Influential factors of cereal crop landscapes on aphidophagous syrphid communities
Citation:
Gabel, Sarah, Influential factors of cereal crop landscapes on aphidophagous syrphid communities, Trinity College Dublin.School of Natural Sciences, 2021Download Item:
Abstract:
Aphidophagous syrphids are a common group of insects in agriculture, attributed with benefiting farmers with pollination and pest control services. Farmed landscapes are also believed to have potential in supporting and conserving syrphid populations. However, there is still much to be understood in terms of how agricultural factors can influence aphidophagous syrphids, both positively and negatively. The more that is understood about influential factors, the more farmers and conservationists can do to optimize their ecosystem service provision and protect syrphid species. In this body of work, I aimed to investigate various agricultural factors for their influence on aphidophagous syrphids, with a focus on Irish cereal grain crops, and Avena sativa in particular.
First, I investigated the potential for the presence of harmful factors in agri-systems both organic and conventional. residues of pyrethroid (i.e. deltamethrin, esfenvalerate, permethrin) and neonicotinoid (i.e. clothianidin, imidacloprid, thiamethoxam) insecticides in nectar, pollen-laden stamens, and aphid food resources. While pyrethroids were not detected in any of the samples, neonicotinoid residues were detected in every sample media type (maximum residues for nectar < 2.40 ng/mL, stamens < 4.19 ng/g, aphids < 11.33 ng/g). Thiacloprid was detected seven times, imidacloprid once, clothianidin not at all, and no sample contained multiple pesticides. Furthermore, neonicotinoid residues were found in organic and conventional oat crops, suggesting mobility of pesticide residues into areas where they are not applied. These results suggest that aphidophagous syrphids can be exposed to dietary pesticide residues in adult and larval stages, even in fields that did not receive direct applications of pesticides.
I then conducted lab-based bioassays to investigate the lethal and sublethal effects on the adult of a common Irish syrphid (Episyrphus balteatus) from acute oral exposure to ten different concentrations of the neonicotinoid thiamethoxam in nectar food resources, non-control concentrations ranging from 0.01 to 24 ng/?L. While we determined that there were differences between some of the survival rates of the different concentrations (P = 0.016), they were not significant enough to be detected after pair-wise test and corrections for multiple testing. Mortality was not high enough to determine a 72-hour LD50, though an acute LD50 was estimated to be about 100-120 ng per fly 12 days after exposure. Temporary sublethal effects were also observed, with neonicotinoid exposure linked with increased time spent resting, decreased time spent flying and grooming, and a reduced ability to grip smooth surfaces. These sublethal effects were not seen beyond three days after exposure. From these results, it is possible that thiamethoxam dietary exposure in the field poses a low risk to aphidophagous syrphid health, particularly when compared to the detected residue levels from the first study.
Finally, I investigated what natural factors (i.e. hedge habitat structure, food resource availability, food resource competitor abundance) may influence their populations in cereal grain crops. Floral abundances were measured by counting floral units along transects in the crops and along the hedge, and timed walks of these same transects were done for observing adult aphidophagous syrphids and other visitors landing on flowers and oats. Aphids, juvenile aphidophagous syrphids and other invertebrate abundances on the oats were also measured along these transects in the crop from timed hand-searches. Both investigated food resources were determined to be influential to aphidophagous syrphid abundances in organic oat crops, where floral abundance had a positive effect, but crop aphid abundance had a negative effect. The pattern of aphid and aphidophagous syrphid abundances throughout the summer indicated a predator-prey dynamic, in which syrphid predatory activity helped control crop aphid abundance. For food resource competitors, flower-visiting bees and parasitized aphid abundances had positive relationships with aphidophagous syrphid abundance, indicating that any competition that occurs is inconsequential on syrphid abundances. Hedge habitat structure did not correlate to aphidophagous syrphid abundance, though this could be due to my methodology.
This work establishes a starting point of knowledge on dietary pesticide residue hazards faced by aphidophagous syrphids in Irish agriculture, which puts this anthropogenic factor into context of various natural factors. Future research can draw upon the findings of this work to further our understanding of pesticide residues in the agricultural landscapes and how syrphids and other beneficial insects are affected by them, which can inform ecologically friendly practices and policies on pesticide use. Farmers and conservationists can also refer to this work for insight into how the agricultural landscape can impact aphidophagous syrphids.
Sponsor
Grant Number
Irish Research Council for Science and Engineering Technology (IRCSET)
Irish Research Council
Environmental Protection Agency
Environmental Protection Agency (EPA)
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APPROVED
Author: Gabel, Sarah
Sponsor:
Irish Research Council for Science and Engineering Technology (IRCSET)Irish Research Council
Environmental Protection Agency
Environmental Protection Agency (EPA)
Advisor:
Stout, JanePublisher:
Trinity College Dublin. School of Natural Sciences. Discipline of BotanyType of material:
ThesisAvailability:
Full text availableKeywords:
Hover fly, Syrphid, Agriculture, Pesticide, Hedge, Predator, PollinatorMetadata
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