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

Abstract

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.