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Tarsal setae in Coleoptera
Int. J. Insect Morphol. & EmbryoL 5(3): 219-221. 1976. Pergamon Press. Printed in Great Britain.
SCIENTIFIC NOTE TARSAL
SETAE IN COLEOPTERA
N. E. STORK and M. E. G. EVANS Department of Zoology, University of Manchester, M13 9PL, England
(Accepted 20 January 1976) ONE OF THE most important facets of animal locomotion is the contact established between the propulsive organ and its substratum. In terrestrial beetles this contact is between the underside of the tarsi and rock, soil or some sort of vegetable material. Clearly, efficient contact (involving both anchorage and rapid detachmen0 is of great importance to plant-inhabiting beetles, particularly those frequenting leaf surfaces. The fact that vegetation walkers include some of the most successful of all beetles (e.g. Curculionidae and Chrysomelidae) indicates that they have satisfactorily solved the contact problem. At present, however, little is known about the beetle/substratum interface, and this note summarises some work which has recently been commenced. The actual contact is made by the tips of setae which extend from the underside of the tarsi. These setae show a remarkable range of structure in different species and even on different parts of a single tarsus. Some examples of different setal types are shown in Fig. 1. Figi~re 1A shows the whole undersurface of a chrysomelid (Lema cyanella) tarsus. Three of the tarsomeres bear setal pads. Setae with discoid tips are found mesally on the first tarsomere and disto-mesally on the bilobed pads of the third tarsomere. Elsewhere on these bilobed pads the setae have bifurcate, spatulate tips. All other tarsal setae have unspecialised, pointed tips. Setae on the protarsus of the curculionid, Strophosomus melanogrammus are shown in Fig. lB. The rounded setal tips are flattened, and have a central concavity which is usually crossed by a ridge. In the chrysomelid, Phyllodecta vulgatissima (Fig. 1C) the flattened setal tips themselves each bear a single setule. In Fig. 1C, the setai shaft clearly shows longitudinal ribbing. This is present in most tarsal setae so far examined, and is probably a strengthening device. In the Carabidae, the male protarsal setae usually help to hold the female during pairing. Figure 1D shows the setae ofLeistus rufescens, which have shovel-shaped tips borne on straight shafts. The latter is in contrast to the curculionid and chrysomelid beetles described above, whose setal shafts show considerable curvatures to aid flexibility. However, in the carabid setae shown there are a number of transverse ridges at the top of the shaft which may give flexibility to the seta when it is applied to the substratum. Both the thickened lateral margins and the longitudinal curvature of the "shovel" will increase the latter's rigidity. Many zoologists, from the seventeenth century onwards, have tried to solve the problem of how some insects can hold onto smooth, steeply inclined surfaces such as walls and ceilings. Although most of these writers studied the tarsi of flies, a few examined those of beetles and bugs. Gillett and Wigglesworth (1932) and more recently Edwards and Tarkanian (1970) have studied the climbing abilities of various reduviids (Hemiptera). Edwards and Tarkanian concluded that meniscus forces and molecular cohesion between the setal tips and the substratum were the most important forces producing attachment to a surface. The wide variety of setal types in coleopteran tarsi strongly suggests that several attachment methods are employed, including those proposed above. Experimental investigations into the structure and functioning of coleopteran tarsal setae are now being made by the senior author (N.E.S.) and will be reported in due course.
Acknowledgements--We thank the Department of Textile Technology, U.M.I.S.T., for the use of their S.E.M., and Mr. L. Lockey for his photographic help. We are grateful to the Science Research Council for a studentship for N.E.S., and to Professor E. R. Trueman for departmental facilities.
Figure 1 overleaf
219
220
N . E . STORK and M. E. G. EVANS
Scientific Note
221
REFERENCES EDWARDS, J. S. and M. TARKANIAN. 1970. The adhesive pads of Heteroptera: a re-examination. Proc. R. Entomol. Soc. Lond. (A) 45: 1-5. GILLE'I'T, J. D. and V. B. WIC_,GLESWORTrt. 1932. The climbing organ of an Insect, Rhodnius prolixus (Hemiptera; Reduviidae). Proc. R. Soc. (]3) 111: 364-76.
FI6.1. A. A montage of ventral surface of right protarsus ofLema cyanella (L.) (Chrysomelidae). x 425. B. Proximo-lateral view of setae near distal end of left pad on bilobed third tarsomere of left protarsus of Strophosomus melanogrammus (Fo.) (Cureulionidae). x 4800 C. Disto-lateral view of distal setae on bilobed third tarsomere of left mesotarsus of Phyllodecta vulgatissima (L.) (Chrysomelidae). x 10,000 D. Lateral view of distal setae on protarsus of a male Leistus rufescens F. (Carabidae). x 2,000 The specimens were all air-dried and observed o n a Cambridge S.E.M. Mark 2. N.B. Magnifications refer to the original 32 cm x 22 cm plate.
SCIENTIFIC NOTE TARSAL
SETAE IN COLEOPTERA
N. E. STORK and M. E. G. EVANS Department of Zoology, University of Manchester, M13 9PL, England
(Accepted 20 January 1976) ONE OF THE most important facets of animal locomotion is the contact established between the propulsive organ and its substratum. In terrestrial beetles this contact is between the underside of the tarsi and rock, soil or some sort of vegetable material. Clearly, efficient contact (involving both anchorage and rapid detachmen0 is of great importance to plant-inhabiting beetles, particularly those frequenting leaf surfaces. The fact that vegetation walkers include some of the most successful of all beetles (e.g. Curculionidae and Chrysomelidae) indicates that they have satisfactorily solved the contact problem. At present, however, little is known about the beetle/substratum interface, and this note summarises some work which has recently been commenced. The actual contact is made by the tips of setae which extend from the underside of the tarsi. These setae show a remarkable range of structure in different species and even on different parts of a single tarsus. Some examples of different setal types are shown in Fig. 1. Figi~re 1A shows the whole undersurface of a chrysomelid (Lema cyanella) tarsus. Three of the tarsomeres bear setal pads. Setae with discoid tips are found mesally on the first tarsomere and disto-mesally on the bilobed pads of the third tarsomere. Elsewhere on these bilobed pads the setae have bifurcate, spatulate tips. All other tarsal setae have unspecialised, pointed tips. Setae on the protarsus of the curculionid, Strophosomus melanogrammus are shown in Fig. lB. The rounded setal tips are flattened, and have a central concavity which is usually crossed by a ridge. In the chrysomelid, Phyllodecta vulgatissima (Fig. 1C) the flattened setal tips themselves each bear a single setule. In Fig. 1C, the setai shaft clearly shows longitudinal ribbing. This is present in most tarsal setae so far examined, and is probably a strengthening device. In the Carabidae, the male protarsal setae usually help to hold the female during pairing. Figure 1D shows the setae ofLeistus rufescens, which have shovel-shaped tips borne on straight shafts. The latter is in contrast to the curculionid and chrysomelid beetles described above, whose setal shafts show considerable curvatures to aid flexibility. However, in the carabid setae shown there are a number of transverse ridges at the top of the shaft which may give flexibility to the seta when it is applied to the substratum. Both the thickened lateral margins and the longitudinal curvature of the "shovel" will increase the latter's rigidity. Many zoologists, from the seventeenth century onwards, have tried to solve the problem of how some insects can hold onto smooth, steeply inclined surfaces such as walls and ceilings. Although most of these writers studied the tarsi of flies, a few examined those of beetles and bugs. Gillett and Wigglesworth (1932) and more recently Edwards and Tarkanian (1970) have studied the climbing abilities of various reduviids (Hemiptera). Edwards and Tarkanian concluded that meniscus forces and molecular cohesion between the setal tips and the substratum were the most important forces producing attachment to a surface. The wide variety of setal types in coleopteran tarsi strongly suggests that several attachment methods are employed, including those proposed above. Experimental investigations into the structure and functioning of coleopteran tarsal setae are now being made by the senior author (N.E.S.) and will be reported in due course.
Acknowledgements--We thank the Department of Textile Technology, U.M.I.S.T., for the use of their S.E.M., and Mr. L. Lockey for his photographic help. We are grateful to the Science Research Council for a studentship for N.E.S., and to Professor E. R. Trueman for departmental facilities.
Figure 1 overleaf
219
220
N . E . STORK and M. E. G. EVANS
Scientific Note
221
REFERENCES EDWARDS, J. S. and M. TARKANIAN. 1970. The adhesive pads of Heteroptera: a re-examination. Proc. R. Entomol. Soc. Lond. (A) 45: 1-5. GILLE'I'T, J. D. and V. B. WIC_,GLESWORTrt. 1932. The climbing organ of an Insect, Rhodnius prolixus (Hemiptera; Reduviidae). Proc. R. Soc. (]3) 111: 364-76.
FI6.1. A. A montage of ventral surface of right protarsus ofLema cyanella (L.) (Chrysomelidae). x 425. B. Proximo-lateral view of setae near distal end of left pad on bilobed third tarsomere of left protarsus of Strophosomus melanogrammus (Fo.) (Cureulionidae). x 4800 C. Disto-lateral view of distal setae on bilobed third tarsomere of left mesotarsus of Phyllodecta vulgatissima (L.) (Chrysomelidae). x 10,000 D. Lateral view of distal setae on protarsus of a male Leistus rufescens F. (Carabidae). x 2,000 The specimens were all air-dried and observed o n a Cambridge S.E.M. Mark 2. N.B. Magnifications refer to the original 32 cm x 22 cm plate.