Fermented Nectar for Pest Control? - How Microbial Brews Boost Beneficial Insects
Wine and beers are typical products of fermentation, and humans recognized very early their benefits (1), but what about the benefits of fermentations for… insects?
Small hint: Fermentation is performed by microbes, which use carbohydrates and amino acids from a starter product, such as milk or juice, for their own metabolism.
The process changes the product's chemical profile, enriching it with a new aroma, taste, texture, and nutrients. As a result, we get wine from smashed grapes and yogurt from milk. However, fermented foods and drinks may not only be valuable for our gut microbes and our… parties. But also for our future pest control management that promotes the ecological balance through the conservation of important beneficial insects in the agroecosystems (2–5). Maybe this is a bold statement, but let me first explain the reasoning behind it.
Intensive agriculture: Attracting our enemies while losing our allies
Nowadays, immense crop production areas are comprised of a few plant species. But the domination of a single plant in the landscape, the so-called monoculture, is highly attractive for the vegetarians of the insect world. Given that most organisms face food limitations in the wild (6), the presence of their favorite crop plant in such abundance seems like an invitation to a food heaven, a vast dining room filled with endless food. In such a biodiversity-depleted landscape, farmers and policymakers in the agricultural sector should not be astonished when they encounter large pest infestations (7,8).
This agricultural landscape may be attractive to the intruders that decimate or spoil a percentage of the yield, but it is indifferent to the enemies of the intruders. These carnivorous insects hunt and then kill or parasitize pests, reducing the pest numbers (9,10). These insects provide a valuable service with a monetary value of billions of dollars, without charging the farmers (11,12).
Syrphid flies, which are usually mistaken by untrained eyes as bees due to their black and yellow patterns, are definitely an iconic example (13). Among them, the species Episyrphus balteatus travels during spring from continental Europe to England. Within a year, the survivors of this long journey visit billions of flowers and give rise to the next generation, which consumes trillions of aphids during the larval stage (14). Overall, their absence in the agricultural landscape could cost $20.92 billion due to pest damage in the United States per year. Another example with a remarkable life history is Hymenoptera, which are called parasitoids or parasitic wasps because they lay their eggs inside the bodies of other insects (15). Then, when their larvae hatch, they eat the insects from the inside out. Just like the movie Alien, this is a horror scenario for the pest itself, but a sustainable way to get rid of insect pests, since parasitoids target only a few species that are harmful and they do not pose a threat to other insects that have nothing to do with our crops (16).
Yet, these beneficial insects are rarely present in intensively agricultural landscapes, which have replaced the once beautiful habitats embellished by colorful flowers (9).
The modern-day landscape planning is not a sustainable option for many other reasons, such as soil erosion, nutrient loss, and depletion (17–19), and therefore, it is misleadingly perceived as profitable, given the high costs of frequent chemical applications (20). In particular, chemical applications pose a further challenge for the enemies of our enemies, the insects that protect our crop production from insect herbivores. Even chemical products with a selective mode of action may harm beneficial insects and arthropods (21,22), while they may also fail to eliminate the target pests (23,24).
What should be done? - And how is nectar even relevant here?
The good news is that consumers’ awareness related to food safety is growing, which establishes the ground for innovative ways to tackle pest infestations (25). And one way is to get inspiration from nature's solutions. To rely less on chemical products and avoid as much as possible the repercussions of their persistence in our foods and environment, we can reintroduce these beneficial insects and arthropods even in greenhouses by restoring the wild flora at the inside space and/ or their surroundings (26–28). Human interventions aiming to protect and enhance the performance of beneficial organisms in the agricultural landscape are usually referred to as Conservation Biological Control strategies (29). Scientists have found many attractive plants that can nurture beneficial insects (30). For example, buckwheat is a common flowering plant in temperate regions (31), and sweet alyssum from the Mediterranean basin (32). The flower strips with different native flowers suitable for each time's climatic conditions can attract the insects in the fields, where they can detect and attack the pests. Nectar is also the sweet reward these flowers give to predators such as the syrphid flies (33) and parasitoids (34), which need the nectar to survive during adulthood.
The divine drink of the Greek gods, when given to good insects after being altered by… microbes
Nectar, a vital energy drink for many beneficial insects, once thought to nurture and grant everlasting life to the ancient Greek gods, is also home to microbes that can actually ferment it! Indeed, several microbes were isolated from the nectar of buckwheat flowers (3). Among the tiny inhabitants of nectar, some bacteria were given scientific names, which are characteristic of their sugary habitats:
- the friend of sugars Terribacillus saccharophilus (from the Greek σάκχαρον - sákcharon meaning sugar and φίλος - phílos, which means friend) and
- the sugar-Bacillus Saccharibacillus endophyticus.
By adding them individually to a mixture of sugar and amino acids that mimicked the chemical composition of natural nectar, we could obtain different fermented nectars from each microbe.
When we successfully obtained the fermented nectars, we didn't stop there. We fed them to a parasitic wasp that attacks the eggs of the southern green stink bug. Apart from its preference for a huge variety of crops, the stink bug is a well-known nuisance due to its horrible odor when disturbed.
Fermentations worked on our side!
Increased longevity of the parasitic wasps was associated with the consumption of fermented nectars by bacteria from the phylum Bacillota (2) and the fermentation of the nectar by one of them proved attractive to the wasps (3)! So, nectar fermentations by these bacteria can lower the pest pressure on the crop by increasing the number of wasps that are encountered with the pest! And our encounters with the stink bug and its unpleasant odors.
Before any application, we still need to test the efficiency of these nectar fermentations by bacteria in field conditions, where the southern green stink bug gathers to eat our food. The fermented nectar can be made accessible in the fields by spraying the flowers with the right microbes or by selecting flowers that usually have these microbes in their nectar. Under greenhouse conditions, the fermented nectar could also be supplied through feeders adequately designed for insect feeding (35).
And who knows, maybe in the future, other studies will prove that these nectar fermentations boost other beneficial insects that also consume nectar and are known to attack different pests. After all, the Olympian gods who consumed nectar and ambrosia to live longer were twelve in total. All kidding aside, thousands of beneficial species are still waiting to be discovered given the diversity of arthropods (36). Numerous ones have not been taken so much into consideration, such as spiders, even though they can be the first line of defense against insect pest invasions before other beneficials arrive (37,38). Overall, since the efforts of many insects and arthropods to protect our crops are monumental, we should treat them with fermented nectar!
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Further reading
Hormesis: How Low-Dose Insecticides Can Enhance Pest Control
7 Modern and efficient ways to protect crops from pests and diseases
Important Beneficial Insects as Natural Enemies of Crop Pests
Biological control of greenhouse pests using natural enemies
What is Biological Control and how to be used in agriculture
Harnessing the Power of Natural Enemies: Biological Control in Almond Tree IPM
