Bacterial transmission by pollinators to flowers – Impacts on floral biology and fruit development in blueberries (Vaccinium corymbosum ‘Duke’)
A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University
(Lincoln University, 2026) Lignon, Valeria Aiko
Pollination involves a tripartite interaction among insect pollinators, plants, and their associated microorganisms. Insect pollinators come into contact with the nectary of blueberries (Vaccinium corymbosum ‘Duke’), potentially facilitating bacterial transmission from pollinator to flower. Following pollination, flowers develop into fruit, the final product of blueberry reproduction. However, whether pollinator-associated bacteria transferred between the pollinator and the flower also colonise the fruit remains unexplored.
The aims of this thesis were to 1) characterise bacterial communities on the external surfaces of various pollinators (bumble bee (Bombus terrestris), drone fly (Eristalis tenax), honey bee (Apis mellifera) and native bee (Lasioglossum sordidum)), 2) assess whether pollinator-associated bacteria are transferred to blueberry flowers and fruits by different pollinators, 3) assess whether different pollinators alter the floral volatile organic compound (VOC) profiles of blueberry flowers after pollination, and 4) assess whether pollinators influence blueberry fruit quality. To answer these objectives, caged experiments were conducted where individual ‘Duke’ blueberry plants were exposed to different pollination treatments and bumble bee densities. Both pre- and post-pollination stages were sampled to analyse floral VOCs using dynamic headspace volatile sampling and to characterise the bacterial community through 16S rRNA Illumina sequencing for the external surface of pollinators, blueberry nectary, fruit surface, berry skin and berry pulp. Fruit quality traits, including diameter, weight, total soluble solids, pH, phenolic content, and sugar content, were also measured.
This was the first study to characterise the external surface of insect pollinators in relation to blueberry in New Zealand. Each pollinator species exhibited distinct bacterial community composition and diversity, with gut-associated genera such as Gilliamella, Lactobacillus, and Snodgrassella detected on external surfaces. Pollination treatments did not significantly affect bacterial composition or diversity in blueberry nectaries or fruits; however, pollinator-associated genera appeared as minor taxa in these samples. Shared amplicon sequence variants (ASVs) belonging to pollinator-associated genera were detected across pollinators, blueberry nectaries, and fruits, suggesting potential bacterial transmission and that blueberry nectaries and fruits may serve as alternative hosts for these bacteria outside their typical habitat. Floral VOC composition was unaffected by pollinator species or densities; the only change observed was between pre- and post-pollination stages, indicating that pollination itself drives VOC shifts. Similarly, fruit quality was influenced by pollination rather than pollinator species or density, affecting only fruit size (diameter and weight), while the other traits appeared to be controlled by fruit maturation and ripening.
This thesis advances our understanding of plant–pollinator–bacteria interactions in blueberry systems. It demonstrates that while pollinator-associated bacteria rarely establish in blueberry nectaries or fruits, there is a transmission pathway from pollinators to the flowers and then fruits, which bacteria can potentially utilise. Furthermore, pollination itself, not pollinator identity or density, drives changes in floral VOCs and fruit size, while other fruit quality traits remain unaffected. These findings refine our perspective on the ecological and agricultural significance of pollinator-mediated bacterial exchange.
What role do spiders play in pest suppression for future food production systems? | Tō te pūngāwerewere tūranga i te tāmoe riha mō ngā punaha whakaputa kai ā mua
A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University
(Lincoln University, 2026) Sullivan, Nicola
Spiders are the dominant, most abundant, and most diverse natural enemies in agroecosystems. They are generalist predators of insect pests, comprising many different functional groups. Spiders contribute economically to crop protection by reducing pest invertebrate numbers both by direct consumption, and non-consumptive effects. Despite this, few studies on spider biodiversity in crop systems have been completed, particularly in Aotearoa New Zealand.
I present a literature review, highlighting international studies showing positive effects of spider conservation biological control in agroecosystems and discuss the eight studies that have been completed on spiders in agriculture in Aotearoa New Zealand. I describe applied biotremology and how it relates to spiders predating on pest insects.
I outline the first survey of spiders in Aotearoa New Zealand horticultural systems, sampling spiders and harvestmen from vineyards, apple orchards, and kiwifruit orchards in three New Zealand locations. Spiders were sampled using pitfall traps, sweep netting, and active timed hand sampling. A total of 1359 spiders and 87 Opiliones were caught from 17 families and 31 species. There were five dominant spider families caught (Araneidae, Lycosidae, Theridiidae, Linyphiidae, and Desidae), and of the adults, there were five dominant species: Anoteropsis hilaris, Tenuiphantes tenuis, Cryptachaea veruculata, Cryptachaea blattea, and Steatoda capensis. I then present a more detailed study of spiders in kiwifruit orchards that are adjacent to either low-disturbance ecosystems (native forest) or high-disturbance ecosystems (maize), using pitfall traps and active sampling. A total of 2710 spiders were collected from 27 families, representing 64 species and eight functional guilds. The four most common species observed were Tenuiphantes tenuis, Erigone prominens, Leucauge dromedaria, and Anoteropsis hilaris. Orb web weavers were the most represented functional group, comprising 45.9% of the total catch. There was limited support for a spill-over effect for spiders, indicating low land connectivity. The findings did not support the Intermediate Disturbance Hypothesis, with the highest abundance and diversity of spiders being observed in the lowest disturbance ecosystem (native forest) rather than the hypothesised intermediate disturbance ecosystem (kiwifruit).
Finally, I describe lab bioassays undertaken to measure the prey consumption rates of three spider species (Maratus griseus, Socca pustulosa and Badumna longinqua) found in Aotearoa New Zealand kiwifruit orchards, on two economically important kiwifruit insect pests (Scolypopa australis (PVH) and Ctenopseustis obliquana (Cob)). I also measured the prey-capture ability of these spiders on these pests under vibrational disturbance (applied biotremology). Badumna longinqua consumed significantly more (mean 10.4 PVH; 7.7 Cob) prey items than M. griseus (mean 4.9 PVH; 2.7 Cob) and S. pustulosa (mean 4 PVH; 2 Cob) over 5 days. In the vibrational disturbance experiment, the percentage of prey items consumed after 24 h varied significantly with spider species (p<0.001), with fewer eaten by S. pustulosa (17%) than by M. griseus (57%) or by B. longinqua (77%). However, the differences between spider species varied with both vibration treatment and prey species (p=0.022 for the 3-way interaction).
These studies demonstrate spiders’ ability to contribute to low-residue, low synthetic input Aotearoa New Zealand orchard systems.
Grubs up? How insects become food in Aotearoa, New Zealand
Grubs up? How insects become food in Aotearoa, New Zealand
A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University
(Lincoln University, 2025) Hyde, Caitlin
The consumption of alternative proteins is often proposed as a means to alleviate global problems such as environmental degradation and food insecurity. However, achieving such changes remains challenging. To explore this issue, this thesis presents an in-depth case study of the edible insect sector in Aotearoa, New Zealand, a small novel food sector that emerged in the mid-2010s before rapidly declining. This thesis explores the sector’s decline by examining what leads to a thing becoming food. Through this process, the conceptual category of food is also interrogated.
This thesis mobilises a sub-field of geography, sometimes referred to as the ‘becoming food’ literature, a relational approach to food which attends to the embodied practices that lead to a thing being eaten. To better understand the differences between practices and their implications, this literature was brought into conversation with the concept of multiplicity from material semiotics. While both approaches are relational and attend to practices, material semiotic approaches conceptualise relationality differently, not drawing a boundary around where relations end. Their integration enables analysis to extend beyond the relations of eater-eaten to explore broader aspects of production and consumption while maintaining a focus on embodied practice.
To attend to differences, this study incorporated various 'site types' including edible insect research projects, restaurants, farms, food events, and retail outlets. Following the emphasis on practices common to becoming food studies and material semiotics, the methods of participant observation and autoethnography were employed, alongside semi-structured interviews and document analysis.
This thesis examines how insects become food by articulating several enactments of edible insects that have emerged in the Aotearoa sector. Insects were variously enacted as 'good food' (positioned as solutions to various problems), as novelty items (contradicting industry efforts to normalise them), and as pests (in tension with their status as food). The tensions between these enactments and the ambiguity in the status of insects as food led to their decline in the Aotearoa market. Unless edible insects performed a distinctive function, they were replaced with less difficult alternatives that could fill the same role.
While edible insects did become food in many situations, the edible insect sector was largely unsuccessful. Becoming food and market success has typically been equated in the becoming food literature. However, by drawing on multiplicity, this thesis demonstrates the need to treat these as distinct phenomena, contributing to a more nuanced understanding of the becoming food process and providing insight into food transitions and novel food acceptance. Although edible insects have not yet fulfilled their initial promise of reducing hunger and environmental pressures, their potential to transform our food system may lie not in mass consumption but in their power to challenge our assumptions about what food is.