The use of chromotropic traps represents a very simple yet highly effective agronomic technique. It has a dual purpose: firstly, to monitor the presence of harmful insects within the vegetable garden or orchard, and secondly, to carry out mass capture of these insects. It becomes immediately clear how this particular prevention strategy can become an excellent ally for organic field care.
There are various color options available, depending on the target insect. The effectiveness of this system depends on several factors, with the most relevant being the intensity of placement in the field.
In this article, we will understand how these traps work, the different variants available, and how to position them. Finally, we’ll see how to make them without too much difficulty.
What are chromotropic traps?
Yellow chromotropic traps
In organic agriculture, the use of chromotropic traps has been widespread and established for a long time. It simply involves special sheets or panels, usually laminated, to which a special adhesive is applied. The colored sheet attracts the harmful insect, and the adhesive captures it, keeping it attached to the surface of the panel.
The objective of this type of traps is twofold:
- Monitoring harmful insects present in the field. This is achieved through direct and periodic observation of the colored panel. Thanks to this approach, we can identify which insects are present in our field, their developmental stage, and population size, helping us determine the best way to intervene.
- Mass capture of insects. If the traps are used with sufficient intensity in the field, placing many of them at close distances, they not only serve the important monitoring function but also capture a significant number of insects. The obvious consequences are a decrease in their presence and a reduction in the damage caused to crops.
In general, this type of trap has a very low environmental impact, provided that the panels are ecologically disposed of. Moreover, it avoids the introduction of toxic substances into the environment and on the plants we want to protect. The adhesives used are specifically designed for agriculture and are formulated not to dissolve with sunlight or drain into the soil.
These traps do not interfere with the use of other allowed products in organic farming, such as natural macerates (nettle, garlic, horsetail, fern), Bacillus thuringiensis, Marseille soap or neem oil. On the contrary, using chromotropic traps together with other organic remedies increases the synergistic efficacy of both approaches.
Chromotropic Trap Colors
In nature, it is easy to observe how insects are more or less attracted to certain shades of color over others. Field experiments have shown that the best colors for chromotropic traps are yellow and blue.
Yellow traps attract most of the harmful insects threatening crops, especially:
- Whiteflies
- Oliver fruit flies
- Aphids
- Tomato leaf miner (Tuta absoluta)
- Cherry fruit flies
- Flies in general
- Cicadas
- Leaf miners
- Some species of scale insects
- Green stink bugs in their nymph stages
Blue chromotropic traps, on the other hand, are used mainly for monitoring and mass capture of thrips. In particular, it attracts the harmful Western flower thrips (Frankiniella Occidentalis), an insect that vectors the devastating tomato spotted wilt virus.
You can find effective chromotropic traps available at an affordable price at this link. They come ready to use, with instructions for usage and specifications for the specific insects you want to capture.
Insect Pheromones
To enhance the effectiveness of chromotropic traps, especially in intensive cultivation, synthetic pheromones are added. In simple terms, pheromones are special odor substances naturally emitted by insects to attract individuals of the opposite sex. Usually, it is the female specimen that emits the pheromone. These pheromones are then synthesized and reproduced to simulate this signal and attract more individuals to the traps.
Typically, pheromones are used in dedicated traps, but as mentioned earlier, they are often added to the colored traps as well.
You can find a variety of pheromones and traps with this specific function available here.
Placement of Chromotropic Traps
Now let’s see how and with what intensity to position the chromotropic traps in the vegetable garden for the functions we just described.
Yellow and Blue Traps
Let’s start with yellow chromotropic traps. For open-field crops, vegetable gardens, or domestic gardens, if you want to proceed with monitoring only, the following distances should be respected: 6 traps per hectare for olive groves and orchards, 4 traps per hectare for vineyards, and 2 traps per 100 square meters for vegetable crops.
While, for mass capture, instead, you should place 1 to 4 traps per olive tree or fruit tree, depending on the size of the land and the degree of infestation detected. Finally, for mass capture in vegetable crops, the intensity increases to 2 traps per 10 square meters.
It’s worth mentioning that the traps are harmless to bees. Unlike what one might think, the simple yellow color does not attract bees. To attract them, the presence of pollen and nectar is necessary, which bees can recognize very well.
In greenhouses, the indications should be increased by 25-30% as harmful insect populations are more significant.
The traps should always be placed near the vegetative apices and raised as the plant grows.
Blue chromotropic traps
Blue chromotropic traps are used for controlling thrips. For monitoring, they should be placed at a rate of 10-12 traps per 100 square meters during the pre-flowering phase. Then, it is necessary to check whether the thrips population tends to increase. If so, place additional traps according to the degree of infestation.
Also, in this case, the traps should be placed at the height of the floral clusters or the tallest shoots. As with yellow traps, raise the traps progressively as the plants grow.
DIY Chromotropic Traps
If you want to create chromotropic traps on your own, simply use simple colored plastic plates. Apply a layer of transparent glue, like the one used for paper, to the plates. The advantage of doing it yourself is undoubtedly cost savings; however, there is a significant concern about the stability of the adhesive used. If used in excess or exposed to high temperatures, the adhesive may melt and easily seep into the soil, introducing harmful substances.
Further Reading
- Cambridge University Press: Assessment of color response and activity rhythms of the invasive black planthopper Ricania speculum (Walker, 1851) using sticky traps.
- Karbala International Journal of Modern Science: Monitoring Diptera species of medical and veterinary importance in Saudi Arabia: Comparative efficacy of lure-baited and chromotropic traps
