26.5 Insectsin stored products
Stored product insects are of tropical or subtropical origin;they live and
reproducebestunderwarm,humidconditions.They are smallin size and
capable of hidingin cracks and crevices.They feedon foodsof low moisture
content.Their reproduction rateis rapid, and most stored product insects
completetheir development within a monthin optimum temperatures. For
example, red flourbeetlepopulationscan increase 70-foldper month.It should
be mentionedthat storedproductinsectsare not knownto transfer pathogenic
microorganismsthat causehumandiseases.
26.5.1 Primaryand secondary insects
In the warmer climates of NorthAmerica a goodexample of a primaryinfesting
insect is the RiceWeevil (Sitophilusoryzae) and the angoumois grainmoth
(Sitotroga cerealella), whichattackthe cropsin the fieldjust before harvest. In
fact,it is this harvest primaryinfestationthat has beenthe original infestation
fromwhichthe grainstores,the silos,truck transport, shipholds, and ware-
housesof moderncommerce also becameinfested. Primaryinsects are uniquely
adapted bothanatomicallyand physiologically to attack the specific foodsupply
theyhaveevolvedwithovertime.The primaryinsect's larvaeand adultsfeed
entirely withinthe kernelsof grainor chewthroughthe outer coatand devour
the insideof the grainor cereal. The commonprimaryinsects are:Sitophilus
oryzae,Sitophilusgranaries(L),Sitophilus zeamaisMotschulsky,Rhizophertha
dominica (F), Lasioderma serricorne (F), Trigoderma granarium Everts,
Bruchidae sp.,Sitotrogacerealella.
Secondary insects are opportunistic insects that feed on the grainonly afterthe
seedcoat has beenbroken eithermechanicallyor by a primaryinsect.Secondary
insects typically feedon materials that are out of conditionand damp, and have
some mouldgrowthpresent.Some secondaryinsects feedon the mouldrather
than the foodproduct.Typically one doesnot find secondaryinsects creatingthe
initialprimary damagein the field;they are insectsthat infestand attackthe food
supply in storage. Secondaryinfestersare not necessarily uniquelyadapted to
attack the foodsupply in the field,althoughtheyhavebecomeadaptedto attack
foodsupplyalreadydamagedby primary fieldinsects. A goodexample of this
wouldbe the saw toothed grainbeetle(Oryzaephilussurinamensis), whichis
typically foundas a secondary infester of cerealgrain,flourand dry fruitsand
vegetables.Othercommonsecondaryinsectsare:Triboliumcastaneum(Herbst),
TriboliumconfusumJacquelin du Val,Cryptolestessp.,Plodiainterpunctella
(Huebner) andEphestiacautella(Walker).
26.5.2 Insectdamage
Veryfew people outside the pest controland hygienic design fieldsrealizethe
value insects extortfrompeople in theirefforts to storeand distribute foodand
other consumable commodities. It is estimated that the annualloss sustained by
414 Handbookof hygiene controlin the foodindustry