Pollinator Behavior in White Clover (Trifolium repens L.) Patches and Its Consequences to Seed Set in a Zoysia-Type Sward

Abstract

In the Trifolium repens population which has been patchily distributed in a Zoysia-type sward, seed production in those patches is an important process in maintaining the population size. In this paper, we examined the nature of pollinator behavior in T. repens patches and its consequences to seed set. Following questions were addressed : (1) Does visitor abundance in individual patches increase with number of flower-heads at flowering in a patch? (2) Does average seed set per patch increase with number of flower-heads at flowering in a patch? (3) Are significant differences in pollinator attractiveness found among flowering stages at flower-head level? We observed pollinator behavior in 10 discrete patches of T. repens and examined seed set 3 weeks later. The most important pollinators were solitary bees. Visitor abundance in individual patches increased with number of flower-heads in a patch (r = 0.982, P <0.01). Averaged data of all patches, mean number of seeds per pod and pod set were 0.472 and 27.4%, respectively. No significant relationships were found between these parameters of seed set and number of flower-heads at flowering in a patch. Significant differences were found in pollinator attractiveness among flowering stages of flower-head : flower-heads at peak flowering were more attractive to pollinators than those at early flowering. Above facts suggest that (1) visitor abundance is different among patches, depending on number of flower-heads at flowering, (2) large patches with more flower-heads at flowering synchronously do not always have higher seed set, and (3) pollinators are likely to select individual flower- heads according to their stages of flowering as well as patches.