Overview
ISO 6639-3:1986 - "Cereals and pulses - Determination of hidden insect infestation - Part 3: Reference method" is the ISO reference procedure for detecting and quantifying insects that are hidden inside cereal and pulse kernels. The method’s intent is to allow any live immature insects present at sampling to develop to the adult stage under controlled conditions so they can be identified and counted. This slow but reliable laboratory technique is designed to determine the nature and number of hidden insect species and express infestation as numbers per kilogram.
Key topics and technical requirements
- Principle: Maintain test samples at controlled temperature and relative humidity so concealed immature insects develop to adults; remove, identify and count emerged insects at close intervals.
- Incubation environment: Room or incubator maintained within ±1 °C in the 25–30 °C range; relative humidity adjusted to 60–65% or 65–70% depending on sample moisture.
- Moisture control: Determine moisture content of the laboratory sample in accordance with ISO 712 prior to testing; moisture influences incubation humidity and test portion size.
- Test portion sizes: Typical test portions are 200–300 g when moisture <15% (m/m) or 70–100 g when moisture >15% (m/m). Samples are held in transparent containers in a single layer (max 50 mm depth).
- Monitoring and interval: Inspect at 3–4 day intervals for at least 36 days; actual incubation may be extended (tables in the standard list species-specific periods up to several weeks) depending on insect species and temperature.
- Apparatus: Airtight storage containers, balance (±1 g), transparent containers, sieves to separate insects, shallow trays/Petri dishes, soft entomological forceps/brush.
- Recording and expression: Record numbers by species and life stage (adults, pupae, larvae, eggs), alive/dead. Express results as number per kilogram. An annex provides a suitable data-record sheet.
- Limitations: Reliable for species that develop within grains; species that feed externally in cracks or are easily shaken off may be underestimated.
Applications and users
- Grain quality control and acceptance testing for mills, grain handlers and traders
- Post-harvest pest surveillance and storage pest management programs
- Official inspection, quarantine and phytosanitary services
- Research and entomology laboratories studying infestation dynamics
- Food processors and commodity auditors requiring verified baseline infestation data
Related standards
- ISO 6639-2: Sampling (related sampling procedures)
- ISO 6639-4: Rapid methods (alternative, faster approaches)
- ISO 6639-7: General principles (framework for the series)
- ISO 712: Determination of moisture content (routine reference method)
- ISO 5223: Test sieves for cereals
Keywords: ISO 6639-3:1986, hidden insect infestation, cereals and pulses, reference method, incubation, moisture content, grain quality control, storage pest detection.
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