Houseflies are an intriguing pest in terms of their visual capabilities and product manufacturers use this to their advantage when designing fly control products. 

For many insects, the chemosensory system and their use of chemical communication is a key driver of their behaviour. However, for the house fly (Musca domestica), its visual senses also come to the fore. You only have to realise the importance of sight to the housefly by looking at the size of its eyes.

Over half of the head of the house fly is devoted to two large compound eyes and a cluster of three ocelli (simple eyes). The compound eyes are associated with colour vision and the perception of detailed images. Houseflies have been shown to be most responsive

to UVA light in the range 340-370 nm and blue-green light in the range 480-510 nm. The ocelli are single-lens, simple eyes that detect movement and can perceive different intensities of light – flies respond positively to dark vertical objects and indeed are attracted to vertical hanging cords as resting sites and tend to follow edges whilst foraging. Understanding the visual abilities of the house y has proven important in developing successful fly control products.

A detailed study conducted at the University of Florida1 showed that houseflies were attracted by blue light but found yellow light somewhat repellent. The addition of black lines to blue targets made them even more attractive, which was thought to be due to the lines adding stimulus to satisfy the scototactic (light/dark preference) tendency of houseflies. The blue attracts the flies and the black lines appear as cracks or crevices for harbourage. Seemingly in conflict, studies from Europe had shown houseflies to have an attraction to yellow light.

Strategies for managing flies is a topic that Ensystex has invested heavily in, working with researchers and conducting its own studies to determine the most effective treatments. Steve Broadbent, regional director for Ensystex, believes environmental factors may be one reason for the differences in coloured light attraction.

“Studies performed by Ensystex and our discussions with researchers suggest blue light is a strong attractant in warm, sunny environments, such as Florida and Australia, whereas yellow may be preferred in darker, cooler environments, such as in animal housing in Europe,” he said.

Ensystex has incorporated this understanding of fly behaviour into its range of products for professional pest managers.

“Trials performed by Ensystex when developing Vectothor Fly Bait saw flies showing a very strong preference for blue granules, when compared to yellow or red granules. The blue granules provide enhanced visual appeal, which is augmented with the female sex pheromone and a sugar attractant to lure flies to the bait where they are killed by the insecticide,” said Mr Broadbent.

Vectothor Fly Bait is formulated as a water-dispersible granule that can be used as a dry granular bait, moistened with water and painted on to surfaces, or diluted and sprayed.

Ensystex also offers Vectothor UVA Flying Insect Traps, which use UVA light together with a REACH-compliant blue glueboard, with black lines, to optimise performance in the trapping of houseflies indoors.

“Bithor Dual Action Insecticide is also available to provide residual control to the walls of buildings,” added Mr Broadbent. “With its two actives, it ensures that control of pyrethroid-resistant houseflies can also be achieved. The Ensystex fly range is completed with Exothor Insect Growth Regulator which can be mixed directly into manure, breaking the fly development cycle by preventing adult emergence.

“Together, these products provide professionals with a total solution to fly management enabling superior control around the exterior of buildings, in poor hygiene areas around garbage disposal areas, supporting the use of the Vectothor UVA Electronic Fly Killers indoors and in HACCP environments.”

1JW Diclaro, LW Cohnstaedt, RM Pereira, A Allan & PG Koehler. Behavioral and Physiological Response of Musca domestica to Colored Visual Targets. J. Med. Entomol. 49(1): 94‹100 (2012).