Yearly Research Highlights

Research Highlights for FY15

Using predators and chemicals together to protect hemlock trees

Albert Mayfield

A non-native insect, the hemlock woolly adelgid, is eliminating an ecologically important tree species, eastern hemlock, from southern Appalachian forests. Systemic insecticide applications and predator beetle releases are being combined to fight this invasive pest. In a study in northern Georgia, trees previously treated with imidacloprid had better crown health and eventually supported as many predator beetles as untreated trees, showing promise for an integrated pest management approach.

Publication: Establishment, hybridization and impact of Laricobius predators on insecticide-treated hemlocks: Exploring integrated management of the hemlock woolly adelgid

Hemlock WooIly Adelgid Predator Beetle Releases and Recovery Efforts in the North Georgia Mountains

Jim Hanula

Eastern hemlock are threatened by the invasive hemlock woolly adelgid, Adelges tsugae that arrived in Georgia in 2003. In order to conserve some mature hemlocks in North Georgia, the USDA Forest Service created over 100 Hemlock Conservation Areas (HCAs) throughout the Chattahoochee National Forest. Sasajiscymnus tsugae, Laricobius nigrinus, and Scymnus sinunodulus are predatory beetles released in some of these areas. Following release, infested hemlock trees were sampled during spring 2010 – 2012 at some of these sites. Non-release sites 0.40 to 1.61 km from release areas were also sampled in 2012 to evaluate spread from release trees. Sasajiscymnus tsugae was found at 3 sites 3 years after release and at 2 other sites 2 years after release. Laricobius nigrinus was found at one site 3 years after release and at two sites 2 years after release. Scymnus sinunodulus was never recovered. Our results demonstrate that S. tsugae and L. nigrinus, are established in North Georgia, however their population sizes, efficacy, and survival rates are still unknown. Sampling at non-release sites showed that the native L. rubidus is a common predator associated with A. tsugae populations, but its effect on them is also unknown.

Publication: Post release recovery of hemlock woolly adelgid predators in the North Georgia mountains.

Insects promote wood decomposition and nutrient cycling in forests.

Michael Ulyshen

Although insects are often overlooked in studies of wood decomposition, two recent review articles written by a Forest Service researcher suggest these organisms may act to speed up the process, promote nitrogen cycling and have the potential to benefit forest productivity. In the first article, published in Biological Reviews (DOI: 10.1111/brv.12158) insects are shown to have variable direct and indirect effects on wood decomposition, with a net collective effect of ~10-20%. In the second article, published in Ecological Entomology (DOI: 10.1111/een.12176), several mechanisms by which insects are likely to influence nitrogen dynamics within decomposing wood are discussed. These include accelerating the release of nitrogen and promoting nitrogen fixation. Because nitrogen is the limiting nutrient in many forests, these effects have the potential to benefit forest productivity. Both articles underscore the benefits to be had from protecting dead wood and insects associated with it in managed forests. Research aimed at specifically exploring the connection between wood-feeding insects and forest productivity is underway.

Wood decomposition as influenced by invertebrates

Insect-mediated nitrogen dynamics in decomposing wood

New “Mesoamerican Pine Beetle” Described by SRS Scientist and Collaborators

Brian T. Sullivan

A newly-discovered species of tree-killing bark beetle in Central America, Dendroctonus mesoamericanus, has been recently described by a group of scientists including Southern Research Station (SRS) research entomologist Dr. Brian Sullivan (SRS 4552, Pineville, LA). Numerous studies by a team including scientists from R8 Forest Health Protection, Mexico, and Norway determined that the species is new to science and provided information needed to manage the insect, which may share responsibility with the southern pine beetle (Dendroctonus frontalis) for the catastrophic damage to pines in Central America in recent years. The two Dendroctonus species appear to work in cooperation to kill trees, and outbreaks of both may be more persistent and destructive than those of southern pine beetle alone. This discovery brings to light a potential exotic threat to the U.S. that was not previously known to exist. Read the full paper in the Annals of the Entomological Society of America.

Publication: A new species of bark beetle, Dendroctonus mesoamericanus sp nov. (Curculionidae: Scolytinae), in southern Mexico and Central America

Research Highlights for FY14

Termites accelerate wood decomposition in southeastern U.S. forests

Michael Ulyshen

The role of termites and other wood-feeding insects to wood decomposition remains largely unknown despite great interest in forest carbon and nutrient cycling. Forest Service scientists recently completed two field studies aimed at exploring this question in the southeastern United States. Both studies involved experimentally protecting logs from insect attack over a several- year period and comparing the amount of wood lost from these to that lost from unprotected logs. The first study showed that wood-feeding insects consume about 15-20% of dead wood volume in loblolly pine forests, with termites causing most of this damage. The second study found that about 14-20% of wood loss in mixed hardwood/pine forests was attributable to termites and other insects. Below-ground termite activity was significantly lower in seasonally- flooded forests compared to unflooded forests, but there was little difference in above-ground activity between forest types. These findings indicate that termites play an important role as decomposers in southeastern U.S. forests and provide baseline information for future studies addressing their contributions to nutrient cycling and forest productivity.

Contrasting effects of insect exclusion on wood loss in a temperate forest

Interacting effects of insects and flooding on wood decomposition.

Removing Chinese privet benefits pollinators for up to five years.

Jim Hanula

Chinese privet invades a forest growing into thickets that crowd out native plants in streamside forests. Even if the woody shrub can be removed effectively, can a forest return to any semblance of its previous condition? Researchers tested two methods for removing privet. In one set of plots, they used a mechanical mulching machine to grind privet to the ground level, leaving the mulch on the plots. In the other set of plots, crews with chainsaws and machetes felled privet by hand. By 2007, the plots had less than one percent of their surfaces covered by privet compared to over 60 percent on control plots where privet was left untreated. After only two years, there were four to five times more bee species in privet-free and three times as many butterfly species on the mulched plots and nearly seven times as many individuals. This increase in pollinators lasted for 5 years and demonstrates the lasting value of removing privet from forested land.

Publication: Removing Chinese privet from riparian forests still benefits pollinators five years later

Wood Heat Treatment Reduces the Risk of Spreading of Thousand Cankers Disease

Bud Mayfield

Black walnut, one of the most valuable hardwood timber species in the United States, is being killed by “thousand cankers disease” which is caused by a tiny bark beetle (the walnut twig beetle) and an associated fungus. The disease organisms can spread to new areas through the movement of infested walnut logs, firewood, or other unprocessed wood products that are transported for commercial trade. Heat is a common treatment applied to wood products to kill pests in the wood or bark and make them safe for transport. By steam-heating infested walnut logs to various temperatures in a kiln, and then sampling/monitoring those logs after treatment, researchers determined that a temperature of at least 56°C in the outer sapwood for 40 minutes is sufficient to kill all live walnut twig beetles and their associated fungus. This heat treatment schedule represents an effective management tool that can be used to reduce the risk of spreading thousand cankers disease through the walnut wood products industry.

Publication: Efficacy of Heat Treatment for the Thousand Cankers Disease Vector and Pathogen in Small Black Walnut Logs

Lure developed for killer of Louisiana baldcypress

Brian T. Sullivan

The land surface of southern Louisiana is sinking as an unwanted result of human channeling of water flow. Constant and deeper flooding of baldcypress forests is stressing these magnificent trees, triggering an outbreak of a previously undetected moth pest, the baldcypress leafroller. The caterpillars of these moths can completely consume a tree’s leaves, and young baldcypress die if this happens for several years in a row. Such loss of young trees will likely hinder regrowth of cypress forests following a large-scale harvest that is planned in the near future.

Sex pheromones, chemicals released into the air by female moths to entice mates, are highly attractive to male moths. By using a variety of chemical analytical methods, Forest Service scientists have identified and then reproduced the chemical composition of the sex pheromone of the baldcypress leafroller. The synthetic pheromone has been formulated into an artificial lure that is strongly attractive to male moths and can be an important tool in efforts to preserve and restore baldcypress forests. Baited traps can detect and monitor moth populations and thus help identify at-risk forests. Furthermore, moth pheromone lures might be distributed throughout the forest as a means to ‘distract’ males and keep the moths from reproducing. This technique might provide an insecticide-free method for controlling this pest in a highly sensitive environment.

Publication: Characterization of an Aggregation Pheromone in Hylesinus pruinosus (Coleoptera: Curculionidae: Scolytinae)

Research Highlights for FY13

California bay laurel is an attractive host for the insect vector of laurel wilt disease

Bud Mayfield

Laurel wilt is a deadly disease of several tree species in the Laurel family (Lauraceae) including redbay, sassafras, and avocado in the southeastern U.S. The disease is caused by a fungus carried by the redbay ambrosia beetle (Xyleborus glabratus), a non-native wood boring insect. California bay laurel (Umbellularia californica) is an aromatic, evergreen tree in coastal Oregon and California and the foothills of the Cascades and Sierra Nevada mountains. Small logs of California bay laurel and several other Laurel-family species were placed in a forest infested with redbay ambrosia beetle in South Carolina in 2012. California bay laurel was as attractive to the redbay ambrosia beetle as known laurel wilt hosts swampbay and sassafras. Also, the redbay ambrosia beetle and another invasive pest, the granulate ambrosia beetle (Xylosandrus crassiusculus), readily attacked, produced brood in, and emerged from California bay laurel at numbers equal to or higher than all other tree species tested. The results indicate that California bay laurel is at risk from the redbay ambrosia beetle and laurel wilt if the beetle becomes established in the western U.S.

Publication: Suitability of California bay laurel and other species as hosts for the non-native redbay ambrosia beetle and granulate ambrosia beetle.

Research Highlights for FY12

Biology and Hosts of a New Invasive Insect, the Kudzu Bug, Megacopta cribraria, and Its Impact on Kudzu Growth

Jim Hanula

The bean plataspid or kudzu bug, Megacopta cribraria (F.), was recently discovered in the United States feeding on kudzu, an economically important invasive vine. We studied its biology on kudzu and its impact on kudzu growth. We also tested its ability to utilize other common forest legumes for oviposition and development. Flight intercept traps operated from May 2010 to May 2011 in a kudzu field near Athens, GA showed three peaks of adult flight activity suggesting there are two generations per year on kudzu. Vine samples examined for eggs from April 2010 through April 2011 and June to October 2011 showed two periods of oviposition activity in 2010 which coincided with the peaks in adult activity. In 2011, the second period of oviposition began on or before June 24 and then egg abundance declined gradually thereafter until late August when we recovered < 2 eggs/0.5 m of vine. In 2011 host range experiments conducted in a kudzu field using 12 legume species, M. cribraria preferentially oviposited on kudzu over soybean, Glycine max, but they still laid 320 eggs/plant on soybean. Lespedeza hirta and Lespedeza cuneata had 122.2 and 108.4 eggs/plant, respectively. Kudzu and soybean were the only species M. cribraria completed development on. Plots protected from M. cribraria by biweekly insecticide applications had 32.8% more kudzu biomass than unprotected plots. Our results show that M. cribraria has a significant impact on kudzu growth and could help suppress this pest weed.

Publication: The biology and preliminary host range of Megacopta cribraria (Heteroptera: Plataspidae) and its impact on kudzu growth