Insect-mediated pollination drives reproductive success and spread of the invasive vine Cynanchum acutum in a hyper-arid agroecosystem

Cynanchum acutum L. (swallow-wort) is a perennial herbaceous vine that has become locally invasive in date plantations in the southern Arava, Israel, a hyper-arid agroecosystem, endangering both young and mature date palms. C. acutum ’s invasiveness is linked to its ecological and phenotypic plasticity, its ability to reproduce asexually through rhizomes, and its ability to reproduce sexually via wind-dispersed seeds. Insect-mediated pollination and its role in C. acutum reproduction and spread were examined by (i) identifying insect visitors and assessing their relative visitation rates throughout the blooming period and (ii) assessing the influence of biotic pollination on fruit and seed set, as well as rhizome development. A standardized survey of insect visitors to C. acutum was conducted in three date plantations. Flies, ants, beetles, butterflies, wasps, and bees (in decreasing order) dominated floral visitation. In a controlled experiment, fruit production differed significantly between pollination treatments ( W = 56, r = 0.73, p = 0.004). Insect-pollinated plants produced significantly more fruit than self-pollinated plants, which failed to produce fruit. Of the 40% of flowers that set fruit, 50% reached seed maturity. Insect-pollinated plants were associated with lower shoot biomass ( r = 0.816, p = 0.021) and root biomass ( r = 0.612, p = 0.055), indicating a reproductive trade-off and a shift in resource allocation toward reproductive output. These findings identify insect-mediated pollination as a key driver of successful seed-based reproduction and spread in C. acutum and provide a basis for phenology-targeted management.