1964] 
Blum and Wilson — Trail Substances 
29 
Table I. Response of Alyrmelachista ramulorum workers to artificial 
trails prepared from three abdominal organs. 
Organ No. of workers tested No. of workers responding 
Poison gland 180 6 
(plus vesicle) 
Accessory gland 180 O 
Hind gut 180 161 
the tips of their gasters to the substrate. This indicated the possi- 
bility that the trail substance is secreted from some abdominal organ. 
In experiments conducted by Blum in 1963, artificial trails were 
made by streaking single organs and their contents onto a piece of 
paper in the form of a circle six inches in diameter. Groups of 20 
living ramulorum workers were then quickly introduced onto the 
center of the circle and their movements followed. If an ant, upon 
encountering the circle, proceeded to follow it closely at least once 
through its entire circumference, a positive response was recorded. 
The principal terminal abdominal organs were tested in this fashion. 
The results of six replications are given in Table 1. They show clearly 
that the hind gut is at least a major source of the trail substance. In 
supplementary experiments, artificial trails prepared from the hind 
gut of Alyrmelachista were also tested on workers of the following 
species: the myrmicines Solenopsis geminata (Fabricius) and Pheidole 
fallax Mayr, the dolichoderines T apinoma melanocephalum (Fabri- 
cius) and Iridomyrrnex melleus Wheeler, and the formicine Para- 
trechina longicornis. The results were all completely negative. 
Paratrechina longicornis. This pantropical species is well known 
both for the efficiency of its recruitment trails and the length and 
complexity of its persistent trunk trails. In experiments conducted 
by Wilson at Bacolet, Tobago, in 1961, workers were first attracted 
in large numbers to sugar baits. Artificial trails were then led from 
the periphery of the feeding groups outward for a distance of 30 
centimeters. A positive response was recorded if an ant followed 
the trail to at least its midpoint. Control experiments using trails 
of tap water produced entirely negative results. In the experimental 
trails, all of the major organs located in the posterior half of the 
abdomen were tested. The results are given in Table 2. They iden- 
tify the hind gut as the primary immediate source of the trail sub- 
stance. 
Discussion 
Our results do not disclose whether the pheromone is produced as a 
