Pollinators, pests and yield – multiple trade-offs from insecticide use in a mass-flowering crop

Multiple trade-offs are likely to occur between pesticide use, pollinators
and yield (via crop flowers) in pollinator-dependent, mass-flowering crops
(MFCs), causing potential conflict between conservation and agronomic
goals. To date, no studies have looked at both outcomes within the same
system, meaning ‘win-win solutions’ for pollinators and yield can only be
inferred. Here, we outline a new framework to explore these trade-offs,
using red clover (Trifolium pratense) grown for seed production as an
example. Specifically, we address how the insecticide thiacloprid affects
densities of seed-eating weevils (Protapion spp.), pollination rates,
yield, floral resources and colony dynamics of the key pollinator, Bombus
terrestris. Thiacloprid did not affect the amount of nectar provided by,
or pollinator visitation to, red clover flowers but did reduce weevil
density, correlating to increased yield and gross profit. Colonies of B.
terrestris significantly increased their weight and reproductive output in
landscapes with (compared to without) red clover, regardless of
insecticide use. Synthesis and Applications: We propose a
holistic, conceptual framework to explore trade-offs between pollinators,
pesticides and yield that we believe to be essential for achieving
conservation and agronomic goals. This framework applies to all
insecticide-treated mass-flowering crops (MFCs) and can be adapted to
include other ecological processes. Trialling the framework in our study
system, we found that our focal insecticide, thiacloprid, improved red
clover seed yield with no detected effects on its key pollinator Bombus
terrestris and that the presence of red clover in the landscape can
benefit pollinator populations.