Ultraviolet (UV) light traps are a well-known tool in pest management, particularly for controlling flying insects. While often associated with general insect attraction, the specific effectiveness of UV light, especially in relation to different fly species like fruit flies and house flies, is a key area of interest. This article delves into the science behind UV light attraction for flies, examining how these traps work and their efficacy based on scientific research.
Understanding UV Light and Insect Attraction
It’s widely documented that many insects, including various fly species, are drawn to light in the ultraviolet spectrum. Research has pinpointed the most attractive wavelengths for house flies (Musca domestica L.) to be within the 310 to 370 nm range. Furthermore, studies indicate a direct link between the intensity of UV light emitted into an area and the number of flies it attracts. This suggests that an optimal UV light trap design would maximize the emission of UV light to enhance its attractiveness to flies. Open-front traps, designed to radiate UV light as broadly as possible, are considered most effective for this reason.
An electrocutor grid UV light trap, designed to attract and eliminate flies.
However, even highly effective traps don’t instantly capture all flies in a given space. Studies have shown that while initial attraction is strong, fly behavior around UV traps is more complex than simple immediate capture.
Illumination Events and Fly Behavior: Insights from Poultry House Studies
Much of the research on UV light traps is conducted in controlled laboratory settings. To better understand real-world effectiveness, studies have also been carried out in environments with high fly populations, such as poultry houses. Observations in these settings reveal interesting fly behaviors in response to UV light traps.
In one preliminary study in Florida, a commercial UV light trap was placed in a darkened poultry house. When activated, there was an immediate surge of house flies towards the trap, particularly from flies within a 10-meter radius. Flies further away then moved in to fill the space, but this activity quickly subsided within minutes as flies seemed to acclimate to the continuous light. Interestingly, turning the trap off and then back on after a short interval resulted in a repeat of this “frenzy” of activity followed by acclimation.
This observation led to the hypothesis that creating “illumination events”—turning traps on and off at intervals—might enhance fly capture compared to constant illumination. To test this, an experiment was designed using pairs of UV light traps in a commercial poultry house.
Experiment: Intermittent vs. Continuous UV Light Trap Operation
To evaluate the impact of illumination events, researchers conducted an experiment in a commercial caged-pullet farm with a significant house fly population. The setup involved pairs of electrocutor-grid UV light traps placed at different locations within a poultry house. Three treatment groups were established to compare different lighting schedules:
- Treatment 1: Continuous Illumination (Control): Both traps in a pair were constantly illuminated throughout the test period. This represented standard continuous operation.
- Treatment 2: 2-Hour Illumination Events: Both traps were turned on for one hour and then off for one hour, repeating this cycle to create an illumination event every two hours.
- Treatment 3: Hourly Illumination Events: One trap in a pair was on for an hour, then turned off as the second trap turned on for an hour, alternating to create an illumination event every hour.
Pairs of UV light traps set up for testing in a poultry house environment.
The experiment ran for 24-hour periods, and the number of flies captured in each treatment group was measured. Treatments were rotated across trap locations to account for any positional bias.
Results: Hourly Illumination Events Show Promise
The results of the experiment showed significant differences in fly capture rates between the treatments.
| Treatment (n = 3) | Daily house fly trap pair mean ± SE |
|---|---|
| 1 (both traps illuminated continuously) | 25,456 ± 2,546a |
| 2 (both traps illuminated 12 h of the 24-h test period) | 13,536 ± 1,459b |
| 3 (one trap and then the other illuminated hourly during the 24-h test period) | 18,466 ± 2,105b |
Means followed by the same letter are not significantly different (P = 0.05).
As expected, continuous illumination (Treatment 1) captured the highest number of flies on average. However, Treatment 3, with hourly illumination events using alternating traps, achieved a mean fly capture rate that was only 27% less than the continuous illumination, and significantly higher than the 2-hour illumination event treatment (Treatment 2).
While not exceeding the performance of constant UV light, the hourly intermittent lighting approach in Treatment 3 demonstrated a surprisingly effective level of fly attraction, especially considering that only one trap was illuminated at any given time, effectively halving the total UV output compared to continuous operation of two traps.
Discussion: Implications for UV Light Trap Efficiency
This study provides initial evidence that intermittent illumination can be a viable strategy for UV light traps. The hourly illumination events appeared to maintain a higher level of fly attraction than continuous light alone, possibly by preventing or reducing fly acclimation to the UV source.
The effectiveness of hourly illumination events suggests that the “startle” effect of a light turning on plays a significant role in attracting flies, potentially overriding the importance of constant, high-intensity UV output. While continuous operation provides maximum total UV brightness, intermittent operation with frequent illumination events seems to optimize the behavioral response of house flies to UV light.
This research opens up possibilities for improving UV light trap efficiency. More frequent illumination events, potentially more than once per hour, could be even more beneficial. However, the longevity of traditional fluorescent UV tubes and ballasts under frequent on-off cycles would need to be considered. The development of more durable and efficient UV sources like LEDs could be a key factor in implementing intermittent lighting strategies in practical fly control applications.
Intermittent UV lighting may be particularly advantageous in indoor environments where UV traps compete with existing ambient lighting. In settings like restaurants or stores, where constant UV traps might blend into the background, pulsed or intermittent UV light could create more noticeable and attractive “illumination events” for flies. While constantly flashing lights might be undesirable in public-facing areas, for back-of-house areas, warehouses, and agricultural facilities, intermittent UV light traps could offer a more efficient approach to fly management.
Acknowledgments
The authors thank Sarah Wren and Haze Brown, USDA-ARS, Gainesville, for their assistance with the light traps and fly collection.
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