I9S3] 
Johnson — Claeoderes hivinaia 
147 
egg to ripen if by chance the female went unmated during her next 
drilling. 
The above arguments do not provide an ultimate explanation for 
why small males of C. /?/v/7/^7/^7 enjoy greater mating success than 
small males of B. anchorago. Comparative studies are planned for 
these two species, which have similar breeding ecologies. Sperm 
competition and methods of detecting rivals will be explored, and 
the behavior and reproductive input of small, medium, and large 
males of both species will be compared. Possibly the system in C. 
bivittata represents an early stage of the development of dual male 
strategies, and may be a step on the evolutionary road to male 
dimorphism (Eberhard 1980). If so, elucidation of the differences 
between C. bivittata and B. achorago could help our understanding 
of the selective environments favoring dimorphic male behavior and 
structure. 
Summary 
Adults of Claeoderes bivittata aggregated on a Quararibea tree 
in Panama. Males ranging in length from 1 1-39 mm guarded and 
mated with females 12-29 mm long as they bored holes in the wood 
for their eggs. Fights often ensued as females tried to pry other 
females from their drilling sites; larger females more often won. 
Males fought males for access to females; larger males won signifi- 
cantly more often. Disputes involving males of similar size could be 
settled by a contest in which the two males stood closely parallel 
head-to-tail, while an antenna lashed a hind leg at either end. Such 
an appendage-lashing contest may permit rivals to assess one 
another’s relative size. 
Although individuals differing by at least 16 mm in length could 
couple, significant size-assortative mating was observed (r = .4). 
Due to the greater aggressive success of larger males and the fact 
that males rejected by females were smaller than males they 
accepted for mating, it was expected that mating males would be 
above average in size. Instead, mating males were significantly more 
likely to be large 31 mm) or small 22 mm). The dispropor- 
tionate mating of small males may be explained in part by the 
tendency of smaller males to wait partly sheltered under a drilling 
female, emerging for copulation when larger males are not guarding 
the female. 
