DOI: 10.13102/sociobiology.v65i1.2095Sociobiology 65(1): 108-111 (March, 2018) Special Issue

Open access journal: http://periodicos.uefs.br/ojs/index.php/sociobiology
ISSN: 0361-6525

Suitable Light Regimes for Filming Termites in Laboratory Bioassays

Introduction

Laboratory bioassays require methods to keep animals 
in conditions as close as possible to their natural ambiance, 
so that to minimize stress and keep individuals alive as long 
as the test demands. However, some experimental procedures 
do require unnatural, potentially stressful conditions, such as 
the illumination demanded for video recordings of termite 
behavior. After all, by living inside nests and galleries and 
foraging only inside tunnels, most termites are better thought 
as accustomed to dark than to light conditions. Illumination 
normally needed for video recordings would, hence, be a 
potential source of stress for these insects.

In fact, termite workers and soldiers – the castes normally 
used in bioassays – show some aversion to open air conditions, 
ducking to darker places when their mound is opened (Williams, 
1959) or when exposed to incandescent light in experimental 
arenas (Park & Raina, 2005). Being eyeless, these termites 
would not be thought to be bothered by light, escaping to 
darken areas for reasons other than typical photophobia. Further 
studies, however, have shown that ultraviolet light percolating 

Abstract
Laboratory bioassays require strategies to minimize stress and keep animals 
alive as long as the test demands. Sometimes, however, experimental procedures 
seem notoriously stressful as, for instance, when exposing termites to the 
illumination needed for video recordings. Being a condition opposed to what 
termites naturally experience, light might easily stress such insects or might 
not affect them at all, as they are blind. Here we check for the effects of 
distinct light regimes on the survival of termites confined in a typical bioassay 
setup involving footage. The survival of Cornitermes cumulans (Termitidae: 
Syntermitinae) workers kept in the dark, or subjected to infrared or to cold 
white light was compared, finding no statistical difference in their survival 
in these three treatments. While pointing directions for further research 
on the reasons for such results, we conclude that video recordings of C. 
cumulans termite workers can be conducted under infrared or cold white 
LEDs, as these light regimes do not affect the survival of tested individuals. 

Sociobiology
An international journal on social insects

YC Carvalho, LO Clemente, MP Guimarães, O DeSouza

Article History

Edited by
Gilberto M. M. Santos, UEFS, Brazil
Received                  26 September 2017
Initial acceptance   06 January 2018
Final acceptance     06 January 2018 
Publication date     30 March 2018

Keywords 
Cornitermes cumulans, infrared, LED, 
Isoptera.

Corresponding author
Og de Souza
Lab of Termitology 
Depto Entomology 
Federal University of Viçosa
CEP 36570-900, Viçosa-MG, Brazil
E-Mail: og.souza@ufv.br

through the unpigmented cuticle of Reticulitermes spp. can 
harmfully react with an alkaloid norharmane present in their 
hemolymph, impairing these termites’ survival (Siderhurst et 
al., 2006)

Whether or not unpigmented termites other than 
Reticulitermes would equally be harmed by UV-light 
exposure, remains to be tested. After all, norharmane is 
produced by endosymbionts (Siderhurst et al., 2005) whose 
species composition varies across termites (Ohkuma, 2008). 
It also remains to be tested whether other electromagnetic 
wavelengths could harm termites as UV-light does.

On the other hand, even species such as Coptotermes 
formosanus, presenting low norharmane amounts (Itakura et 
al., 2008), do show aversion to light (Park & Raina, 2005), 
reinforcing the idea of light as a potential source of stress, 
irrespective of norhamane content, at least for the so called 
“lower termites”.

On their turn, many “higher termites”, belonging to the 
family Termitidae, present unpigmented workers and cryptic 
habits similar to those of Reticulitermes and Coptotermes, 
being hence potentially affected by light exposure. Among 

Lab of Termitology, Department of Entomology, Federal University of Viçosa, Viçosa-MG, Brazil

RESEARCH ARTICLE - TERMITES

mailto:og.souza@ufv.br


Sociobiology 65(1): 108-111 (March, 2018) Special Issue 109

these, the Neotropical Cornitermes cumulans, would seem 
to deserve attention. Being easily captured from conspicuous 
and populous nests, this species large individuals allow video 
recording without macro lenses, and are hence an obvious 
choice for lab bioassays footage. Miramontes et al. (2014), for 
instance, studying patterns of spatial exploratory behavior 
in individual termites, video-recorded the movement of C. 
cumulans workers continuously for 5-6 hours. In order to 
accurately track every termite cartesian location during the 
assay, the arena was constantly illuminated by a cold white 
fluorescent lamp.

 Here we intend to contribute to this type of study, 
testing the effects of distinct light regimes on the survival of 
C. cumulans workers confined in arenas, as typically done 
in many lab bioassays. Three light regimes were tested: no 
lights (i.e. darkness), infrared, and cold white lights. Infrared 
illumination is the closest to darkness an affordable camera 
could record whereas cold white illumination is suitable to 
footage by any type of camera. If C. cumulans is harmed by 
illumination (as in Reticulitermes affected by UV-lights), we 
expect their survival to differ between these light regimes, no 
difference in survival being found otherwise. 

Materials and Methods

Focal species

C. cumulans live inside epigeous nests and feed on 
living and dead grasses and herbs, which they reach through 
subterranean tunnels, occasionally foraging under a fine layer 
of soil-sheeting (de Negret & Redford, 1982). Their mounds 
are abundant in grasslands in the Neotropics, and are found 
in pastures, monocultures, savannas (Araujo, 1970) and even 
in gardens in urban areas. This species builds mounds with a 
very hard outer shell of soil which surrounds a soft inner core 
of carton (fecal material, comminuted plant material and bits 
of soil) (de Negret & Redford, 1982). C. cumulans is a key 
species in grasslands, providing stable and predictable shelter 
for other termites, invertebrates, and vertebrates (Redford, 
1984; Campbell et al., 2016). 

Data collection

The study was carried out in Viçosa, in the state of 
Minas Gerais State, Southeastern Brazil, located at 20º45’ S 
42º51’ W, in the facilities of the Lab of Termitology, Federal 
University of Viçosa (‘UFV’ in Brazilian acronym). The 
experiment aimed to verify the effect of distinct illumination 
regimes on the survival of C. cumulans workers kept in Petri 
dishes in the lab. Termites were collected from colonies found 
in the UFV’s campus on three occasions: 30 May, 2nd June 
and 5th June 2017. Fragments from three different nests were 
collected per date, totaling nine nests. Each nest fragment was 
taken to the lab, where 20 workers (third instar and beyond) 
were extracted to form an experimental unit confined in a 
closed Petri dish (59 mm internal diameter). A total of nine 
experimental units were formed, three for each illumination 

regime: (i) dark; (ii) cold white LED (OUROLUX™12W; 
color temperature: 6500K; luminous flux: 1200lm; luminous 
efficacy: 100lm/W); (iii) infrared light (ILS, OSLON IR 1 
PowerStar IR Star LED, peak wavelength: 850nm, radiant 
flux 1070mW, radiance angle: ±45, 2-pin, SMD, using 
current=1.12A;voltage=15v). Experimental units were then 
taken to BOD incubator, under 25ºC±1, within which one of 
the three types of illumination regimes was set up. No food or 
water was provided in the Petri dishes. 

Since group size can affect survival in termites, and 
this survival is associated with the spatial density termites are 
subjected to, we kept each experimental group at a density 
of 0.14 (the ratio between the total area occupied by termites 
and the total area of the arena’s floor). This is within the 
range 0.10 to 0.19 considered to favor survival in termites 
(Miramontes & DeSouza, 1996; DeSouza et al., 2001; DeSouza 
& Miramontes, 2004) 

Counting of dead and live individuals proceeded every 
hour in each Petri dish for the first 12 h after which it was 
halted for the next 8 hours. Then the hourly tally was resumed 
until all individuals were dead. 

Data analysis

Data were subjected to censored survival analysis under 
Weibull distribution, similar to what DeSouza et al. (2009) 
have done, using survival package in R (R Core Team, 2015). 
Survival analysis is the statistical analysis of data where the 
response of interest is the time, t, from a well-defined time origin 
to the occurrence of some given event (end-point) (Martinussen 
& Scheike, 2006). In our case, time origin is when we put the 
Petri dish inside the BOD incubator and the end-point is when 
we record the death of a termite worker in this arena. 
The general model for this analysis follows the equation:

loge S(t)=μ 
- α t α

Where S(t) is the accumulated proportion of dead 
termites until time, t; the mean time μ is the time elapsed 
until 50% of termites are dead in a given treatment; and α is 
the shape parameter for the survival curve. When α=1, the 
probability of a termite dying does not change as time elapses. 
If α<1 this probability reduces as time elapses, the opposite 
happening when α>1.

Statistical analysis was used to check whether the light 
regime would affect the mean time, μ, until termites are found 
dead in a given treatment. Under the null hypothesis, the mean 
time, μ, does not differ between light regimes, hence, time, t, 
alone explains S(t). That is, under the null hypothesis, termite 
deaths are not speeded up nor delayed by the light regime. 
Alternatively, if the light regime affects the time at which a 
termite dies, a typical μ can be calculated for each regime. 

Modelling proceeded by building a full model with 
a single term, light regime, represented by a categorical 
variable with three levels: darkness, infrared light, and white 
light. Model simplification was performed removing this term 
from the full model and inspecting the consequent change 



YC Carvalho et al. – Suitable lights for filming termites in laboratory assays110

in deviance. In case of significant changes (i.e., P≤0.05), 
the term would have been returned to the model to proceed 
further simplification amalgamating its levels. 

Results

Cornitermes cumulans termite workers confined 
in Petri dishes in a BOD incubator kept at 25ºC did not 
show any obvious quantitative changes in behavior along the 
whole experiment. Within each of these experimental arenas, 
termites circulated normally, stopping to interact or simply 
passing by when meeting a given conspecific. Interactions 
involved antennations, allogrooming, mouth-to-mouth contacts 
(presumably, oral trophallaxis), and occasional mouth-to-anus 
contacts (presumably, anal trophallaxis).

Survival curves presented a shape parameter α>1 
(α=3.369), implying that mortality tended to be more 
expressive towards the end of the experiment. In fact, after 
500 min had elapsed, more than 80% of the termites were still 
alive in all treatments. Mortality crossed the 50% threshold 
more than 1000 min after the beginning of the experiment (Fig 1).

Light intensity experienced by termites in the 
experimental units varied from 0 lux (darkness) to 5 lux 
(infrared) to 672 lux (white LED light). This has led to an 
average survival time of 1085 min for termites kept in the 
dark, 1065 min for termites kept under white LED light and 
1102 min for termites exposed to infrared light. These timings 
and hence their respective light regimes, however, did not 
differ statistically (Table 1, P=0.31). 

Discussion

We did not observe any effect of the distinct light 
regimes on the mortality of C. cumulans workers in this 
work: such termites presented similar survival patterns when 
confined in darkness, under cold white light, or under infrared 
light (Fig 1, Table 1). While arising intriguing theoretical 
issues, these results have important practical connotations. 

On the theoretical front, these results would evoke the 
question of why these termites, as opposed to Reticulitermes, 
were not harmed by the light regimes under test? Among 
plausible hypotheses, one has to consider the possibility that the 
light regime of highest intensity here applied (672 lux) was still 
below any harmful potential. This hypothesis, still to be tested, 
gains significance from the fact that daylight illuminance under 
bright sun attains not less than 100,000 lux, or 20,000 lux in the 
shade. An alternative hypothesis would point to the absence 
of phototoxic compounds in the hemolymph of C. cumulans. 
In order to answer it, one would have to inspect the presence 
of compounds such as norhamane, which is responsible for 
phototoxic effects in other termites (Siderhurst et al., 2006). 
Clearly, these hypotheses are beyond the aims of this work but 
we present them here in an attempt to sign the research avenues 
they could open. 

On the practical front, our results validate the use of infrared 
and cold white lights in studies that demand video recording with 
C. cumulans, as none of these light regimes affected workers 
survival. Being closest to dark that we can record with a video 
camera, infrared would seem the best choice for such assays. As 
a drawback, not any camera can record video under infrared, and 
those which can, are normally more expensive (albeit many are 
still within the affordable price range). Compared to infrared 
lights, cold white LEDs are cheaper and easier to find. Better 
still, all cameras can record under this type of light. 

As a word of caution, it must be considered that our 
test regards survival only. Despite not observing any obvious 
behavioral changes while counting dead and alive individuals 
for our test, no quantitative behavioral parameter was inspected 
(and this is, incidentally, another possible development from the 
current work). We conclude, therefore, that video recordings of 
C. cumulans termite workers can be conducted under infrared or 
cold white LEDs, as these light regimes do not affect the survival 
of tested individuals. 

Acknowledgements

We thank Helder Hugo dos Santos for providing us the 
infrared lights used in this study. This work was partially supported 
by CNPq, Fapemig, Capes. YCC, LOC, MPG hold MSc grants 
from CAPES. ODS holds a CNPq fellowship (#307990/2017-
6). This work is part of the IV SymTermes Community at 
https://zenodo.org/communities/symtermes/?page=1&size=20, 
where it is identified by DOI 10.5281/zenodo.894421. This is 
contribution # 71 from the Lab of Termitology at Federal Univ. 
of Viçosa, Brazil (http://www.isoptera.ufv.br).

Fig 1. Survival of C. cumulans workers confined in Petri dishes in the 
dark, exposed to white lights, or exposed to infrared lights, in a BOD 
incubator kept at 25ºC. Curves do not differ statistically (P=0.31).

Df Deviance Resid. Df -2*LL Pr (> χ²)
 Null 178.00 2660.90
Light regime 2.00 2.31 176.00 2658.59 0.31

Table 1. Analysis of deviance for the effects of light regime on the 
survival of C. cumulans termite workers confined in Petri dishes. 
Three light regimes were applied continuously to the experimental 
arenas: darkness, infrared light, and cold white light. See Material & 
Methods for more detail. “LL” = log-likelihood.



Sociobiology 65(1): 108-111 (March, 2018) Special Issue 111

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