Remote sensing and spatial analysis represent useful tools for modeling species’ dispersal, characterizing the spread of invasions and the invasability of a region, and thus allowing more accurate predictions for developing mitigation strategies. American chestnut,
Exotic species invasions pose a substantial threat to biological integrity and sustainability. In our increasingly global economy, the rate of species’ invasions is increasing exponentially, compromising biodiversity and altering ecosystem function. Non-native invasive species can affect plant, animal, and human health, and these invasions can have devastating economic impacts (
Emerging technologies such as remote sensing improve our ability to better understand factors influencing an invasion, including the invasability of an area, the dynamics of an invasion, predictions about invasiveness (
To predict the impacts of the invasive hemlock woolly adelgid,
American chestnut,
However, chestnut is again under threat from an additional exotic invader, the Asian chestnut gall wasp (ACGW),
Since its initial introduction into North America in Peach County, Georgia, in 1974, the gall wasp has spread throughout the natural range of American chestnut (
On a localized scale, gall wasps disperse by active flight. Winds play a crucial role in influencing adult cynipid flight, with the direction of dispersal being consistent with that of prevailing winds (
In 2010 the Asian chestnut gall wasp was discovered on a single Chinese chestnut in Lexington, Kentucky (USA). Lexington lies in the heart of the Bluegrass Region (
The city of Lexington, Kentucky was systematically surveyed for
Data on chestnut location and condition were georeferenced and included in a GIS using ArcGIS10 (ESRI, Redlands, CA, USA). Additional data obtained for spatial analysis included Fayette County boundaries, major roads, topographic information and digital orthoimages from the Kentucky Geographic Network website (
These additional data were combined with the results of our survey using ArcGIS10 to produce maps. Digital elevation models were used to visualize slope and aspect (9.1 m = 30 ft DEM) and land shape (high resolution 1.5 m = 5 ft DEM). Land shape was visualized by applying a dynamic range adjustment to the DEM (
Wind direction and speed were extracted from the monthly climatological data of the Kentucky Climate Center (
Our survey revealed the presence of 27
In 2010 the gall wasp was found only on a single tree (L17) facing southeast (
The trees newly infested in 2011 had very low gall wasp populations, and were 700 - 2700 m from the source tree, in a primarily south-southwest direction (
There was a 12 days period of adult gall wasp flight in 2010 (June 23 - July 4) during which ambient conditions were relevant. The average daily temperature during this period was 24.3 °C, well within the acceptable temperature range for adult wasp flight (
In 2010 we located a single heavily gall-infested source tree. In 2011, sixteen of the 21 trees (76%) located southwest and east of the source tree were infested. Prevailing winds during adult flight (June 23 - July 4, 2010) were sufficient to account for the pattern of gall wasp-infested chestnuts documented in our surveys (
Our data suggest that proliferation of the gall wasp through the city of Lexington was determined by host plant distribution and was strongly affected by prevailing winds. Wind is a well-documented factor influencing insect dispersal (
Not all hosts southwest of the source tree were infested. The gall-free trees L08 and L09 were heavily pruned in winter 2010, potentially removing infested buds and locally extinguishing the gall wasp population. Trees L1, L2, L3 and L20 are surrounded by vegetation that may have perturbed wind flow, disrupting exposure to prevailing winds that would carry adult wasps and lead to gall wasp infestations. Vegetation, buildings, and other windbreaks do impact local insect movement (
The maximum distance the gall wasp dispersed in Lexington during the 2010 flight period was the distance between the source tree L17 and the L4 L5 L6 cluster, approximately 3 km (
We used remotely sensed data and GIS technology to characterize local proliferation of a newly arrived exotic insect, the Asian chestnut gall wasp, attacking a sporadically occurring tree in the Bluegrass Region of Kentucky. We sought to understand how host plant distribution, landscape characters, and prevailing winds might influence the gall wasp’s spread in the formative stages of the invasion and barring movement of infested plant material by humans.
This is the first use of remotely sensed data and GIS analysis to document movement of the invasive Asian chestnut gall wasp. Our analysis provides insight into factors that affect the local spread and proliferation of the gall wasp in a newly invaded area. The gall wasp colonized 17 sporadically distributed hosts found at a very low density within a 40 km2 area. Our analysis demonstrates how the invasiveness of the gall wasp is enhanced by abiotic factors. This work will provide a useful tool and model system to test hypotheses and to make predictions about the spread of this invasive pest on local scale, leading to appropriate mitigation efforts.
The authors thank Demetrio Zourarakis for assistance with experimental protocol, Melanie Sprinkle for field assistance, and Josh Adkins, Luke Dodd, and two anonymous referees for reviewing early versions of this manuscript. This work was funded in part by the Italian Fulbright Commission (to IG), the Northern Nut Grower’s Association, the American Chestnut Foundation, the USDA Forest Service, and McIntire Stennis Funds from the Kentucky Agricultural Experiment Station, and is published as Experiment Station Project 12-08-032.
Distribution and spread of the Asian chestnut gall wasp in North America since its introduction in 1974 (updated: December 2011).
Area in Lexington, KY, surveyed for
Location of
Digital elevation modeling (1.5 m resolution) demonstrates that chestnut occurs at relatively consistent elevations in the study area. See also
Hypothesized movement of the chestnut gall wasp in Lexington in the period June 23 - July 4 2010, resulting in newly infested trees in 2011.
Location and characteristics of
No. | Chestnutspecies | Location | Setting | Elev (m) | Slope (%) | Aspect | Height (m) | Diametera (cm) | Crownconditionb | ACGWinfestationc | Initial report (yr) |
---|---|---|---|---|---|---|---|---|---|---|---|
L01 |
|
Arboretum | park | 317.6 | 5.8 | S | 2 | 5 | 1 | none | - |
L02 |
|
Arboretum | park | 318.3 | 3.7 | S | 4.5 | 14 | 1 | none | - |
L03 |
|
Arboretum | park | 318.3 | 3.4 | S | 3 | 7 | 1 | none | - |
L04 |
|
Arboretum | park | 318 | 1.5 | W | 5 | 12 | 1 | low | 2011 |
L05 |
|
Arboretum | park | 318.2 | 1.4 | W | 4 | 9 | 1 | low | 2011 |
L06 |
|
Arboretum | park | 317.9 | 1.1 | W | 8.5 | 26 | 2 | low | 2011 |
L07 |
|
Cooper | yard | 313.2 | 4.5 | NE | 10 | 46 | 1 | low | 2011 |
L08 |
|
Cooper | yard | 318.3 | 2.9 | NW | 5.5 | 25 | 1 | none | - |
L09 |
|
Cooper | yard | 319.1 | 1.3 | W | 5.5 | 26 | 1 | none | - |
L10 |
|
Cassidy | street | 316.6 | 0.2 | NE | 8 | 32 | 1 | low | 2011 |
L11 |
|
Cassidy | street | 316.4 | 0.6 | SE | 8 | 38 | 2 | low | 2011 |
L12 |
|
Cassidy | street | 316.4 | 0.6 | SE | 8.5 | 42 | 2 | low | 2011 |
L13 |
|
Cassidy | street | 316.2 | 1.3 | NE | 9 | 38 | 2 | low | 2011 |
L14 |
|
Cassidy | street | 316.1 | 2.2 | NW | 9.5 | 44 | 2 | low | 2011 |
L15 |
|
Cassidy | street | 316.1 | 2.4 | NW | 9.5 | 37 | 2 | low | 2011 |
L16 |
|
Fontaine | yard | 315.7 | 3.5 | NE | 8.5 | 32 | 1 | low | 2011 |
L17 |
|
Fincastle | yard | 310.3 | 3 | SW | 8.5 | 31 | 2 | high | 2010 |
L18 |
|
Oldham | yard | 303.7 | 0.5 | NW | 13.5 | 38 | 2 | low | 2011 |
L19 |
|
Oldham | yard | 304.4 | 0.6 | W | 8.5 | 22 | 1 | low | 2011 |
L20 |
|
Arboretum | park | 316.7 | 6.4 | SW | 1.5 | 4 | 1 | none | - |
L21 |
|
Tateswood | yard | 308.5 | 2.9 | S | 11 | 39 | 1 | low | 2011* |
L22 |
|
Garden | yard | 314.1 | 2 | SW | 3.5 | 6 | 1 | low | 2011* |
L23 |
|
Garden | yard | 313.9 | 2 | SW | 6.5 | 22 | 2 | low | 2011* |
L24 |
|
Garden | yard | 314 | 2 | SW | 7.5 | 22 | 2 | low | 2011* |
L25 |
|
Wilson | yard | 307 | 5.5 | NE | 8.5 | 30 | 2 | none | - |
L26 |
|
Wilson | yard | 306.5 | 4 | NE | 7.5 | 30 | 3 | none | - |
L27 |
|
McConnell | woods | 282.4 | 13.2 | N | 4 | 7 | 1 | none | - |
Ambient conditions in Fayette Co., KY (USA), during the adult flight period of
Date | Mean T(°C) | Precipitation(mm) | Solar radiation(MJ/m2) | Humidity | Winddirection | |
---|---|---|---|---|---|---|
minimum (%) | maximum (%) | |||||
23-Jun | 27.3 | 0 | 27.5 | 47 | 90 | SW |
24-Jun | 25.8 | 4.6 | 17.5 | 48 | 88 | W |
25-Jun | 24.8 | 0 | 29.5 | 40 | 86 | NNE |
26-Jun | 25.4 | 0 | 27.4 | 50 | 95 | SW |
27-Jun | 27.6 | 0 | 25.7 | 57 | 89 | SW |
28-Jun | 24.2 | 3.8 | 15.9 | 63 | 96 | WSW |
29-Jun | 24.9 | 0 | 24.6 | 39 | 98 | NW |
30-Jun | 21.3 | 0 | 30 | 38 | 83 | NE |
1-Jul | 20.1 | 0 | 31.2 | 32 | 77 | NE |
2-Jul | 20.8 | 0 | 31.5 | 31 | 78 | ENE |
3-Jul | 23.7 | 0 | 27.8 | 37 | 75 | SSW |
4-Jul | 25.7 | 0 | 24.8 | 47 | 93 | SSW |