Winter-active parasitoids and pollinators

: Uncovering evidence of floral resource competition

Abstract

Milder temperate winters have resulted in an increase in the winter activity of many beneficial insects, including the parasitoid wasp and biological control agent Aphidius ervi Haliday (Hymenoptera: Braconidae), at a time when floral resources are scarce. Parasitoids obtain fitness benefits through nectar-feeding and, for this reason, supplementary floral resources can enhance winter survival, and in turn parasitism rates and biological control provision. However, parasitoids are vulnerable to competition with larger foragers like the buff-tailed bumblebee (Bombus terrestris) (Hymenoptera: Apidae), whose populations have begun to produce a second generation in lieu of entering diapause. Laboratory cage experiments were performed to explore the impact of B. terrestris presence on A. ervi under winter conditions when given access to a floral resource (buckwheat Fagopyrum esculentum or white mustard Sinapis alba). Experiment 1 explored the impact of bee presence on the parasitism rate of A. ervi on the English grain aphid (Sitobion avenae). Whilst a significant main effect of bee presence on parasitism indicated that competition with B. terrestris may reduce parasitism rates, post-hoc testing was unable to identify any individual differences across treatments. Additionally, diet treatment did not impact parasitism rate. Experiment 2 employed Raspberry Pi microcomputers to investigate flower and wheat visitation to uncover potential interference competition. Although bee presence did not affect the number or duration of visits, low data obtained from video footage means this should be taken with caution. Upon completion of parasitism rate experiments, parasitoids were frozen for metabolomic profiling to investigate nutritional status and potential exploitative competition. Metabolomic profiling, performed by an external facility, could not be completed within the submission timeframe and, as such, evidence for exploitative competition could not be established. Overall, winter-active parasitoids may be impacted by competition with B. terrestris but further research, and the results from metabolomic profiling, are needed for confirmation.

Date of Award	20 Jan 2026
Original language	English
Awarding Institution	University of Bristol
Supervisor	Lucy Alford (Supervisor) & Martin J How (Supervisor)