A blend of formic acid,benzoic acid,and aliphatic alkanes mediates alarm recruitment responses in western carpenter ants,Camponotus modoc

Formicine ants in distress spray alarm pheromone which typically recruits nestmates for help. Studying the western carpenter ant, Camponotus modoc Wheeler (Hymenoptera: Formicidae), our objectives were to (1) determine the exocrine glands that contain alarm recruitment pheromone, (2) identify the key alarm recruitment pheromone components, and (3) ascertain the pheromone components that are discharged by distressed ants. In Y-tube olfactometer experiments, extracts of poison glands, but not of Dufour’s glands, elicited anemotactic responses from worker ants. Gas chromatographic-mass spectrometric analyses of poison gland extracts revealed the presence of (1) aliphatic alkanes (undecane, tridecane, pentadecane, heptadecane), (2) aliphatic alkenes [(Z)-7-pentadecene, (Z)-7- and (Z)-8-heptadecene], (3) two acids (formic, benzoic), and (4) other oxygenated compounds (hexadecan-1-ol, hexadecyl formate, hexadecyl acetate). Testing the responses of worker ants in Y-tube olfactometers to complete and partial synthetic blends of these compounds revealed that the acids and the alkanes are essential alarm pheromone components. In two-choice arena bioassays, micro-locations treated with synthetic alarm pheromone recruited worker ants. Acids and alkanes were abundant in the poison gland and the Dufour’s gland, respectively, suggesting that the alarm pheromone components originate from both glands. Moreover, alarm pheromone sprays of ants differed in that all sprays contained formic acid but only some also contained alkanes, implying that ants can independently discharge the content of either one or both glands in accordance with the type of distress incident they experience.     

Female odours promote the activation of sheltered kissing bug Rhodnius prolixus males and modulate their orientation

The existence of a pheromone emitted during copulation has been reported for Rhodnius prolixus (Hemiptera: Reduviidae) Stål. Adults possess one pair of metasternal glands (MGs) from which female R. prolixus release volatiles mainly at night. We investigated whether these volatiles emitted by adult R. prolixus can modulate sexual‐related behaviours of opposite and/or same sex individuals. We first used a shelter bioassay to test if adult activity patterns can be affected by chemical signals emitted by opposite sex conspecifics. We observed that males left the shelter more frequently in the presence of females, showing higher activity and an increase of intrasexual copulation attempts. Females showed no shelter‐related activation in the presence of male odours. Second, we used a locomotion compensator device to investigate whether females or males show oriented responses to odours emitted by adults. We found that males oriented towards air currents carrying female odours but females did not orient towards odours emitted by adults. Finally, we observed that males oriented towards the female MG compounds. Thus, a volatile chemical signal emitted by females from their MGs promoted the activation of sheltered males and modulated orientation to air currents.     

Identification of feeding attractants in oak sap for adults of two nymphalid butterflies, Kaniska canace and Vanessa indica

The active compounds of oak‐sap odour in attracting adults of two butterflies, Kaniska canace (L.) and Vanessa indica (Herbst) (Lepidoptera: Nymphalidae), were identified by chemical analyses, electroantennogram (EAG) and two behavioural assays: proboscis extension reflex (PER) and attraction to artificial tree models. Fourteen compounds were identified from two sap samples collected in 1997 and 1998, of which the major volatiles were ethanol and acetic acid (≈ 900 p.p.m. and 500 p.p.m. in sap, respectively). However, the chemical composition of the minor volatiles varied considerably between the two samples. Among 13 chemicals tested, V. indica showed strong PER to five aliphatic acids (acetic, propionic, butyric, isobutyric and isovaleric), 2‐methylpropan‐1‐ol and 3‐hydroxybutan‐2‐one, whereas the PER‐active compounds for K. canace were these seven compounds and also ethanol, 3‐methylbutan‐1‐ol and 1‐hydroxypropan‐2‐one. In two‐choice behavioural bioassays, the model scented with a sap‐odour mimic, which was an aqueous mixture of the PER‐active compounds, was more attractive to the two butterflies than an unscented control. These results demonstrated that the sap odour stimulates foraging behaviour of the butterfly. Although EAG responses of both butterflies to 3‐methylbutan‐1‐ol and that of V. indica to 2‐methylpropan‐1‐ol were positively dose‐dependent, responses to other compounds were not strong and not dose‐dependent at 1–100 μg doses. These EAG responsiveness suggests that the olfactory receptors for these compounds might be few in the antenna and that the butterflies have enough olfactory sensitivity to the dose of 1 μg.     

Alarm behaviour in Eciton army ants

The effective communication of alarm can be critical for social animals so that they are able to deal with threats posed by predators and competitors. In the case of many of the most ecologically dominant, large‐colony ant species, these alarm responses are aggressive and coordinated by alarm pheromones, produced generally from the mandibular glands. In the present study, the alarm behaviour of two Neotropical army ant species is examined, the swarm raiding Eciton burchellii (Westwood) and the column raiding Eciton hamatum (Fabricius). Both species exhibit aggressive alarm responses in response to crushed heads, suggesting that the alarm pheromone is indeed produced by the mandibular glands in these ants. The most abundant component of the mandibular gland secretion, 4‐methyl‐3‐heptanone (10 µL on a rubber septum), stimulates a substantial alarm response, although this is less than the response to a single crushed head. This suggests that 4‐methyl‐3‐heptanone may be an alarm‐stimulating compound in Eciton. The alarm response of E. burchellii involves more workers than that of E. hamatum, although major workers play a much greater role in the response of the latter species. The differences in the alarm response of the two closely‐related species may relate to their foraging strategies, with E. burchellii relying more on quantity rather than the caste of ants responding and possibly using alarm pheromones for offensive as well as defensive functions.     

Cues of Predation Risk Induce Instar‐ and Genotype‐Specific Changes in Pea Aphid Colony Spatial Structure

Deploying collective antipredator behaviors during periods of increased predation risk is a major determinant of individual fitness for most animal groups. Pea aphids, Acyrthosiphon pisum, which live in aggregations of genetically identical individuals produced via asexual reproduction warn nearby conspecifics of pending attack by secreting a volatile alarm pheromone. This alarm pheromone allows clone‐mates to evade predation by walking away or dropping off the host plant. Here, we test how a single alarm pheromone emission influences colony structure and defensive behavior in this species. Relative to control colonies, groups exposed to alarm pheromone exhibited pronounced escape behavior where many individuals relocated to adjacent leaves on the host plant. Alarm pheromone reception, however, also had subtle instar‐specific effects: The proportion of 1st instars feeding nearest the leaf petiole decreased as these individuals moved to adjacent leaves, while the proportion of 2nd–3rd instars feeding nearest the leaf petiole remained constant. Fourth instars also dispersed to neighboring leaves after pheromone exposure. Lastly, alarm pheromone reception caused maternal aphids to alter their preferred feeding sites in a genotype‐specific manner: Maternal aphids of the green genotype fed further from the petiole, while maternal aphids of the pink genotype fed closer to the petiole. Together, our results suggest that aphid colony responses to alarm pheromone constitute a diversity of nuanced instar‐ and genotype‐specific effects. These behavioral responses can dramatically change the spatial organization of colonies and their collective defensive behavior.     

Divergent pheromone-mediated insect behaviour under global atmospheric change

While the effects of global atmospheric changes on vegetation and resulting insect populations(‘bottom‐up interactions’) are being increasingly studied, how these gases modify interactions among insects and their natural enemies (‘top‐down interactions’) is less clear. As natural enemy efficacy is governed largely by behavioural mechanisms, altered prey finding and prey defence may change insect population dynamics. Here we show that pheromone‐mediated escape behaviours, and hence the vulnerability of insects to natural enemies, are divergent under atmospheric conditions associated with global climate change. Chaitophorus stevensis, a common aphid on trembling aspen trees, Populus tremuloides, have diminished escape responses in enriched carbon dioxide (CO₂) environments, while those in enriched ozone (O₃) have augmented escape responses, to alarm pheromone. These results suggest that divergent pheromone‐mediated behaviours could alter predator–prey interactions in future environments.     

Dislodgement effect of natural semiochemicals released by disturbed triatomines: a possible alternative monitoring tool

The quick detection of domestic and peridomestic triatomines in their environments becomes difficult without the use of dislodgement substances that flush them out from their shelters. At present, tetramethrin 0.2% is being widely used in control programs. Although it is an efficient dislodging agent, its toxicity might affect the health of captured triatomines, of other insects and, to a lesser extent, of other animals, including humans. Here, we tested if semiochemicals released by disturbed adults of Triatoma infestans and/or Rhodnius prolixus can make larvae of the same species exit from their refuges. In a walking olfactometer we found that: 1) larvae of T. infestans were repelled by the odors released by disturbed adults of their own species and of R. prolixus, 2) larvae of R. prolixus did not change their behavior in the presence of odors released by adults of both species, and 3) activity levels were not modulated by these odors in any of both species. Besides, in pseudo‐natural conditions we found an increased flushing‐out activity of larvae of T. infestans when their shelters were sprayed with isobutyric acid or 3‐pentanol, and of larvae of R. prolixus when sprayed with 3‐methyl1butanol. We succeeded in this work to dislodge larvae of triatomines from artificial shelters using natural volatile compounds, allowing the capture of live bugs for further investigations (e.g., xenodiagnosis or genetic studies) and favoring ecological aspects (e.g., minimizing environmental insecticide‐contamination and non‐targeted mortality).     

Synthesis and secretion of volatile short‐chain fatty acids in Triatoma infestans infected with Beauveria bassiana

Physically disturbed Triatoma infestans (Hemiptera: Reduviidae) adults, as well as adults of other Chagas' disease vectors, secrete a mix of volatile organic compounds (VOCs) with alarm and possible sexual and defence functions. The aim of the present research was to test whether infection with the entomopathogenic fungus Beauveria bassiana (Ascomycota: Hypocreales: Clavicipitaceae) has an effect on VOC secretion in disturbed T. infestans and on the expression of two genes (Ti‐brnq and Ti‐bckdc) potentially involved in VOC biosynthesis. The volatiles released by insects at different time periods after fungal treatment were identified and their relative amounts measured. Isobutyric acid was the most abundant volatile found in both healthy and fungus‐infected insects and underwent no significant relative changes through the infection process. The secretion of propionic acid, however, was significantly higher at 1–4 days post‐infection (d.p. i.) compared with that in controls. A slight induction of both Ti‐brnq and Ti‐bckdc genes was found by real‐time polymerase chain reaction at 4 d.p. i., with expression values reaching up to three‐fold those in controls. The early stages of fungal infection seem to affect the composition of the alarm pheromone by changing the expression pattern of both genes analysed. These results help to elucidate the impact of fungal infections on the chemical ecology of triatomine bugs.     

Antipredator responses to alarm pheromone in groups of young and/or old thrips larvae

Many prey species suffer from different predators in the course of their ontogeny. Hence, the alarm signal a small prey individual sends can have a different meaning than the signal a large prey individual sends, both for small and for large receivers. Larvae of Western Flower Thrips face predators that attack only small larvae, or predators that attack small larvae and large larvae. Furthermore, thrips larvae release a two‐component alarm pheromone, which varies in composition with larval age. Here, we study whether their response to alarm pheromone varies with composition of the pheromone. First, we confirmed that large and small larvae respond when nearby larvae of both sizes were prodded with a brush to induce alarm pheromone excretion. Subsequently, we tested whether thrips larvae of a given size respond differentially to alarm pheromone excreted by a small or large companion larva. We analyzed two types of behavior used in direct defense against a predator and one type of escape response. Only small (not large) larvae attempted to escape more frequently in response to excretions from a large larva. This difference in response could have been due to the alarm pheromone or to the companion larva in the vicinity. We subsequently tested for, but did not find, an effect of size of the companion larva on the behavior of the test larva when exposed to synthetic pheromone mimicking that of a large larva. Finally, we tested how pheromone composition affects antipredator behavior by exposing thrips larvae to synthetic pheromones differing in amount and ratio of the two components. Only for small larvae, we found significant changes in escape behavior with pheromone amount, and a trend with the ratio. Overall, we conclude that small thrips larvae respond differentially to alarm pheromones excreted by small and large larvae and that this differential response is due to differences in pheromone quantity and possibly also quality. Our results suggest that responses to alarm signals can vary with the chemical composition of those alarm signals.     

Volatile compounds emitted by Triatoma dimidiata,a vector of Chagas disease: chemical analysis and behavioural evaluation

In this study, we evaluated the responses of Triatoma dimidiata Latreille (Hemiptera: Reduviidae) to volatiles emitted by conspecific females, males, mating pairs and metasternal gland (MG) extracts with a Y‐tube olfactometer. The volatile compounds released by mating pairs and MGs of T. dimidiata were identified using solid‐phase microextraction and coupled gas chromatography‐mass spectrometry (GC‐MS). Females were not attracted to volatiles emitted by males or MG extracts; however, they preferred clean air to their own volatiles or those from mating pairs. Males were attracted to volatiles emitted by males, females, mating pairs, pairs in which the male had the MG orifices occluded or MG extracts of both sexes. However, males were not attracted to volatiles emitted by pairs in which the female had the MG orifices occluded. The chemical analyses showed that 14 and 15 compounds were detected in the headspace of mating pairs and MG, respectively. Most of the compounds identified from MG except for isobutyric acid were also detected in the headspace of mating pairs. Both females and males were attracted to octanal and 6‐methyl‐5‐hepten‐2‐one, and males were attracted to 3,5‐dimethyl‐2‐hexanol. Males but not females were attracted to a seven‐compound blend, formulated from compounds identified in attractive MG extracts.     

A sophisticated,modular communication contributes to ecological dominance in the invasive ant <Emphasis Type="Italic">Anoplolepis gracilipes</Emphasis>

The ecological success of ants is founded on cooperative behaviour and a well functioning communication. Particularly invasive ants are able to act highly cooperatively, out-compete other species, and become ecologically dominant. Since ant communication is to a large extent chemical, we investigated the pheromone functions involved in foraging and alarm behaviour of the invasive tropical formicine Anoplolepis gracilipes. Our results suggest that long-lasting orientation cues are located in hindguts, while Dufour glands contain short-term attractants that trigger an effective recruitment. Poison gland effects were intermediate between hindgut and Dufour gland in terms of orientation, attraction and longevity. In contrast to the other pheromone sources, mandibular glands have a repellent effect and are most likely involved in alarm behaviour. Taken together, the pheromone glands of A. gracilipes contain functionally distinct signals with considerable differences in persistence. In this respect, its communication is exceptional in formicine ants. A strikingly similar communication system was previously detected in Paratrechina longicornis, another opportunistic and invasive formicine ant. Based on these similarities and the differences compared to non-invasive formicine ants, we discuss the role of chemical signals for the coordination of efficient foraging. We conclude that a sophisticated communication system can contribute significantly to ecological dominance and invasive success, in concert with other well known traits.     

Production of butanol by Clostridium puniceum in batch and continuous culture

Summary The pink-pigmented, amylolytic and pectinolytic bacterium Clostridium puniceum in anaerobic batch culture at pH 5.5 and 25–30°C produced butan-1-ol as the major product of fermentation of glucose or starch. The alcohol was formed throughout the exponential phase of growth and surprisingly little acetone was simultaneously produced. Furthermore, acetic and butyric acids were only accumulated in low concentrations, and under optimal conditions were completely re-utilised before the fermentation ceased. Thus, in a minimal medium containing 4% w/v glucose as sole source of carbon and energy, after 65 h at 25°C, pH 5.5 all of the glucose had been consumed to yield (g product/100 g glucose utilised) butanol 32, acetone 3 and ethanol 2. Butanol was again the major product of glucose fermentation during phosphate-limited chemostat culture wherein, although the organism eventually lost its capacity to sporulate and to synthesize granulose, production of butanol continued for at least 100 volume changes. Under no growth condition was the organism capable of producing more than 13.3 g l^-1 of butanol. At pH 5.5, growth on pectin was slow and yielded a markedly lesser biomass concentration than when growth was on glucose or starch; acetic acid was the major fermentation product with lower concentrations of methanol, acetone, butanol and butyric acid. At pH 7, growth on all substrates produced virtually no solvents but high concentrations of both acetic and butyric acids.     

添加有机酸对Clostridium acetobutylicum合成丙酮和丁醇的影响

为提高丙酮-丁醇梭菌厌氧发酵生产丙酮和丁醇的能力,在发酵过程中添加有机酸（乙酸和丁酸）,考察其对菌体生长、溶剂合成影响。实验表明：当添加1.5 g/L乙酸时能够促进菌体的生长,促进丙酮的合成,在600 nm处的最大OD值比参照值高出18.4%,丙酮的最终质量分数提高了21.05%,但不能促进丁醇的合成;当添加1.0g/L丁酸时能够促进菌体生长,促进丁醇的合成,在600 nm处的最大OD比参照值高22.29%,丁醇的最终质量分数比对照组提高了24.32%,但不能促进丙酮的合成。     

Mating behavior of the hematophagous bug Triatoma infestans: role of Brindley's and metasternal glands

We investigated if Brindley's and metasternal glands are involved in the sexual behavior of Triatoma infestans. In laboratory assays, we analyzed the effect of selective occlusion of Brindley's and metasternal glands of the female (separately and together) on the behavior of males. Control assays without occlusion of glands were also performed. We quantitatively tested if such glands affect mating occurrence, the copulatory attempts of males, and the aggregation of males around a mating couple. The number of mating attempts by males did not differ between treatments, demonstrating that likelihood of males mating did not depend on which gland is occluded in the female. In the absence of any occlusion, T. infestans mated and males aggregated. The proportion of copulations and aggregation behavior of males did not differ between treatments when female's Brindley's glands were occluded. However, when metasternal glands were occluded, the proportion of mating couples decreased and males did not aggregate. We demonstrated that the metasternal glands of the female are involved in the sexual behavior of T. infestans, while Brindley's glands seem to have no effect on mating behavior. Copulation and aggregation behavior of males likely result from the eventual release of volatiles from the female's metasternal glands.     

Essential oils as spatial repellents for the brown marmorated stink bug,Halyomorpha halys (Stål) (Hemiptera: Pentatomidae)

The brown marmorated stink bug (BMSB), Halyomorpha halys (Stål), native to Northeastern Asia, is a serious invasive pest in the United States, Canada, Switzerland, Germany and France. Several common essential oils and their compositions were tested against BMSBs as potential repellents. All the tested individual essential oils and a ternary oil blend showed significant repellency to both BMSB nymphs and adults. Clove oil, lemongrass oil, spearmint oil, ylang‐ylang oil, and the ternary oil mixture (clove, lemongrass and spearmint) almost completely blocked attraction of BMSBs to the stink bug attractant‐baited traps; whereas wintergreen oil, geranium oil, pennyroyal oil and rosemary oil resulted in 60–85% trap catch reductions. Over 20 BMSB antennally active compounds were identified from SPME headspace samples of the eight repellent essential oils using GC‐EAD and GC‐MS techniques. Among the synthetic EAD‐active compounds tested in the field, eugenol, l‐carvone, p/l‐menthone, pulegone, methyl salicylate, trans/cis‐citral, methyl benzoate and β‐caryophyllene significantly reduced trap catches of BMSBs by 72–99%; these compounds are likely responsible for the repellency of their corresponding essential oils. Surprisingly, a synthetic mixture of the predacious spined soldier bug (SSB) [Podisus maculiventris (Say)] aggregation pheromone (trans‐2‐hexenal, α‐terpineol and benzyl alcohol) also showed a significant inhibition of BMSB response to its attractants. These repellent essential oils and their active compounds, as well as the synthetic SSB pheromone, are potentially useful as part of an efficient, environmentally sound semiochemical‐based IPM programme to combat this serious invasive stink bug.     

Solvent production byClostridium pasteurianum in media of high sugar content

Summary The fermentation end products ofClostridium pasteurianum ATCC 6013 are normally acetic and butyric acids. When grown in media of high sugar content however, significant quantities of solvents (acetone, butanol and ethanol) were produced. Solvent production was not stimulated by added acetic and butyric acids, nor was the effect due to a low water activity of the mediumper se.     

Effects of butyric and acetic acids on acetone-butanol formation by Clostridium acetobutylicum

The actions of butyric and acetic acids on acetone-butanol fermentation are investigated. Production of butyric and acetic acids are controlled by the extracellular concentrations of both acids: acetic acid added to the medium inhibits its own formation but has no effect on butyric acid formation, and added butyric acid inhibits its own formation but not that of acetic acid. The ratio of end metabolites depends upon acetic and butyric acid quantities excreted during the fermentation. In contrast to acetic acid, which specifically increases acetone formation, butyric acid increases both acetone and butanol formations. Acetate and butyrate kinase activities were also examined. Both increase at the start of fermentation and decrease when solvents appear in the medium. Coenzyme A transferase activity is weak in the acidogenic phase and markedly increases in the solvent phase. Acetic and butyric acids appear to be co-substrates. On the basis of these results, a mechanism of acetic and butyric acid pathways, coupled to solvent formation by C. acetobutylicum glucose fermentation is proposed.     

Social Insect Pheromones: Their Chemistry and Function

Exocrine secretions of social insects are often characterizedby extraordinarily complex mixtures of natural products. Thus,chemical communication in social insects must be interpretedin terms of signals generated by multicomponent systems, theindividual constituents of which can affect the informationalcontent of the message. Alarm pheromones have been identified chiefly in three subfamiliesof ants and their distribution appears to be chemosystematicallysignificant. Myrmicine genera emphasize 3-alkanones as alarmreleasers, whereas methyl ketones, primarily of terpenoidalorigin, are widely utilized as alarm pheromones in the subfamilyDolichoderinae. Formicine species may employ formic acidas analarm pheromone in addition to the compounds produced in themandibular and Dufour's glands. The mandibular gland pheromonesare chiefly acyclic monoterpene aldehydes (e.g., citronellal)which are relatively low boiling compounds. Higher boiling n-alkanesare produced in the Dufour's glands and may serve as more persistentreleasers of alarm behavior. Alarm pheromones as well as thecaste-specific pheromones of male bees and ants, probably alsoserve as defensive products. In many cases it is likely thatpheromones were originally utilized as defensive compounds andtheir communicative function is a secondary development.     

Chemical alarm and defence in the oribatid mite Collohmannia gigantea (Acari: Oribatida)

The multicomponent oil gland secretion of Collohmannia gigantea, a middle-derivative mixonomatan oribatid mite, is demonstrated to possess alarm pheromonal and allomonal properties. Four components of the secretion, namely the monoterpenes neryl formate, neral, geranial and the aromatic 2-hydroxy- 6-methyl-benzaldehyde (2,6-HMBD), showed moderate to strong alarm pheromonal activity in adult mites. Naturally elicited response is due to neral (about 50% of the secretion) and probably 2,6-HMBD (only 5% of the secretion, but strong alarm pheromonal activity). This is the second report of an alarm pheromone in Oribatida. Tridecane and pentadecane (=the hydrocarbon fraction of the secretion) did not evoke evident behavioural reactions, and most likely serve as solvents and spreading agents for the pheromonal-active components. Alarm reactions were characterized by a short recognition phase (waving movements with legs I), followed by shrinking back and panic escape from the scent source. In addition, all six components of the oil gland secretion, including the hydrocarbons, exhibited strong allomonal properties against a model oribatid predator, the scydmaenid beetle, Euconnus (Tetramelus) oblongus. Considering the widespread semiochemical properties of oil gland secretions in astigmatid mites (=a highly derivative oribatid group), these results furnish evidence for a phylogenetically early origin of defensive and communicative roles of oil gland secretions in oribatids. These roles include alarm communication, defence and the production of anti-fungal compounds.     

Evidence for Caste Differences in Anal Droplet Alarm Pheromone Production and Responses in the Eusocial Thrips Kladothrips intermedius

Thrips (Thysanoptera) are tiny insects that produce anal secretions when threatened. Several studies have shown that, depending on the species, the droplets may contain alarm pheromones and/or repellents against enemies. In the eusocial gall‐inducing thrips Kladothrips intermedius both larvae and adults produce such droplets. There are two castes of adults in this species, soldiers (the sub‐fertile and gall‐bound defenders) and dispersers (winged and capable of initiating a gall). We tested the proclivity of secreting anal droplets by the two castes and whether the anal droplets induce different behavioural responses in relation to the emitter–receiver's caste in a contact chemoreception bioassay. Although secretion patterns were similar between castes, exposure to anal droplets emitted by different castes elicited different behavioural responses in adults in the bioassay. When exposed to soldiers’ anal droplets, dispersers significantly reduced the distance moved while soldiers significantly increased the distance moved, compared to when they were exposed to hexane control. In contrast, no differences in the distance moved were observed for any caste when exposed to dispersers’ anal droplets versus hexane control. Increased activity in soldiers when exposed to their own anal droplets is a predicted response to enhance the overall defence of the gall when under threat, whereas dispersers should slow down their activity when exposed to such ‘warning signal’. Thus, the behavioural data indicate that the anal droplets emitted by soldiers are likely to contain an alarm pheromone.