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Psyche 
[Vol. 90 
not be worth the energy expenditure for a large male to keep small, 
persistent males from the vicinity of the female. Despite matings by 
small males, large males may enjoy most of the paternity. 
A true answer to the question of the relative reproductive success 
of large and small males awaits determination of the mode of sperm 
competition in C hivittata. Whatever the mode, the relative repro- 
ductive success of a small male is probably less than the relative 
number of matings he achieves. If there is sperm mixing, the small 
males (which in the six cases observed here averaged 200 mg lighter 
than the males with which they co-occurred), probably transfer less 
sperm per copulation than the large ones. In two species of helico- 
niine butterflies, for example, smaller males transfer smaller sper- 
matophores (Boggs 1981). If there is sperm precedence, we would 
expect large males, with the advantage of weight and strength in 
aggressive encounters, to copulate at will when the probability of 
fertilizing the egg is the highest. Small males, mating when they 
could, might or might not transfer sperm at the opportune time. 
The mode of sperm competition is unknown in C. hivittata; 
however, sperm displacement has been found thus far to be the rule 
in Coleoptera (Walker 1980). If sperm displacement does occur in 
C. hivittata, the last male to mate before oviposition would have 
the advantage in paternity. That last male advantage occurs in C. 
hivittata is suggested by the fact that copulation immediately pre- 
cedes oviposition, and that when the female ceases to explore the 
trunk and drill, the male ceases to guard her. 
I would argue, then, that small males of C. hivittata do not enjoy 
nearly as much reproductive success as their proportion of the copu- 
lations would suggest, and that there has not been intense- selection 
for large males to assiduously expend energy excluding them from 
drilling females they are guarding. For small males, however, there 
must at times be an advantage to lingering near a female guarded by 
a larger rival, for otherwise one would predict that small males 
would avoid such females. If there is complete or partial sperm 
mixing in C. hivittata, there exists a possibility, however small, that 
a given copulation by any male at any time will result in fertiliza- 
tion. Even if sperm displacement is complete, there remains the 
possibility that the larger rival, distracted by competitors or a more 
attractive female, will not return before oviposition begins, leaving 
the way open for the small male to copulate last. Similarly, a small 
male that mates just after oviposition might still fertilize the next 
