We know of numerous cases of cooperation between the insect world and plants, yet, just as with microorganisms, when we encounter conditions we dislike, we often judge insects’ activities as harmful.
But are they truly harmful?
Just because something doesn’t serve our interests at a given moment or we find it displeasing doesn’t mean it’s not beneficial for a specific plant or the natural cycle.
At first glance, this seems like a clear parasitic relationship, where the fly benefits (gaining a breeding site and food) while the tree seemingly loses, as its fruit is damaged. But is there anything in this process that could benefit the cherry tree?
Beyond survival, reproduction is a primary goal for plants, which, for a cherry tree, means ensuring its seeds are dispersed as far as possible to colonize new areas. Birds are the primary helpers in this task for cherries. Fruits affected by cherry fruit fly larvae are often softer and more fermented than intact, harder cherries, making them more attractive to birds like thrushes and starlings.
Protein is crucial in birds’ diets, especially during the chick-rearing period. A worm-infested cherry offers both sugar (from the fruit’s flesh) and protein (from the larva), making it more appealing than a plain fruit. Starlings, for instance, actively seek out insects in berries because they provide extra energy.
The cherry’s pit is hard and resistant; it is neither damaged by the larva nor digested by birds. After a bird eats the fruit—larva and all—it can carry the pit far away, potentially kilometers from the tree’s original location, through its droppings. This long-distance dispersal benefits the cherry tree by reducing local competition around the parent tree and allowing it to colonize new areas.
The cherry tree has not developed specific defenses against the fly (e.g., thicker skin or toxic compounds in the fruit), suggesting that the larvae do not pose a threat to its survival or reproduction significant enough to trigger an evolutionary response.
Another key role of the insect world is decomposition. For example, ants are nature’s ecological cleaners. At first glance, it may seem like they damage our plants, especially when we consider the ant-aphid partnership, but in reality, something entirely different is happening.
Ants and aphids share a well-known mutualistic relationship. Aphids feed on plant sap and excrete a sugary substance called honeydew, which is a valuable carbohydrate source for ants. In return, ants protect aphids from predators (e.g., ladybugs or lacewings) and “tend” to them—moving them to better feeding sites on the plant or sheltering them in their nests during winter to survive the cold.
Ants “milk” aphids by gently tapping them with their antennae, prompting the aphids to release honeydew. This is a form of “agriculture” that ants have practiced for millions of years.
But what determines which plants they choose as targets?
A plant’s vitality is closely tied to environmental conditions, which determine how susceptible it is to insects or other stressors. When plants thrive in their environment with adequate nutrients, water, and sunlight, they become robust—their metabolism is strong, their tissues are resilient, and their defense mechanisms (e.g., tougher skin or production of secondary compounds) function effectively. Insects either don’t settle on them or do so with difficulty. However, if plants are stressed or weakened, they become more accessible to insects.
When a plant suffers from water deficiency or other stressors, its cell walls thin, its sap changes—containing less sugar or water—and it often releases stress compounds (e.g., amino acids or volatile substances). This decline signals an alarm to aphids, ants, or other insects, which accelerate the process by sapping the remaining juices, preparing the plant debris for soil-dwelling microbes.
For example, in my garden, when I neglected to water my pepper plants, they began to wilt, and aphids immediately settled on them. But once the plants were watered again and regained their vitality, the aphids moved on without any intervention on my part. The peppers’ optimal condition was enough to convince the sap-suckers they had chosen the wrong target.
Returning to cherry fruit flies, it’s worth re-examining their role in decomposition. The same principle applies to cherry trees: if a tree isn’t thriving, it becomes more accessible to insects.
If an older fruit tree has a heavy crop, “carrying” all that fruit requires significant energy. If the tree faces a period of low nutrients or drought, its priority shifts to survival rather than ripening a large quantity of fruit.
In such cases, the weakened cherry tree “invites” compatible insects, like cherry fruit flies, to relieve it of this burden. It “offers up its children” for an accelerated decomposition process, allowing the fallen fruit to quickly provide water and nutrients to the soil.
This phenomenon is similar to what we see in the world of marsupials, such as kangaroos. Because it’s unpredictable whether there will be enough food to raise offspring, a joey crawls from the mother’s womb to her pouch after about 30 days, making it easy to abandon if necessary. In times of scarcity, the mother doesn’t have to risk her own vitality for months to ensure the offspring’s survival. (If the mother dies, the offspring is unlikely to survive long without her.)
Insects represent a kind of microcosm in our living world, while our microorganisms form a nanocosm. In both cases, it’s true that if there’s no need for their presence, they don’t appear. Of course, it’s not always easy to prioritize the perspective of nature or plants over our own interests…
It is important to note that this paper does not aim to be exhaustive, I have only touched on part of the topic. The nature of animal conflicts and plant reactions may vary depending on the living conditions of individuals and species, so the exact causes should be considered on a case-by-case basis, taking into account the species, the environment and the animal/plant producer.
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