Survivability of the Subterranean Termite Heterotermes aureus
(Snyder) (Isoptera: Rhinotermitidae) When Exposure to Different
Temperatures and Relative Humidity
August 16, 2005
BRIAN E. WEEKS_ & PAUL B. BAKER
Department of Entomology
ABSTRACT.
Survivability of Heterotermes aureus (Snyder) was tested under varying temperature and
relative humidity regimes in laboratory incubators over seven day periods. Initial tests
showed that RH had a strong influence on H. aureus survival. Survival was significantly
higher (P<.05) at 90% RH than 50% RH when held at a constant temperature of 29.4o C.
Four temperatures were tested at a constant RH of 90%. Survival was highest at
temperatures of 19.4oC (91.8%) and 21.1oC (97.3%). Survival was significantly lower for
the higher ranger temperatures of 29.4oC (91.2%) and 32.2oC (69.2%).
Key Words-_ Termite, Heterotermes aureus, Temperature, Relative Humidity, Survival
INTRODUCTION
Getting Heterotermes aureus to survive for long periods in the laboratory can be a
challenging task. H. aureus is much more difficult to keep alive compared to many other
termite species and keeping them alive is essential for laboratory bioassays (Baker 2001).
In order to conduct laboratory experiments it is necessary to determine what temperature
and humidity levels will optimize H. aureus survival. Few studies have looked at how
termites respond to temperature and moisture changes. Smith and Rust (1994) found
western subterranean termites Reticulitermes hesperus to prefer temperatures between 29
and 32oC and that these termites were never found at temperatures of 40oC in the field.
__________________________________
This is a part of the University of Arizona College of Agriculture 2006 Turfgrass and Ornamental Research
Report, index at: http://cals.arizona.edu/pubs/crops/az1421/
Strack and Myles (1997) determined that the eastern subterranean termite Reticulitermes
flavipes remained active from temperatures ranging from 20oC to 10oC but slowed when
temperatures reached 5oC. Mackay et al. (1986) concluded that subterranean termites in
the Chihuahuan Desert of New Mexico did not respond to soil temperature differences
and that most of the variation in soil surface activity was due to soil moisture.
Only one study has looked directly at how temperature and moisture differences affect
H. aureus. Haverty (1974) looked at how temperature differences in the laboratory and
soil moisture differences in the field affected H aureus foraging activity. His study
concluded that H aureus forages maximally at a temperature between 28 and 32o C in the
laboratory and that foraging intensities in the field increase with increasing soil moisture.
Our objective was to determine a temperature/RH regime at which Heterotermes aureus
survived best.
MATERIALS AND METHODS
Experimental chambers were cylindrical, clear plastic containers of 5 cm diameter and
depth of 3.5 cm were used in which substrate and termites were placed (Figure 1). A 4
cm hole was burned in the top of each container with a soldering iron and then covered
with nylon gauze (the gauze became attached to the molten plastic) for ventilation of the
chamber. Fifty grams of sterilized sandy loam soil was placed in each container along
with an 8 cm2 wedge of filter paper for food. Five ml of distilled water was then placed
on the filter paper in order to provide the introduced termites with an initial moisture
source. The initial moisture source was necessary after preliminary tests show that H.
aureus becomes desiccated by dry soil and dies very quickly (< 8 hours) after exposure.
All termites used in the study were collected from cardboard rolls at a single location 20
miles southwest of Tucson, Arizona on 27 March 2002. After the termites were collected,
they were stored at room temperature (ca. 25oC) in plastic buckets for 24 hours prior to
being used in the study. One hundred undifferentiated workers of H. aureus were put in
each container immediately after adding moisture and were placed in the appropriate
incubator. There were 10 replications of this setup for each temperature/RH regime. Tests
were run in two PercivalTM incubators that could be controlled for temperature and RH.
An OnsetTM humidity logger was placed inside an empty experimental chamber within
both incubators to determine any differences from incubator settings. The first test was
run to determine survivability between RH of 50% and 90% at 29.4 oC (Table 1). After
analysis showed that survival was highest at 90% RH, a second test was set up at four
different temperatures with RH held constant at 90% (Table 2). Another 10 replications
were left out of the incubator and were made up with no soil or filter paper and only
contained termites. These replications served as controls to contrast with the incubator
tests. All tests lasted for 7 days at the end of which the termites were taken out of the
containers and counted. Those termites still showing movement were counted as alive
while those showing no movement were counted as dead.
RESULTS
Tests of RH effects on H. aureus proved conclusive in showing that H. aureus survives
best in higher humidity environments. Relative humidity loggers in the experimental
chambers showed a complete symmetry with the incubator settings. Thus the chambers
themselves had no effect on temperature or RH. Tests run at 50% RH/29.4oC had no
survival after 24 hours while tests run at 90%RH/29.4oC had significantly (P<.05) higher
survival after 7 days (Table 1). Temperature appeared to have less influence on H. aureus
survival but tests did show a significant difference (P<.05) between the four temperatures
tested at 90% RH (Table 2). Survival was highest (97.3%) at 21.1oC, which significantly
differed (P<.05) from survival at 19.4oC (91.8%), 29.4oC (91.2%) and 32.2oC
(69.2%).Termites in the chambers left out of the incubators with no soil or filter paper
began to die at 24 hours and complete mortality had taken place by 72 hours.
DISCUSSION
Relative humidity appears to have more of a key role in H. aureus survival than
temperature. This significance was seen in preliminary tests for this study where H
aureus were exposed to dry soil with no added moisture. The termites died much more
quickly (<8 hours) than those left in chambers with no soil (<72 hours).This does not
mean H. aureus cannot survive in dry soil. When access to a moisture source was given,
the termites survived well. Although temperature did play a role in H aureus survival, it
is likely that finding access to a moisture source is highest priority in a frequently dry
environment and that H. aureus is well adapted to the extremes in temperature
encountered in the desert Southwest. This suggests that H aureus colonies must always
have access to a moisture source such as deep soil layers and plant roots especially during
long, dry periods.
Haverty (1974) suggested that H. aureus foraging intensity increases with temperature
to a limit of 32oC. Our findings suggest that although foraging intensity may increase
with increasing temperatures, survival is best at the lower range of the temperatures
presented. At the temperature of 32.2oC/90%RH survival decreased significantly and we
suspect with even higher temperatures it would rapidly decline even further. Those
wanting to maintain laboratory populations of H. aureus can increase survival for longer
periods by keeping RH at a high level (around 90%) and keeping temperature moderated
at around 21oC.
_ B. Weeks, Clemson University, Clemson, S.C.
LITERATURE CITED
Baker, P. B. 2001. Laboratory rearing of winged adults, and pre-soldiers of Heterotermes
aureus snyder (Isoptera:Rhinotermitidae). Pan-Pacif. Entomol. 77(4):277.
Haverty, M. I. 1974. The significance of the subterranean termite, Heterotermes aureus
(Snyder), as a detritivore in a desert grassland ecosystem. Ph. D. Dissertation,
University of Arizona.
Mackay, W. P. S. Silva, D. C. Lightfoot, M. I. Pagani, and W. G. Whitford. 1986. Effect
of increased soil temperature on a desert soil arthropod community. Am. Mid.
Nat. 116(1): 45-46.
Smith, J. L. and M. K. Rust. 1994. Temperature preferences of the western subterranean
termite, Reticulitermes hesperus (Banks). Journ. Arid Environ. 28(4): 313-323.
Strack, B. H. and T. G. Myles. 1997. Behavioural responses of the eastern subterranean
termite to falling temperatures (Isoptera: Rhinotermitidae). Proc. Entomol. Soc. of
Ontario. Dec, 1997; 128: 13-17.
Footnotes
Table 1. Heterotermes aureus survival at RH of 50% and 90% at a constant temperature
of 29.4oC
Temperature (oC)
RH
Mean Percent Survival1
29.4
50%
0.0±0.0
a
29.4
90%
96.1±1.1
b
1
Means followed by different letters are significantly different at p<.05(Duncan).
Table 2. Heterotermes aureus survival at four different temperatures with a constant
RH of 90%.
Temperature (oC)
RH
Mean Percent Suvival1
19.4
90%
91.8±1.4
ab
21.1
90%
97.3±1.3
a
29.4
90%
91.2±2.2
b
32.2
90%
69.2±2.7
c
1
Means followed by different letters are significantly different at p<.05(Duncan)
Figure Caption: Experimental chamber setup
Figure 1
Nylon Gauze (4cm hole)
3.5cm
Filter Paper
Sterilized Soil
(50g)
5cm