Attractants

Attractants - What do biting flies smell?

Biting fly behaviour around traps can be influenced greatly through the use of odour baits. Chemicals mimicking natural host odours not only attract flies from a distance but also result in increased investigation of the trap. Regardless of the mechanism, the net effect is often a large increase in the catch of certain kinds of flies. Some flies (e.g. stable flies, Stomoxys) are attracted to and will land on cloth traps in the absence of odour cues, relying on visual cues only. Other flies (e.g. most tsetse species, Glossina) largely ignore artificial objects when host odour cues are not present.

Sticky Triangle

This principle is illustrated at left with a simple experiment set up in Kenya to interpret how flies behave towards an object with minimal visual information, roughly the size and shape of a triangular tsetse trap. The "trap" was constructed by wrapping a plastic film covered in a sticky material around three poles. When unbaited over a 24-h period, the trap caught a few thousand Stomoxys, about 25 Glossina pallidipes, and just a few Glossina longipennis. Addition of odour baits resulted in only a small change in the catch of Stomoxys. In contrast, the presence of baits increased the catch of G. pallidipes by up to 10-20 times - most likely because of an increase in the range of attraction. For G. longipennis, a bait consisting of carbon dioxide and octenol had a synergistic effect, resulting in a 100-fold increase. These major improvements in catch are possible only for some species; we are still a long way from exploiting practical attractants for many biting flies.

Much of what we know about natural attractants was learned through experiments with ventilated pits, a technique developed by Glyn Vale and colleagues in Zimbabwe. In this technique, animals are placed in an underground pit, so that no visual cues from the animals are present aboveground. The odours from the pit are extracted through a large pipe and blown out next to an electrocuting net. A visual target such as a horizontal drum covered in black cloth (a surrogate for a wart hog) is placed next to the net to provide a visual focus for fly activity. By comparing the numbers of flies electrocuted with and without animals present in the pit, researchers were able to identify many of the important compounds that attract tsetse and other biting flies. Variations on this technique continue to be used to help separate visual and olfactory cues.

In parallel with the work in Zimbabwe in the 1980s, Mary Owaga in Kenya made the fortuitous discovery that tsetse flies are attracted to aged buffalo urine. Bacteria convert trace chemicals in the urine to phenolic compounds that attract some species of tsetse, as well as most horse flies. Along with chemicals from breath (carbon dioxide in large quantity, and trace amounts of acetone and octenol), there are many useful baits for attracting flies to artificial objects. Unfortunately, the efficient and economic use of baits for different insects is still a specialised field - requiring careful use of the scientific literature. I present only a few examples of some practical applications below.

A convenient introduction to the use of odour baits with a reasonable level of technical detail can be found in the Electronic Training Resources section of the PAAT Information System, specifically in Volume 4 of the Training Manual for tsetse control.

URINE - A practical substitute for pure phenols is the aged urine of a "BOVINE" such as a cow or a buffalo. The appropriate phenols are likely present in most ruminant farm animals (Martin, 1982). Aged urine has been demonstrated to be more attractive than fresh urine for some tsetse species, but little is known about this phenomenon for other biting flies. Krčmar et al. (2005, 2006) have shown that aged urine from various farm animals is extremely useful as a trap bait for several species of horse flies in Croatia. There is lots of potential for further tests of urine in other environments. Levels of phenols in human urine appear to be too low for any practical applications.

Although it sounds awkward, urine can be collected without undue effort (e.g. by throwing cold water onto the back of an animal first thing in the morning - we collected rhinoceros urine this way)!

When exposed to bacteria in air (Okech & Hassanali, 1990), and then aged for at least a few days to several weeks (Madubunyi et al., 1996), phenol levels in urine appear to greatly increase from the activity of certain bacteria, especially the potent attractant 4-methylphenol or p-cresol. These phenols are present in even fresh urine and attract many species of both tsetse and horse flies. This phenomenon has been studied extensively in Africa with ongoing research on the nature of the phenols present (Torr et al., 2006).

Cow urine can be used for months with occasional topping up and still be effective. Any container with a medium to large aperture will do (e.g. 3 - 6 cm opening). Large apertures will result in an increase in catch until an asymptote is reached. Practical advice on techniques for dispensing urine in large-scale control programs can be found in Brightwell et al. (1991).

Krčmar, S., Mikuska, A. & Merdić (2006) Response of Tabanidae (Diptera) to different natural attractants. Journal of Vector Ecology, 31, 262-265. Free PDF

Krčmar, S., Hribar, L.J. & Kopi, M. (2005) Response of Tabanidae (Diptera) to natural and synthetic olfactory attractants. Journal of Vector Ecology, 30, 133-136. Free PDF

Martin, A.K. (1982) The origin of urinary aromatic compounds excreted by ruminants 3. The metabolism of phenolic compounds to simple phenols. British Journal of Nutrition, 48, 497-507. Free PDF

Madubunyi, L.C., Hassanali, A., Ouma, W., Nyarango, D. & Kabii, J. (1996) Chemoecological role of mammalian urine in host location by tsetse, Glossina spp. (Diptera: Glossinidae). Journal of Chemical Ecology 22, 1187-1199.

Okech, M. & Hassanali, A. (1990) The origin of phenolic tsetse attractants from host urine Studies on the pro-attractants and microbes involved. Insect Science and its Application 11, 363-368.

Torr, S.J., Mangwiro, T.N.C. & Hall, D.R. (2006) The effects of host physiology on the attraction of tsetse (Diptera: Glossinidae) and Stomoxys (Diptera: Muscidae) to cattle. Bulletin of Entomological Research, 96, 71-84.

Before using attractants, you should educate yourself on chemical safety information for key compounds such as 4-methylphenol , acetone , etc. (e.g. at the United States National Institute of Occupational Safety and Health in the Pocket Guide to Chemical Hazards). Detailed technical information is available for most compounds from the US Environmental Protection Agency in their Integrated Risk Information System.

ACETONE - Acetone is a highly volatile trace component of breath; it is an attractant for many, but not all biting flies. When dispensed in combination with urine, it may produce a large synergistic increase in catch, hence it can be a very useful attractant. Bulk industrial grades of acetone are suitable; they should be dispensed separately from urine or phenols in a container with a small hole (e.g. puncture the cap of a small soda bottle with a nail, or use a bottle opening for a higher evaporation rate). As with urine, there are many considerations in terms of optimal dose rate, and the cost-effectiveness of using high dose rates. Retail costs of acetone in Canada, for example, are US$3.70 per litre. This is rather prohibitive for routine use.

Some species of tsetse and horse flies are caught in large numbers with a combination of acetone and cow urine or phenols, others are not. Results with stable flies are variable, but generally negative. Technical details for dispensing various chemicals are provided by Torr et al. (1997). In Canada, I have only just recently tested the usefulness of acetone as an attractant for tabanids in a home application. At an affordable high dose rate (e.g. 30-90 ml per day depending on temperatures), acetone alone had no effect on the catch of tabanids in Nzi traps.

OCTENOL - An interesting bait for almost all biting flies is 1-octen-3-ol, a volatile trace chemical found in breath. It smells distinctly like mushrooms. It can be purchased in bulk from major chemical suppliers and dispensed from heat-sealed polythene sachets made from lay flat tubing. In large-scale operations, octenol and phenols are typically mixed in specific ratios and dispensed in large sachets that release odours at a nearly constant rate for many months. Octenol is an important attractant for small biting flies (midges, mosquitoes, stable flies) as large, synergistic increases in catch can sometimes be obtained when it is dispensed simultaneously with carbon dioxide. Used on its own, octenol does not always produce dramatic increases in catch for all biting flies. Carbon dioxide as a gas or as dry ice is, however, a nearly universal attractant, but it is rarely used outside of research applications.

Octenol Lure at Back of Trap 15k Sophisticated (i.e. expensive) traps that dispense carbon dioxide and/or octenol have been on the market for several years for consumer use in mosquito control (see Mosquitoes & Black Flies). Octenol is therefore now readily-available at hardware stores. The Biosensory lure from the Dragonfly trap is pictured at left, suspended from a wire at the top back corner of a Nzi trap (24.5% octenol, 3.72 g octenol in a wax base). In experiments at my home in Russell, Ontario, an octenol-baited Nzi trap caught twice as many biting flies as an unbaited trap (stable flies, and most species of horse flies and deer flies). Hence, if one can afford the cost, it is clearly useful as an attractant. In May 2005, this octenol lure was availalble by mail order directly from Biosensory for US$5 per lure. The exact same lure is also available at consumer outlets under other names, e.g. the Lentek "Octenol Biting Insect Attractant" sold at Home Hardware in Canada, at Can$10 per lure.

Magnet Lure 10k Octenol lures prepared in other formats should also enhance trap catches of most biting flies. For example, the small lure at left from the interior of the Mosquito Magnet� of American Biophysics Corp. (55.2% octenol, 1.66 g octenol in a very small cartridge) is also available in Canada.. I compared catches for the Dragonfly and the Mosquito Magnet lures one experiment and obtained identical results. Biosensory claims that its lure is superior because of the wax base (controlled release over perhaps 30-60 days depending on temperature; 21 days in some of the more recent product literature). Both lures retain a strong "mushroom" odour for about a month, or slightly longer. The Biosensory lure has the advantage of being in a safe package.

The Office of Pesticide Programs at the US EPA has produced a Fact Sheet on octenol. Information on registered suppliers and details on the octenol content of products can be obtained from a chemical search on octen-3-ol (PC code #069037) at the US EPA. Each product is different. Technical information can be found at Bedoukian Research.

Dog Model Attractants may affect any component of fly behaviour at or around traps, e.g. the overall radius of visual plus olfactory attraction, circling and investigatory behaviour, landing on trap surfaces, entry and escape from the body or cone of the trap, etc. When simply counting flies ultimately caught by an effective trap, it is impossible to differentiate which behaviour(s) have been affected.

To understand what flies do around objects or animals, researchers study fly behaviour with video, or intercept flies with electrocuting nets or sticky materials (Efficiency). Here is an example of an experiment using a stuffed dog wrapped in transparent sticky film. I tested this model to see how deer flies would react to a suitable, but stationary, host mimic (baited with octenol). Where I live, Chrysops vittatus bites my very similar pet in large numbers, mostly on the ears. Despite this observation, I caught no tabanids of any kind with this model. This shows how difficult it is to exploit simple devices that mimic the features of a natural host.

WARNING

Chemicals should only be used with traps in a restricted research environment. One must consider safety, and anticipate what might happen if an animal or person investigates the trap. Pets, children and even curious adults can easily interfere with an unattended trap.

Blue bottle 13k A bizarre result of using the "Fly Banquet" fly attractant with the Advantage flying insect trap is the attraction of household pets, along with filth flies (Calliphoridae or blue bottles)!

Dogs love these smelly, sulphurous baits (which are often based on chicken & fish protein) and go to great lengths to lap them up. I am skeptical that any of the formulations sold for household, barnyard, etc. "FLIES" actually attract biting flies such as stable flies, horse flies and deer flies.

For further practical baits consult the Natural Resources Institute, UK
Catching Tsetse.