Instrumentation & Measurement Magazine 24-7 - 25

Fig. 4. (a) Example of waveform and (b) spectrogram of defensive buzzing in Bombus impatiens colony. Black arrow denotes the onset of physical disturbance to
the colony. Note that acoustical energy extends to ultrasonic regions.
However, this study had only two replicates and has since not
been repeated.
Bumble Bee Acoustics On or Near
Flowers
Flight Buzzes
Beyond the colony, bumble bees generate sounds as they
fly from flower to flower (Fig. 5). Flight buzzes have historically
received little notice from researchers but have recently
garnered attention for remotely monitoring foraging bumble
bees. Computational auditory scene analysis (CASA) was
used to detect bumble bee buzzes in environments with low
signal to noise ratios [19]. In particular, spectral clustering
and novel 'focal templates'-dynamic T-F filters corresponding
to known parameters of event of interest-were employed
to detect and characterize faint bumble bee buzzes at floral resources.
Importantly, this algorithm showed high levels of
detection accuracy-on par with or exceeding human performance-from
audio collected in noisy natural environments.
The authors of [20] used this software to monitor bumble
bee behavior during a total solar eclipse and [21] built
upon this work to show that flight buzz acoustics can be used
to identify different functional groups (based on body size,
tongue length and fundamental frequency) and to estimate
overall bumble bee activity. The authors of [21] also showed
that buzzes can predict pollination services of two different
alpine clovers. If these results translate to other bumble beepollinated
plants, such as orchards and food crops, AMT may
have applications for real-time monitoring and assessment of
crop pollination. In this vein, [22] demonstrated an integrated
IoT system that uses machine learning and sensor arrays to
October 2021
monitor insect movement across large agricultural fields, and
[23] used machine learning and audio analyses to distinguish
insect types in the field.
Additionally, researchers in [24] showed that flight buzzes
may be used to identify bumble bees to the species level.
They used machine learning and rule-based identification to
differentiate queens and workers of 12 species in eastern Europe
based on fundamental frequencies and audio spectra.
Flight buzzes can be detected in noisy environments and are
replete with useful information, demonstrating promise for
further application. Major next steps for bumble bee flight
buzz research include: continue to refine software to identify
species and functional groups in other geographical areas; develop
semi-permanent or permanent microphone arrays that
use long-life batteries or solar power and transfer data via
Bluetooth technology; and connect acoustic analyses from microphone
arrays near flowers and within bumble bee colonies
to a user-friendly interface.
Buzz-pollination
Buzz-pollination, or sonication, is the act of vibrating anthers
of flowers to release pollen and has been studied extensively
in bumble bees. Approximately 20,000 species of plants have
their pollen 'locked' in poricidal anthers and require sonication
to undergo pollination and thus reproduction. Bees use
a unique buzz that is different than their flight and defensive
buzzes and from pollination buzzes of other bumble bee
species [25], [26] (Fig. 5). The fundamental frequency of pollination
buzzes can be predicted in part by body size [27] and
has harmonics that extend above 2000 Hz [28].
The amount of pollen released by buzz-pollination depends
on several factors. In one study, amplitude and duration
IEEE Instrumentation & Measurement Magazine
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