David L. Rowney

Effects of oxidant air pollutants on western pine beetle (Coleoptera: Scolytidae) populations in southern California.

The attack rates, brood survival, and emergence rates of the western pine beetle, Dendroctonus brevicomis LeConte, and incidence of entomophagus associates, were compared between photochemical oxidant damaged, and apparently healthy, ponderosa pine trees, Pinus ponderosa Dougl. ex Laws in the San Bernardino Forest in Southern California. The results from this study suggest that oxidant-damaged trees attacked by western pine beetle produced about the same total brood with lower initial attacks when compared with healthier trees, whereas the numbers of predators and parasitoids were higher in the healthier trees. This higher productivity trend for western pine beetle is most evident in trees attacked by the first beetle generation. Trees attacked by the second generation, both damaged and healthy, produced much less western pine beetle brood than generation 1 attacked trees, regardless of oxidant damage. The implication of these results is that, in stands with a higher proportion of oxidant damaged trees, a given population of western pine beetle could kill more trees, and increase at a greater rate, than in a stand with a lower proportion of damaged trees.

Insect pest management in forest ecosystems

Understanding the role of insects in forest ecosystems is vital to the development of environmentally and economically sound pest management strategies in forestry Most of the research on forest insects has been confined to phytophagous species associated with economically important tree species The roles of most other insects in forest environments have generally been ignored, including the natural enemies and associates of phytophagous species identified as being important In the past few years several investigations have begun to reevaluate the role of phytophagous species responsible for perturbation in forest ecosystems, and it appears that these species may be playing an important role in the primary productivity of those ecosystems Also, there is an increasing awareness that forest pest managers have been treating the symptoms and not the causes of the problems in the forest Many insect problems are associated with poor sites or sites where trees are growing poorly because of crowding As a result, there is considerable emphasis on the hazard rating of stands of trees for their susceptibility to various phytophagous insects The next step is to manipulate forest stands to make them less susceptible to forest pest complexes A thinning study in California is used as an example and shows that tree mortality in ponderosa pine (Pinus ponderosa) attributable to the western pine beetle (Dendroctonus brevicomis) can be reduced by commercial thinning to reduce stocking

Development of integrated pest management programs in urban forests: the elm beetle (Xanthogaleruca luteola (Müller)) in California, USA

Abstract The elm leaf beetle (ELB) causes severe damage to Californias elms. The goal was to develop a management system based on long-term population monitoring for decision making, and environmentally sound control methods. English and Siberian elms with ELB populations in 25 locations from the northeast to the central coast of California were sampled from 1985 to 1990. Population monitoring has indicated that each ELB generation (two to three per season) varies unpredictably in its potential for causing foliage damage. Each generation needs to be sampled and decisions made for control measures most suitable for that generation. From the data base, we have developed a sampling system in which heat accumulation above 11 °C at ELB sites, measured in degree-days, indicates when to sample and, if necessary, when to treat. Sampling elm branch terminals for the presence of ELB eggs during the limited time when egg laying is near its peak provides a cost-effective means of predicting foliage damage, and thus of deciding whether control actions are necessary. Two control options compatible with ELB natural enemies have been tested: trunk banding with Carbaryl and Bacillus thuringiensis foliar sprays. A number of strains of the egg parasitoid Tetrastichus gallerucae have been released and at least one strain has survived over winter. When the number of these parasitoids has increased sufficiently, either through same season releases or from overwintering survival, they have exerted substantial control.

Bird foraging on incense-cedar and incense-cedar scale during winter in California

The response of birds to variaIions in Ihe density of incense-cedar (Colocedrw decvrem [Toe] Florin.), and Ulmugh exclosure experiments, theimpact of bird fonging on the density of the scaleinsect ~Xvlococculur mncrocnrone). was studied in the mixed-.. canifer zone of the western Siena Nevada during winter. Buds concenuated foraging activities on Ihe bark of small (a0 cm d.b.h.) cedar. Indices of abundance for manv bird specieswereloweronsiteswiIh10W~cedardensity halysisofforagingactivitiesindicated that birds reduced the density of scale insects on cedar and avoided sites with low-cedar density. Theresultsindi~atethataminimumdensil~ of>150smallcedar/hamayberquired to prevent areduction in the abundance of birds ovenvinteringin Ihese study areas. Small cedar apparently provide needed cover and fwd for much of the bird community. These findings m conuay to current thinking of forest managersin themanagement ofincense-cedar.