Albert E. Mayfield

Laurel wilt is a vascular disease caused by a non‐native pathogen ( Harringtonia lauricola ) and an associated beetle vector (redbay ambrosia beetle; RAB; Xyleborus glabratus ) affecting several members of the Lauraceae family in North America, including the ecologically and culturally important sassafras ( Sassafras albidum ). Since discovery of the vector in 2002 and the disease in 2004 near Savannah, GA, laurel wilt has spread widely throughout the eastern United States, causing widespread mortality to redbay, sassafras, and other lauraceous species. The objective of this study was to assess the spread of H. lauricola through sassafras roots in the absence of the beetle vector. Four spatially independent forest plots containing sassafras were identified in the Clemson Experimental Forest, and 1–2 mature trees in each stand were inoculated with H. lauricola in May of 2020. All sassafras in each plot were counted and categorized by size class and crown damage over a 4‐year period. Harringtonia lauricola was confirmed in sassafras roots up to 3.6 m from inoculated trees 1‐year post‐inoculation in the absence of RAB. Sassafras stems closer to the inoculated tree experienced greater wilt symptoms and mortality. Despite significant mortality and wilt, nearly 50% of the sassafras stems across all sites were still living 4 years post‐inoculation. These results demonstrate that laurel wilt can spread from one sassafras stem to others via underground movement of the pathogen through root suckers in natural stands, but that many trees can survive years after inoculation. Development of management strategies for laurel wilt in sassafras will need to account for this mechanism of disease spread.

In the eastern United States, feeding by introduced predators Laricobius nigrinus Fender and Laricobius osakensis Shiyake and Montgomery are likely insufficient to sustainably regulate the invasive hemlock woolly adelgid (HWA), Adelges tsugae Annand, due to adelgid population rebound postpredation. This suggests that additional predators may be needed in eastern North America to achieve effective biological control. In the Pacific Northwest, there is evidence that multiple specialist predators, including La. nigrinus, Leucotaraxis piniperda (Malloch), and Le. argenticollis (Zetterstedt) contribute to maintaining HWA populations below damaging levels on western hemlock. We report on a 2-yr, 5-location study to evaluate the combined effect of predators, La. nigrinus, La. osakensis, and Le. piniperda on HWA populations and eastern hemlock health in the eastern United States. Three assessments targeting different stages of predator-prey activity were conducted annually by installing mesh cages on HWA-infested branches where La. nigrinus was established. Predation by Laricobius spp. caused measurable spring HWA ovisac disturbance, and Le. piniperda predation caused measurable summer HWA ovisac disturbance during both years. Proportion of new shoot growth and mean length of new shoot growth did not differ among treatments for both years. This suggests that a longer-term study may be needed to better understand the combined effects these predators may have on eastern hemlock health, or that additional predators such as Le. argenticollis should also be evaluated.

The laurel wilt disease complex is a destructive combination of a non-native beetle vector [redbay ambrosia beetle (RAB), Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae)] and a symbiotic fungus (Harringtonia lauricola (Ophiostomataceae) T.C. Harr., Fraedrich & Aghayeva), which serves as a pathogen in the host trees infested by RAB. The complex originated from Asia and was first discovered in the United States near Savannah, GA in 2002, and has rapidly made its way across the southeastern US, causing mortality for redbay and other important Lauraceae species, including sassafras, giving this disease complex the potential to have far-reaching ecological effects across North America. Our goal with this study was to examine the spatial distribution of RAB attacks in redbay and sassafras trees along the leading edge of disease progression. RAB attacks were clustered in both tree species, with attacks being most concentrated on the south side of the tree in sassafras, and with RAB clustering more with other RAB attacks on redbay. When comparing bolts that produced adult RABs, the average number of RABs emerged was higher in redbay compared to sassafras. Entrance hole density, RAB emergence, and moisture content were higher near the base of the stem compared to stems sections higher on the bole of both tree species. Our results suggest that physiological differences, such as size and structure of vessels, between these tree species may drive beetle attack patterns and, therefore, affect the progression and spread of disease throughout sassafras and other Lauraceae.

In 2009, we determined the effects of the enantiomeric composition of the kairomone, α-pinene, on trap catches of arboreal beetles (Coleoptera) in stands of eastern pine trees with resin dominated by (+)-α-pinene. We hypothesized that the responses of beetles would correlate with the predominant enantiomer of α-pinene found in host pines. Lures of (+)-, racemic (±), and (−)-α-pinene were added separately to ethanol-baited multiple-funnel traps. Species such as Monarthrum mali (Fitch), Dendroctonus terebrans (Olivier), Ips grandicollis (Eichhoff), and Pachylobius picivorus (Germar) (Coleoptera: Curculionidae) showed a preference for traps co-baited with (–)-α-pinene. α-Pinene enhanced attraction of Hylastes salebrosus Eichhoff, Hylastes porculus Erickson and Hylastes tenuis Eichhoff (Coleoptera: Curculionidae) to ethanol-baited traps with no effects from enantiomeric composition of α-pinene. The attraction of the ambrosia beetles, Xyleborinus saxesenii (Ratzeburg) and Dryoxylon onoharaense (Murayama) (Coleoptera: Curculionidae) to ethanol-baited traps was interrupted by the addition of α-pinene, regardless of enantiomeric composition. Species such as Xylosandrus germanus (Blandford), Cnestus mutilatus (Blandford) and Stenoscelis brevis (Boheman) (Coleoptera: Curculionidae) were unaffected by the presence of α-pinene. Trap catches of some species of longhorn beetles and bark beetle predators (Coleoptera: Cerambycidae, Cleridae, Elateridae, Histeridae, and Trogossitidae) were increased by the addition of α-pinene, although results varied by location. Platysoma spp. (Coleoptera: Histeridae) showed a marked preference for traps co-baited with (+)-α-pinene in Florida and Georgia. In summary, we found that the enantiomeric composition of α-pinene in hosts was not a good predictor of enantiomeric preferences by beetles.

Laurel wilt (LW) is a vascular disease caused by the fungus Harringtonia lauricola (previously Raffaelea lauricola) and transmitted by its primary vector, the redbay ambrosia beetle (Xyleborus glab...

A predator, Laricobius osakensis Montgomery and Shiyake (Coleoptera: Derodontidae), is being mass-produced and released for the biological control of the invasive hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae). To better understand and predict the seasonality of this predator in North America, the development and reproduction of L. osakensis were evaluated at constant temperatures ranging from 5 to 22°C. The predicted seasonal biology was compared with data from field collections. L. osakensis did not complete development from egg to adult at the two lowest temperatures tested, 5 and 8°C, but did so at the highest temperature of 22°C. The minimum development thresholds were estimated for eggs (4.2°C), first (1.8°C), second (5.5°C), third (4.6°C), and fourth instar (4.1°C), prepupa (3.6°C), and pupa (7.5°C). Oviposition rates were significantly greater at 5 and 10°C than at 20 and 25°C. Head capsule width significantly increased for each of the four larval instars with a mean of 0.19, 0.26, 0.35, and 0.44 mm, respectively. Laboratory and field data were used to develop a phenology forecasting model to predict the occurrence of all developmental stages of L. osakensis. This model will allow land managers to more accurately predict the optimal timing for L. osakensis larval sampling throughout its established range.

Laurel wilt is a destructive vascular disease of trees in the laurel family (Lauraceae) caused by a nonnative insect/pathogen complex. This study monitored the recent spread and impact of laurel wilt in sassafras (Sassafras albidum [Nutt.] Nees) from the Gulf-Atlantic Coastal Plain region of the southeastern United States (US) into the adjacent Piedmont/Sandhills and Mountain regions. Laurel wilt was detected at thirteen of forty-six sassafras sites including seven outside the Coastal Plain. Compared to nondiseased sites, sassafras mortality due to laurel wilt increased rapidly from 2018 to 2020 and occurred in all diameter classes monitored (≥ 5 cm diameter at breast height, dbh). Flight trapping for the laurel wilt vector, the redbay ambrosia beetle (RAB, Xyleborus glabratus Eichhoff), with α-copaene lures did not enhance early detection of latent laurel wilt infections. Seasonal flight activity of the RAB in the Piedmont and Mountains suggested two generations per year with little to no flight from December through March.