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version ISSN 0104-7930
J. Venom. Anim. Toxins vol. 2 n. 1 Botucatu 1996
CHEMICAL COMMUNICATION IN Apis mellifera:
TEMPORAL MODULATION OF ALARM BEHAVIORS.
1 Department of Biology, Institute of Biosciences of Rio Claro, State of São Paulo, Brazil, 2 Center for the Study of Social Insects - CEIS - UNESP, State of São Paulo Brazil, 3 Center for the Study of Venoms and Venomous Animals - CEVAP - UNESP, State of São Paulo, Brazil.
ABSTRACT. The effect of pheromones and their chemical analogues in honeybee alarm behaviors was studied in observation boxes. Defensive behaviors, as follows: a) attraction to scent source, b) elevation of wings in "V", c) abdomen elevation, d) abdomen elevation and pumping and e) first leg pair elevation had been temporarily registered when the following compounds were presented: isoamyl alcohol, octyl alcohol, benzyl alcohol, n-butyl acetate, n-octyl acetate, isopentyl acetate, benzyl acetate and 2-heptanone. The results were as follows: 1. the bees elicited some characteristic behaviors when chemical alarm messages were presented, 2. agression (stinging) was not completed with any compound tested, probably because there was not a target (visual stimulus), 3. in all situations the attraction to scent source was low, 4. all the behaviors were elicited in a temporarily different way, 5. the compounds that elicited stronger responses and a greater number of the investigated behaviors were: isopentyl acetate, 2-heptanone, octyl acetate and n-octyl alcohol. In all situations, the first behavior response (and the most intense one) was the elevation and pumping the abdomen. This suggests that the chemical message was promptly recognized and then transmitted to each worker. So, the results obtained in the present work, suggest that chemical alarm messages may be recognized by different mechanisms of neural integration.
KEY WORDS: Apis mellifera, defensive behavior, alarm behaviors, pheromones, hybrid honey bees, chemical communication.
Colony defense among honeybees involves a number of defensive behaviors stinging being only one of them. Collins et al. (2) proposed a model for honeybee defensive behavior which includes four steps: alerting, activating, attracting and culminating. So, when a colony is molested or attacked, the bees which are at the nest entrance (3) or on the periphery (6) assume initially an alert position, rising their abdomen and exhibiting many characteristc defensive behaviors (4). Afterwards, they can react in the following ways: a) exhibiting an alarm response by opening and protruding their sting chamber, releasing alarm pheromone that will stimulate their nest mates, b) moving away from the disturbance area or c) proceeding to the next step of the model sequence described above.
The two main types of stimulus that can elicit alarm behaviors in African honeybees are chemical and visual. In the present work, the possibility honeybee workers may have to recognize alarm substances in the absence of visual stimuli was studied. An attempt to elucidate the individual function of each alarm pheromone component was also made.
MATERIAL AND METHODS
These experiments were conducted at the Institute of Biosciences of Rio Claro, São Paulo State University, Brazil, (22°, 25' S, 32' WGR), from March to September 1990 and from December 1991 to March 1992.
Thirty-day-old Apis mellifera workers were collected and taken to the laboratory where their behavior against some alarm pheromes was observed. Thirty-day old workers were chosen because at this age their olfatory system is already developed (5) and thus they are more sensitive to alarm pheromones. They have also performed all inner nest activities being skilful foragers.
Groups of 10 workers were collected and placed in wooden boxes (10 cm long X 10 cm high X 7 cm wide), covered by a transparent glass, with one of the faces having a 3 cm-diameter hole, covered by a nylon net for aeration.These groups were given 5 microliters of each pheromone on 2 cm-diameter filter paper discs. These discs were fixed outside the box on the hole with an adhesive tape.
The following pheromones were used: isoamyl alcohol, octyl alcohol, benzyl alcohol, n-butyl acetate, n-octyl acetate, isopentyl acetate, benzyl acetate and 2-heptanone. Octyl alcohol was chosen because it was similar to 2-nonanol which was not available during the experiments.
Observation occurred for fifteen minutes when defensive behaviors such as: a) attraction to scent source, b) elevation of wings in "V", c) abdomen elevation, d) abdomen elevation and pumping and e) first leg pair elevation were temporarily registered. The observation period was divided into 5 intervals (0-3, 3-6, 6-9, 9-12, 12-15 min). The above mentioned behaviors were grouped according to their frequence, considering the intervals.
Two control groups were tested in the absence of chemical stimuli, as follows: one with a filter paper disc and the other without the disc.
Each experiment was conducted three times.
RESULTS AND DISCUSSION
As shown in Figures 1 to 4, the bees elicited some characteristic behaviors when chemical alarm messages were presented. The following behaviors were registered: a) attraction towards scent source, b) elevation of wings in V c) abdomen elevation, d) abdomen elevation and pumping and e) first leg pair elevation.
The compounds that elicited stronger responses and a greater number of the investigated behaviors were: isopentyl acetate, 2-heptanone, octyl acetate and n-octyl alcohol. These results are shown in Figure 1, Figure 2, Figure 3 and Figure 4, respectively.
The other compounds are not represented because they only elicited minimum responses and a few number of the investigated behaviors.
Aggression was not completed with any compound tested, probably because honeybees did not receive any visual stimuli. This result agrees with other data in literature.
In all situations the attraction to the scent source was low.
All behaviors were elicited in a temporarily different way to each compound presented. Thus, the behavioral sequence for isopentyl acetate was d, a, e, c (b was absent), for 2-heptanone d, c, b, a, d (e was absent), for octyl acetate d, a, c, e, b and for octyl alcohol d, a, b, e, b (c was absent).
It can be observed (Figures 1 to 4) that the first behavioral response and even the most intense one was the elevation and pumping of the abdomen. This suggests that the chemical message was recognized promptly and then transmitted to each worker.
These results are similar to those obtained by Collins & Blum (1) although these authors have not mentioned which alarm behaviors had been considered as "bee reactions" during their assays using young bees.
The results obtained in the present work suggest that chemical alarm messages may be recognized by different mechanisms of neural integration.
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02 COLLINS AM., RINDERER TE., TUCKER KW., SYLVESTER HA., LACKETT JJ. A model of honey bee defensive behaviour. Jour. Apic. Res., 1980, 19, 224-31. [ Links ]
03 MASCHWITZ UW. Alarm substances and alarm behaviour in social Hymenoptera. Nature, 1964, 204, 324-7. [ Links ]
04 MASCHWITZ UW. Alarm substances and alarm behavior in social insects. Vitam. Horm. New York, 1966, 24, 267-90. [ Links ]
05 MASSON C., ARNOLD G. Ontogeny, maturation and plasticity of the olfatory system in the worker bee. J. Insect Physiol., 1984, 30, 7-14 . [ Links ]
06 MORSE RA. Honeybee colony defense at low temperatures. J. Econ. Entomol., 1966, 59, 1091-3. [ Links ]
H. COSTA, Departamento de Biologia do Instituto de Biociências, Caixa Postal 199 - CEP 13.506-900 - Rio Claro - São Paulo - Brasil.