( HYNENOPTERA FORMICIDAE ) By
Total Page：16
File Type：pdf, Size：1020Kb
-1— SCENT AND LIGHT ORIENTATION BY FORAGING 4C.1.' ( HYNENOPTERA FORMICIDAE ) by C.T. David, B.Sc.. A thesis submitted for the degree of Doctor of Philosophy of the University of London. Imperial College of Science and, Technology, Field Station, • Ashurst Lodge, Ascot, Berkshire. April 1973. -2- ABSTRACT. After a brief description of the laboratory maintenance of the ants and of the design of the foraging arena, the method of testing for a light orientation in a foraging ant is given. Two methods of orientation are described; pottering and menotaxis. The times taken by ants to complete unsuccessful foraging journeys in the arena are given, and these are compared with figures for other species. The method used by the ants to orient towards the nest is discussed theoretically and experimentally. Experiments were performed to discover the factors maintaining menotaxis in ants leaving the nest, and to investigate the factors affecting the angle of this orientation to the light. Ante orient towards food by different mechanisms. These are described and discussed in relation to various theories of klinokinesis. The method of orienting towards the nest by fed ants is examined, and is found to differ from that of unfed ants. A correlation was found between the distances walked before feeding by an ant, and the distance it subsequently walks towards the nest after feeding. The mechanism of this was investigated. Ants lay trails from food sources too large to carry to the nest in one journey. Experiments are described dealing with the existence and lifetime of trails; the sensory cues associated with the presence of more food than can be carried to the nest; the absence of any intrinsic orientation in an odour trail; the method of orientation of ants following odour trails; and the factors influencing the taking up of a menotaxis in trail following ants. -3- CONTENTS. Page. Section 1. Introduction. 5 Section 2. Materials and methods. Menotaxis and pottering. 11 Section 3. Length of foragint trips. 17 Section 4. Memtaxis in foraging ants, 30 Section 5. Directions taken by ants leaving the nest. 38 Section 6. Klinotaxis or Tropotaxis. 54 Section 7. Klinokinesis. 57 Section 8. The return to the nest, After feeding on outward menotactic orientation 68 After feeding whilst pottering. 75 Section 9. Trail laying behaviour. 81 Evidence for the existence of trails. 84 Stimuli necessary to initiate trail laying. 86 Life time of trails 90 -4- Page. Section 10 Recruitment by odour trails. - 97 Intrinsic orientation of the trails 100 Orientation of ants following trails. 103 Factors affecting menotaxis in trail following ants 111 Section- 11 Summary. 128 Acknowledgements. 131 References 132 -5- SECTION I. INTRODUCTION. A critical summary of the more important works on ant orientation is given by MacGregor (1948), later work has been reviewed by Vowles(1955) and Wilson (1971). Three senses have been widely thought to govern the homing of ants; the antennal sense of odour, the sense of sight, and a kinaesthetic sense. The last of these has never been rigorously demonstrated, howeVer in Sections 6 and lb evidence is given that Mvrmica scabrinodis is able to measure the distance it has walked, which might be considered a form of kinaesthetic sense. Much of the work given here has been concerned with studying the interactions between scent and light orientations in foraging ants. Foraging ants are considered to be those that leave their nest entrance, without carrying any object in their mandibles, and then walk away from the nest entrance for any distance, however small. Ants carrying objects in their mandibles when they leave the nest entrance are not considered any further since their behaviour is different from that of ants without a burden. They leave the nest entrance and take up a menotaxis and walk in a straight line for a few centimetres, then deposit the object they were carrying on the substrate, and return to the nest entrance by reversing the angle of their orientation to the light. it is shown in Section 5 that foraging ants often show a bias in the directions in which they leave the nest, but no such bias could be detected in the directions in which these burdened ants left the nest, even when such a bias was detected in foraging ants. The family Formididae tc which all ants belong has been subdivided into various subfamilies. The latest classification is given by Wilson (1971). He recognises nine subfamilies with living representatives,but considers that these can be divided into two groups, whose common ancestor may not even have been a social insect, and which certainly did not have typical -6- ant like mandibles or antennae. This implies that many factors of ant behaviour, especially those relating to social life such as reactions to trail pheromones, have probably been independently evolved- by the different groups of ants. Because of this it is a mistake to put too much emphasis on similarities between ants in different groups, Even within the subfamily Myrmicinae, three different organs have been found to produce trail pheromones, the poison gland, the Dufour's gland, and glands in the hind tibiae, and the responses of the ants to the pheromones are probably just as varied. So that the relevance of work on other species of ant to this work on the behaviour of Myrrnica can be evaluated there follows a list of the genera of ant mentioned in this thesis together with the subfamily to which they belong, and the larger groups,as classified by Wilson. Group. Subfamily. Genus. Myrmecioid Complex. Dolichoderinae. IIPLE921. Formicinae. Formica. Lasius(Acanthomyops) Camponotus. Poneroid Complex. Dorylinae. Eciton. Neivamyrmex. Myrmicinae. Manica. Myrmica. Pheidole. Solenopsis. Monomorium. Atta. Crematogaster. Pogonomyrmex. Tetramorium. Messor SECTION 2. -7- MATERIALS AND METHODS ANT COLONIES Colonies of Myrmica scabrinodis Nyl. were collected from Chobham Common, Surrey; Silwood Park, Berkshire; and Guernsey, Channel Islands. The ants were identified using keys in Collingwood (1964) and Bernard (1968) and by comparison with specimens in the British Museum (Natural History). NESTS AND MAINTENANCE All colonies used had one or more fertile queens and the ratio of queens to workers was kept at about 1 - 100 by removal of surplus workers. This was done in order to try to keep the conditions inside the nest as standard as possible between different colonies. The colonies were housed in glass and plaster of Paris observation nests filled with sand kept damp by a cotton wick. The nests were connected by interlocking plastic tubes to plastic sandwich boxes with a ring of 'Fluon' painted on the inside wall to prevent the escape of the ants. This design of nest proved very successful and some colonies were kept in them for more than three years. The nests were kept in a 20°C constant temperature room with a 16 hour day, 8 hour night light cycle. The ants were fed on 0.5 Molar sucrose solution contained in glass tubes stoppered at the ends with cotton wool, and on flies (Lucilia spp.). FORAGING ARENA The arena consisted of a wooden table 1.8 x 0.65 m covered with a hardboard board that was in turn covered with a replaceable blank newsprint sheet to give an uniform surface that could be changed in a few minutes. This surface wasdivided by pencil lines into 10 cm squares enabling the paths of the ants to be copied accurately onto sheet s of paper marked with a plan of the arena. These marking lines seemed to have no effect on the orienta- tion of the ants, the lines were not followed by the ants which would cross them at all angles with no signs of any change in direction or speed of move- ment. The arena surface was levelled by means of a spirit level. Ants gained access to the table through a hole, lined by a polythene tube,drilled near to the centre of the table. The nests were connected to this tube by interlocking tubes. -8- Ants did not climb off the table even when it was illuminated from underneath, however there was a considerable edge effect, foraging ants often walking for considerable distances along the edge of the table. The arena was surrounded by fine muslin curtains and covered by a paper roof in order that the movements of the observer would not disturb the ants and that all visual features could be controlled. The arena was lit by two fluorescent tubes above its paper roof, which produced an uniform diffuse light over the arena surface. When these alone were switched on no evidence was found that the ants could orient to any visual features of the arena. Their movements were exactly similar to the movements of ants in dim red light (Page 15 ), so it is unlikely there were any features in the arena by which the ants could orient. There were also light bulbs at each end of the arena in order to provide orienting stimuli for the ants. All these lights were shielded with black paper to reduce light leakage and thus reflections from the walls. The lights could be controlled from the observer's seat beside the table. The arena was housed in a dark room with a minimum temperature of 20°C. All experiments and observations were made at between 20°C and 22°C, though on hot days the temperature in the room sometimes reached 28°C. It is felt that an arena of this size provides a large enough area for most of the natural activities of a Myrmica nest to be carried out. The area 2 of the arena was 1.17 m . Brian (1956) recorded a density of 4.2 nests per square metre for Myrmica scabrinodis in Scotland.