Temperature
Temperatures above40 ÎC are not favourablefor the developmentof most stored
product insect pests, while temperatures below 21 ÎC will retard insect
development. Food temperatures of 18 ÎC or below significantly inhibit
reproductionof primary graininfesterssincetheydo not lay eggsat these
temperatures.
Food
Store product insects feed on plant material except for insects of the
Dermestidae familywhichfeedon animalskins. However, the typeof food
that insects consumedirectlyaffectstheirabilityto increase theirpopulations.A
good example of this is the cocoa moth: apart from the proteins and
carbohydrates the mothneedsto buildbodypartsand supply energy,this moth
cannotdevelop, thriveor compete withoutvitamin B. Insects that bite and chew
theirfoodmay drinkwater;however, mostof the dried storagepests obtaintheir
necessarymoisture fromthe solidfoodtheyconsume. Someinsects that infest
verydry foodmaterial obtaintheirwatersupplythroughcondensationdue to
temperaturechanges in the product.
Light
The effects of changes in light intensity or photoperiodicity on insect
developmenthas shown its importance in relationto the maturationof the
reproductiveorgans in storedproduct insects.
Atmospheric gases
Atmospheric gasessuchas oxygenand carbon dioxidehavea direct effecton an
insect's abilityto survive. In fact,insects cannotsurvive in the absence of
oxygen.Graininsects sealedup in air-tightvessels, withor withoutwheat, die as
soonas the oxygenhas beenusedup, and correspondingamountof carbon
dioxide is produced by live wheat.Thereis also an optimum moisture contentin
the wheatthat willresultin maximumproductionof carbondioxide.Wheat
storedin airtightcontainers,at the optimum moisturelevel,will renderitself
immune to insect attack. Highlevelsof carbon dioxideare less deadlythanthe
effect of diminishingoxygen,but it has an intoxicatingeffect on the insects.
Insects are able to survive for a long period in the presence of high
concentrationsof carbon dioxide particularly in low temperatures.Immature
stages of many speciesshowhigherlevelsof tolerance thanadults.
Insect density
Competitionbetweeninsectsmaytakethe formof competitionfor foodand
competitionwithpredators and parasites. Competitionfor foodis most severe
between speciesthathavethe same nutritional requirements and the same
temperatureand humidity preferences.Sometimes insects mayenterinto severe
competition if the temperature is suitable to both; however, a drop in
temperatureor changein moisturecontentcan be detrimental to one species,
416 Handbookof hygiene controlin the foodindustry