Bank plants

Bank plants: silent allies in organic control

Unfortunately, decades of misleading information have created a false belief when it comes to crop protection; the image that often comes to mind is that of plant protection products or direct interventions against harmful insects. In nature, however, there is a much more elegant approach: creating an ecosystem in which the natural enemies of pests are always present and ready to act. This is precisely the principle of plant banks.

What are plant banks?
Plant banks are plant species cultivated not for fruit or flower production, but to host organisms useful for crop protection. This is a preventative biological control system that allows beneficial insect and mite populations to be maintained even when pests are still absent or present in low numbers.
The idea is simple: provide beneficial organisms with a continuous source of food, shelter, and reproduction, so they can respond quickly as soon as an infestation appears.

How does a plant bank work?
A plant bank hosts an insect or other small prey that does not pose a threat to the main crop. This organism provides food or host to beneficial insects, allowing them to complete their life cycle without having to wait for the actual pest to appear.
When the pest arrives, its natural enemies are already present in the environment and can immediately contain its spread.
This strategy transforms prevention into a fundamental element of crop protection.

The best-known system: barley, aphids, and small wasps
One of the most common examples in professional greenhouses uses barley.
A typical cereal aphid, Rhopalosiphum padi, is grown on barley. This aphid is unable to infest crops such as tomatoes, peppers, or cucumbers. This aphid hosts tiny parasitoid wasps of the genus Aphidius.
When harmful aphids appear in the main crop, the wasps are already present and immediately begin parasitizing them, limiting the infestation without resorting to chemical treatments.
The same principle can also be applied to wheat and oats, which perform a similar function.

From greenhouses to orchards: when plants become reservoirs of biodiversity
The concept of plant banks can also be extended to outdoor agricultural environments through what is called conservation biological control. In this case, the goal is not to introduce beneficial insects, but to create favorable conditions for them to live and reproduce spontaneously in the landscape.
A particularly interesting example concerns the Judas tree (Cercis siliquastrum), an ornamental species that is attracting the attention of researchers and fruit growers for its role in biological defense of pear trees.
The Judas tree hosts a specific psyllid, Cacopsylla pulchella, which lives exclusively on this tree and is unable to infest pear trees. This psyllid is home to the small parasitoid hymenopteran insect Trechnites psyllae, one of the most effective natural enemies of the pear psyllid (Cacopsylla pyri), one of the most harmful pests of this crop.
The presence of the Judas tree near pear orchards allows the parasitoid to maintain a stable population throughout the year. When the pear psylla begins to develop, Trechnites psyllae is already present in the environment and can quickly move onto cultivated plants, helping to naturally contain its population.
Technically, the Judas tree is defined as a reservoir plant or refuge plant, rather than a true bank plant. However, the ecological principle is very similar: maintaining beneficial organisms in the agroecosystem thanks to the presence of an alternative host that is harmless to the main crop.
This example demonstrates how agricultural landscape design, through trees, hedges, and ecological strips, can become a fundamental tool for strengthening natural pest control mechanisms.

Plant Banks for Predatory Mites
Not all plant banks function through an alternative insect.
Some species produce large quantities of pollen, a valuable food source for predatory mites used in biological control.
Castor oil plant, for example, provides pollen that supports populations of mites such as Amblyseius swirskii and Neoseiulus cucumeris, highly effective predators against thrips, whiteflies, and small phytophagous mites.
Corn and cattail (Typha latifolia) pollen are also often used for this purpose, especially in professional greenhouses.

Plants that Feed Beneficial Insects
There is also a group of plants that, while not hosting an alternative organism, provide nectar and pollen to adult beneficial insects.
Among the most interesting are:
– phacelia;
– buckwheat;
– coriander;
– fennel;
– dill;
– yarrow;
– marigold;
– alyssum (Lobularia maritima).
These blooms provide a constant source of energy for hoverflies, lacewings, ladybugs, and small parasitoid wasps, increasing their survival, fertility, and permanence in the environment.

Bank plants and refuge plants: they are not the same thing
The two terms are often confused.
Bank plants host an organism that allows beneficial insects to maintain their life cycle.
Refuge plants, on the other hand, provide food, pollen, nectar, or an alternative host to beneficial organisms, without posing a risk to the main crop. The Judas tree in pear orchards is one of the most effective examples of this strategy.
Both solutions have the same goal: increasing the stable presence of natural antagonists and making the agroecosystem more balanced.

The advantages of the technique
The use of bank plants and reservoir plants offers numerous benefits:
– reduces the use of insecticides;
– allows for preventive rather than curative interventions;
– maintains a stable population of beneficial insects;
– increases the biodiversity of the agroecosystem;
– makes biological control more effective and long-lasting;
– limits the risk of sudden outbreaks of pest populations;
– promotes the creation of permanent ecological infrastructures within farms.
For this reason, these strategies are now adopted not only in tomato, pepper, cucumber, eggplant, and floriculture greenhouses, but are also increasingly being used in orchards, vineyards, and organic vegetable gardens.

An investment that benefits the farmer and the environment
Bank plants, reservoir plants, and refuge plants represent much more than a simple crop protection technique: they are an investment in the health of the agroecosystem.
For the farmer, the primary benefit is economic. Maintaining a stable population of beneficial insects means being able to intervene preventatively, reducing the number of pest treatments, product purchasing costs, the labor hours dedicated to pest control, and the risk of production losses due to infestations. A balanced ecosystem is also more resilient to climate fluctuations and sudden outbreaks of pests, making production more stable over time and less dependent on emergency interventions.
Added to these benefits is an increasingly important value: the farm’s environmental quality. Hedges, trees, flowerbeds, and bank plants increase biodiversity, favor pollinators, provide shelter for numerous species of insects and small vertebrates, and help rebuild the ecological network that intensive agriculture has often simplified.
The benefits, however, don’t stop at the farm’s borders. Less dependence on insecticides means a reduced risk of soil and water contamination, greater protection for pollinating insects and other beneficial organisms, and a better quality of the rural landscape. The entire community benefits, which can count on more sustainable agricultural production, more biodiverse ecosystems, and a healthier environment.
In this way, conservation biological control is not just a technical strategy for controlling pests, but becomes a management model capable of reconciling productivity, profitability, and the protection of natural capital. Every bank plant, every reservoir tree, and every flowering band contributes to building an agriculture that works with nature rather than against it, transforming biodiversity from a simple ecological asset to a true productive resource for the present and the future.