THE EFFECT OF MALE SIZE AND OPERATIONAL SEX-RATIO ON MALE MATING SUCCESS IN THE COMMON SPIDER-MITE, TETRANYCHUS-URTICAE KOCH (ACARI, TETRANYCHIDAE)

The effect of male size and operational sex ratio (number of adult males/number of adult males + number of females available for mating) on male mating success in the spider mite was studied both in the field and in the laboratory. Larger males defended females less intensely and for shorter periods, but had a higher probability of mating with a previously guarded female than smaller males. With increasing operational sex ratio agonistic interactions between males occurred more frequently and lasted longer. Large males guarded more selectively, i.e. spent less time guarding, than small ones. With increasing density of quiescent females (females in the final juvenile stage) all mates became more selective. Only small males guarded less selectively with increasing male bias. Females mated repeatedly. A female’s first mating lasted longer on average than subsequent matings. In the absence of male-male competition, absolute mate size was positively correlated with the duration of the first mating. When males competed for females, the larger males were better able to resist attempted interference in mating than smaller males. Compared with balanced or female-biased operational sex ratios, mating interferences tended to be more common, although not significantly so, when the operational sex ratio was biased towards males. A male’s chance to mate twice with a given female decreased with increasing operational sex ratio. Depending on the degree of male-male competition in a spider mite colony, the effects of male size on fighting ability, chance to mate, duration of precopulatory mate guarding and duration of mating will contribute to variation in male reproductive success in natural populations. Copyright © 1993 The Association for the Study of Animal Behaviour.