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Termites have evolved diverse defence strategies to protect themselves against predators, including a complex alarm communication system based on vibroacoustic and/or chemical signals. In reaction to alarm signals, workers and other vulnerable castes flee away while soldiers, the specialized colony defenders, actively move toward the alarm source. In this study, we investigated the nature of alarm communication in the pest Reticulitermes flavipes. We found that workers and soldiers of R. flavipes respond to various danger stimuli using both vibroacoustic and chemical alarm signals. Among the danger stimuli, the blow of air triggered the strongest response, followed by crushed soldier head and light flash. The crushed soldier heads, which implied the alarm pheromone release, had the longest-lasting effect on the group behaviour, while the responses to other stimuli decreased quickly. We also found evidence of a positive feedback, as the release of alarm pheromones increased the vibratory communication among workers and soldiers. Our study demonstrates that alarm modalities are differentially expressed between castes, and that the response varies according to the nature of stimuli.
1 3
Insectes Sociaux
Chemical andvibratory signals used inalarm communication
inthetermite Reticulitermes flavipes (Rhinotermitidae)
O.Delattre1,2· J.Šobotník1· V.Jandák3· J.Synek1· J.Cvačka4· O.Jiříček3· T.Bourguignon1,5· D.Sillam‑Dussès2,6
Received: 22 November 2017 / Revised: 3 December 2018 / Accepted: 4 December 2018
© International Union for the Study of Social Insects (IUSSI) 2018
Termites have evolved diverse defence strategies to protect themselves against predators, including a complex alarm com-
munication system based on vibroacoustic and/or chemical signals. In reaction to alarm signals, workers and other vulnerable
castes flee away while soldiers, the specialized colony defenders, actively move toward the alarm source. In this study, we
investigated the nature of alarm communication in the pest Reticulitermes flavipes. We found that workers and soldiers of R.
flavipes respond to various danger stimuli using both vibroacoustic and chemical alarm signals. Among the danger stimuli,
the blow of air triggered the strongest response, followed by crushed soldier head and light flash. The crushed soldier heads,
which implied the alarm pheromone release, had the longest-lasting effect on the group behaviour, while the responses to
other stimuli decreased quickly. We also found evidence of a positive feedback, as the release of alarm pheromones increased
the vibratory communication among workers and soldiers. Our study demonstrates that alarm modalities are differentially
expressed between castes, and that the response varies according to the nature of stimuli.
Keywords Communication· Defence· Pheromones· Positive feedback· Vibratory behaviour
Alarm communication is common in social animals, and it
increases rates of survival (Wyatt 2003; Hunt and Richard
2013). Almost all social insects use alarm communication
to coordinate the defensive activities of the entire colony
(Leonhardt etal. 2016). These alarm signals are shared
through different communication channels, with vibratory
and pheromonal communication being the most common
(Greenfield 2002; Cocroft and Rodríguez 2005). In ter-
mites, as well as their sister group, the subsocial roaches
Cryptocercus (Seelinger and Seelinger 1983; Connétable
etal. 1999; Röhrig etal. 1999; Reinhard and Clément 2002;
Hager and Kirchner 2013; Delattre etal. 2015), vibratory
and/or chemical signals are produced by disturbed colony
members and induce the retreat of workers and other vulner-
able castes while attracting soldiers (Reinhard and Clément
2002; Šobotník etal. 2008a, 2010). These mechanisms are
essential for termite colony defence, and greatly contribute
to their ecological success. For example, tamandua anteaters
are specialized predators of Nasutitermes, which they find
in wood pieces, but they are unable to feed on this termite
directly in the nest where the soldier proportion is higher
(Lubin and Montgomery 1981).
Insectes Sociaux
Electronic supplementary material The online version of this
article (https :// 0-018-00682 -9) contains
supplementary material, which is available to authorized users.
* J. Šobotník
1 Faculty ofForestry andWood Sciences, Czech University
ofLife Sciences, Kamýcká 129, 16521Prague6Suchdol,
2 Institute ofResearch forDevelopment, Sorbonne Universités,
Institute ofEcology andEnvironmental Sciences ofParis, U
242, 32 Avenue Henri Varagnat, 93140Bondy, France
3 Faculty ofElectrical Engineering, Czech Technical
University inPrague, Technická 2, 16627Prague6,
4 Institute ofOrganic Chemistry andBiochemistry, Academy
ofSciences oftheCzech Republic, Flemingovo nám.,
16610Prague, CzechRepublic
5 Okinawa Institute ofScience andTechnology Graduate
University, 1919-1 Tancha, Onna-son, Kunigami-gun,
Okinawa904-0495, Japan
6 Laboratory ofExperimental andComparative Ethology,
EA4443, University Paris 13, Sorbonne Paris Cité, 99
Avenue Jean-Baptiste Clément, 93430Villetaneuse, France
O.Delattre et al.
1 3
Many termite species produce substrate-borne vibra-
tions by hitting their heads and/or abdomens on the sub-
strate (Connétable etal. 1999; Röhrig etal. 1999; Hager
and Kirchner 2013). All colony members are able to detect
vibrations with their subgenual organs, specialized chordo-
tonal vibroreceptors, located on the leg tibiae (Howse 1962,
1965a; Chapman 1998). Such unique alarm communica-
tion mechanism may have evolved only once in the com-
mon ancestor of termites and Cryptocercus (Seelinger and
Seelinger 1983), probably after its diet switched from loose
substrates to wood, a material through which vibratory sig-
nals easily spread. The vibratory alarm signals are generated
using several types of oscillatory movements in termites.
In this paper, we will follow the terminology introduced by
Hill (2014), who recognized two categories of vibrational
mechanisms: (1) drumming, commonly used in termites to
produce substrate-borne vibrations; (2) tremulation, a body
movement performed without any hit on the substrate, used
to propagate the alarm selectively to calm nestmates (Kettler
and Leuthold 1995; Šobotník etal. 2008b).
Another mean of alarm signalling is the chemical chan-
nel. Social insects evolved a rich set of exocrine glands (Bil-
len and Šobotník 2015) producing a wide range of infoche-
micals. In termites, alarm pheromones are produced either
by the frontal or labial glands, which are the defensive
glands of soldiers (Šobotník etal. 2008a, 2010; Delattre
etal. 2015). Alarm compounds are mostly mono- or sesqui-
terpenes (see Šobotník etal. 2010 for a review), except in
Mastotermes darwiniensis, that uses benzoquinone (Delattre
etal. 2015).
In certain termite species, the efficiency of alarm signal-
ling is enhanced by positive feedback, a mechanism imply-
ing amplification of the signal by newly alerted specimens
(Vrkoč etal. 1978; Roisin etal. 1990; Röhrig etal. 1999;
Hager and Kirchner 2013; Cristaldo etal. 2015; Delattre
etal. 2015). Vibratory positive feedback has been demon-
strated in M. darwiniensis (Delattre etal. 2015), in several
Macrotermitinae (Termitidae; Connétable etal. 1999; Hager
and Kirchner 2013; Röhrig etal. 1999), and in Constric-
totermes cyphergaster (Termitidae: Nasutitermitinae; Cris-
taldo etal. 2015). Chemical positive feedback relies upon
the alarm pheromone present in soldier defensive secretion
and is known in M. darwiniensis (Delattre etal. 2015) and in
several Nasutitermes species (Termitidae: Nasutitermitinae)
(Roisin etal. 1990; Vrkoč etal. 1978).
While the nature of vibratory or chemical alarm signals
is well-known and has been the focus of many studies, the
alarm transmission mechanisms have seldom been investi-
gated. Cristaldo etal. (2015) demonstrated that individuals
react to alarm pheromone stimulation by vibratory alarm sig-
nalling in C. cyphergaster, and Delattre etal. (2015) showed
that artificial vibratory alarm signals trigger the release of
the alarm pheromones in M. darwiniensis. In this study, we
carried out a careful examination of alarm communication
mechanisms in Reticulitermes flavipes (Kollar, 1837) (Rhi-
notermitidae), including a vibrational and chemical analy-
sis of this behaviour. Since only the basal termites and the
most derived termites have been studied, this study aims to
improve our understanding of the evolution of alarm com-
munication in termites. Reticulitermes is a temperate genus
that includes many pest species responsible for billions of
dollars of damage annually worldwide (Su and Scheffrahn
2000). We characterized the vibratory and chemical com-
munication in workers and soldiers, and determined their
responses to particular danger stimuli, including the alarm
pheromones of their colony mates.
Materials andmethods
Insect material
All the experiments were carried out on one colony of Retic-
ulitermes flavipes collected in Île d’Oléron (France) in 1998,
and kept in laboratory stable conditions (26°C, 90% relative
humidity) since then.
Behavioural experiments
All experiments were performed at 26°C under dimmed red
light. We first conducted a behavioural experiment to assess
how R. flavipes workers and soldiers react to various danger
stimuli. To avoid any effect of social deprivation, we formed
groups (N = 12) of 38 workers and 2 soldiers (natural caste
ratio; see Haverty 1977) that were put in 85mm Petri dishes
lined with moist clean Whatman No. 1 filter paper. The groups
were left to settle for at least 2h prior to testing, and between
two tests. The stimuli set included: (1) light flash (3s, 800lx
intensity, 5500–6000K colour temperature), (2) blow of air,
delivered through a fine straw for 3s, which mimics a breach
into the colony, (3) one crushed worker head and (4) one
crushed soldier head. Crushed heads were prepared by cut-
ting termites at the level of the prothorax and the heads were
crushed on filter paper using a small spatula, allowing the
impregnation of the filter paper by the contents of the frontal
gland (soldier frontal gland is known to produce alarm phero-
mone; Reinhard and Clément 2002). We recorded group activ-
ity without any stimulation as controls for experiments (1) and
(2). For experiments (3) and (4), the controls consisted in the
insertion of a blank filter paper. Pieces of filter paper were
carefully inserted into the Petri dish through a fine slit in the
lid. Each stimulus was tested six times in random order and
on randomly chosen groups (3 stimuli per group in random
order). Behavioural reactions were recorded using a Canon
EOS 6D combined with EF 100mm f/2.8L Macro IS USM
for 3min before stimulation and 6min after the stimulation.
Chemical andvibratory signals used inalarm communication inthetermite Reticulitermes
1 3
We chose to analyse the speed-of-motion of individuals, to
assess their reaction to our stimuli. Speed-of-motion increases
as workers flee the disturbance source, and soldiers gather
next to it (Reinhard and Clément 2002; Šobotník etal. 2008a,
2010). We tracked two randomly chosen workers and both
soldiers per group for each record. We estimated the group
behaviour 1min before the stimulus introduction, and 1 and
6min after (short-term and long-term responses, respec-
tively), using the Mouse-Tracer Software (see Šobotník etal.
2008a). We then computed the variation of speed-of-motion
for all the stimuli using the difference between the mean speed
before and after the introduction of the stimulus. This method
allowed us to normalize the variance between the different
termite groups. Variations in speed-of-motion for all danger
stimuli were compared to their respective controls.
Chemical analyses
We carried out two experiments to identify the alarm com-
pounds in workers and soldiers of R. flavipes. In the first
experiment, 20 termites were cut at the level of the prothorax
and the anterior parts were successively extracted with 60µl
and 40µl of hexane. Both extractions took place over two
successive nights at 4°C. Both extracts were merged and one
termite equivalent was injected in a 6890N gas chromato-
graph (Agilent, Santa Clara, CA, USA). The most abundant
compounds were identified based on spectral characteristics
and published records (summarized in Šobotník etal. 2010).
In the second experiment, we crushed heads of five individu-
als of each caste in a 1.2mL glass vial with a Pasteur pipette.
The headspace extraction of volatiles was carried out using
SPME fibre holder for manual sampling equipped with a
fused silica fibre coated with 30µm polydimethylsiloxane
(Supelco, Bellefonte, USA). The analytes were desorbed at
220°C in a split/splitless injector of a 5975B quadrupole
mass spectrometer coupled to a gas chromatograph. The
separation was achieved on a DB-5ms capillary column
(30m × 0.25mm, a film thickness of 0.25µm, Agilent) at
a constant flow mode (1mL/min) with helium as a carrier
gas. The column temperature was held at 40°C (1min),
gradually increased at 5°C/min to 200°C, then gradually
increased at 15°C/min to 320°C, and held at 320°C for
3min. The temperatures of the transfer line, ion source and
quadrupole were 280, 230, and 150°C, respectively. The
compounds were ionized at 70eV electrons.
Vibroacoustic experiments
To decipher the vibratory component of R. flavipes behaviour,
we formed ten new groups of termites, using the same ratio we
used in our behavioural experiments. The aim of this experi-
ment was to determine the interaction between a chemical
stimulation and the vibratory component of alarm signalling
in R. flavipes. We crushed one worker and one soldier head on
different pieces of filter paper (following the same protocol as
the behavioural experiment), and used another identical piece
of blank filter paper for control. Due to methodological con-
straints and to avoid the absorption of the termite-produced
vibrations, termite groups were placed into a 85mm Petri dish
without filter paper, and moisture was provided by a piece of
wet cotton attached to the lid. The bottom of the Petri dish was
heavily scratched to allow termites to walk. Our experiments
were carried out in an anechoic room at the Czech Technical
University in Prague under dimmed red light. All experiments
took place on a table hung from the ceiling to avoid any per-
turbations from the experimenters (see Supplementary video
SV1). All experiments were recorded using a SONY DCR-
SR72 camera in night-shot mode fixed above the experimental
arena. These records were only used to link the behaviour of
termite groups to recorded vibrations, and were not used for
behavioural analyses.
Vibratory communication was recorded using accelerom-
eters (Brüel and Kjær type 4507 B 005) glued to the bottom
of Petri dishes. We analysed the recorded vibratory signals
using a Soft dB Tenor recorder (24 bits, sampling frequency
48kHz) and Matlab software (R 2012a; see ESM 1). Prior to
each experiment, we recorded high-resolution videos of both,
disturbed and undisturbed groups of termites, to decipher the
repertoire of vibrations generated by R. flavipes workers and
soldiers. We considered recorded frequencies below 15Hz
as low-frequency vibrations, and frequencies above 15Hz as
high-frequency vibrations. These preliminary tests were also
used to determine the optimal parameters of frequency fil-
ters used for post-processing of vibration records of R. flavi-
pes groups in the described environment. This allowed us to
reduce the background noise.
In these experiments, because termite signals overlap, we
were unable to analyse individual signals. Therefore, we com-
puted the total amount of energy produced by group vibratory
signals after each stimulation. This variable ER, was computed
using the following equation:
in which TA is the evaluation period after disturbance (60s
and 360s, respectively), TB is the evaluation period before
disturbance (60s), and xf(t) is the filtered acceleration signal
(bandpass filter 50–500Hz) and is a function of time (t).
We performed Kruskal–Wallis tests and two-by-two post
hoc permutation tests (10,000 permutations) for independent
R=10. log
O.Delattre et al.
1 3
samples, and we carried out Friedman tests and two-by-two
post hoc permutation tests (10,000 permutations) for paired
samples. Bonferroni–Holm corrections (Holm 1979) were
applied for multiple comparisons among groups. All sta-
tistical tests were performed with StatXact software (Cytel
Studio, version 9.0.0, 2010).
Behavioural experiments
All groups significantly reacted to all experimental stimuli.
We found significant differences among stimulations for
both soldiers and workers, both 1 and 6min after stimu-
lations (short-term vs. long-term responses, respectively;
Workers were sensitive to the blow of air, the crushed
soldier head (CSH) and light flash exposure, but not to the
crushed worker head (CWH). Soldiers revealed similar
responses, but were also sensitive to the crushed worker
head during the first minute after the stimulus introduction
(Fig.1, Fig. S1).
Chemical analyses
Analytical approaches revealed a set of monoterpenes pre-
sent in soldier extracts and SPME, while no candidate com-
pound was detected in workers, irrespective of method used
(Table2). Extracts of workers and soldiers also contained
the cuticular hydrocarbons specific to R. flavipes (see, e.g.
Bagnères etal. 1990; Vauchot etal. 1998; Perdereau etal.
Vibroacoustic experiments
In response to the stimuli, soldiers and workers displayed
body vibrations that they used to spread alarm within the
groups. Using vibroacoustic preliminary tests in conjunc-
tion with high-resolution video recordings, we observed
that these vibrations were mainly drumming or tremula-
tion. Drumming was produced by abdomen hits against the
substrate, while tremulation was produced by tactile stimu-
lation of nestmates with the head. In a few cases, soldiers
displayed another kind of drumming signal consisting in
powerful hits to the ground with their mandibles.
We found that drumming and tremulation were used in
combination by workers and soldiers, forming thus com-
plex vibrations. These vibrations occurred in two kinds of
bursts (series of hits). The first kind of burst was at a high
frequency of 31 ± 4Hz, while the second kind of burst
occurred at a low frequency of 7.4 ± 1.3Hz. High and
low-frequency vibrations were often performed together,
the high-frequency bursts preceding the low-frequency
bursts (Fig.2, video SV1). This could be defined as the
typical pattern of vibratory behaviour in R. flavipes.
Occasionally, the high- and low-frequency bursts were
performed separately after disturbance. A third kind of
drumming burst was specifically displayed by soldiers,
Table 1 Differences in speed-of-motion between all stimulations after
stimulus introduction for workers and soldiers in R. flavipes
Kruskal–Wallis for multiple comparisons statistic values (H5) and P
values are provided for both castes
Workers Soldiers
Short-term response
(1min) H5 = 46
P < 0.001 H5 = 39.61
P < 0.001
Long-term response
(6min) H5 = 46.01
P < 0.001 H5 = 27.24
P < 0.001
Fig. 1 Change in speed-of-motion of workers (white bars) and sol-
diers (grey bars) in R. flavipes during a 1-min period after exposition
to experimental stimuli in comparison to controls. N = 12 for each
caste and each stimulus. Box plots show the median and 25–75th per-
centiles. Whiskers show all data excluding outliers outside the 10th
and 90th percentiles (circles). Statistical differences are given for
P < 0.05. CWH crushed worker head, CSH crushed soldier head
Table 2 Chemical compounds identified by GC–MS from Reticulit-
ermes flavipes worker and soldier samples (hexane extracts or head-
space SPME)
Ø no volatile compound detected, CHC cuticular hydrocarbons
Extracts SPME
Workers Soldiers Workers Soldiers
CHC α-Pinene Ø α-Pinene
β-Pinene β-Pinene
Limonene Limonene
CHC Unknown compound
Chemical andvibratory signals used inalarm communication inthetermite Reticulitermes
1 3
and consisted of repeated hits to the substrate with the
mandibles, at an average frequency of 26 ± 2Hz. Unfor-
tunately, this particular behaviour occurred too scarcely
(only 40 series recorded in all experiments combined) to
be analysed in our vibroacoustic work.
Reticulitermes flavipes groups reacted to the alarm
pheromone by producing vibroacoustic signals (Fig. S2).
The intensity of these signals was nearly identical 1 and
6min after the stimulation, with the exception of the
response to CSH, which was lower after 6min (Table3;
Fig.3). The responses to CSH were stronger in the first
minute after the stimulus introduction, while CWH stimu-
lation triggered a long-lasting effect increasing with time
during the timeframe of the experiment (Table4).
Alarm communication is an important component of the
defensive strategies of many gregarious, colonial and
social animals, and is used to coordinate defensive activi-
ties. In Reticulitermes flavipes, alarm signals are spread
via tremulations, substrate-borne vibrations and alarm
pheromones. Irrespective of the communication channel,
two modes of alarm transmission can be distinguished in
natural situations: general alarm responses follow strong
disturbance and affect large termite groups, while subtler
specific alarm communication involves a few specimens
reacting to low-level disturbance, such as the encounter
of alien individual into the gallery system (Howse 1965b;
Stuart 1963, 1988).
Here we studied the general alarm responses of R. flavi-
pes, and clearly showed that potential dangers, represented
Fig. 2 Example of vibratory behaviour showing the typical structure
of the vibratory movements of workers and soldiers of Reticulitermes
flavipes. The complex vibrations occurred at two distinct frequencies,
described as high- (31Hz) and low- (7.4Hz) frequency bursts
Table 3 Differences in vibratory behaviour (permutation tests for
paired samples) recorded in termite groups (N = 10) before and after
the introduction of the stimulus
CO control blank paper, CWH crushed worker head, CSH crushed
soldier head
Stimulation Short-term response
CO − 0.959
P = 0.359
− 0.5501
P = 0.5977
CWH − 2.067
P = 0.021
− 2.279
P = 0.014
CSH − 1.908
P = 0.006
− 1.574
P = 0.057
Fig. 3 Energy ratio difference in vibrations recorded in groups
(N = 10) before and after the introduction of the stimulus. Box plots
show the median and 25th–75th percentiles. Whiskers show all data
excluding outliers outside the 10th and 90th percentiles (circles). Sta-
tistical differences are shown for *P < 0.05 and **P < 0.01. CO con-
trol blank paper, CWH crushed worker head sample, CSH crushed
soldier head sample
Table 4 Comparison between vibrational responses to crushed ter-
mite heads (N = 10) (permutation tests for paired samples)
CO control blank paper, CWH crushed worker head, CSH crushed
soldier head
Stimulation comparison Short-term response
CO vs. CWH − 1.839
P = 0.063
− 2.378
P = 0.027
CO vs. CSH − 1.841
P = 0.047
− 1.579
P = 0.088
O.Delattre et al.
1 3
by air current, light flash, or crushed nestmate heads,
are treated with differing types of alarm responses. The
responses to air currents and crushed soldier heads were
the most pronounced, and triggered immediate increase
of speed-of-motion and quantity of vibroacoustic signals
in workers and soldiers. These behavioural changes were
abrupt and often lasted over 6min.
The observed vibroacoustic signals were made of com-
plex vibratory movements, combining drumming and
tremulations. They were produced by workers and soldiers
repeatedly hitting their abdomen on the substrate. These
examples of vibroacoustic communication combine two
kinds of bursts differing in beat frequencies, as described
in Coptotermes gestroi, another species of Rhinotermitidae
(see Hertel etal. 2011). A duration-dependent effect could
be perceived and CSH samples elicited the strongest reaction
during the first minute after the stimulation.
CSHs were not the only stimuli which could trigger
vibrations, CWH revealed significant effect as well, as evi-
denced by the walking activity of soldiers and vibratory
activity of both soldiers and workers. Our results concur
with previous observations on C. cyphergaster (Termitidae,
Nasutitermitinae) (Cristaldo etal. 2015), in which the CWH
also provoke marked behavioural responses in soldiers. C.
cyphergaster workers possess enlarged mandibular glands
with defensive function (Costa-Leonardo and Shields 1990),
which are possibly the source of chemicals responsible for
the change in behaviour. In contrast, no gland with defensive
role is known in R. flavipes workers, and the source of the
excitement remains unknown.
Soldiers of R. flavipes also used their head and mandibles
to perform powerful hits to the substrate, which produced
a strong substrate-borne vibratory drumming-like signal,
much stronger than the abdominal drumming. The same
way of drumming has also been observed in Archotermop-
sidae (Kirchner etal. 1994), Rhinotermitidae (Hertel etal.
2011) and Macrotermitinae (Termitidae) (Connétable etal.
1999; Hager and Kirchner 2013; Kettler and Leuthold 1995;
Röhrig etal. 1999). The strongest signals are probably used
to warn nestmates and recruit soldiers from deeper inside
the colony.
Our chemical analysis showed high quantity of α- and
β-pinene, and limonene produced by the frontal gland of R.
flavipes soldiers. These compounds form the alarm phero-
mone in R. flavipes, as it has been previously suggested by
several authors (Bagnères etal. 1990; Parton etal. 1981;
Reinhard etal. 2003), although not all compounds might be
necessary for the function, as they were never tested sepa-
rately. The alarm pheromones involve various compounds
classes, such as monoterpenes (also in R. flavipes), sesquit-
erpenes (for review see Šobotník etal. 2010) or quinones
(Delattre etal. 2015), and are known to be released from
the soldier defensive glands, namely the labial glands in
Mastotermitidae and the frontal gland in Rhinotermitidae
and Termitidae (Delattre etal. 2015; Kaib 1990; Kriston
etal. 1977; Pasteels and Bordereau 1998; Reinhard and Clé-
ment 2002; Roisin etal. 1990; Šobotník etal. 2008a; Vrkoč
etal. 1978).
Until recently, alarm positive feedback was only dem-
onstrated either for vibroacoustic (Connétable etal. 1999;
Delattre etal. 2015; Hager and Kirchner 2013; Röhrig
etal. 1999) or chemical signals (Roisin etal. 1990; Vrkoč
etal. 1978). Integrative studies appeared only recently, and
vibroacoustic feedback to chemical alarm has been shown
only in the basal Mastotermes (Mastotermitidae; Delattre
etal. 2015) and the derived Constrictotermes (Termiti-
dae: Nasutitermitinae; Cristaldo etal. 2015). In this study,
we found the third example of vibroacoustic feedback to
chemical alarm, as workers’ and soldiers’ speed-of-motion
increased after exposure to head volatiles. Moreover, as
showed in Connétable etal. (1999), it is likely that termites
spread the alarm further using complex vibratory communi-
cation based on tremulations and drumming, contributing to
the general state of colonial defensive activity (i.e. running
away from the threat).
Our work is the first exhaustive study on the alarm com-
munication strategies in a species of Rhinotermitidae. Both
workers and soldiers of R. flavipes reacted to all stimulations
(light flash, air currents and crushed nestmate heads) with
various degrees of excitement and displaying different vibra-
tory movements. These observations show specialized alarm
communication strategy based on complementary modali-
ties, which could trigger an efficient response according to
the nature and intensity of endangering stimulus. Moreover,
R. flavipes is a pest species in Western USA (Evans 2011;
Evans etal. 2013) and has been introduced to several places
around the world (Bagnères etal. 1990; Smith etal. 2006;
Evans etal. 2013), where it became invasive (originally
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... In spite of the crucial importance of alarm communication for termite colony survival, only fragmented reports have hitherto been published about this topic, most of which focused on either vibroacoustic or pheromonal communication of isolated species 27,36,59,60,[63][64][65][66][67][68][69][70][71] . The evolutionary trajectories of alarm signals, and their significance within complex ecological constraints across extant termite lineages, have not previously been investigated, and there is no report on alarm communication in soilfeeding termites, which represents over half of termite diversity 70 . ...
... As the specific alarm signaling in termites (comparable to panic in ants) is a subtle behavior 71,72 out of the scope of this work, general alarm is accompanied by a dramatic change in the group behavior. The general alarm typically involves many individuals disturbed at foraging sites, or present in a part of the nest that has been locally damaged 27,36,59,60,[63][64][65][66][67][68][69] . The alerting termites search for quiet termites, touch them with their antennae, and perform tremulations to alert them 36 . ...
... Alarm pheromones. Alarm pheromones in termites originate from soldiers' defensive glands only: the labial glands in Mastotermes 27 and the frontal gland in Neoisoptera (the derived group comprising Stylotermitidae, Rhinotermitidae, Serritermitidae, and Termitidae) 36,59,[63][64][65][67][68][69] . Similar signals are widely used in some cockroaches, produced by the abdominal sternal or tergal glands (Eurycotis 74 ; Therea 75 ; Blaberus 76 ). ...
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Termites (Blattodea: Isoptera) have evolved specialized defensive strategies for colony protection. Alarm communication enables workers to escape threats while soldiers are recruited to the source of disturbance. Here, we study the vibroacoustic and chemical alarm communication in the wood roach Cryptocercus and in 20 termite species including seven of the nine termite families, all life-types, and all feeding and nesting habits. Our multidisciplinary approach shows that vibratory alarm signals represent an ethological synapomorphy of termites and Cryptocercus. In contrast, chemical alarms have evolved independently in several cockroach groups and at least twice in termites. Vibroacoustic alarm signaling patterns are the most complex in Neoisoptera, in which they are often combined with chemical signals. The alarm characters correlate to phylogenetic position, food type and hardness, foraging area size, and nesting habits. Overall, species of Neoisoptera have developed the most sophisticated communication system amongst termites, potentially contributing to their ecological success. The vibroacoustic and chemical alarm communication in the wood roach Cryptocercus and in 20 termite species are studied to reveal that the Neoisoptera species have developed the most sophisticated communication system, which could contribute towards their ecological success.
... Indeed, laser vibrometers used here allow more precise measurement of each type of body-shaking with their specific durations and number of pulses. In another study from Delattre et al. 9 , they detected the emission of high and low frequencies often performed together, which could be compared to the BS1 and BS2 we observed. The authors quantified vibrations by measuring groups of individuals composed of workers and soldiers. ...
... Moreover, vibration measurements were not directly connected to real-time behavioural observations. Nevertheless, Delattre et al. 9 9 , the group were a mixed of workers and soldiers and because emitted vibrations are not directly linked to body-shaking events only, direct comparisons are difficult to draw with our study. Overall, our results show that the produced vibrations are diversified, context dependent, and could be transmitted through the substrate. ...
... Moreover, vibration measurements were not directly connected to real-time behavioural observations. Nevertheless, Delattre et al. 9 9 , the group were a mixed of workers and soldiers and because emitted vibrations are not directly linked to body-shaking events only, direct comparisons are difficult to draw with our study. Overall, our results show that the produced vibrations are diversified, context dependent, and could be transmitted through the substrate. ...
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Vibratory behaviours are widespread in social insects, but the produced vibrations remain poorly explored. Communication using vibrations is an efficient way to transmit information in subterranean environments where visual and odorant signals are less efficient. In termites, different vibratory behaviours are performed in different contexts like reproductive regulation and alarm signalling, but only few studies explored the structure of the produced vibrations (i.e., duration, number of pulses, amplitude). Here, we described several types of vibrations produced by a vibratory behaviour widespread in termites (body-shaking), which can be transmitted through the substrate and detected by other colony members. We analysed the structures of the emitted vibrations and the occurrence of the body-shaking events in presence/absence of reproductives and/or in presence/absence of a stress stimuli (flashlight) in the subterranean termite Reticulitermes flavipes . Interestingly, only the presence of the reproductives did influence the number of pulses and the duration of the emitted vibrations. Moreover, the first part of the emitted vibrations seems to be enough to encode reproductive information, but other parts might hold other type of information. Body-shaking occurrence did increase in presence of reproductives but only briefly under a flashlight. These results show that vibratory cues are complex in termites and their diversity might encode a plurality of social cues.
... With exposure to a sufficient concentration of conidia, recognition of the pathogen, demonstrated by elevated LOMs, was followed by termites slowing their movement and aggregating so that they could apparently clean each other of conidia that had attached to their cuticular surfaces. After pathogen detection, the release of alarm pheromones may have also contributed to this response, although alarm pheromones are usually associated with an increase in motion and not the decrease that we observed [23]. The observed correlation between HRs and the number of allogrooming bouts was not significant for the comparison of different strains of Metarhizium; however, our 12 min snapshots of the initial response to infection missed a substantial amount of elevated allogrooming that occurs over a 24-h period and that is clearly critical for protection [16]. ...
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In social insects, alerting nestmates to the presence of a pathogen should be critical for limiting its spread and initiating social mechanisms of defense. Here we show that subterranean termites use elevated vibratory alarm behavior to help prevent fatal fungal infections. The elevated alarm leads to elevated social hygiene. This requires that termites coalesce so that they can groom each other’s cuticular surfaces of contaminating conidial spores. Groups of 12 Reticulitermes flavipes workers varied in their response when immersed in conidia solutions of nine different strains of Metarhizium. Pathogen alarm displays of short 2–7-second bursts of rapid longitudinal oscillatory movement (LOM), observed over 12 min following a fungal challenge, were positively correlated with the time that workers spent aggregated together grooming each other. The frequency of these LOMs was inversely correlated with fatal fungal infections. The variation in fatalities appeared to be largely attributable to a differential response to Metarhizium brunneum and Metarhizium robertsii in the time spent in aggregations and the frequency of allogrooming. Isolated workers challenged with conidia did not display LOMs, which suggests that the alarm is a conditional social response. LOMs appear to help signal the presence of fungal pathogens whose virulence depends on the level of this emergency alert.
Machadotermes is one of the basal Apicotermitinae genera, living in tropical West Africa. Old observations suggested the presence of a new gland, the intramandibular gland, in Machadotermes soldiers. Here, by combining micro-computed tomography, optical and electron microscopy, we showed that the gland exists in Machadotermes soldiers only as an active exocrine organ, consisting of numerous class III cells (bicellular units made of secretory and canal cells), within which the secretion is produced in rough endoplasmic reticulum, and modified and stored in Golgi apparatus. The final secretion is released out from the body through epicuticular canals running through the mandible cuticle to the exterior. We also studied three other Apicotermitinae, Indotermes, Duplidentitermes, and Jugositermes, in which this gland is absent. We speculate that the secretion of this gland may be used as a general protectant or antimicrobial agent. In addition, we observed that the frontal gland, a specific defensive organ in termites, is absent in Machadotermes soldiers while it is tiny in Indotermes soldiers and small in Duplidentitermes and Jugositermes soldiers. At last, we could also observe in all these species the labral, mandibular and labial glands, other exocrine glands present in all termite species studied so far.
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Termite colonies, composed of large numbers of siblings, develop an important caste-based division of labor; individuals in these societies interact via intra-or intercaste chemical communications. For more than 50 years, termites have been known to use a variety of pheromones to perform tasks necessary for maintenance of their societies, similar to eusocial hymenopterans. Although trail-following pheromones have been chemically identified in various termites, other types of pheromones have not been elucidated chemically or functionally. In the past decade, however, chemical compositions and biological functions have been successfully identified for several types of termite pheromones; accordingly, the details of the underlying pheromone communications have been gradually revealed. In this review, we summarize both the functions of all termite pheromones identified so far and the chemical interactions among termites and other organisms. Subsequently, we argue how termites developed their sophisticated pheromone communication. We hypothesize that termites have diverted defensive and antimicrobial substances to pheromones associated in caste recognition and caste-specific roles. Furthermore, termites have repeatedly used a pre-existing pheromone or have added supplementary compounds to it in accordance with the social context, leading to multifunctionalization of pre-existing pheromones and emergence of new pheromones. These two mechanisms may enable termites to transmit various context-dependent information with a small number of chemicals, thus resulting in formation of coordinated, complex, and rational chemical communication systems.
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Alarm signalling is of paramount importance to communication in all social insects. In termites, vibroacoustic and chemical alarm signalling are bound to operate synergistically but have never been studied simultaneously in a single species. Here, we inspected the functional significance of both communication channels in Constrictotermes cyphergaster (Termitidae: Nasutitermitinae), confirming the hypothesis that these are not exclusive but rather complementary processes. In natural situations, the alarm predominantly attracts soldiers, which actively search for the source of a disturbance. Laboratory testing revealed that the frontal gland of soldiers produces a rich mixture of terpenoid compounds including an alarm pheromone. Extensive testing led to identification of the alarm pheromone made of abundant monoterpene hydrocarbons (1S)-α-pinene and myrcene, along with a minor component, (E)-β-ocimene. The vibratory alarm signalling consists of vibratory movements evidenced as bursts, series of beats, produced predominantly by soldiers. Exposing termite groups to various mixtures containing the alarm pheromone (crushed soldier heads, frontal gland extracts, mixture of all monoterpenes, and the alarm pheromone mixture made of standards) resulted in significantly higher activity in the tested groups and also increased intensity of the vibratory alarm communication, and the responses are clearly dose-dependent. The lower doses of the pheromone provoked higher numbers of vibratory signals compared to higher doses. Higher doses induced a long-term running of all termites without stops necessary to perform vibratory behaviour. Surprisingly, even crushed worker heads led to low (but significant) increases in the alarm responses suggesting that other unknown compound in the worker's head is perceived and answered by termites. Our results show the existence of different alarm levels in termites, with lower ones being communicated through vibratory signals, and higher levels causing general alarm or retreat being communicated through the alarm pheromone.
We are entering one of the most exciting periods in the study of chemical communication since the first pheromones were identified some 40 years ago. This rapid progress is reflected in this book, the first to cover the whole animal kingdom at this level for 25 years. The importance of chemical communication is illustrated with examples from a diverse range of animals including humans, marine copepods, Drosophila, Caenorhabditis elegans, moths, snakes, goldfish, elephants and mice. It is designed to be advanced, but at the same time accessible to readers whatever their scientific background. For students of ecology, evolution and behaviour, this book gives an introduction to the rapid progress in our understanding of olfaction at the molecular and neurological level. In addition, it offers chemists, molecular and neurobiologists an insight into the ecological, evolutionary and behavioural context of olfactory communication.
Insect life strategies comprise all levels of sociality from solitary to eusocial, in which individuals form persistent groups and divide labor. With increasing social complexity, the need to communicate a greater diversity of messages arose to coordinate division of labor, group cohesion, and concerted actions. Here we summarize the knowledge on prominent messages in social insects that inform about reproduction, group membership, resource locations, and threats and discuss potential evolutionary trajectories of each message in the context of social complexity.
Chemical signals evaporating from secretions of different exocrine glands modulate the caste-specific polyethism in termite societies in a context-dependent manner. The sternal gland, the labial glands, and the frontal gland from Schedorhinotermes lamanianus are described. The chemical signals from the secretions of these glands have multiple intra- and interspecific functions and may be interactive