality in southwestern mixed conifer forests

Fuel Loadings 5 Years After a Bark Beetle Outbreak in South-western USA Ponderosa Pine Forests

Abstract. Landscape-level bark beetle (Coleoptera: Curculionidae, Scolytinae) outbreaks occurred in Arizona ponder- osa pine (Pinus ponderosa Dougl. ex Law.) forests from 2001 to 2003 in response to severe drought and suitable forest conditions. We quantified surface fuel loadings and depths, and calculated canopy fuels based on forest structure attributes in 60 plots established 5 years previously on five national forests. Half of the plots we sampled in 2007 had bark beetle- caused pine mortality and half did not have mortality. Adjusting for differences in pre-outbreak stand density, plots with mortality had higher surface fuel and lower canopy fuel loadings 5 years after the outbreak compared with plots without mortality. Total surface fuels averaged 2.5 times higher and calculated canopy fuels 2 times lower in plots with mortality. Nearly half of the trees killed in the bark beetle outbreak had fallen within 5 years, resulting in loadings of 1000-h woody fuels above recommended ranges for dry coniferous forests in 20% of the mortality plots. We expect 1000-h fuel loadings in other mortality plots to exceed recommended ranges as remaining snags fall to the ground. This study adds to previous work that documents the highly variable and complex effects of bark beetle outbreaks on fuel complexes

Modeling Wind Fields and Fire Propagation Following Bark Beetle Outbreaks in Spatially-Heterogeneous Pinyon-Juniper Woodland Fuel Complexes

We used a physics-based model, HIGRAD/FIRETEC, to explore changes in within-stand wind behav- ior and fire propagation associated with three time periods in pinyon-juniper woodlands following a drought-induced bark beetle outbreak and subsequent tree mortality. Pinyon-juniper woodland fuel complexes are highly heterogeneous. Trees often are clumped, with sparse patches of herbaceous veg- etation scattered between clumps. Extensive stands of dead pinyon trees intermixed with live junipers raised concerns about increased fire hazard, especially immediately after the trees died and dead needles remained in the trees, and later when the needles had dropped to the ground. Studying fire behavior in such conditions requires accounting for the impacts of the evolving heterogeneous nature of the wood- lands and its influence on winds that drive fires. For this reason we used a coupled atmosphere/fire model, HIGRAD/FIRETEC, to examine the evolving stand structure effects on wind penetration through the stand and subsequent fire propagation in these highly heterogeneous woodlands. Specifically, we studied how these interactions changed in woodlands without tree mortality, in the first year when dried needles clung to the dead trees, and when the needles dropped to the ground under two ambient wind speeds. Our simulations suggest that low wind speeds of 2.5 m/s at 7.5-m height were not sufficient to carry the fire through the discontinuous woodland stands without mortality, but 4.5 m/s winds at 7.5-m height were sufficient to carry the fire. Fire propagation speed increased two-fold at these low wind speeds when dead needles were on the trees compared to live woodlands. When dead needles fell to the ground, fine fuel loadings were increased and ambient wind penetration was increased enough to sustain burn- ing even at low wind speeds. At the higher ambient wind speeds, fire propagation in woodlands with dead needles on the trees also increased by a factor of ∼2 over propagation in live woodlands. These simulations indicate that sparse fuels in these heterogeneous woodlands can be overcome in three ways: by decreasing fuel moisture content of the needles with the death of the trees, by moving canopy dead needles to the ground and thus allowing greater wind penetration and turbulent flow into the woodland canopy, and increasing above-canopy wind speeds. 2012 Elsevier B.V. All Rights Reserve