80 Science & technology The Economist June 11th 2022
AgriculturalentomologySon, et lumière
I
nsectscausebillionsofdollarsofdam
age to crops every year, driving farmers
to apply pesticides on an industrial scale,
at huge expense and often with unwel
come ecological sideeffects. They take
this carpetbombing approach because
they lack information about where and
when it is best to hit pests, and nobody
wants to use too little pesticide and thus
risk losing crops. Technologists at Farm
Sense, a firm in Riverside, California, hope
to change that.
The established approach to detecting
insect pests, moths in particular, is to em
ploy pheromonebaited sticky traps. Pher
omones are chemicals which animals use
to communicate—and especially to attract
members of the opposite sex. An appropri
ately baited sticky trap gives a fair idea of
the number and type of pests around, but
not with sufficient detail for the precise
application of pest control measures. Such
traps have, however, changed little in de
cades, except that some now come with a
digital camera which transmits a daily pic
ture of the trapped insects. FarmSense’s re
searchers reckon they can do better.
The company’s device, FlightSensor,
has been in fullscale tests on farms since
2020 and is about to be made generally
available. It does not trap insects. Rather, it
scans them with a laser as they fly by. The
developers’ insight was that the shadows
of passing wings produce the same oscil
lating signal as the sound of the wing beats
recorded by a microphone. This approach
is similar to bouncing a laser beam off a
glass window to detect the vibrations of a
conversation in the room beyond, a tech
nique employed in espionage for decades.
FlightSensor’s technology builds on the
work of Eamonn Keogh, one of FarmSens
e’s founders, who is also a professor at the
University of California’s Riverside cam
pus. Dr Keogh helped pioneer the field of
“computational entomology”, in which
special algorithms receive data from scan
ners and learn to determine the sex and
species of passing critters. FarmSense
claims to have more digital data on insects
than the rest of the world combined.
For the first tranche of targets the re
sults are impressive. Navel orangeworm
moths, in particular, are a common pest of
almond and pistachio trees—both impor
tant to Californian agriculture. FlightSen
sor can identify them accurately more than
99% of the time. And the algorithm is stillimproving its capability, and adding new
species as it gets more data. Sometimes it
can distinguish insects which, to a human
eye, look identical.
FarmSense’s optical approach works
better than microphones for recording
wing beats because the insects under in
vestigation are quiet and the sound they
emit thus easily lost in background noise.
Bees and houseflies buzz about noisily. But
moths and the trichogrammatid wasps
that parasitise them (or, rather, their cater
pillars), and are therefore of almost equal
interest to farmers, are all but inaudible.
They are easily detectable by laser, though.
And while sticky traps are at least an alter
native for large moths, the FarmSense sen
sor picks up everything, down to tricho
grammatids a thousandth of the size of the
moths these wasps are interested in.
In contrast to existing traps, which re
port only total numbers captured in a given
period, the new sensors record each insect
as it arrives, revealing diurnal and noctur
nal patterns of activity. In one case, Farm
Sense was able to show a farmer that navel
orangeworm moths appeared in her fields
only between three o’clock and five o’clock
in the morning. So, rather than spraying
disruptive pheromones throughout the
hours of darkness, she is able to restrict the
puffing around of these chemicals to times
when moths are active, cutting the amountof pheromone required by 80%. American
farmers spend hundreds of millions of dol
lars a year on pestreducing pheromones,
so reducing their use in this way should
bring useful savings.
There should be ecological benefits as
well. In particular, pesticides of all sorts of
ten have sideeffects on benign, and even
desirable insects. Using a more targeted
approach which deployed less of them
would reduce that problem.
A further advantage of the new sensors
is their lack of need for maintenance.
Sticky traps eventually stop being sticky,
because of a buildup of either dust or of
dead insects, so someone has to replace the
sticky cards. FlightSensors will function
for months at a time, reducing the labour
and other associated costs.
The sensors should also prove useful
for academic entomologists. Marta Skow
ron Volponi of the University of Gdansk, in
Poland, is employing them to look at bee
mimicking clearwing moths. They may
help her discover how the insects manage
to sound like bees as well as looking like
them. Meanwhile, at the University of Cali
fornia’s campus in Davis, Joanna Chiu is
using them to study the daily activity of
Drosophila, a fruit fly that is one of the
workhorses of genetics.From farm to lab,
then, listening toinsects with light may
soon be all the rage.nTechnology used by spies is detecting
pesky mothsAfossilfeast
This is part of the oldest known mayfly swarm. It was collected, by a team led by
Zhang Qianqi of the Nanjing Institute of Geology and Palaeontology, from a site near
Hezhou, in southern China, and is reported in the latest edition of Geology. Some 180m
years ago, during the early part of the Jurassic period, this site was a lake where may
flies lived and swarmed to mate, as they do today, providing, as a sideeffect, a feast
for local insectivores. These probably included small pterosaurs, but not birds, which
had not yet evolved. Insects rarely fossilise well in rock (though they do in amber), but
in this case exquisite anatomical details of the creatures are visible in the mudstone
that has solidified from the lake’s sediments.