1981] 
Duelli & Johnson — Green Lacewings 
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drumming and/or abdominal vibration is known from certain 
Psocoptera (Pearman 1928), Orthoptera (refs, in Rupprecht 1968 
and Morris 1980), Megaloptera (Rupprecht 1975) and Mecoptera 
(Rupprecht 1974). Wing fluttering is also involved in courtship of 
Panorpa spp. (Mecoptera) (Rupprecht 1974) and three genera of 
Coniopterygidae (Johnson and Morrison 1979). 
The function of the abdominal motion in flight is unknown. In 
the Diptera, the halteres (modified second pair of wings) have been 
shown to act as specialized organs to maintain flight stability 
(Pringle 1948). They vibrate in a vertical or nearly vertical plane 
and, as gyroscopic indicators, reveal any change in the spatial 
orientation of the thorax via sensors at their bases. The halteres 
vibrate with the same frequency as the wings, but in antiphase. Since 
the same is true for the abdominal movements in lacewings, it is 
tempting to regard their abdominal vibration as an analogous 
gyroscopic mechanism to stabilize the orientation of the thorax 
during the slow hovering flight, thus keeping the insect in an upright 
position with regard to the horizontal plane. This possibility is 
supported by the similar orientation and abdominal movements of 
flying Plecoptera, Megaloptera ( Sialis spp. and Neohermes sp.) and 
Mecoptera ( Panorpa spp.) as observed in the field. 
Indirect morphological evidence also supports this possibility. 
Whereas most other nocturnal insects have large ocelli, chrysopids 
and most other Neuroptera lack ocelli. An important function of the 
ocelli in locusts and other insects is to recognize relative changes in 
the height of the horizon (Taylor 1981) and thus to stabilize the 
flight position. 
Based on the similarities between abdominal vibration during 
flight and courtship behavior, we suggest that tremulation behavior 
in lacewings and perhaps other slow-flying insects may have evolved 
from a particular “pre-adapted” feature in the take-off and flight 
behavior, where its main function might be flight stabilization. 
Acknowledgments 
We wish to thank Dr. P. A. Adams for verifying the identifica- 
tions of the species studied, Dr. K. S. Hagen for his helpful 
discussions and Dr. F. M. Carpenter for his suggestions regarding 
the manuscript. 
