Molasses fly trap

Skip to Navigation


  • Published: Feb 1, 2007
  • Author: Steve Down
  • Channels: Base Peak
thumbnail image: Molasses fly trap

The common house fly, Musca domestica, has been described as the world's most dangerous bug, more so even than the tsetse fly or the mosquito. This might seem an ungenerous label but consider this: the fly is thought to be a carrier for more than 100 pathogens which cause disease in humans and animals, including typhoid, cholera, gangrene, tuberculosis, gonorrhoea, bubonic plague, leprosy, hepatitis, diphtheria, scarlet fever, anthrax and poliomyelitis.

The pathogenic organisms are picked up as the flies land on excrement, garbage, sewage and various other filthy substances. They are transferred to our food via the fly faeces, from direct contact with contaminated body parts and from the regurgitated fluid that the fly expels in order to liquefy food for consumption. Some estimates put the number of bacteria on the feet of one fly as high as 6 million.

House flies can also transmit the eggs of parasitic worms which thrive in our digestive systems, hatching and multiplying quickly to invade other parts of the body. Add to all this the nuisance value of just one fly in the house or office and they rise high up in the global unpopularity charts.

The fast reproductive cycle of the house fly is responsible for their immense numbers. It has been estimated that one pair of flies would expand to 191,010,000,000,000,000,000 in four months if all survived. This would be enough to cover the whole planet with a coat of flies 47 feet deep. Happily for us, their numbers are slashed by parasites, predators and other lethal factors.

Historically, many substances have been used as lures to attract flies, including fish heads, ice cream, egg slurries and banana extract. Another is farm-grade blackstrap molasses, which is used as a cattle feed. This thick, viscous material is prepared from the third boiling of sugar cane syrup. The low water content, less than 20%, discourages bacterial growth.

House flies enjoy feasting on the sugars present in blackstrap molasses but it is not a very attractive material to use as an indoor domestic bait. It has an unpleasant smell and its sticky, viscous nature makes it difficult to handle. So, US scientists from the USDA have undertaken a comprehensive study to identify the compounds in blackstrap molasses that attract the flies. These can then be evaluated as attractants to house flies and other fly species.

Brian Quinn and colleagues from the Mosquito and Fly Research Unit at the Center for Medical, Agricultural, and Veterinary Entomology in Gainesville conducted two separate experiments. Firstly, a commercial blackstrap molasses was diluted with aqueous sodium chloride and extracted with diethyl ether or hexane to give the organic compounds.

Alternatively, a sample of mill run blackstrap analyses was warmed in a sealed gas sampling bag and the volatiles that collected in the headspace were transferred to a canister. The liquid extracts and the volatiles were both analysed by GC/MS with electron ionisation, the former by direct injection and the latter via a three-trap system. The compounds were identified by a combination of retention time, comparison with the NIST mass spectral database and by running samples of analytical standards.

Almost 50 compounds were identified in the liquid extracts, covering many classes. These included many substituted phenolic compounds, which the researchers presumed to be breakdown products of naturally occurring phenols that formed during the production of molasses. Heterocyclic compounds such as pyrazines, furans and pyranones, which are sugar degradation products, were also observed.

Several of the compounds have been reported in earlier studies of cane juice, obtained by pressing fresh sugar cane, and in cane molasses, obtained by a gentler thermal process than blackstrap molasses.

The 15 volatile organic compounds identified in the molasses headspace included acetaldehyde, ethanol, acetone, dimethyl sulphide, short-chain alkanols and ketones and toluene.

In bioassay studies, containers baited with a hexane extract of blackstrap molasses trapped almost as many flies as pure blackstrap molasses, indicating that the extract retained most of the attractant compounds found in the raw product.

The next step for the researchers is to identify the behaviourally active compounds within the group of volatile compounds. This will eventually lead to the provision of an indoor bait, intended for the military and the general public, which is easier to handle than molasses and has a more favourable smell.

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

A house fly feeding
Courtesy Museum Victoria, Melbourne. Image by Alan Henderson
Fly pupae after being eaten by wasp larvae, showing the hole from which the wasp emerged  

Social Links

Share This Links

Bookmark and Share


Suppliers Selection
Societies Selection

Banner Ad

Click here to see
all job opportunities

Most Viewed

Copyright Information

Interested in separation science? Visit our sister site

Copyright © 2018 John Wiley & Sons, Inc. All Rights Reserved