1978] 
Sivinski — Stick Insects 
397 
covilleae was determined by measurement of freshly killed speci- 
mens ( D . veliei — 48 males and 34 females; D. covilleae — 20 males 
and 19 females). 
Results and Discussion 
Mating in both species is initiated by the male mounting the 
female dorsally and gripping her body and legs with his tarsi. 
Females seldom attempted to dislodge a suitor, and were never 
successful. The male abdomen curves underneath the female and his 
clasping organ attaches just anterior to the vulva (sometimes 
attachment is initially well above the vulva). The resulting position 
is typical of the order (Key 1970; Bedford 1978). Some male 
copulatory postures may aid in avoiding takeovers. Alexander’s 
(1964) phylogenetic scheme of orthopteroid mating positions initi- 
ates with female above which then radiates to include a number of 
male above or end to end arrangements. These derived postures are 
conceivably more effective for male control of the area around the 
mating pair. In Diapheromera the dorsal position blocks the length 
of the female abdomen and facilitates additional means of prevent- 
ing attachment by a second male. 
At the approach of another walkingstick the consort almost 
invariably bends the tip of the female abdomen down upon itself 
with his clasping organ. The angle is sometimes sufficiently acute to 
bring the ventral surfaces of the female abdomen on both sides of 
the claspers into contact. A large part of the typical site of attach- 
ment is thereby denied to competitors. Less frequently, mating 
males strike out at approaching males with their forelegs. 
Striking motions and manipulation of the abdomen are effective 
defenses and most attempts of intruding males to attach to a mating 
female were futile. Occasionally second males clasped the female 
abdomen and sometimes succeeded in inserting their genitalia into 
the vulva. This usually occurred when the consort was no longer in a 
dorsal position but had moved to the side of the female to feed. For 
periods of a few minutes to an hour, such “menages a trois” were 
maintained with incident. In 6 of over a score of double couplings 
and combats observed in D. veliei the entire sequence was recorded 
from approach of the second male to resolution of the competition. 
On one occasion the intruder left in less than an hour without 
harassment. In all other cases, fights occurred which followed a 
similar pattern. 
