In early August 2023, I embarked on a new project to investigate the relationship between moths and flowering plants.
I contacted Surrey Wildlife Trust a few months earlier, hoping to use some of their reserves to study moth-plant pollination interactions for my Southampton Biology BSc dissertation. The dissertation, whilst initially daunting, was exciting, as I had the chance to focus on an area of ecology that is critically understudied and which I initially knew very little about.
The intensification of agriculture and the loss of existing habitat have left little room for pollinators, resulting in devastating declines of many pollinator species across Europe. There is a moral obligation as well as a practical reason to conserve pollinators. Pollinator’s mutualistic relationship with plants means pollinator declines can reduce the reproductive success of plant species, directly impacting species dependent on those plants, including us. Conserving remnant valuable pollinator habitat is really important.
Chalk and limestone deposits from seas during the Cretaceous period formed the base for calcareous grasslands. These grasslands support massive floral diversity, allowing them to sustain an exceptional range of pollinator species. They are a haven for many threatened species and can ‘spill’ pollinators into the surrounding landscape.
The value of calcareous grasslands to plants and pollinators is largely dependent on their management. As calcareous grasslands are semi-natural, good management is required to prevent the establishment of small trees and shrubs and keep them in optimal condition.
Traditionally, calcareous grasslands have been managed by grazing livestock. Conservation management of calcareous grasslands usually entails sheep or cattle grazing at an intermediate pressure. The alteration of plant competition through selective herbivory can boost biodiversity. However, in many instances, managing calcareous grassland by grazing is not feasible, and alternative management practices such as mowing take grazing’s place.
Surrey Wildlife Trust manages a number of calcareous grassland reserves through grazing and a number through other means, including by hand. This provided a great opportunity for me to compare the effect of grazing on habitat quality and moth-plant interaction networks to alternative management practices.
Interactions between moth and plant species can be recorded and used to create moth-plant visitation networks. The pattern of interactions (network structure) between moth and plant species can be quantified and used to determine the stability of those interactions and the persistence of those interacting species, an excellent indicator of ecological health.
The most influential species from both plants and moths can be identified in these networks. This can be very informative to conservation efforts. Moth plant-pollinator interactions remain understudied despite moths having been found to be influential pollinators. There is a concern that we are losing moth-plant interactions before we have even begun to understand them.
Sampling moths for pollen can be used to infer what plant species moths have visited and, therefore, be used to generate moth-plant interaction networks. Currently, all published studies euthanise moths prior to sampling for pollen. Perhaps the most valuable result from my study was the creation of a live moth pollen sampling technique using a grocery fruit net sewn into a cone. This was used to gently immobilise trapped moths, regardless of size and shape, and allowed access to their heads for pollen sampling, using a gel extruded from a 1ml syringe, before being released unharmed. This method was used to sample 804 moths for pollen.
Interestingly, Buddleia, a non-native plant genus, was central to the grazed and non-grazed interaction networks. The taxonomic order Lepidoptera made up of moths and butterflies, is known to visit flowers based on nectar abundance, and Buddleia is an excellent nectar source.
Buddleia may initially appear to positively influence ecological health as so many moths visit it. However, it may monopolise existing interactions between native plants and moths, reducing native plants' reproductive success. The centrality of Buddleia in the interaction network reflects previous findings relating to the integration of invasive species into pollinator plant mutualistic networks. Importantly, pollinators can start to depend on non-native species as native plant species decline, meaning that the removal of those non-native plant species could cause the collapse of that ecological interaction network.
Buddleia dominated moth pollen loads. 18,144 Buddleia pollen grains were counted on moth samples. This pollen dominance likely reduces the chance of successful native pollen transfer from moths to native plants. Much more research is needed to conclusively determine the overall impact of Buddleia on ecological health, as sampling did not take place over a range of temporally distinct periods and did not assess its impact on diurnal pollinators, which likely interact differently with flowering plants. These considerations are essential in accurately determining Buddleia’s overall ecological impact.
The value of calcareous grasslands for pollinators stems from the exceptional floral diversity it can support. I found grazed reserves to have higher floral diversity than those that were not grazed. Promoting floral diversity through grazing at an intermediate pressure is the main management recommendation from my dissertation.
It has been a great experience working with Surrey Wildlife Trust. I loved spending a lot of time in wonderfully biodiverse calcareous grassland reserves, sampling a staggering variety of moth species (62 species). The results are valuable, as they uncover important research gaps which could have a big impact on current understanding and conservation practice. This is also the first study to create the first novel live moth pollen sampling method, which should be applied to future Lepidoptera studies aiming to minimise their impact.
Alexander Bayley