Instrumentation & Measurement Magazine 24-7 - 21

What's the Buzz About?
Progress and Potential of
Acoustic Monitoring Technologies
for Investigating Bumble Bees
Zachary J. Miller
P
ollination is a vital ecosystem service for both natural
and agricultural ecosystems. Most flowering
plants-including many staples in the human diet
such as fruits, vegetables and nuts- require animals for pollination.
The majority is done by over 20,000 species of bees,
some of which are managed commercially to provide these
services. The global industry of pollination is valued at US
$153 billion annually and is increasing in demand to meet
the needs of a growing human population [1]. However, both
managed and wild bees, especially the ecologically and economically
important bumble bees (Bombus spp.), are suffering
alarming declines worldwide, presenting serious implications
for food security and biodiversity. Despite numerous pleas by
farmers and scientists for improved management and monitoring
methods [2], [3], precision techniques for these essential
pollinators are still lacking.
Recent advances in acoustic monitoring technologies
(AMT) show promise for bumble bee investigations. Bumble
bees create a range of distinguishable sounds while flying,
sonicating (buzzing on flowers to eject pollen) and interacting
within the colony, making them amenable for acoustical
surveys (Fig. 1). While acoustic-based techniques have been
used to study bumble bees, most of these efforts pre-date advancements
in computer programming, machine learning and
automation, and thus have not been widely adopted. Current
standard practices in bumble bee monitoring include netting,
trapping, and in-person observations, which are laborious,
costly and often require lethal collection of bumble bees. AMT
offer an alternative approach that is affordable, scalable and
non-destructive, with potential to augment conservation and
agricultural practices.
The sounds produced by bumble bees may be useful to
researchers and farmers regardless of their implications for
survival and reproduction. The types of questions that can be
answered will differ, as some bumble bee sounds produced
have roles in communication with other bumble bees or with
predators-e.g., 'buzz runs' and defensive 'hisses'-making
them amenable for eavesdropping on colony behavior; others
are by-products of non-communicative activities- e.g., flight
October 2021
buzzes-providing opportunities to remotely track and monitor
bees foraging on flowers. This review focuses on audio
signals that are distinguishable rather than biological signals
that are communicative; the former includes the latter, but not
vice versa.
Application of AMT to investigate bumble bees is still nascent
in development, and improvements are needed across
all stages of the AMT process, from sensor technologies and
data transfer to audio classification and user interfaces. Here,
I review the sound-producing activities of bumble bees, highlighting
extant research and underscoring opportunities for
further investigation. For each sound or soundscape, I emphasize
the acoustic features that make it unique to particular
behaviors and discuss how AMT could benefit bumble bee
research and agriculture. In particular, I examine sounds produced
from within bumble bee colonies and from bumble bees
on or near flowers; I then discuss the potential application of
AMT to study a major threat to bumble bees, and I conclude by
reiterating the importance of cross-disciplinary collaboration
between ecologists and computer scientists to monitor and
manage species of conservation concern.
Acoustics of the Bumble Bee Colony
There are over 250 species of bumble bees, and they are distributed
in most temperate and mountainous regions worldwide.
They are important pollinators for many wildflowers and
crops such as tomatoes and berries. Like honeybees and ants,
bumble bees are social, exhibiting both cooperation and division
of labor within their colonies. Bumble bee colonies vary
in size from 20-400 individuals, depending on the species,
and provide shelter for many stages of life history including
egg-laying, wax cell construction, rearing workers, resource
caching and producing the next season's queen bees. Fertilized
queens overwinter underground and then begin colonies
anew the subsequent spring. Wild bumble bees establish their
colonies in old animal burrows or other small cavities; colonies
reared for commercial use in crop pollination are housed
in small plastic or wooden containers that can be moved
among greenhouses during flower blooms. The soundscape of
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