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UVA LIGHT TRAPS – A STICKY SUBJECT?

UVA light traps used in the food industry are required to use glueboards to capture and retain the flying insects. Glueboard-based UVA light traps offer the only method that attracts, kills and collects insects within the HACCP framework, and allows for the counting of insect numbers and species identification with no contamination and no pesticides.

Old-style control units, often called ‘zappers’, use a high-tension electrical grid that kills by an electrical discharge so powerful that particles of the insect body (wings, legs, heads) tear off. These fragments may eventually find their way into food and cause serious contamination, which is why high-tension grid units should never be used in food environments.

It is well known that visual stimulus is the most important determinant in fly behaviour. Anatomically, flies have half of their head covered by two large compound eyes, with a cluster of three simple eyes, or ‘ocelli’. High sensitivity to near-ultraviolet light was recorded in flies as early as 1932 by Lloyd M. Bertholf.

The fly is characterised by its two large compound eyes

UVA fly traps make use of this near-ultraviolet (UVA) light, often referred to as ‘black light’ since it is not visible to the human eye. This is an important point: many people assume that because they can see the blue light emitted by the lamp, it must be attracting flies. The blue light is only placed in the light spectrum so people can see if the unit is switched on. The actual UVA light that attracts the flies can only be measured by using a meter, such as the Vectothor UV Tester. It is a highly beneficial tool, as it is often found that the fly traps in an establishment are not emitting any UVA light.

Whilst much has been covered with respect to the importance of using of premium quality UVA light tubes, e.g. the Vectothor Astron lamp, to attract flies to the glueboard, little consideration has been shown to the actual glueboard that must capture the flies. The idea that ‘it’s just a glueboard’ is common, yet the glueboard is the heart of a UVA fly trap system and makes an enormous difference to performance.

High quality models of glueboard have a larger surface area and improved high-tack glue to ensure more flies can be caught. Cheaper glueboards dry out sooner and are either not tacky enough to catch and hold insects, or are so tacky that the technician finds themselves coated in glue during the changeover!

Ensystex showed this quite dramatically recently in Thailand. A well-known chain of stores had installed more than 4,000 Vectothor Osprey units. Fly catches were impressive, as shown in Figure 1, which followed initial installation in one of the stores.

Figure 1: Vectothor Osprey unit showing successful fly capture

A cost-saving measure was later implemented to use a cheaper, locally made glueboard. Catch rates dropped immediately and dramatically! This is because a tremendous amount of formulation expertise is required to develop the adhesives used in high-performance glueboards. The adhesive requires very special characteristics to grab, and then hold, very light but often powerful insects for extended periods of time, under very demanding conditions. The insects need to stick to the surface after the application of very light pressure, often from just their tarsi or a wing tip.

The pressure-sensitive adhesives developed for insect trapping are unique products due to these very specific demands placed on them. The adhesion phenomenon depends on the creation of an interfacial glue-substrate bond, and the bond strength. Three mechanisms take place in this process: wetting, the setting up of the interfacial bonds, and cohesion.

To be efficient, the glue must be fluid enough to ‘wet out’ on the surface of the insect’s legs and form the largest interface. Once intimate contact is made, the strength and nature of the bond depends upon the chemical constituents at this interface. The larger the interface, the more numerous the bonds. Experience has shown that good adhesion alone is not enough to provide a good adhesive.

The bond strength depends upon the chemical nature, but also upon the molecular cohesion inside the glue. Cohesion is a phenomenon in which the molecules in the adhesive are held together by primary and secondary bonds, as well as entanglements. Adhesion calls for viscosity that acts by diffusion as well as the elasticity of the material.

To sum up, we can say that pressure-sensitive adhesives used for insects show features characteristic of both liquid and solid behaviour. That’s why they are made of polymers that are ‘viscoelastic’. Vectothor insect glues are made of three main constituents: an elastomer, a tackifying resin and a softener.

Another key factor in the development of modern glueboards is the European Union’s REACH legislation. Enacted by the European Chemicals Agency (ECHA) to protect human health and the environment, this has led to a requirement for less toxic adhesives. Ensystex’s Vectothor glueboards are made in Europe and all are REACH compliant for your safety.

Fly captured by Vector insect glue

Ensystex strongly recommends the use of Vectothor Blue Glueboards. Several published scientific studies have reported blue as being attractive to flies in regions of high warmth and sunlight, like Australia. Hecht (1970) stated that the addition of black lines to blue targets made the targets more attractive by adding stimulus to satisfy the scototaxis tendency (dark/light preference)

of house flies. It appears house flies perceive the blue visual target as a potential resting area and the black lines as cracks or crevices that can be used as harbourages (Declaro, 2012).

To the uninitiated, one electronic fly killer may look very much like any other. But scratch a little deeper and there is a whole world of cutting-edge technology behind the development and manufacture of these products.

Steve Broadbent, Regional Director, Ensystex