Insects, Diseases, and Invasive Plants

Insects, Diseases, and Invasive Plants

The mission of the Insects, Diseases, and Invasive Plants Research Work Unit (RWU-4552) is to provide the basic biological and ecological knowledge and innovative management strategies required for management and control of native and non-native insect pests, disease pathogens and invasive plants in changing forest ecosystems.

Overview
Insects
Diseases
Invasives
People
Resources

Insects

Ecology, biology and management of bark beetles and other native insects
A lack of economic incentives for harvesting pine timber, coupled with loss of numerous synthetic pesticides for control of bark beetles, has created a need for the development of alternative management and control tactics for bark and wood boring insects. Semiochemicals (whether attractant, anti-aggregant, or anti-feedant) have shown some promise for managing bark beetles and invasive insects, as have systemic and new pesticides. However, few of these strategies have been adequately tested, deployed or optimized, thus limiting their potential use.

Detection, biology and management of non-native insects
The steady influx of non-native insect species calls for development of improved detection and monitoring strategies for important forests pest groups. Rapid detection can play a key role in preventing the establishment of new pest species. Established populations of non-native insects often spread quickly and can be extremely difficult to control. When this is due, at least in part, to a lack of effective natural enemies in the introduced range, classical biological control can be a useful long-term strategy for reducing pest populations. Because invasive insects also often encounter limited resistance from naïve host plants, classical biological control often cannot succeed in isolation. A truly integrated management approach (i.e., combining biological, chemical and cultural control methods with host plant improvement), informed by basic biological research, will be needed to combat some of the most aggressive invasive pest problems.

Effects of forest management and species invasion on insect biodiversity and ecosystem processes
Many questions remain about how native forest insect communities are impacted by management practices and invasion by exotic plant species. Two insect groups are of particular concern due to the ecosystem services they provide, their importance to biodiversity, and documented population declines. The importance of bees and butterflies to the pollination of crops is widely acknowledged, for instance, but it remains largely unknown how these organisms are affected by forest management or invasion. There is an urgent need for research in this area given documented declines in pollinator populations. Similarly, saproxylic insects (i.e., species directly or indirectly dependent on dead wood) account for about one third of all forest insect species and are also suffering population declines in many parts of the world. Although the ecosystem services provided by saproxylic insects remain largely unstudied, these organisms may contribute importantly to wood decomposition, nutrient cycling and pest control, thus promoting forest health and resilience.

Diseases

Insect-microbial associations and insect-pathogen disease complexes
The laurel wilt disease pathogen (Raffaelea lauricola) exemplifies the potential for fungal symbionts of traditionally secondary insects (e.g. ambrosia beetles) to cause catastrophic effects when introduced into novel ecosystems. Additional research on the identity, relationships and functional roles of fungi and other microorganisms associated with insects such as bark beetle (e.g. walnut twig beetle) and wood wasps (e.g. Sirex noctilio or native Siricidae) are needed to understand the epidemiology of certain diseases and determine appropriate management strategies for potential introductions of insect-pathogen complexes in the South.

Other diseases of forest ecosystems
In addition to diseases caused by insect-pathogen complexes, other forest disease occurrences or epidemics may occasionally demand research attention due to their complex diagnosis or impact on local or regional ecosystems, forest resources or communities.

Forest nursery diseases
Historically, a variety of fungal pathogens and plant parasitic nematodes have impacted seedling production in forest tree nurseries. The introduction of fumigation with methyl bromide in the 1950’s provided a means for broad spectrum control of many soil borne pest problems. Methyl bromide has been identified as an ozone depleting chemical and its use is being phased-out under the terms of the Montreal Protocol. We plan to continue our work on the influences of nursery cultural practices on pathogenic fungi and plant parasitic nematodes to minimize subsequent disease development and increase seedling production. As methyl bromide is phased out, we will continue to assess application methods, distribution, efficacy and fate of alternative soil fumigants and other pesticides.

Invasive Plants

Prevention, detection, and characterization of invasive plant species
Research is needed to contribute to prevention of entering invasive propagules, efficient detection of nascent establishing populations, and the identification and characterization of invasive plant populations.

Invasive plant species control and management
Additional research is needed to optimize the types, rates, methods, timing, and frequency of herbicide applications for persistent invasive plant problems (e.g., cogongrass) under varied forest types and management. Significant research gaps exist in the integration of chemical control with other management methods including manual, mechanical, biological and silvicultural tactics. Even when a target invasive plant is eradicated or suppressed, few methods exist to rehabilitate or restore communities and the ecosystem services therein to pre-invasion levels, or at least recoup some of the losses.

Facilities Information

Forestry Sciences Laboratory
320 Green Street
Athens, GA 30602

Tel: 706-559-4272

Alexandria Forestry Center
2500 Shreveport Highway
Pineville, LA 71360

Phone: 318-473-7268

The southern pine beetle and other bark beetles attacking conifers in southern forests are the most destructive insect pests in our region. When their populations are low, bark beetles are natural agents of tree mortality, especially of lightning struck or weakened trees. During outbreaks, however, bark beetles cause great economic damage and threaten the function and sustainability of forest ecosystems. SRS 4552 has been a leader in research on these insects for decades and continues to focus on understanding their biology and developing control strategies for them.

Several of the most serious pest problems addressed by our scientists in recent years (see scientists and publications) were either absent from, or only emerging in, the Southern Region a decade ago (for example, laurel wilt disease and redbay ambrosia beetle, thousand cankers disease and walnut twig beetle, emerald ash borer, and hemlock woolly adelgid). Due to their expertise and experience, our scientists have also been called upon to contribute to research on the detection, management and understanding the biology of new or recent pest outbreak problems in other regions or countries, such as gold spotted oak borer and other exotic wood borers, Erythrina gall wasp, Sirex woodwasp, “Mesoamerican” pine beetle, and mountain pine beetle.

Given international and interstate movement of pests through infested host material, coupled with changing land use patterns and climate, we anticipate a need to stay responsive to new forest pests and pest complexes. We seek to balance this with continuing research on existing, high-impact problems, many of which are still poorly understood and managed, and are of importance to stakeholders. These insects and diseases impact seed orchards, nurseries, and forest productivity.

Although pests receive the most attention, insects and fungi are integral parts of healthy forest ecosystems. For example, insects pollinate 85% or more of the forest plant species. Evidence produced by our unit suggests that insect pollinators have declined in southern forests as a result of changes in forest management, fire exclusion and invasive plants. These declines coincide with a growing awareness of declining pollinators worldwide and their decline represents a serious forest health threat.

Scientists Specializing in Insects

Redbay tree infected with the fungus causing laurel wilt disease Diseases caused by insect-pathogen complexes (e.g., laurel wilt, thousand cankers disease), sudden oak death, and the continued challenges posed by chestnut blight and Phytophthora root disease to restoration of American chestnut, are only a few recent examples illustrating the need to maintain expertise in forest pathology. Unit scientists are currently working on etiology and epidemiology of laurel wilt on redbay, sassafras and other relate

Diseases caused by insect-pathogen complexes (e.g., laurel wilt, thousand cankers disease), sudden oak death, and the continued challenges posed by chestnut blight and Phytophthora root disease to restoration of American chestnut, are only a few recent examples illustrating the need to maintain expertise in forest pathology. Unit scientists are currently working on etiology and epidemiology of laurel wilt on redbay, sassafras and other related species in the southeastern USA. They are developing phytosanitary log treatments and characterizing fungi associated with thousand cankers disease killing walnut trees in the southeastern US; studying the biology and management of plant parasitic nematodes killing seedlings in forest tree nurseries; and, studying the effect of arbuscular mycorrhizae (AM) for improving seedling quality.

Unit scientists have also been involved in investigating shoot blight of hemlock, sugarberry/hackberry decline, problems with redbud, oak dieback/decline, sweetgum dieback, and numerous other problems.

Scientists Specializing in Diseases

Invasive plants, such as cogongrass and Chinese privet, continue to hinder forest management in the South and their control increasingly requires novel and integrated strategies involving chemical, silvicultural and biological methods. Research is being conducted on the impacts of invasive plants on ecological processes and community structure in natural and managed systems; biological control of Chinese privet; mitigating and preventing exotic plant invasions in Southern forest communities; and understanding the characteristics associated with successful biological invasions utilizing both population and landscape genetics.

Initial focus for much of this work is on cogongrass, an exotic, invasive, warm-season grass that negatively impacts both the ecology of natural systems and economics of the timber industry throughout the “woodbasket” of the South. Cogongrass populations throughout the Southern region and around the globe are currently being studied to determine invasion dynamics in the this region, and to identify the source of populations in the South and around the world.

Scientists Specializing in Invasive Plants