1959 ] 
Wilson and Pavan — Chemical Releasers in Ants 
75 
workers in similiar tests, caused in Tapinoma sessile either no visible 
effect or mild excitement in the nest, and increased the outside worker 
force from minus- 1 to 9. A mixture of nepetalactone (oil of catnip) 
and oil of peppermint caused mild excitement in the nest and an 
exodus of 2 to 24 workers. Propyl-isobutyl-ketone caused mild to in- 
tense excitement in the nest and an exodus of 12 to 2 3 workers; 
many of the workers were in maximum intensity of excitement and 
ranged widely over the foraging table. Methylheptenone caused mild 
to intense excitement in the nest, and an exodus of 4 to 69 workers, 
many of which were maximally excited and ranged widely over the 
foraging table. In one trial using methylpeptonone, a queen, several 
callows, and other workers carrying brood also left the nest tempo- 
rarily. 
In two subsequent experiments, small Tapinoma sessile colonies 
were exposed in the manner just described to prolonged doses of 
methytheplenone. In both cases, excitement within the nest and 
individual worker exodus declined to about the normal level within 
10 minutes. Shortly afterward, however, workers began mass move- 
ments along odor trails to secondary shelters away from the main 
nest. Within 90 minutes almost the entire colony had emigrated to 
the new nest sites, leaving behind only a few workers in the main 
nest. 
Summary 
In Iridornyrmex humilis Mayr, I. pruinosus (Roger), and 
Monacis hispinosa (Olivier), representing two genera phylogenetically 
far apart in the Dolichoderinae, the principal or exclusive source of 
the odor trail is the ventral organ, an exocrine gland opening behind 
abdominal sternite VI. Cross-species tests were made with the odor 
trails of these species and of Liometopum occidentale Emery and Tapi- 
noma sessile Say. The trail-substances were found to be species- 
specific. The ventral organ is peculiar to the Dolichoderinae and the 
ancestral Aneuretinae, and it is interpreted as an example of a “social 
organ’’ that has been evolved de novo as part of the colonial communi- 
cation system. 
Volatile alarm substances are produced in the anal glands of each 
of the species except Iridornyrmex humilis . These releasers are not 
species-specific. The volatile anal secretions of Tapinoma nigerrimum , 
methylheptenone and propyl-isobutyl-ketone, when tested with work- 
ers of Tapinoma sessile, produced typical alarm behavior. Prolonged 
exposure induced colony emigration, which was then organized by 
the laying of odor trails. 
