396 
Psyche 
[December 
observed aggression may result from a paucity of observers, a 
consequence of the Phasmatodea being . . less studied than any 
other order of the Orthopteroidea . . (Bradley and Galil 1977). 
This paper describes conflict between males in the walkingsticks 
Diapheromera veliei and D. covilleae. Results of an experiment are 
presented relating male size to ability to monopolize females. Data 
on sex-related size-dimorphism in the 2 species are compared to 
published values for other members of the order to reach tentative 
correlations between population structure, mating strategies and the 
relative size of males. 
Materials 
Adult Diapheromera veliei were obtained in Bernalillo Co., New 
Mexico, from the legume Dalea scoparia, and specimens of D. 
covilleae from creosote bush ( Larrea tridentata ) in Dona Ana Co., 
New Mexico. Observations were made on insects contained with the 
appropriate host plant in 10-gallon aquaria. Densities within 
aquaria varied from 3 to 10 adults. These densities, while high, were 
not unnatural. Up to 7 adult males and a single female have been 
found on a bush whose greatest dimension was 1.5 meters. Insects 
are often unevenly distributed in nature, and it was not unusual to 
see several adult males within 30 cm. of a mating pair. 
The effect of size on the ability of male D. veliei to maintain 
attachment to females was examined by keeping a small (x = 67 
mm.) and a large (x = 87 mm.) male with a female in each of ten 10- 
gallon aquaria. Tandem duration was recorded by checks at 2-hour 
intervals between 8:00 A.M. and 8:00 P.M. 
To determine the distribution of sexual size-dimorphism within 
the Phasmatodea, body lengths of 155 species were obtained and a 
male-over-female ratio calculated for each (data from material 
deposited in the Florida State Collection of Arthropods, Gaines- 
ville, Florida; random selections in Brunner Von Wattenwyl and 
Redtenbacker 1908; the whole of the relevant material in Leigh 
1909; Hebard 1923; Rehn and Rehn 1939; Gurney 1947; Salmon 
1955; Korboot 1961; Bedford and Chinnick 1966; Gustafson 1966; 
Stroheker 1966; Paine 1968; Moxey 1971; Clark 1974). Many of 
the specimens were dried, and the possibility of differential shrink- 
age of the sexes was examined with specimens of D. veliei. 
Shrinkage in both sexes was 0 to 3% of live length after a drying 
period of 2 weeks. The sexual dimorphism of D. veliei and D. 
