1977] Leuthold & Bruinsma — Behavior in Hodotermes 
113 
Airborne Pheromonal Attraction 
A female motivated for pairing is clearly attracted from a dis- 
tance apparently by a volatile chemical stimulus from the male. 
When the female crossed a zone 250 cm or less down-wind from 
the male, an immediate reaction of intensified excitement and 
orientation towards the male was always observed. [Eleven ob- 
servations on the natural ground were recorded in which some fe- 
males were used for a second run after experimental displacement. 
Reactions over distances up to 3 m or even more seemed to be 
possible but have not been systematically recorded. The wind was 
a light breeze, windspeed in one case determined roughly 1.5 m/ 
sec.] The possibility that visual cues from the male could be re- 
sponsible for the accurate female orientation was clearly disproved, 
since the same pattern of orientation was observed when the male 
was not visible to the female. Another argument for pheromone 
mediated orientation is the strong correlation of sex attraction re- 
sponse with the exposure of the male sternal gland. When this was 
retracted (after a female had joined the male) another searching 
female was no longer attracted, even if the male was visible. Fe- 
males within the active space of attractive pheromone approached 
the goal in a fast agitated run (5 to 10 cm/sec) performing a char- 
acteristic orienting pattern (Fig. 2). The female’s body-axis altered 
its direction in short irregular turns, performing an irregular broken 
zig-zag line. In superimposed movement the insect walked a greater 
waveline or zig-zag along the main axis leading to the source. A 
female in up-wind position relative to the male oriented positively 
only at distances closer than 6 to 10 cm. This was observed under 
natural conditions and after experimental displacements of the fe- 
male. The observed overall pattern of orientation (Fig. 2) is prin- 
cipally compatible with the theoretical model of airborne chemical 
orientation as reviewed and discussed by Farkas and Shorey (1974). 
This postulates, first, motivation of the insect by the chemical stimu- 
lus to anemotactic orientation, i.e. steering in general up-wind direc- 
tion. Secondly, the course is finely adjusted by a mechanism of 
orientation (e.g. osmoklinotaxis, osmotropotaxis ora combination) 
that involves correction of the lateral deviation from the central 
axis of the aerial trail and enables the insect to remain within the 
odor plume. At close range, where the gradient of concentration 
