The Economist - USA (2020-08-08)

TheEconomistAugust 8th 2020 Science & technology 65

I

nsects dominate dryland. About1m

specieshavebeendescribed,morethan

twiceasmanyasallothermulticellularan-

imalspecies,terrestrialandmarine,putto-

gether.Severaltimesthatnumberarereck-

oned to await discovery. The oceans,

though,aremostlyinsect-free.A fewskate

overthesurface,butnonedivewillingly

belowthewaves.

Atleast,thatwastheconsensusuntilre-

cently.ButSoledadLeonardiatconicet-

cenpatinArgentinaandClaudioLazzariat

theUniversityof Tours, inFrance, have

foundanexception:the 13 speciesoflice

thatlatchontoseals.Thatsealshaveliceis

notnews.ButDrLeonardiandDrLazzari

haveshownthat,contrarytopreviousbe-

lief,thesepassengersdonotabandonship,

asit were,andremainondrylandwhenthe

sealsgoswimming.Instead,theyclingon

and brave not only the hostile, saline

chemistryofseawater,butalsothetremen-

douspressuresimposedwhentheirhosts

divetodepthsofseveralhundredmetresin

searchofprey.

DrLeonardiandDrLazzaridisposedof

thesalinityquestionin 2014 bythesimple

procedureofdunkingsealliceinseawater

for prolonged periods, and discovering

thattheydidnotdie.Now,astheyreportin

theJournal of Experimental Biology, they

havedealtwiththequestionofpressure.

Todoso,theycollectedrepresentatives

ofthelousespeciesthatdwellsuponthe

deepest-divingpinnipedofthemall,the

South Atlanticelephant seal, whichcan

diveasfaras2,000metres.Usingtweezers,

theyprised 75 licefromtheflippersof 15

weaned seal pups that were sitting by

themselvesonthebeach.Theythenput

theirtrophiesintoa bronzecompression

chamber, filledwithsalt water, and ex-

posed the insects to pressures ranging

fromamild30kg/cm^2 (muchlikeswim-

ming 300 metres below the surface) to

200kg/cm^2 (the full two kilometres).

That 69 of the lice survived this treat-

ment suggests that, far from abandoning

their hosts when they go for a swim (which

always sounded a slightly desperate ap-

proach, given that it meant surviving on

the beach until another host came along),

the lice almost certainly stay on board for

the ride. Indeed, an accidental extension of

the experiment caused by an equipment

malfunction suggests 200kg/cm^2 is pea-

nuts for an elephant-seal louse. The mal-

function caused one louse to suffer a

whopping 450kg/cm^2 for several minutes

before the system could be shut down. The

bug survived the ordeal intact.

Assuming lice are typical of the wider

class of insects, it seems that neither chem-

istry nor pressure prevent insect colonisa-

tion of the oceans. As parasites, lice of all

sorts lead fairly pampered lives compared

with their free-living insect cousins. Per-

haps that is the difference. Or maybe respi-

ration is the obstacle—for insects, like

seals, are air-breathing creatures, and

would need, as seals do, to come to the sur-

face to breathe until they evolved gills. But

some freshwater insects (dragonfly

nymphs, for example) have gills, so that

does not seem an unimaginable step. Pos-

sibly, the explanation is that all the oceanic

niches which insects might inhabit are al-

ready taken by their close relatives the

crustaceans. But some crustaceans (woo-

dlice and coconut crabs, for example) have

managed the journey in the opposite direc-

tion, in the face of insect competition. So

what is actually keeping free-living insects

out of the sea remains a mystery. 7

Anexceptiontotherulethatthereare

nomarineinsects

Entomology

Parasitesunder

pressure

A

s theyreopenafterlockdown,

manyrestaurantsarefiringuptheir

barbecues.Dinersappreciatefoodgrilled

overglowingcharcoalembers,butthe

neighboursoftendonot.Pollutionlevels

nearrestaurantscanbenotablyhigher

thanaverage,largelybecauseofemis-

sionsfromkitchens.Withtheincreasing

popularityofindoorbarbecuing,it isa

problemthatissettogetworse.

Facedwithcomplaintsfromresidents

aboutfumesandlingeringsmells,the

GermanEnvironmentAgencyasked

MohammadAleysa,anexpertincom-

bustiontechnologyattheFraunhofer

InstituteforBuildingPhysicsinStutt-

gart,toinvestigate.Theresultsofhis

experimentsweresoshockingthey

droveDrAleysaandhisresearchteamto

inventa cleanersystemforindoorchar-

coalgrilling.

Theresearcherstesteda commercial

grill,completewiththesortofmulti-

stagefilteringsystemusedinmany—

thoughbynomeansall—restaurants.

Apartfromtypicalpollutantssuchas

nitrogenoxides,carbonmonoxideand

particulate matter, they also discovered

polycyclic aromatic hydrocarbons. These

cancer-causing chemicals are mainly

produced by the incomplete combustion

of fats and oil-based marinades.

The researchers estimated that if their

half-a-square-metre grill was used for

nine hours a day, it would release be-

tween 400 and 500 kilograms of fine and

ultrafine particulate matter into the air,

along with 1.5 tonnes of hydrocarbons,

every year. With many restaurants using

2.5-square-metre grills 16 hours a day, the

level of pollution from most commercial

operations would be much higher.

The researchers are investigating

which extraction systems best protect

neighbours and restaurant employees.

Taller chimneys are one option. But Dr

Aleysa suspects they would just shift the

pollution elsewhere. The results of these

tests will be published next year.

Meanwhile, Dr Aleysa’s team have

come up with their own solution: a new

kind of grill, which they reckon can cut

pollutants by 90%. Dr Aleysa is reluctant

to go into specifics. But the basic idea is

that before being vented to the outside,

the fumes are sucked back down through

the embers and into a “combustion

zone”, where hydrocarbons and odour

compounds are fully burnt. That lessens

the need for expensive extraction sys-

tems and fiddly filters that must be regu-

larly cleaned.

An industrial partner is keen to put

the grill into production. It could go on

sale by the middle of next year. It will

cost a bit more than a standard grill, says

Dr Aleysa. But he believes that would be

offset by lower maintenance costs. Better

air quality around restaurants would be

welcome. But the big test will be whether

chefs believe the new grill can produce

that same barbecue flavour.

A good grilling

Cookery

Indoorbarbecuesarepopularbut polluting. A fix may be on the way

All of the flavour; none of the fumes