When it comes to food pest control, most casual observers of the food chain will think of the growing stage as the key problem area. Not so. One of the principle problems associated with crop pest control is when produce is placed in storage.
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And here’s another area of misconception: It would be wrong to think that pest control in stored products centers largely on grain and cereal silos. There are problems in just about every stage of the chain; manufacturing and processing plants, supermarket warehouses, restaurants, shipping containers and so on.
This article will explore a variety of insect pests that prevail in these different areas of food storage – all of which have become highly adapted to their environments and are not commonly found elsewhere – and some of the innovative techniques emerging to combat them.
Moths, beetles and weevils are the principal pests in question. These are the groups that target stored products and pose a whole set of serious problems. When they defecate on the product, toxins are produced by the fungi and disease is created.
These toxins can cause human illness and – potentially – the production of deadly mycotoxins that not only lead to illness in most livestock, but also have also been linked to some forms of human cancer. Aside from these dangers, one should not overlook the fact that pests also pose a serious consumer annoyance in the form of discolored or mutilated food products. To say nothing of the fact that certain types of pests can destroy or damage the foods nutritional value.
As with crop situations, pest populations in stored product can be monitored and managed in a number of ways. Pesticides are commonly used, with storage areas being fumigated or surface dressings of insecticide applied and mixed directly into the crop. But concerns about chemical residues are causing a seismic shift in this area of the pest control industry.
One example is the broad spectrum pesticide methyl bromide. It has been commonly used as a fumigant of stored produce and, indeed, has been very effective. Over $431 million in U.S. exports were treated with methyl bromide in 1994, but it has been listed as a suspected ozone-depleting compound and will be phased out of use in developed countries across the course of this year.
However, such is the dependence on methyl bromide, that in 1999, the ARS had a budget of $14.4 million and no less than 41 scientists working at 20 different locations across the U.S. researching alternatives to this chemical. Indeed certain produce cannot be legally exported without being treated with methyl bromide in particular to eliminate quarantine pests.
Before any alternative strategies can be considered, it’s worth noting a key hurdle. Controlling pests in food processing plants can be especially difficult as production and storage is continuous throughout the year. In these situations, the opportunity to clean or treat affected areas is very limited and requires the shutting down of whole sections of the facility for cleaning and pest control to take place.
With this hurdle in mind, the pest control industry is looking to manage pests in the aforementioned areas of food storage while at the same time, cut down or completely remove the use of pesticides. Integrated pest management (IPM) can be applied to weevils, beetles and moths. Each is a whole universe of science and expertise and – for the sake of this article – we’ll focus just on moths.
Sex, Eggs and Sustenance
Much of the behavior of insect pests in stored products is associated with either their search for food, sexual partners or egg laying sites. If the pheromone of the female species of any insect pest can be synthetically recreated then, the latter two factors can be addressed and the pest controller is in a position of great power.
The first stored-product insect phero-mone was chemically identified in 1966 from the black carpet beetle, Attagenus unicolor. Since that time, pheromones have been identified from over 40 species of stored product insects. They fall into two distinct major classes: Sex and aggregation pheromones, and in most cases, are highly species-specific.
Pheromones for Monitoring
For some years, synthetic pheromones have taken a strong-hold in pest monitoring, as opposed to eradication, for some years. Monitoring and detection are the most common uses of pheromones in managing stored-product insect pests in food plants and warehouses. As such, numerous traps and lures have been developed for use in such programs and their use has increased greatly in the last decade.
A recent survey, conducted by the USDA in cooperation with the American Institute of Baking, assessed the level of adoption and usage of pheromone traps by various components of the food industry (Mullen 2000). Of the respondents (3,000), 38.6 percent were food processors; 27.2 percent were managing warehouses; 19.3 percent were food-packaging facilities; 12.6 percent were engaged in bulk storage; and only 2.3 percent were retail food outlets. More than 90 percent of respondents felt that traps provided useful information, confirming that these tools have experienced widespread adoption in the pest monitoring side of food storage.
From Monitoring to Mating
Based on research by Professor Philip Howse during his 30 years at Southampton University’s School of Biological Sciences, Exosect has developed a unique method of managing pest populations in food storage, by breaking down their mating cycle. It centers on a pheromone-based system, which employs an electrostatic powder that coats the moth with small electrostatic charges developed by the moth in flight.
The process involves a synthetic female sexual pheromone is used to attract male moths into a dispenser. Once in the dispenser, this pheromone adheres to the moth via the charged powder, which is triggered by this electrostatic charge. It coats them and their antennae. With the moth’s sensors overwhelmed, they cannot detect virgin females desirous of mating. Furthermore, they act as a false lure for other males and, through attempted mating, spread the powder to these other males. As a result the mating cycle breaks down and the moth population crashes.
David Cary is technical manager at Exosect Limited (Southampton, U.K). He can be reached at +44 (0)23 8076 3838.