|TEXAS FOREST SERVICE
A Part of The Texas A&M
How to Conduct a Southern Pine Beetle
Aerial Detection Survey
by Ronald F. Billings and James D. Ward1
1Principal Entomologist, Texas Forest Service,
and Entomologist, U.S. Department of Agriculture, Forest Service
Periodic aerial surveys of the pine timberlands of the South provide the primary means
for early detection of southern pine beetle (SPB) outbreaks. During warm months,
beetle-infested trees become visible from the air within 3-6 weeks after attack as their
crowns turn from green to yellow and eventually to orange, red, and brown (see cover).
Early detection of new infestations is the first step in controlling SPB and in reducing
This handbook explains how to plan and conduct an aerial sketchmap survey to detect new
SPB infestations (spots) throughout the beetle's range in the southern United States. It
is designed to supplement USDA Agriculture Handbook 560 entitled "An Aerial
Observer's Guide to Recognizing and Reporting Southern Pine Beetle Spots" (Billings
and Doggett 1980).
Purpose of an Aerial Detection Survey
The purpose of an aerial detection survey is to accurately locate infestations, to
determine their relative size and number, and to evaluate the need for control. This is
accomplished for SPB by conducting periodic flights over pine forests in small, fixed-wing
aircraft and plotting suspected SPB spots (groups of dead and dying pine trees) onto maps
or aerial photographs. Once detected from the air, suspected spots are visited on the
ground to confirm the causal agent and assess the need and priority for control (Billings
and Pase 1979).
In most commercial forest situations, expanding SPB spots should be controlled to avoid
additional timber losses, using one of the approved control methods of salvage,
cut-and-leave, chemical sprays, or pile-and-burn (Swain and Remion 1981).
Planning an Aerial Detection Survey
Cessna 182, a four place, high-wing monoplane commonly used for aerial
detection surveys. (Texas Forest Service photo)
The success of an aerial detection survey depends largely on preflight
preparation and planning as well as the skill and dedication of the aerial observers.
Single-engine, high-wing aircraft are commonly used for aerial
detection surveys. High-wing aircraft offer better visibility than low-wing airplanes.
Four and six-place aircraft are preferred to two-place airplanes. Survey aircraft should
be capable of slow flight since most detection surveys are flown at 90-100 mph. Survey
aircraft should be able to take off and land on relatively short runways and carry
sufficient fuel for at least 5 hours of flight. The most common survey aircraft are Cessna
Aircraft Corporation2 models 172,
182, 185, 206, and 210 (fig. 1).
2Mention of commercial products does not imply
endorsement by Digital Arborist or Texas Forest Service.
Equipment used in aerial detection surveys should be assembled in kit form and taken on
every flight. Suggested equipment includes the following:
- Maps (or photos) of area to be flown
- Colored pencils or grease pencils
- Air sickness sack or canister (coffee can)
- 35 mm camera with color film
- Small tape recorder
- Radio for ground communications
- Electronic navigational unit
- Sunglasses (yellow lenses preferred)
- Motion sickness remedy
Flight Maps and Plans
Appropriately scaled flight maps should be chosen to completely cover the area to be
flown. Aerial photographs, photo index maps, or photo mosaics also may be used. Choosing
an adequate scale is particularly important. A large-scale map such as a 7 1/2-minute
quadrangle map (scale = 1:24,000) will allow more accurate plotting but will cover a
smaller area than a 15-minute quadrangle map (scale = 1:62,500). Thus, four 7 1/2-minute
quadrangle maps will be required for the same size area covered by one 15-minute
quadrangle map. Many large scale maps, however, may present a handling problem in the
Up-to-date maps that show identifiable landmarks (roads, lakes, power lines, etc.), as
well as current features such as forest plantations and agricultural fields, are
particularly helpful for accurate plotting.
||Figure 2. Portion of a
15-minute quadrangle map showing parallel 2 1/2-mile flight lines and locations of
suspected SPB infestations. The symbol 20/1 indicates a newly detected spot having 20
visibly infested trees and a priority 1 for ground checking. (Texas Forest Service photo)
Parallel flight lines (except for very mountainous terrain) should be drawn on maps
prior to the detection flight (fig. 2). Each flight line should start and end at a
recognizable landmark, such as a road intersection, river, or power line. Depending on the
intensity of the survey, flight lines should be drawn at 1-, 2 1/2-, or 5-mile intervals
in either a north/ south (N/S) or east/west (E/W) direction. The distance between flight
lines and maximum scanning distance per observer will determine the percent coverage
(table I, page 8). If flight lines are set at intervals of 2 1/2 miles, each observer
would be responsible for detecting infestations out to a lateral distance of 1 1/4 miles
to obtain 100 percent coverage of the survey area.
If aerial photographs (scale = 1:15,840 or 1:20,000) are used, no flight lines need to
be drawn. The plane simply flies down the center of each sequential photo as the observers
scan up to 1 1/4 miles (or half the photo width) on each side of the plane.
The accuracy of sketchmapping surveys (number of spots overlooked) will depend on
various factors, including visibility, size of spots to be detected, flying altitude,
aircraft speed, and flight line interval. When detecting small spots (one to four trees),
the width of strip each observer scans should be restricted to 1/2 mile (flight lines 1
mile apart). If only spots with five or more trees are plotted, a 1- or 1 1/4-mile-wide
strip can be observed from each side of the plane (flight lines 2 to 2 1/2 miles apart)
(table 1). During periods of poor visibility or when beetle infestation levels are high,
it is best to fly lines 1 to 2 miles apart to assure complete coverage. In mountainous
terrain, it may be best to fly along contours rather than to follow parallel flight lines.
The space in survey aircraft is limited. Thus, an efficient way to handle bulky survey
maps or aerial photo files should be developed in advance of the survey flight. Large maps
can be folded once parallel to the flight lines and then fanfolded into smaller sections
perpendicular to the flight lines. This method has certain disadvantages, however. Flight
lines laid out near the lengthwise fold are difficult to follow unless the maps are
refolded. Also, if used for numerous surveys, maps may become worn and information lost at
Another approach is to cut the survey maps into strips of a convenient size. Strips
covering the planned flight route are pasted end-to-end and deployed on a map-rolling
device (fig. 3). The observer winds the roller knobs to advance the strip and plots the
desired information on the flat writing surface.
Prior to the second and for subsequent detection flights in a given year, flight maps
should be updated to show the current status of all previously detected spots. By marking
which spots have recently been reported as controlled or inactive, the observer can check
these spots during the aerial survey to determine whether there are any reinfestations
(breakouts). Suggested symbols for use on SPB flight maps are listed in table 2, shown on
Visual orientation over flat, poorly defined terrain can be difficult. Accurate
navigation can be assured by installing and using electronic navigation systems in the
survey aircraft. The most dependable and useful of these systems is portable and can be
easily installed in different aircraft (Dull 1980).
Table 1. - Percent coverage for increasing flight intervals
and observation limits in survey flights with two observers.
Percent coverage if each observer scans
1 1/4 mile
2 1/2 miles
||Figure 3. A map-rolling
device, specifically designed for long straight flight lines over flat terrain, aids the
handling of survey maps during aerial detection surveys (Texas Forest Service photo).
Frequency of Flights
The frequency and timing of aerial detection flights will depend upon several factors,
including the season of the year, level of SPB activity, and geographic location. In the
western gulf coastal States, SPB may be active throughout the year, but the rate of crown
discoloration and the abundance of new spots vary seasonally. Most new infestations become
visible to aerial observers between April and September (fig. 4A). Accordingly, detection
flights may begin as early as April and continue at intervals of 4 to 6 weeks until
hardwood foliage begins to change color in the fall.
The detection of new spots is hampered during early spring months when hardwood trees
are leafing out and again in the fall when the foliage of hardwood and cypress trees
discolors. Also, new spots are small, scattered, and difficult to detect from December
through March. Thus, peak detection typically occurs during May, June, and July. During
outbreak years, however, a midwinter detection flight may be useful to locate large
overwintering infestations or new spots that were initiated during the previous fall.
In the Atlantic Coastal Plain and Piedmont regions of North Carolina, South Carolina,
Virginia, and Tennessee, peak detection occurs in late summer. In these States, one summer
detection flight near the end of June and a second in late September are usually
sufficient (fig. 4B, page 11). A midwinter flight also is useful during outbreak years to
pinpoint the location of overwintering beetle populations. Spots detected in this winter
flight should be controlled prior to beetle dispersal in the spring.
Table 2. - Suggested symbols to use on SPB flight maps
1Some organizations prefer to use a square
symbol to indicate that a spot's location may not be accurately plotted.
Figure 4. Seasonal detection patterns
for southern pine beetle infestations in gulf coastal areas (A) and southeastern, Piedmont
and mountain areas (B). Arrows indicate recommended (I) and optional (I) flight dates for
Attributes of an Effective Aerial
A trained aerial observer is the key to a successful SPB detection survey. Attributes
of an aerial observer should include:
- A working knowledge of SPB and its infestation characteristics at different seasons.
- An ability to recognize SPB infestations from the air and to distinguish them from
damage due to other causes (see Billings and Doggett 1980).
- A willingness to fly and not be abnormally subject to motion sickness.
- Good eyesight and normal color perception (not color blind).
- An ability to read maps and to orient between air and ground. Local knowledge of the
area to be flown is particularly useful for accurate plotting.
- At least 50 hours in the air and similar experience on the ground participating in
routine detection and evaluation surveys.
Training is essential to prepare new workers to be effective aerial observers. Training
sessions should include instructions on how to use maps and how to recognize and evaluate
SPB spots from the air. Color slides showing examples of SPB spots at different times of
the year and in different stages of development provide effective training aids. But
proficiency at aerial detection must ultimately come from actual experience in the air.
Conducting an Aerial Detection Survey
The number of observers required for a detection survey may vary from one to three.
Over flat terrain, a common arrangement is to use three observers. One observer sits in
the right front seat of the plane and acts as a navigator to keep the pilot on course.
From the rear seat, the other two observers detect and map those infestations visible on
their respective sides of the aircraft. If only two observers are used, either observer
can inform the pilot if the plane strays from the designated flight line. For training
purposes, a trainee/observer may be seated in the right rear seat behind an experienced
navigator/observer. In this manner, comparisons can be made of plotting accuracy between
an experienced observer and a trainee.
Scheduling Detection Flights
Weather can greatly affect survey efficiency and accuracy. Cloudy, overcast conditions
reduce visibility. Turbulent conditions cause physical discomfort, often resulting in
disorientation. The pilot should avoid flying through clouds and during thunderstorms.
Surveys should be scheduled for clear days with low wind velocities and minimal haze,
if possible. They should be conducted between 9:00 a.m. and 3:00 p.m. to avoid long
shadows. To reduce observer fatigue, survey flights should last no more than 4 consecutive
hours without landing. Two shorter flights on consecutive days, for example, are likely to
be more effective than one long, uninterrupted flight.
For SPB detection surveys, the altitude of flight above ground will depend on weather
conditions and the size of infestations to be reported. If visibility is good, an altitude
of 1500-3000 feet is preferred for detecting and evaluating multiple-tree infestations
containing 10 or more trees. Under overcast or partially cloudy conditions or if smaller
infestations (less than 10 trees) are to be recorded, flight altitudes will need to range
from 1000-1500 feet above the ground.
Lower flight altitudes, however, make it more difficult to pick out key landmarks and
maintain orientation. Also, historical records in Texas show that small infestations (one
to five trees) are soon vacated by SPB or are caused by agents other than SPB. In
contrast, spots most likely to expand and require control tend to have 10 or more trees at
detection, particularly in mid- to late summer months. Therefore, the lower size limit of
infestations to be plotted (detection threshold) is often set at 10 trees. These
"high priority" spots are detectable from higher altitudes.
Plotting SPB Infestations
When areas of dead or dying pine trees are located from the air, the observer should:
- decide whether or not the infestation is likely to be an SPB spot.
- check the map to see whether it has been plotted on an earlier flight.
- look for signs of recent beetle activity (yellow-crowned trees except during winter
- estimate the relative size of the spot (total number of dead and/or infested trees) and
record this estimate on the map next to the spot location.
- assign a ground check priority to the spot and record this on the map.
If the spot appears to be an SPB infestation, meets the minimum spot size to be
recorded (detection threshold), and contains signs of recent attacks, the location of the
spot should be plotted on the map as accurately as possible using an appropriate symbol
(table 2, page 10). The observer should take note of visible landmarks (road
intersections, clearings, powerlines, etc.) to assure accurate plotting. During spring,
summer, and fall surveys, the presence of pines with fading (yellow) crowns indicates
spots with recent beetle activity and those most likely to expand. During winter and early
spring months, yellow-crowned trees may not be visible and a large portion of the beetle
population will reside in red or bare-crowned trees.
An estimate of the relative size of the spot should be listed next to the spot location
on the map (fig. 2). Two methods exist for estimating spot size. One is to record the
total number of dead and dying trees which is indicative of the amount of salvageable
timber. The other method is to note only those trees with red and yellow crowns but not
those having lost most or all of their foliage. This latter method provides a better
measure of trees that still contain beetles. (Admittedly, during summer months most
beetles will have emerged from trees with red crowns. However, inclusion of red-crowned
trees in the spot size estimate will help to compensate for those recently infested trees
that still may have green crowns. Such green-crowned trees may harbor a sizeable portion
of the beetle population in the spot, but are indistinguishable from unattached trees to
the aerial observer.)
Before selecting one method for estimating spot size over the other, check the survey
policy of your organization. And be sure to inform the ground crews of which system you
use. Finally, a priority for ground checking is assigned to the spot (fig. 2, page 7).
Details on how to recognize SPB spots and set ground check priorities from the air are
given in USDA Agriculture Handbook 560 (Billings and Doggett 1980).
To accurately determine the location of the spot, it often is necessary to depart from
the N/S or F/W flight line and circle the spot. Once the spot is mapped correctly, the
aircraft should be returned to the flight line and the survey resumed. The need for
accurate plotting cannot be overemphasized. A misplotted spot can cause ground crews to
waste many hours searching for a spot in the wrong area.
The same set of maps should be used throughout the season. This way, previously
detected spots will not be reported more than once. Furthermore, spots reported as
controlled or inactive can be observed for signs of renewed beetle activity (breakouts) in
later flights. Also, spots plotted on maps from previous flights may serve as landmarks in
large roadless areas.
A pencil with a different color lead should be used for each flight to avoid confusion
among different detection flights. For each survey flight, the flight map should be noted
to indicate flight date, color of pencil used to plot spots, names of observers, and any
unusual conditions (bumpy, hazy, etc.).
Reporting and Evaluating
Once a detection flight has been completed, the spot locations, numbers of affected
trees in each spot, and other pertinent information should be provided to ground crews. It
is recommended that inexperienced aerial observers also participate in ground check
activities to share in the frustrations associated with poorly plotted spots.
To aid interpretation and evaluation, survey results should be summarized in table form
by spot size for each area flown. The summary should show number of spots in increasing
spot size classes, as shown in table 3. If a 10-tree detection threshold is used, common
spot size categories would be 10, 11-20, 21-50, 51 + trees. Particular attention should be
paid to spots with more than 20 actively infested trees, since these are likely to account
for a majority of the timber losses if left uncontrolled. One significant statistic
obtained from the aerial survey is the number of spots (or infested trees) per 1000 acres
of host type. This statistic is useful for evaluation of the level of SPB activity in an
area, for comparison between areas, or for comparison of number of spots between detection
flights over the same area. In general, when the SPB population level exceeds one spot per
1000 acres of host type, beetle activity is considered to have reached an outbreak level.
Table 3.Suggested format for summarizing aerial
survey data from a single SPB defection flight
(number of redtops and faders)
... number of
Late Season Evaluation Flight
During years when beetle populations are high, it may be useful to conduct a late
season evaluation flight just prior to hardwood foliage fade. The main purpose of this
survey is to revisit all previously detected spots that have yet to be reported as
inactive or controlled. Each spot should be reevaluated for evidence of recent beetle
activity. If needed, a new spot size estimate and ground check priority should be assigned
to each spot.
In many cases, spots which appeared active at first detection may no longer contain
yellow-crowned trees by the end of the summer. Such spots can be assigned a low ground
check priority, or considered as inactive. In contrast, other spots that appeared small in
early summer may have expanded to considerable size by September, requiring urgent
attention (Billings 1979). Methods for updating spot size and priority data on flight maps
are shown in table 2.
- Decide on area to be flown.
- Delineate parallel flight lines at equidistant intervals (N/S or E/W) on maps of
appropriate scale and prepare maps for convenient use in the aircraft.
- Prior to each flight, update flight maps to show previously detected spots that have
recently been controlled or found to be inactive.
- Schedule flight for good, clear weather during the appropriate season.
- Request an experienced pilot and proper aircraft and schedule a preflight briefing so
the pilot and navigator clearly understand where to go and what will be done.
- Limit duration of each flight to no more than 4 hours.
- Stay on flight lines, except to circle suspected spots when needed to assure accurate
- Record location of detected spots on map, together with estimate of spot size and
priority for ground checking.
- Take advantage of flight to inspect previously controlled spots for breakouts or to
reevaluate uncontrolled spots; also, replot any spots from previous flight that ground
crews were unable to locate.
- Report detection information to ground crews promptly.
Aldrich, R.C.; Helter, R.C.; Bailey, W.F. Observation limits for aerial
sketchmapping southern pine beetle damage in the southern Appalachians. Jour. For.
Anonymous. Detection of forest pests in the southeast. Atlanta, Ga:
U.S. Department of Agriculture, Forest Service, State and Private Forestry, Southeastern
Area. 51 p.; 1970.
Billings, R. F. Detecting and aerially evaluating southern pine beetle
outbreaks: operational guides. South. J. Appl. For. 3:50-54; 1979.
Billings, R. F.; Doggett, C. An aerial observer's guide to recognizing
and reporting southern pine beetle spots. Agriculture Handbook No. 560. Washington, D.C.:
U. S. Department of Agriculture, Forest Service; 1980. 19 p.
Billings, R. F.; Pase III, H. A. A field guide for ground checking
southern pine beetle spots. Agriculture Handbook No. 558. Washington, D. C.: U. S.
Department of Agriculture, Forest Service; 1979. 19 p.
Dull, C. W. Loran-C radio navigation system as an aid to southern pine beetle surveys.
Agriculture Handbook No. 567. Washington, D. C.: U. S. Department of Agriculture, Forest
Service; 1980. 15 p.
Klein, W. H.; Tunnock, S; Ward, J. G. D.; Knopf, J. A. E. Aerial sketchmapping. Forest
Insect and Disease Survey Methods Manual. Washington, D. C.: U. S. Department of
Agriculture, Forest Service; 1983. 15 p.
Swain, K. M.; Remion, M. C. Direct control methods for the southern pine beetle.
Agriculture Handbook No. 575. Washington, D. C.: U. S. Department of Agriculture, Forest
Service; 1981. 15 p.
Issued June 1984
Modified for Internet August 1998