Floral visitors, pollinators and floral rewards of the Australian dioecious arid zone shrub Pimelea microcephala subsp. microcephala

Abstract

ABSTRACT Entomophilous dioecious plants may present opportunities to conserve insect populations as they often possess flowers accessible to a diversity of visitors and potential pollinators. Additionally, flowers of each sex can vary in the nutrients they provide. Two South Australian populations of the largely dioecious arid zone shrub Pimelea microcephala subsp. microcephala (Thymelaeaceae) were investigated to determine the conservation utility of the species to conserve insect populations by assessing floral visitor and pollinator diversity and the nutritional quality of pollen and nectar. Fifty-five visitors representing species in six insect orders were recorded at Baron Station, while 49 visitors from three insect orders were recorded at Clements Gap. Thirty-nine of the observed visitors were captured, of which two species of Hymenoptera, two of Diptera and one of Hemiptera were carrying pollen and thus potential pollinators. Visitation rates were higher for male than female plants at Clements Gap, but the reverse at Baron Station. Pollen from male plants had low protein content (2.5% dried weight (DW)) compared to co-flowering hermaphroditic angiosperms at the sites (5.3–14.0% DW). In contrast, floral extracts from male plants had at least 2× greater cumulative sugar concentrations than those of females at the same site, but female extracts had at least 4× higher protein content than male ones. As a food resource plant, P. microcephala subsp. microcephala may represent an important plant species for revegetation efforts that support the conservation of insect diversity in arid regions and throughout its broad range.