Translator Disclaimer
1 December 2016 A Field-Based Method to Estimate Densities of Laricobius nigrinus (Coleoptera: Derodontidae), an Introduced Predator of Hemlock Woolly Adelgid (Hemiptera: Adelgidae)
Author Affiliations +
Abstract

This study investigated the use of emergence traps to assess densities of Laricobius nigrinus Fender (Coleoptera: Derodontidae), a predator of hemlock woolly adelgid (Hemiptera: Adelgidae), in an area of release and establishment. Results indicate that traps effectively collect emerging adults and allow systematic population estimates of L. nigrinus. The incorporation of this method in future monitoring efforts could enable population estimates across the release range of L. nigrinus, thereby enhancing the evaluation of establishment and long-term persistence of this predator.

The hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), has had well-documented negative impacts on eastern hemlock, Tsuga canadensis (L.) Carrière (Pinaceae), throughout much of the tree's native range in the eastern U.S. (Ellison et al. 2005; Eschtruth et al. 2006; Ford et al. 2012). Biological control has been a major component in management programs implemented against A. tsugae in forest systems (Reardon & Onken 2011; Havill et al. 2014). One of the primary species used in biological control programs directed against A. tsugae is Laricobius nigrinus Fender (Coleoptera: Derodontidae) (McClure 2000; Reardon & Onken 2011). Laricobius nigrinus is native to western North America, and since 2003 more than 200,000 adults have been released in the eastern U.S. (Havill et al. 2014).

Documentation of establishment and biology of L. nigrinus in areas of release has been crucial to biological control efforts; however, the use of traps to evaluate adult emergence and seasonal biology in the field is uncommon. Much of the research on seasonality and biology of L. nigrinus has involved field collections in areas of release using beat-sheets or branch clippings (Mausel et al. 2008, 2010; Hakeem et al. 2011), sleeve-cage studies in the field (Lamb et al. 2005, 2006; Mausel et al. 2008), or studies in the laboratory (Zilahi-Balogh et al. 2002, 2003a,b; Lamb et al. 2007). The use of traps may be an effective method to monitor L. nigrinus adults emerging from the soil following aestivation over the summer months, and enable land managers to assess population densities of this important predator. This method would provide more accurate population estimates in areas of release than many of the current means of sampling. Therefore, in 2010, a multi-year study was initiated to estimate densities of emerging adults of L. nigrinus based on emergence trap collections.

The study site was near Elkmont Campground, Great Smoky Mountains National Park (35.66417°N, 83.59028°W; about 640 m elevation; spanning the border between North Carolina and Tennessee), where 866 L. nigrinus adults were released on hemlocks at the edge of an open field on 14 Mar 2006. Establishment of L. nigrinus at this site was determined in 2009 (Grant et al. 2010).

To assess emergence of L. nigrinus in an area of release and establishment, emergence traps were placed beneath hemlock canopies at Elkmont. Traps consisted of a wood frame (4-sided pyramid shape, 77.5 × 77.5 × 50 cm, approximately 0.60 m2 area per trap) covered with anti-virus screen (266 × 818 microns mesh size) (Green-Tek, Edgerton, Wisconsin), which guided beetles to a collecting head (120 mL unvented plastic specimen cup) (Lermer Plastics, Inc., Garwood, New Jersey) mounted to a wooden plate at the top of the trap (Wiggins et al. 2016). On 3 Oct 2010, 6 traps were placed under each of 4 canopies (tree heights ranged from about 7 m to about 14 m) of trees growing at the edge of an open field and monitored through 3 Mar 2011. Under each canopy, 3 traps were placed with the outer-most edge of the trap 1 m from the trunk (inner traps), and 3 traps were placed with the outer-most edge of the trap 2 m from the trunk (outer traps). The following season (on 6 Oct 2011), traps were moved to trees in the adjacent forest (within 50 m of the forest edge) to allow populations of L. nigrinus associated with previous study trees to grow, and have open ground on which to drop and develop in Spring 2012. Unlike Fall 2010, 3 traps were placed under each of 8 tree canopies, and traps were monitored until 1 Mar 2012. In Fall 2012, emergence traps were moved back to hemlock on the border of the field, and traps were placed in the same configuration under each of 4 trees as in Fall 2010. Traps were monitored from 26 Sep 2012 to 27 Mar 2013. During each sampling period in each sampling year, traps were monitored every 5 to 14 d.

Based on the total number of L. nigrinus adults that emerged under each tree each season, beetle density was estimated for each tree canopy by averaging the number of beetles per m2 collected in traps under each canopy. Additionally, the area underneath each tree canopy was approximated by measuring the distance from the trunk to the dripline and calculating the area. The total number of beetles per tree canopy was estimated by multiplying the beetle density by the total area under each canopy.

Density estimates of beetles per m2 from emergence trap collections at Elkmont ranged from 3.37 to 7.03 in 2010, 0.28 to 1.97 in 2011, and 1.41 to 14.90 in 2012 (Table 1). The extrapolated estimated total number of beetles per study tree ranged from 8 in 2011 to 658 in 2012. The average number of beetles estimated to occur beneath each study tree varied from 284 during 2010, to 35 during 2011, to 348 during 2012.

Table 1.

Total numbers of Laricobius nigrinus adults observed in emergence traps for each tree, and estimated numbers of adults per tree, Elkmont, Great Smoky Mountains National Park, 2010 to 2012.

t01_805.gif

The numbers of L. nigrinus adults collected under canopies varied across years and may have been more similar in the 2010 and 2012 collections compared with the 2011 collections due to the location of trees sampled. Trees used during 2010 and 2012 were partially open grown and had fuller canopies, whereas trees during 2011 were in the forest or close to forest margins with less dense canopies. Partially open grown trees with fuller canopies provide more potential host material for A. tsugae, which, in turn, would facilitate greater numbers of L. nigrinus per tree. In some areas of release, greater numbers of L. nigrinus have been reported on release trees that are more exposed to direct sunlight (McDonald 2010). Despite differences in densities, emergence traps during all 3 yr were effective at collecting L. nigrinus. When compared with beat-sheet sampling conducted concurrently on the same study trees, traps collected similar numbers of L. nigrinus adults (Wiggins et al. 2016), with the added advantage of enabling population estimates. These estimates provide insight into the establishment and growth of L. nigrinus populations over time. The initial (and only) release of L. nigrinus at this site in 2006 was 866 individuals, and an estimated 1,394 adults were collected from 4 trees in 2012. Considering the numerous hemlock trees infested with A. tsugae in the area immediately adjacent to the 4 study trees, L. nigrinus populations have increased greatly since the initial release. Future use of emergence traps could enable the long-term evaluation of these populations and assist resource managers with collections of L. nigrinus for redistribution.

These results demonstrate that in addition to detecting L. nigrinus in areas of release and estimating its emergence period, emergence traps are useful for quantifying L. nigrinus populations in an area. Although beat-sheet sampling or branch clipping is effective at detecting L. nigrinus and estimating the seasonality of different life stages, the volume of a tree canopy is difficult to calculate, and therefore, the insect numbers based on that volume are difficult to extrapolate. The area underneath hemlock canopies is less difficult to estimate, and collections in a uniform unit area underneath the canopy allow for easier extrapolation of populations of L. nigrinus. This method can be used to estimate the number of insects per unit area for L. nigrinus and could be adapted for use with other biological control agents that have a life stage that emerges from the soil.

References Cited

1.

Ellison A, Bank M, Clinton B, Colburn E, Elliott K, Ford C, Foster D, Kloeppel B, Knoepp J, Lovett G, Mohan J, Orwig D, Rodenhouse N, Sobczak W, Stinson K, Stone J, Swan C, Thompson J, Von Holle B, Webster J. 2005. Loss of foundation species: consequences for the structure and dynamics of forested ecosystems. Frontiers in Ecology and the Environment 3: 479–486. Google Scholar

2.

Eschtruth AK, Cleavitt NL, Battles JJ, Evans RA, Fahey TJ. 2006. Vegetation dynamics in declining eastern hemlock stands: 9 years of forest response to hemlock woolly adelgid infestation. Canadian Journal of Forest Research 36: 1435–1450. Google Scholar

3.

Ford CR, Elliott KJ, Clinton BD, Kloeppel BD, Vose JM. 2012. Forest dynamics following eastern hemlock mortality in the southern Appalachians. Oikos 121: 523–536. Google Scholar

4.

Grant JF, Hakeem A, Rhea JR, Wiggins GJ, Lambdin PL, Taylor G. 2010. Recovery and establishment of introduced predators of hemlock woolly adelgid in the southern Appalachians, pp. 21–23 In Fifth Symposium on Hemlock Woolly Adelgid in the Eastern United States, 17–19 Aug 2010, Asheville, North Carolina,  http://www.na.fs.fed.us/fhp/hwa/pubs/proceedings/2010_proceedings/fifth_symposium_hwa.pdf (last accessed 8 Sep 2016). Google Scholar

5.

Hakeem A, Grant JF, Wiggins GJ, Lambdin PL, Rhea JR. 2011. Establishment and coexistence of two predators, Laricobius nigrinus and Sasajiscymnus tsugae, introduced against hemlock woolly adelgid on eastern hemlock. Biocontrol Science and Technology 21: 687–691. Google Scholar

6.

Havill NP, Vieira LC, Salom SM. 2014. Biology and control of hemlock woolly adelgid. United States Department of Agriculture, Forest Service, Forest Health Technology Enterprise Team, FHTET-2014-05,  http://www.fs.fed.us/foresthealth/technology/pdfs/HWA-FHTET-2014-05.pdf (last accessed 8 Sep 2016). Google Scholar

7.

Lamb AB, Salom SM, Kok LT. 2005. Survival and reproduction of Laricobius nigrinus Fender (Coleoptera: Derodontidae), a predator of hemlock woolly adelgid, Adelges tsugae Annand (Homoptera: Adelgidae), in field cages. Biological Control 32: 200–207. Google Scholar

8.

Lamb AB, Salom SM, Kok LT, Mausel DL. 2006. Confined field release of Laricobius nigrinus (Coleoptera: Derodontidae), a predator of the hemlock woolly adelgid, Adelges tsugae (Hemiptera: Adelgidae), in Virginia. Canadian Journal of Forest Research 36: 369–375. Google Scholar

9.

Lamb AB, Salom SM, Kok LT. 2007. Factors influencing aestivation in Laricobius nigrinus (Coleoptera: Derodontidae), a predator of Adelges tsugae (Hemiptera: Adelgidae). The Canadian Entomologist 139: 576–586. Google Scholar

10.

Mausel DL, Salom SM, Kok LT, Fidgen JG. 2008. Propagation, synchrony, and impact of introduced and native Laricobius spp. (Coleoptera: Derodontidae) on hemlock woolly adelgid in Virginia. Environmental Entomology 37: 1498–1507. Google Scholar

11.

Mausel DL, Salom SM, Kok LT, Davis GA. 2010. Establishment of the hemlock woolly adelgid predator, Laricobius nigrinus (Coleoptera: Derodontidae), in the eastern United States. Environmental Entomology 39: 440–448. Google Scholar

12.

McClure MS. 2000. Biological control of hemlock woolly adelgid in the eastern United States. United States Department of Agriculture, Forest Service, Forest Health Technology Enterprise Team, FHTET-2000-08,  http://na.fs.fed.us/fhp/hwa/pubs/fhtet/hwa_bio_control_01.pdf (last accessed 8 Sep 2016). Google Scholar

13.

McDonald D. 2010. Key cues and factors for improving HWA predator recovery efforts, pp. 7–16 In Fifth Symposium on Hemlock Woolly Adelgid in the Eastern United States, 17–19 Aug 2010, Asheville, North Carolina,  http://www.na.fs.fed.us/fhp/hwa/pubs/proceedings/2010_proceedings/fifth_symposium_hwa.pdf (last accessed 8 Sep 2016). Google Scholar

14.

Reardon R, Onken B. 2011. Implementation and status of biological control of the hemlock woolly adelgid. United States Department of Agriculture, Forest Service, Forest Health Technology Enterprise Team, FHTET-2011-04,  http://na.fs.fed.us/pubs/fhp/hemlocks/bio_control-2012.pdf (last accessed 8 Sep 2016). Google Scholar

15.

Wiggins GJ, Grant JF, Rhea JR, Mayfield AE, Hakeem A, Lambdin PL, Lamb Galloway AB. 2016. Emergence, seasonality, and hybridization of Laricobius nigrinus (Coleoptera: Derodontidae), an introduced predator of hemlock woolly adelgid (Hemiptera: Adelgidae), in the Tennessee Appalachians. Environmental Entomology https://doi.org/10.1093/ee/nvw128. Google Scholar

16.

Zilahi-Balogh GM, Kok LT, Salom SM. 2002. Host specificity tests of Laricobius nigrinus Fender (Coleoptera: Derodontidae), a biological control agent of the hemlock woolly adelgid, Adelges tsugae (Homoptera: Adelgidae). Biological Control 24: 192–198. Google Scholar

17.

Zilahi-Balogh GM, Humble LM, Lamb AB, Salom SM, Kok LT. 2003a. Seasonal abundance and synchrony between Laricobius nigrinus (Coleoptera: Derodontidae) and its prey, the hemlock woolly adelgid (Hemiptera: Adelgidae). The Canadian Entomologist 135: 103–115. Google Scholar

18.

Zilahi-Balogh GM, Salom SM, Kok LT. 2003b. Development and reproductive biology of Laricobius nigrinus, a potential biological control agent of Adelges tsugae. Biocontrol 48: 293–306. Google Scholar
Gregory J. Wiggins, Jerome F. Grant, James R. Rhea, Abdul Hakeem, and Paris L. Lambdin "A Field-Based Method to Estimate Densities of Laricobius nigrinus (Coleoptera: Derodontidae), an Introduced Predator of Hemlock Woolly Adelgid (Hemiptera: Adelgidae)," Florida Entomologist 99(4), 805-807, (1 December 2016). https://doi.org/10.1653/024.099.0442
Published: 1 December 2016
JOURNAL ARTICLE
3 PAGES


SHARE
ARTICLE IMPACT
Back to Top