Technical pest management news

21 February 2023

Preventing insect damage in dry food storage

PPC110 | Technical

Mike Kelly presented this article at the International Association of Operative Millers (IAOM) Conference 2022 in Zanzibar.

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Fumigation is a simple technique designed to alter the air a target species breathes to prevent it from surviving. While simple in essence, fumigation as a pest control technique requires a good understanding of the whys and wherefores. Get it wrong, and the wrong species can die!

I have spent over 45 years doing real fumigations and running fumigation training courses in lots of the warmer climates. Infestation of mites or insects can easily occur both during milling and particularly during storage of the milled products.

These contaminants are completely against the standards required throughout the developed world. They will be an immediate no-go in all human foods, yet they so commonly occur because so few people understand how and why they occur, or have yet to develop successful pest prevention programmes. 

It would be more accurate to say that effective invertebrate detection systems remain rare, despite the commonness of the pests within the industry worldwide.

An additional and very significant issue is that the pest control systems in use are always many times more hazardous to humans than the invertebrate contaminants.

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Successful systems will often include poison gas fumigation, usually involving phosphine gas. We have long moved away from methyl bromide fumigation due to this risk to human health. Using heat is a non-toxic control method, but requires a huge energy cost.

The only practical way of de-infesting a substantial bulk storage of dried foods, without damaging or de-naturing the food, is fumigation, which a trained and professional fumigation contractor must do. Water must not contact the fumigant.

The fumigation must be continuously monitored so any gas leakage can be immediately detected and the leaking area sealed quickly for human safety.

This will require careful planning, in order to ensure sufficient trained and expert staff can handle all the activities which will occur throughout the entire fumigation procedure.

This planning will occur days or weeks in advance to ensure there are no last-minute glitches that could otherwise be dangerous to warehouse staff. And again, remember that the fumigant in use will be more lethal to humans than to the target insects or mites.

In most countries, fumigation must only be attempted by trained and certificated professional staff that have access to effective and calibrated gas detection and monitoring equipment.

This is usually set up and operated from outside the storage facility. Gas readings will be viewed from behind this barrier ie remotely.

Where the scale of the fumigation is very large, there will probably be a site planning meeting to ensure that all eventualities are considered. Ideally, all senior staff will contribute comments on all aspects of the fumigation as envisaged.

This means that staff holidays must be planned into the timescales, and only when everyone agrees to the outcome can the actual fumigation start.

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Some of the most damaging insect pests in the world

Tobacco beetle

Never forget that high standards of good hygiene will always pay dividends. The tobacco beetle lays its eggs in tobacco dust as well as on dried tobacco fragments. It may be noted that there’s no shortage of funds in the tobacco industry to ensure high standards.

Know your beetles 

Here are a small group of similar-in-appearance beetles which can easily be mistaken, but not all are serious pests. It’s worth asking a professional entomologist for identification before spending large amounts to attempt control.

All species are very small, approximately 1-2mm and light brown.

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From top left to bottom right: Grain weevil larva; A freight container after overnight pheromone trapping; Cigarette beetles by the score; Grain weevil (Sitophilus granarius)

“It’s worth asking a professional entomologist for identification before spending large amounts to attempt control.”

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From top left to bottom right: Cigarette (or tobacco) beetle (Lasioderma serricorne); Rust-red grain beetle (Cryptolestes ferrugineus); Drugstore beetle (Stegobium paniceum); Khapra beetle (Trogoderma granarium)

CASE STUDY: South Africa

One large-scale fumigation I was involved with in southern Africa resulted in several steel warehouses being completely destroyed because the fumigation took place over a ‘quiet’ Christmas break, which unfortunately coincided with heavy tropical storms. The warehouse management knew in advance that the corrugated roofs were not watertight.

During a thunderstorm, lightning struck one of the warehouses, allowing heavy rain inside, which created a fire (the phosphine generating material is often magnesium phosphide, which will catch fire if wetted).

This was a real incident a few years ago, and it makes you question the technical training and the simple lack of common sense.

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A hired drone shows just what had happened – several of the warehouses and storage units and goods totally destroyed, with only the office block in the foreground acting as a firebreak against further damage.

The photo shows the extent of the widespread destruction. Water and phosphine do not mix!

None of the work was particularly complicated, but the timing of the work coincided with the Christmas break. Christmas parties took place, and warehouses of valuable dried goods needed to be locked up when not actually being worked in, so the fires could not easily be accessed by fire-fighting workers, and the local fire brigade was kept out for too long while they searched for keys.

The warehouse staff had not been charged with maintaining a watchful eye on their warehouses throughout the fumigation.

All people with experience in this part of South Africa know for certain that heavy thunderstorms frequently take place over the Christmas period.

The warehouse manager also knew that the roofs leaked in the rain. There had been no pressing urgency to fumigate these stocks over Christmas. In any case, there are no surviving stocks to be fumigated or warehouses to contain the tobacco now.

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