Pollination and floral insect visitors of non-native Crataegus monogyna Jacq and Crataegus mexicana DC (Rosaceae) in the Eastern Cape Province, South Africa

Abstract

Crataegus species (Rosaceae) or hawthorns form dense thickets and displace native vegetation out of their native range. In South Africa, Crataegus monogyna and C. mexicana are under surveillance but there is lack of information on their pollination ecology. Therefore, this study sought to investigate the pollination mechanism and potential insect pollinators of these plants. Pollinator exclusion experiments were conducted on ten plants each of C. monogyna and C. mexicana near the towns of Hogsback and Seymour respectively, in the Eastern Cape Province. Flowers of each of these species were also observed to determine the diversity and distribution of insect visitors throughout the day (i.e. morning, mid day and afternoon). The results showed that C. monogyna and C. mexicana are capable of self and cross-pollination. Fruit set from open inflorescences of C. monogyna was 40.88 ± 0.08%, significantly higher than bagged inflorences. Fruit set from open inflorescences of C. mexicana was 48.18 ± 0.03%, significantly higher than those of bagged inflorescences. Hymenopterans were the most frequent visitors on C. monogyna flowers while dipterans were the most frequent visitors on C. mexicana flowers. The distribution of insects did not vary with the time of day for each plant species. Insect pollination, therefore, plays a significant role in the fruiting of C. monogyna and C. mexicana in the Eastern Cape. The results of this study contribute to the understanding of the ecology and phenology of Crataegus species in South Africa and thus the evaluation of their invasive status.