334 
Psyche 
[Vol. 87 
laboratory N. viridula females and parasitoids interacted more fre¬ 
quently with larger males. Larger males may be more competitive 
than smaller males in aggressive encounters over females resulting in 
non-random mating in insects (McCauley and Wade, 1978; Thorn¬ 
hill, 1980b; Alcock, 1979; Hamilton, 1979). Adult N. viridula males 
are very aggressive. Males are frequently observed attempting to 
dislodge mating pairs. 
Alternatively, a large male may be more likely to attract a female 
if the quantity of pheromone emission is related to male size. The 
relationship between the level of parasitoidization and male size 
supports this suggestion. 
Since the hatching percentage of fertilized eggs was higher when 
females had mated larger males, selection may have acted on 
females to choose larger males even at the increased risk of 
parasitoidization. It has been suggested that when males contribute 
nothing but thier gametes to females, as with N. viridula, the female 
chooses males whose genetic contributions to her progeny maxi¬ 
mizes her fitness (Borgia, 1979; Lacy, 1979; Walker, 1980). How¬ 
ever, it may be doubted that sufficient genetic variation for male 
fitness characters exists to promote this basis of female choice 
(Williams, 1975; Powell and Morton, 1979). There is no reason to 
suspect that larger N. viridula males are genetically preferable to 
smaller males since size in stink bugs often varies greatly with the 
quality of the diet. Thus, environmental patchiness could contribute 
to size variation in males. If size has low heritability it may still 
correlate highly with male health, as indicated by the experimental 
results. Male health may then correlate with the quantity or viability 
of the sperm. Therefore, male size may be a suitable criterion for 
female choice since it may correlate with gamete viability. 
This study does not investigate all of the possible selective forces 
which may promote prolonged copulation. For instance, females 
may benefit from greater sperm transfer if the sperm or associated 
proteinaceous secretions could be used as a nutritional source 
(Mitchell and Mau, 1969; Friedel and Gillot, 1977). Preliminary 
experiments employing captive toads, Bufo woodhousei, and teth¬ 
ered N. viridula indicate that mating bugs are less succeptible to 
attack than single bugs. Also, predatory attempts on mating stink 
bugs are less frequently successful than attempts on single bugs. 
This study does suggest that the behavior, prolonged copulation, 
which appears adaptive in the context of sperm competition is also 
adaptive in other contexts. 
