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Advisor(s)
Abstract(s)
In nature, honeybee workers acquire their stable gut microbial community
by the 7th day post-emergence, with older bees transmitting
microorganisms to younger bees in the comb, thereby establishing natural
microbial diversity. In contrast, younger caged bees sampled for
laboratory trials (OECD Guideline No. 245) are in contact with older bees
for only a few hours. Newly emerged bees harbor minimal to no bacteria,
potentially resulting in lower diversity, richness, and bacterial loads in
their gut. However, this method best simulates the natural state within a
controlled environment.Existing studies have modified standardized protocols to simulate the
microbiota present in the honeybee digestive tract within the hive
environment. A common approach involves diluting the gut contents of
forager bees and incorporating this into the diet of caged bees.
In our trials, we strictly adhered to OECD Guideline No. 245 (Chronic Oral
Toxicity Test; 10-Day Feeding), exposing newly emerged Apis mellifera
carnica workers to a single concentration of the insecticide
flupyradifurone (FPF, 36 ppm). The standard reference dimethoate (1
ppm) and control groups (pure food and food + acetone) were also
included. DNA was extracted individually from the bee abdomens, and
full-length 16S rRNA amplicon metagenomics were sequenced using
PacBio Sequel II (HiFi/CCS mode).
The absolute abundance of four bacterial genera comprising the core
honeybee microbiota revealed a Lactobacillus-dominated gut in both
treated and untreated bees. Treated bees exhibited a twofold increase in
the bacterial load of Snodgrassella, contrasting with a 50% reduction in
Bifidobacterium and the complete absence of Gilliamella compared to
untreated bees. Our findings demonstrate that FPF significantly disrupts
the honeybee gut microbiota.
This study presents, for the first time, the composition of the gut
microbiota in honeybees strictly subjected to the OECD guideline without
modifications or adaptations. Results from OECD-based tests already meet
reliability requirements for risk assessments. Therefore, following OECD
standards strictly illuminate three distinct advantages: (1) streamlining the
process leading to a ring test, (2) reducing variations introduced by
external factors potentially brought into hives by foraging bees, and (3)
reducing bacterial diversity in lab-tested bees, thereby facilitating the
establishment of acceptable fluctuations in microbiota composition.
We have developed a new approach, overlooked in risk assessments
studies so far, to assess the impact of pesticides on bee health. We
propose adopting this approach as a new endpoint in pesticide risk
assessments. Specifically, we advocate for the inclusion of honeybee gut
microbiota dysbiosis as a sublethal effect in the first screening step of risk assessments, and as a key parameter to assess pollinator's health. We will present a summary of the most relevant bacteria for bee health, alongside
fluctuations in the microbiota and diversity indices. Additionally, we will
provide recommendations on the most suitable indicators for assessing
gut microbiota dysbiosis.
Description
Keywords
Gut microbiota Honey bee Pesticide Risk assessment
Citation
Rosa-Fontana, Annelise; Aguado-López, Daniel; Uriel Clara, Jabal; Martín-Hernández, Raquel; Higes, Mariano; Pinto, M. Alice; Henriques, Dora; Tosi, Simone; Rodríguez Gomez, Juan Miguel (2024). Honeybee gut microbiota is an imperative endpoint for pesticide risk assessment. In 16th International Symposium Hazards of Pesticides to Bees. Sevilla, p. 51-53
Publisher
International Commission for Plant-Pollinator Relationships