Dairy

Research Dairy - Lethbridge, Alberta, Canada In late summer and autumn of 1999, I monitored the catch on a daily basis in an unbaited Nzi trap set in the vicinity of large numbers of beef and dairy cattle at the Lethbridge Research Centre of Agriculture and Agri-Food Canada. The trap was placed right next to a small paddock that contained a few Holsteins. The research centre is in a dry, windy prairie habitat. Late in the season, few tabanids and no black flies were present. The trap routinely caught many stable flies (Stomoxys calcitrans) and some horn flies (Haematobia irritans). The highest catch was about 1,500 stable flies on 21 September (at left). Flies associated with animals (Anthomyiidae, Muscidae, Sarcophagidae, Otitidae, Calliphoridae, Scatophagidae) were also caught in modest numbers, as well as many other flying insects. Detailed graphs of fly numbers

Stable Fly (Stomoxys calcitrans) Information on the biology of stable flies in southern Alberta Lysyk (1993) Lysyk (1995)
Observations on Trap Efficiency By the end of August, fly catches were above 500 per day during calm, warm weather. Early on the morning of 1 September at 4°C, following a night with high winds (80 km/h), 250 stable flies were resting on the leeward side of the trap. By noon the trap had caught 122 stable flies and one horn fly. Cows were highly agitated and were clearly stressed by biting flies. They were grouped into a defensive huddle, kicking and running as stable flies bit their legs.
	Flies rested on the animals' backs, mostly on the black areas. The arrow points to 34 flies, mostly stable flies, and a few horn flies. Cows had about 100 or more flies on their bodies at any one time, with 1/4 to 1/3 of them on the legs.
At noon at 12 °C, with the sun falling on the front and on one side of the trap, about 600 stable flies were resting or landing on the trap. Most of these flies were on the bottom half of the blue cloth in direct sun. About 120 flies were on each of the wings at the front, 80 were on the horizontal blue shelf, and another 80 were on the inner black cloth (60 in sun, 20 in shade). By 4:30 at 15 °C, the sun was falling only on the front of the trap. As before, most of the 300 flies resting or landing on the trap were in direct sun. From noon to 4:30, the trap caught 573 stable flies and 27 horn flies. By the next morning (3 °C, calm) , the trap had caught a further 152 stable flies and 8 horn flies; about 40 stable flies were on the trap (immobile due to the cold). The large numbers of flies landing on blue cloth (especially on the bottom half of the wings), and their sun-seeking behaviour, was typical of other counts conducted during the summer. Flies sought shaded trap surfaces only at very high temperatures. Hence, during cloudy weather, flies were more evenly distributed on all trap surfaces.
Sticky Materials - Some Preliminary Observations
To obtain a crude estimate of efficiency, I stretched a transparent, sticky panel (Rentokil Fly Control Adhesive) across the lower front of the trap on 16 September. The weather on this day, and on the preceding and following days, was constant and was good for fly activity (sunny and warm with highs between 25 and 28°C). The data below provide an indication of trap performance in terms of the proportion of various flies caught, of those presumably investigating the area of the trap. Similar data on stable fly behaviour towards sticky materials set near traps have also been collected in preliminary studies in Ontario.

Fly	Day 1	Day 2		Day 3
Fly	Trap	Trap	*Sticky*	Trap
Stable fly Male, Female	200, 58	345, 203	885, 259	486, 179
Horn fly	3	3	0	2
House fly	1	3	149	1
Phoridae	110	230	10,000	356
Anthomyiidae	30	15	53	98
Syrphidae	4	3	9	5
Scatophagidae	3	7	2	1
Sarcophagidae	2	1	0	0
Calliphoridae	3	2	1	0

Although it is impossible to validate results from this "experiment", the catches suggest that trap efficiency for stable flies is similar to the values obtained for other species of Stomoxys in Africa. The trap appears to have caught about a third of the stable flies attracted to it (548/1692). In contrast, the efficiency for house flies (Musca domestica) was poor (3/152). This is typical of nonbiting Muscidae. Traps designed for biting flies induce many nonbiting flies to land, but, they only catch large numbers when they are baited with attractants like carbon dioxide (Mohamed-Ahmed & Mihok, 1999).

Non-Target Insects

The arrow points to a small fly in the family Phoridae (PH) stuck to the sticky panel near a Stomoxys calcitrans (SC) and a common house fly (HF). Phoridae were sometimes abundant due to the presence of large amounts of silage. Most of these small flies were able to pass through the mesh of the trap and the collector, and hence only small numbers were caught. In this situation, the use of a small mesh size would have been problematic, as the collector would have accumulated large numbers of Phoridae. The selection of an appropriate mesh size for both the trap cone and the collector is critical when one is attempting to either exclude or catch some of the smaller flies (e.g. biting midges, black flies).

The arrow points to a hover fly (Syrphidae, SY). These flies feed at flowers and look like honey bees. They were regularly caught, along with a variety of other Diptera. The trap also caught a few wasps and hornets, particularly yellow jackets. Only a single honey bee was caught in about 100-trap days of work at Lethbridge. Overall, the catch of non-target insects was modest (see complete counts). Non-target catches are somewhat higher at my residence in a farming area of eastern Ontario. Since the Nzi trap has interception features in common with traps such as the Malaise trap, one should always consider possible effects on non-target insects when siting traps.

To Bait or Not to Bait?

These studies were conducted with an unbaited trap on the assumption that the environment was already saturated with host odours. Octenol is a useful attractant for many species of stable flies in natural environments (Mihok et al., 1996), but it does not always increase catches in agricultural settings (Mihok et al., 1995; Cilek, 1999). Since these experiments were done, I have baited traps with octenol in a residential setting at my home in eastern Ontario with success. Octenol in this situation doubled the catch of most species, including stable flies.

Further work needs to be done on this topic with efficient sampling devices to clarify how baits modify either the attractiveness of traps or their capture efficiency. There may be potential for improving catches through the development of novel attractants, e.g. phenylpropanoids (Hammack & Hesler, 1996). However, to date, there is still no further evidence of any useful attractants for stable flies besides octenol.