Observation of key phenological stages of hemlock woolly adelgid (Hemiptera: Adelgidae): using citizen science as a tool to inform research and management.

Increasing efficiency of data gathering at the landscape scale on the growing number of pests and pathogens threatening forests worldwide has potential to improve management outcomes. Citizen science is expanding, with growing support and utility in environmental and conservation fields. We present a case study showing how citizen science observations can be used to inform research and management of a devastating forest pest. Hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), was introduced to eastern North America, leading to decline and mortality of eastern [Tsuga canadensis (L.) Carrière] (Pinales: Pinaceae) and Carolina hemlock (Tsuga caroliniana Engelmann) trees. Management activities, most notably biological control, rely on observations of A. tsugae phenology to inform the timing of releases and monitoring surveys of their highly synchronized specialist predators. In this article, we outline a citizen science program and report phenological observations on A. tsugae. Additionally, we report data comparing A. tsugae estivation break in Virginia (VA) and New York (NY) State, revealing that estivation break is synchronized between NY and VA. This observation is supported by 6 years of citizen scientist observations, showing similar patterns throughout NY, with egg laying shown to be much more variable than estivation break.

Phenology of Leucotaraxis argenticollis, a specialist predator of the invasive hemlock woolly adelgid, in the eastern United States.

In hemlock stands within eastern US forests, classical biological control has been one of the main strategies used to manage the hemlock woolly adelgid, Adelges tsugae Annand. Specialist predator species may offer a management solution to help regulate A. tsugae populations. In the Pacific Northwest, a suite of specialist predators has been a focus of research and includes 2 species of silver fly, Leucotaraxis argenticollis (Zetterstedt) and Leucotaraxis piniperda (Malloch) (Diptera: Chamaemyiidae). Leucotaraxis spp. phenology has been documented in the Pacific Northwest, but the phenology of either western Leucotaraxis species is unknown in the eastern United States. This study sought to document the phenology of Le. argenticollis in NY in 2021 and in VA in 2021 and 2022. Nylon mesh cages were applied over eastern hemlock branches infested with A. tsugae to contain Le. argenticollis adults. Biweekly and monthly branch samples were taken in 2021 and 2022, documenting all life stages of A. tsugae and of Le. argenticollis that were observed. In 2021 and 2022, Le. argenticollis adults and eggs were present during the oviposition stage of the 2 generations of A. tsugae. In addition, Le. argenticollis larvae were present when A. tsugae ovisacs had eggs and while A. tsugae nymphs of both generations were present. These observations indicate that Le. argenticollis phenology is well synchronized with A. tsugae in the eastern United States.

Augmentative biological control for squash bug (Hemiptera: Coreidae) using the egg parasitoid, Hadronotus pennsylvanicus (Hymenoptera: Scelionidae).

The squash bug, Anasa tristis (De Geer) (Hemiptera: Coreidae), is a serious pest of cucurbit crops across the United States. Conventional growers commonly use broad-spectrum insecticides to manage squash bugs, however organic growers lack these effective chemical tools and must rely on alternative management strategies. Biological control of A. tristis is largely understudied, specifically the potential of natural enemy, Hadronotus pennsylvanicus (Ashmead) (Hymenoptera: Scelionidae), as an augmentative biological control agent. For this reason, we performed early-season field releases of H. pennsylvanicus on organic farms in southeastern Virginia to test if this would improve A. tristis egg parasitism. We chose organic vegetable farms growing summer squash (Cucurbita pepo L.) as release sites and nearby Virginia Tech Agricultural Research Extension Centers (AREC) as no-release sites. Parasitoids were reared in the lab and deployed as parasitized egg masses (~2-3 females wasps/plant) in June 2020 and 2021. Before parasitoid deployment, host eggs collected from release and no-release sites displayed low levels of H. pennsylvanicus parasitism in 2020 (<21%) and 2021 (<8%). In both years, the percentage of A. tristis eggs parasitized within 2 weeks post deployment was significantly greater at release sites (~60%) than at no-release sites (~14%). High rates of H. pennsylvanicus parasitism (>72%) were further observed at release sites 4, 6, 8, and 10 weeks following parasitoid deployment. Our study demonstrates that releases of lab-reared H. pennsylvanicus can increase A. tristis egg parasitism rates and subsequently decrease successful nymph hatch rates in early summer squash plantings.

3D X-ray analysis of the subterranean burrowing depth and pupal chamber size of Laricobius (Coleoptera: Derodontidae), a specialist predator of Adelges tsugae (Hemiptera: Adelgidae).

The non-native hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae), has caused a significant decline of eastern hemlock, Tsuga canadensis L. (Pinales: Pinaceae), and Carolina hemlock, Tsuga caroliniana Engelmann (Pinales: Pinaceae), in eastern North America. Biological control of HWA has focused on the use of 2 Laricobius spp. (Coleoptera: Derodontidae), natural predators of HWA, which require arboreal and subterranean life phases to complete their development. In its subterranean phase, Laricobius spp. are subject to abiotic factors including soil compaction or soil-applied insecticides used to protect hemlock from HWA. This study used 3D X-ray microcomputed tomography (micro-CT) to identify the depth at which Laricobius spp. burrows during its subterranean lifecycle, characterize pupal chamber volume, and determine whether soil compaction had a significant effect on these variables. The mean burrowing depth in the soil of individuals was 27.0 mm ± 14.8 (SD) and 11.4 mm ± 11.8 (SD) at compaction levels of 0.36 and 0.54 g/cm3, respectively. The mean pupal chamber volume was 11.15 mm3 ± 2.8 (SD) and 7.65 mm3 ± 3.5 (SD) in soil compacted at 0.36 and 0.54 g/cm3, respectively. These data show that soil compaction influences burrowing depth and pupal chamber size for Laricobius spp. This information will help us better identify the effect of soil-applied insecticide residues on estivating Laricobius spp. and soil-applied insecticide residues in the field. Additionally, these results demonstrate the utility of 3D micro-CT in assessing subterranean insect activity in future studies.

Dendrochronology reveals different effects among host tree species from feeding by Lycorma delicatula (White).

The spotted lanternfly, Lycorma delicatula (White) (Hemiptera: Fulgoridae), was first detected in the United States in Berks County, Pennsylvania, in 2014. Native to China, this phloem-feeding planthopper threatens agricultural, ornamental, nursery, and timber industries in its invaded range through quarantine restrictions on shipments, as well as impacts on plants themselves. The long-term impacts of L. delicatula feeding on tree species have not been well studied in North America. Using standard dendrochronological methods on cores taken from trees with differing levels of L. delicatula infestation and systemic insecticidal control, we quantified the impact of L. delicatula feeding on the annual growth of four tree species in Pennsylvania: Ailanthus altissima, Juglans nigra, Liriodendron tulipifera, and Acer rubrum. The results suggest that L. delicatula feeding is associated with the diminished growth of A. altissima, but no change was observed in any other tree species tested. The results also suggest that systemic insecticides mitigate the impact of L. delicatula feeding on A. altissima growth.

Temperature-dependent Development, Survival, and Oviposition of Laricobius osakensis (Coleoptera: Derodontidae): A Specialist Predator of Adelges tsugae (Hemiptera: Adelgidae).

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.

Subterranean Survivorship and Seasonal Emergence of Laricobius spp. (Coleoptera: Derodontidae), Biological Control Agents for the Hemlock Woolly Adelgid.

Following the adventive arrival, subsequent spread, and ensuing impact of Adelges tsugae Annand (Hemiptera: Adelgidae), the hemlock woolly adelgid (HWA) in the eastern United States, a robust initiative was launched with the goal of decreasing ecosystem impacts from the loss of eastern hemlock (Pinales: Pinaceae). This initiative includes the use of biological control agents, including Laricobius spp. (Insecta: Coleoptera). Laboratory production of these agents is limited by subterranean mortality and early emergence. Therefore, the subterranean survivorship and timing of emergence of a mixture of Laricobius spp. was investigated. PVC traps internally lined with a sticky card and covered with a mesh screen were inserted into the soil to measure the percent emergence of adults based on the number of larvae placed within. The number of emerged adults in the field and laboratory-reared larval treatments was adjusted based on emergence numbers in the control and used as the response variable. Independent variables included in the final model were: treatment (field-collected vs. laboratory-reared), organic layer depth (cm), soil pH, and April-to-December mean soil moisture. No differences were found in survivorship between field-collected and laboratory-reared treatments. As pH and organic layer increased survivorship decreased, significantly. Although the majority of emergence occurred in the fall, emergence also occurred in spring and summer. The occurrence of spring and summer emergence and low survivorship (17.1 ± 0.4%) in the field across all treatments suggests that these are characteristics of Laricobius spp. field biology in their introduced range and not artifacts of the laboratory rearing process.

Phenology of Lycorma delicatula (Hemiptera: Fulgoridae) in Virginia, USA.

The spotted lanternfly, Lycorma delicatula (White), is an invasive planthopper that was first discovered in North America in Berks County, Pennsylvania in 2014. Currently, L. delicatula has spread to eight additional states and threatens agricultural, ornamental, and timber commodities throughout the United States. The timing of insect life events is very important in the development of pest management tools and strategies. In 2019 and 2020, L. delicatula phenology was successfully documented in Winchester, Virginia using weekly 5-min observational surveys at established monitoring plots. Each year, L. delicatula were active in the environment from May to November with initial detections of first, second, third, fourth, and adults occurring in May, May, June, June, and July, respectively. Cumulative average growing degree days were also calculated for the onset of each L. delicatula life stage using local weather data and a lower developmental threshold of 10°C. First-instar L. delicatula were initially observed at 135 and 111.5, adults at 835 and 887, and egg masses at 1673.5 and 1611.5 in 2019 and 2020, respectively. Combined, these data can be used by growers and land managers to facilitate timing of effective pest management strategies.

Historic Assessment and Analysis of the Mass Production of Laricobius spp. (Coleoptera: Derodontidae), Biological Control Agents for the Hemlock Woolly Adelgid, at Virginia Tech.

Laricobius nigrinus (Coleoptera: Derodontidae) Fender and Laricobius osakensis (Coleoptera: Derodontidae) Montgomery and Shiyake have been mass produced by Virginia Tech as biological control agents for the hemlock woolly adelgid (HWA), Adelges tsugae (Hemiptera: Adelgidae) Annand, for the past 15 and 9 yr, respectively. Herein, we describe modifications of our rearing procedures, trends and analyses in the overall production of these agents, and the redistribution of these agents for release to local and federal land managers. Based on these data, we have highlighted three major challenges to the rearing program: 1) high mortality during the subterranean portion of its life cycle (averaging 37% annually) reducing beetle production, 2) asynchrony in estivation emergence relative to the availability of their host HWA minimizing food availability, and 3) unintended field collections of Laricobius spp. larvae on HWA provided to lab-reared larvae complicating rearing procedures. We further highlight corresponding avenues of research aimed at addressing each of these challenges to further improve Laricobius spp. production.

The Inability of Spotted Lanternfly (Lycorma delicatula) to Vector a Plant Pathogen between its Preferred Host, Ailanthus altissima, in a Laboratory Setting.

With the recent introduction of the non-native spotted lanternfly (Lycorma delicatula) to the USA, research and concern regarding this insect is increasing. Though L. delicatula is able to feed on many different plant species, its preference for the invasive tree-of-heaven (Ailanthus altissima) is apparent, especially during its later life stage. Therefore, management focused on A. altissima control to help limit L. delicatula establishment and population growth has become popular. Unfortunately, the control of A. altissima is difficult. Verticillium nonalfalfae, a naturally occurring vascular-wilt pathogen, has recently received attention as a potential biological control agent. Therefore, we studied if L. delicatula fourth instars or adults could vector V. nonalfalfae from infected A. altissima material to healthy A. altissima seedlings in a laboratory setting. We were unable to re-isolate V. nonalfalfae from the 45 A. altissima seedlings or from the 225 L. delicatula utilized in this experiment. We therefore, found no support that L. delicatula could effectively vector this pathogen between A. altissima in laboratory conditions. Since L.delicatula's ability to vector V. nonalfalfae has implications for the dissemination of both this beneficial biological control and other similar unwanted plant pathogens, future research is needed to confirm these findings in a field setting.

Differences in Early Season Emergence and Reproductive Activity Between Spathius agrili (Hymenoptera: Braconidae) and Spathius galinae, Larval Parasitoids of the Invasive Emerald Ash Borer (Coleoptera: Buprestidae).

Both Spathius agrili Yang and Spathius galinae Belokobylskij and Strazanac are host-specific parasitic wasps introduced for biological control of emerald ash borer in North America. Spathius agrili is native to northeastern China and S. galinae comes from a more northern, colder climate in the Russian Far East. Their origin may lead to differing abilities to adapt to climate and their host in North America. We conducted both field and laboratory experiments to determine the timing of early season emergence and synchronization of each parasitoid species to their host in the United States, and if manipulating prerelease conditions could affect emergence time. A cold acclimatization treatment prior to parasitoid emergence was assessed and compared with untreated control group reared with standard rearing protocols. Stands of naturally emerald ash borer-infested ash were sampled at two locations in Virginia throughout the experiment to determine when the parasitoid-susceptible life stage (third to fourth instar) occurred. Untreated S. galinae emerged approximately 2 wk earlier than any other cohort, whereas cold acclimatized S. galinae emerged later than any other cohort. Emergence time of S. agrili was unaffected by cold acclimatization. Cold acclimatization treatment did not affect the parasitism rate of either species, nor did it have multigenerational effects. Emergence time of the subsequent generation of S. agrili was delayed by cold acclimatization treatment, whereas S. galinae experienced no multigenerational effects. At Virginia field sites, susceptible EAB larvae were present during the emergence time of all four groups of parasitoids. Untreated S. galinae had the least overlap with any susceptible EAB larvae.

Seasonal Assessment of Supercooling Points for Two Introduced and One Native Laricobius spp. (Coleoptera: Derodontidae), Predators of Adelgidae.

The hemlock woolly adelgid, Adelges tsugae Annand, is an invasive insect that threatens hemlock species in eastern North America. Several species from the genus Laricobius are predators of A. tsugae in its native areas of Asia and the western United States. Two Laricobius species have been released as biological control agents: Laricobius nigrinus Fender, and Laricobius osakensis Montgomery and Shiyake. Laricobius rubidus LeConte is an adelgid predator native to the Eastern United States, where it can feed and complete development on A. tsugae opportunistically. Laboratory assays were conducted to assess the cold hardiness of these three Laricobius species, including two distinct populations of L. osakensis, by measuring the supercooling points of each species from November 2016 through March 2017. This information may be useful for choosing the best-suited biological control agent for a particular region to control A. tsugae. There was a significant difference between the overall mean supercooling point of L. rubidus compared to the other Laricobius spp. There were also significant differences of supercooling points between L. rubidus and both strains of L. osakensis in January, and significant differences between L. rubidus and all other strains in February. L. rubidus appear better adapted to cold extremes in the eastern U.S. than imported Laricobius spp.

Phenology of the Pine Bark Adelgid, Pineus strobi (Hemiptera: Adelgidae), in White Pine Forests of Southwestern Virginia.

The pine bark adelgid, Pineus strobi Hartig (Hemiptera: Adelgidae), is a native herbivore of eastern white pine, Pinus strobus L. (Pinales: Pinaceae), in eastern North America. P. strobi does not appear to have any dominant overwintering lifestage in southwest Virginia, as it does in its northern range. Eggs can be found consistently from late March through early December and may be produced sporadically later throughout the winter during warm periods. Two distinct generations were observed in the spring, after which life stage frequencies overlapped. Adult body size varied seasonally and was greatest in the spring. The present study constitutes the first recording of phenological details of the P. strobi in its southern range, informing biological control efforts aimed at closely related invasive pests. The phenological plasticity observed between northern and southern P. strobi populations provides insight into the potential effects of climate on the population dymanics of this and related species.

Fitness and physiology of Adelges tsugae (Hemiptera: Adelgidae) in relation to the health of the eastern hemlock.

The hemlock woolly adelgid, Adelges tsugae Annand is an invasive insect that frequently causes hemlock (Tsuga spp.) mortality in the eastern United States. Studies have shown that once healthy hemlocks become infested by the adelgid, nutrients are depleted from the tree, leading to both tree decline and a reduction of the adelgid population. Since A. tsugae is dependent on hemlock for nutrients, feeding on trees in poor health may affect the ability of the insect to obtain necessary nutrients and may consequently affect their physiological and population health. Trees were categorized as lightly or moderately impacted by A. tsugae based on quantitative and qualitative tree health measurements. Population health of A. tsugae on each tree was determined by measuring insect density and peak mean fecundity; A. tsugae physiological health was determined by measuring insect biomass, total carbon, carbohydrate, total nitrogen, and amino nitrogen levels. Adelges tsugae from moderately impacted trees exhibited significantly greater fecundity than from lightly impacted trees. However, A. tsugae from lightly impacted hemlocks contained significantly greater levels of carbohydrates, total nitrogen, and amino nitrogen. While the results of the physiological analysis generally support our hypothesis that A. tsugae on lightly impacted trees are healthier than those on moderately impacted trees, this was not reflected in the population health measurements. Adelges tsugae egg health in response to tree health should be verified. This study provides the first examination of A. tsugae physiological health in relation to standard A. tsugae population health measures on hemlocks of different health levels.

Characterization of physical and chemical defenses in the hemlock woolly adelgid.

The invasive hemlock woolly adelgid (Adelges tsugae Annand, Hemiptera: Sternorrhyncha: Adelgidae) causes significant mortality to eastern and Carolina hemlock (Tsuga canadensis Carrière and T. caroliniana Engelmann, respectively) throughout the eastern United States. Adelges tsugae produces vast quantities of a wax covering that surrounds most of the instars as well as the adult and eggs. Using direct probe EI mass spectrometry, this wax covering was characterized as a diketoester wax, 17-oxohexatriacontanyl 11-oxotriacontanoate, and accounted for ≈ 42 % of A. tsugae total biomass. The presence of the anthraquinone, chrysophanol, and its precursor anthrone, chrysarobin, in A. tsugae has only been briefly described. Further study confirmed these compounds in all A. tsugae life stages. Additionally, several predatory beetles in use or under consideration as biological control agents for this species appear to ingest and excrete these compounds when feeding on A. tsugae. The production of both a physical and a chemical defense may represent a significant energy investment by A. tsugae.

Impacts of trunk and soil injections of low rates of imidacloprid on hemlock woolly adelgid (Hemiptera: Adelgidae) and eastern hemlock (Pinales: Pinaceae) health.

Eastern hemlocks (Tsuga canadensis Carrière) at two sites in southwestern Virginia were treated by trunk and soil injections of imidacloprid to determine the insecticide's impact on hemlock woolly adelgid, Adelges tsugae Annand. Treatments were 25, 50, and 100% of the highest labeled dosage rates for both stem and soil injection. Three and 4 yr after treatment, the half and full rates had significantly reduced A. tsugae populations, which were accompanied by increased new hemlock shoot growth and higher hemlock health scores on a visual rating of tree appearance. Imidacloprid and metabolite concentrations in tissue of treated trees were determined by liquid chromatography-tandem mass spectrometry, and A. tsugae density decreased as imidacloprid concentrations increased in wood tissue. There were no observed A. tsugae populations in all trees with imidacloprid tissue concentrations >413 ppb. Olefin, di-hydroxy, and 6-chloro-nicotinic-acid metabolites were the imidacloprid metabolites recovered in the highest concentrations. This suggests that hemlock metabolism of imidacloprid may increase efficacy of the parent compound. Stem and soil treatments of low rates of systemic imidacloprid reduce adelgid populations and promote hemlock health, but still may provide a remnant food source for beneficial predators.

Potential feeding deterrents found in hemlock woolly adelgid, Adelges tsugae.

The nonnative hemlock woolly adelgid (Adelges tsugae Annand, Hemiptera: Sternorrhyncha: Adelgidae) has been a significant mortality agent of eastern hemlock (Tsuga canadensis Carriere) throughout a large portion of its geographic range. During a study investigating adelgid vigor in relation to host health, it was noted that adelgid extracts ranged from a yellow to a deep red color. Analysis by GC-MS identified the presence of the anthraquinone, chrysophanol and its anthrone precursor, chrysarobin in the extract. These compounds are predator deterrents in several other insects, including chrysomelid beetles. It is hypothesized that these compounds serve a similar purpose in the hemlock woolly adelgid.

Lethal and sublethal effects of imidacloprid on hemlock woolly adelgid (Hemiptera: Adelgidae) and two introduced predator species.

Eastern hemlock, Tsuga canadensis (L.) Carrière, branchlets were systemically treated with imidacloprid and bioassayed with hemlock woolly adelgid, Adelges tsugae (Annand) (Hemiptera: Adelgidae), and predators. After 10 d, two hemlock woolly adelgid predators, Laricobius nigrinus Fender (Coleoptera: Derodontidae) and Sasajiscymnus tsugae Sasaji & McClure (Coleoptera: Coccinellidae), were allowed to feed on remaining hemlock woolly adelgid for 20 d on branches systemically treated with 1, 10, or 100 ppm imidacloprid. Every 5 d, mortality, mobility (measured as flip time), number of hemlock woolly adelgid consumed, and degree of intoxication of each individual beetle were recorded. Liquid chromatography-mass spectrometry was used to quantify imidacloprid and some of its major metabolites in hemlock wood tissues and in the predator beetles postmortem. Probit analysis of hemlock woolly adelgid mortality and imidacloprid concentrations recovered from branch wood tissues determined the 30 d LC50 to be 242 ppb. A topical application of imidacloprid to the ventral abdomen of individual beetles resulted in a 6 d LD50 value of 1.8 and 0.71 ng imidacloprid per beetle for L. nigrinus and S. tsugae, respectively. In no-choice tests, L. nigrinus mortality was significantly higher on hemlock branchlets treated with 100 ppm imidacloprid than on controls, but S. tsugae mortality was not. S. tsugae consumed the same number of adelgids on treated branchlets as on controls, but L. nigrinus consumed fewer adelgids from the 100 ppm branchlets than on controls. In choice tests, beetle mortality and flip times were generally not significantly different from controls. At times, both beetle species displayed intoxication symptoms after feeding on adelgids from treated branchlets and imidacloprid was recovered from both beetle species postmortem. These results suggest that systemic imidacloprid displayed both lethal and sublethal effects on these two nontarget predators of the hemlock woolly adelgid.

Evaluation of ELISA for imidacloprid detection in eastern hemlock (Tsuga canadensis) wood and needle tissues.

BACKGROUND: Imidacloprid is the primary insecticide used against the exotic invasive insect hemlock woolly adelgid, Adelges tsugae Annand, a pest of eastern hemlock [Tsuga canadensis (L.) Carrière] trees in the eastern United States. A competitive enzyme-linked immunosorbent assay (ELISA) was evaluated for quantification of imidacloprid in eastern hemlock wood and needle tissues. RESULTS: Matrix effects in the form of false positives and overestimated imidacloprid concentrations were observed in both wood and needle extracts. Tissues required a 100-1000-fold dilution with water in order to reduce matrix effects. Standard curves in 1% wood or needle extract were not significantly different from standard curves prepared in water. Matrix effects were more pronounced at concentrations in the lower working range of the kit, with recovery of 5 microg L(-1) imidacloprid more accurate than recovery of 0.2 microg L(-1). CONCLUSION: ELISA remains a valuable tool for semi-quantitative imidacloprid detection within the hemlock system because of its sensitivity, cost and ease of use. However, a 1000-fold dilution of hemlock tissue extract is recommended to ensure accurate imidacloprid determinations.

Binomial sequential sampling plan for hemlock woolly adelgid (Hemiptera: Adelgidae) sistens infesting individual eastern hemlock trees.

The hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), is an exotic insect pest that is killing eastern hemlock, Tsuga canadensis (L.) Carrière, and Carolina hemlock, Tsuga caroliniana Engelmann, in the eastern United States. We used the sequential interval procedure to develop a binomial sequential sampling plan for A. tsugae sistens on individual eastern hemlock trees that uses nondestructive sampling of new shoots. The actual a (type I) and beta (type II) error rates were essentially 5 and 10%, respectively. Tallies of new shoots infested by at least one A. tsugae sistens were compared with stop values for thresholds of 10 and 30% of new hemlock shoots infested. Twenty to 80 new shoots had to be examined per tree to render a low, high, or indeterminate classification, which took < 2 min per tree regardless of the threshold used. This plan should be an efficient and cost-effective tool in the management of A. tsugae infestations on individual, high-value eastern hemlock trees.