takingtemperaturereadingson a continuousbasis.The readingscan be taken
using either portable temperature probes or permanent installations of
thermocaples,capableof providingreadingsfromall depthsof the grainbulk.
Moisturemeasurements are a very importantcriterionfor grainstorability.
The measurementsare carriedout usingspecialmoisturemeters and alsoby
laboratorymethods.
26.6.2 Chemicaland physicalcontrol measures
Although thereare manytoolsand methods available to helppreventinsect
infestation,it is almostimpossibleto stopthe entryof insecteggsinto grain
storageareasand in driedproductprocessing and packagingplants.As a result
thereare a numberof chemical and physicalcontrol measures availableas a
supplementto preventivemeasures.
Chemicalcontrols
It must be consideredthat most pestcontrolprocedures usually involvethe
application of chemicals. These include fumigants, aerosols and residual
insecticides.
Fumigationis the most effectivemethodfor insectcontrol.Undercontrolled
temperaturesthe fumigant can penetrate into packagingmaterialsand bulk grain
to kill all stagesof insectdevelopment.The componentsare highlytoxicand
needto be handled withgreatcare.However, theirtoxicity and penetrating
ability makethemhighlyeffective.In fumigationa toxicsubstance in the form
of a gas is addedto an enclosure (fumigantchamber or silo)or structure
(building/processingplantor warehouse) or undergas-proofsheets,whichcan
be keptsufficientlygas-tightfor this purpose.The requiredconcentrationof gas
must be maintainedfor a specific periodof time,withthe containeror building
ventilatedaftermeetingminimumtimesand concentrations. Theamount of
fumigantis dependent on the targetinsect, temperature,and levelof container or
building tightness.
Twomajorfumigants are verycommonfor the controlof storedproduct
insects, methylbromide and phosphine(PH 3 ). Methyl bromide is classified as a
seriousozone-depletingsubstance and its use will be phased out in the near
future in all developedcountries.Studies also revealedthat insects are develop-
ing resistanceto phosphine.Besides,PH 3 is corrosive and slowacting,withan
exposure timeof between4 and 28 days,whichdepends on temperature and the
commodity. PH 3 is availablein a numberof formulations:in bags,plates,
pellets, tablets,sachets and alsocylinderformulation,phosfume(a pre-mixed
phosphine in 98%CO 2 ). Three types of solidphosphineformulationshavebeen
developedand can be usedfor variouspurposes: aluminumphosphide for hot
ambient;magnesium phosphide for coldambient and methylphosphide against
resistant insects. Amongotherfumigants, sulfuryl fluoride(Vikane ProFume)is
usedas a spacefumigant primarily for controlling dry woodinsects, termites and
other pestsof structure. Ethylformateand methyliodideare not licensedyet.
420 Handbookof hygiene controlin the foodindustry