Unsuccessful introduced biocontrol agents can act as pollinators of invasive weeds: Bitou Bush (Chrysanthemoides monilifera ssp. rotundata) as an example

Abstract

The extent of self‐compatibility and reliance on pollinators for seed set are critical determinants of reproductive success in invasive plant species. Seed herbivores are commonly used as biocontrol agents but may also act as flower visitors, potentially resulting in pollination. However, such contrasting or potentially counterproductive interaction effects are rarely considered or evaluated for biological control programs. We investigated the breeding system and pollinators of Bitou Bush (Chrysanthemoides monilifera ssp. rotundata), an invasive species in Australia that has been the subject of biocontrol programs since 1987. We found the species to be obligate outcrossing in all six populations tested. From 150 video hours, we found 21 species of potential pollinators, including Mesoclanis polana, the Bitou Seedfly, native to South Africa and released in Australia as a biocontrol agent in 1996. Mesoclanis polana transferred pollen to stigmas and was the most common pollinator (52% of pollinator visits), followed by the syrphid fly Simosyrphus grandicornis (9%) and introduced honeybee, Apis mellifera (6.5%). Fruit‐to‐flower ratios ranged from 0.12 to 0.45 and were highest in the population with the greatest proportion of Mesoclanis polana visits. In an experimental trial, outside the naturalized range, the native bee Homalictus sphecodoides and the native syrphid Melangyna viridiceps were the primary pollinators, and fruit‐to‐flower ratios were 0.35, indicating that Bitou Bush would have ready pollinators if its range expanded inland. Synthesis. Invasive Bitou Bush requires pollinators, and this is effected by a range of generalist pollinators in eastern Australia including the Bitou Seedfly, introduced as a biocontrol agent, and the major pollinator detected in this study. Fruit‐to‐flower ratios were highest when the Bitou Seedfly was in high abundance. This study underscores the importance of evaluating the pollination biology of invasive species in their native ranges and prior to the introduction of biocontrol agents.

Increased reproductive success through parasitoid release at a range margin: Implications for range shifts induced by climate change

“…This positive relationship between pollinator gall numbers and seed set per syconium is consistent with results from studies of developing pollinator and seed numbers in other Ficus species (Bronstein et al, ; Peng et al, ) and in other nursery pollination systems (e.g. Gross, Whitehead, Silveira de Souza, & Mackay, ; Kula, Castillo, Dudash, & Fenster, ; Riley, ). However, this relationship varies among Ficus species (Herre, ), often according to syconium size.…”

Long term monitoring of recruitment dynamics determines eradication feasibility for an introduced coastal weed

“…Supporting this are the soil seed bank studies indicating that the number of viable seeds is approaching zero. Also supporting the feasibility of eradication is bitou's reproductive system, where it appears that cross pollination is necessary (Gross et al 2017). This means that isolated plants can become large enough for detection, often by the presence of flowers, without the risk of contributing to the seed bank.…”

“…Taken together, these observations provide circumstantial support for bitou bush being an obligate outcrossing species, perhaps with a very low level of selfing. Gross et al (2017) performed cross pollination experiments on six populations from eastern Australia and found that in all populations bitou bush was an obligate outcrossing species. This implies that invasion would be more difficult than if the species was self-fertile (Baker's law;Baker 1955), although there are many examples of colonists with obligate outcrossing and the ideal of a "law" is questioned (Pannell et al 2015).…”

The Impact of Invasive Aliens Species of Plant in Dryland Crop Production

“…According to Nel et al [28] the presence of invasive plants become competitors of other plants that can reduce pollination by insects. The statement was supported by Gross et al [29] which states that an estimated more than 85% of plants in the world take the role of insect pollinators. Pattison et al [30] stated that the presence of invasive alien plants can affect vegetation dynamics.…”

“…This is caused because of some invasive plant species have shapes and floral display more exotic and able to attract insect pollinators. This resulted in the frequency of attendance at local plant-insect pollinator decline and direct impact on the amount of the resulting production [13]. Also, invasive plants can cause structural changes in the soil, the decomposition process, and soil moisture [14].…”