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- Harmonia axyridis spreads parasitic fungi when mating and grouping together, which makes infections rise as much as 40%.
- Microsporidia protect ladybugs that have moved into new areas by sending out antibacterial substances that hurt local predators.
- Beauveria fungi infect and kill ladybugs by going into their hard outer shells, which is a way to control pests naturally.
- Some ladybug fungi live together without causing problems, but others are like biological weapons or deadly germs.
- Scientists are looking into using Beauveria bassiana to cut down on ladybug populations that have moved into new areas and are in farm areas.
Ladybugs might seem cute, but they have a hidden world of tiny fungi that hitchhike, act as killers, and work as bodyguards. From the beetle hanger parasite to the protective microsporidia and the deadly Beauveria fungus, ladybugs are home to different kinds of fungi that can be helpful or deadly. Looking at these connections gives us an interesting view of the variety of fungi and shows how useful—and sometimes surprising—fungi can be in nature, pest control, and farming that helps the environment.
Meet Harmonia axyridis: The Ladybug That Moves In
Among the roughly 6,000 kinds of ladybugs around the world, the multicolored Asian ladybug (Harmonia axyridis) is noticeable because of how it looks and how it affects the environment. This beetle, which is originally from eastern Asia, was brought to North America and Europe in the 20th century to fight pests on farms, especially aphids and scale insects. Harmonia axyridis eats a lot—up to 200 aphids each day—and quickly became a popular helper for farmers wanting to manage pests in a natural way.
But this success in new places had negative effects. Unlike local types that live peacefully in their environments, this newcomer competed with local ladybugs, spread quickly to different places, and acted aggressively. It ate pests, but also the eggs and young of local ladybugs, which further reduced the variety of life.
H. axyridis has also become a problem in homes, not just fields and forests. When it gets cold, they look for warmth by gathering in walls, attics, and basements, sometimes in groups of thousands. If disturbed, they release a yellow liquid—a bad-smelling defense called "ladybug taint." This can stain cloth, bother people with allergies [Goetz, 2009], and even ruin wine if the beetles accidentally get into grapes that are picked [Mansell, 2009].
Here Come the Fungi: Three Roles, Three Stories
Ladybug problems in new places are not just about insects and insects. These beetles are home to three kinds of fungi—some are friends, some are enemies—each with its own purpose and way of working. From parasites you can see on the outside to hitchhikers you can't see inside, these fungi show the wide range of relationships between animals and tiny living things. To be specific:
- Beetle hangers (like Hesperomyces virescens) attack from the outside, causing minor but physical burdens;
- Microsporidia work inside to help their host and get rid of rivals;
- Beauveria fungi, which are very good at killing insects, make things fairer for local types and farmers.
Let’s look more closely at each one.
The Annoying Fungus: Beetle Hangers (Hesperomyces virescens)
Hesperomyces virescens grows on the outside of ladybugs. It is part of the Laboulbeniales group—tiny fungi known for living on the outside of arthropods. There are over 2,000 known kinds, and most Laboulbeniales fungi only infect one type of insect. H. virescens is like this, targeting beetles like Harmonia axyridis very precisely.
If you look with your eyes, these parasites look like golden-yellow spots on the beetle’s shell. But if you use a microscope, you can see they have complicated shapes like small clubs or chandeliers. This noticeable shape, and the way they seem to “hang” on, is why they are called “beetle hangers”—a name that goes back to 19th-century naturalists like [Cooke, 1892].
A Parasitic Way of Being Precise
Hesperomyces virescens doesn’t just grow on the ladybug—it goes into it. When its spore lands on the beetle’s outer shell, it uses a special anchor called a haustorium to grab on and poke through the shell. This structure, described in detail by Thaxter and later looked at with electron microscopes [Weir & Beakes, 1996], is like an “o-ring” and lets the fungus take in food without causing quick or major harm.
Above the base, reproductive parts grow. These eventually release ascospores that spread when the host touches something or cleans itself. These spores don't go far in the air, they spread best by moving directly from beetle to beetle.
Not Deadly... Just Needy
It's interesting that H. virescens usually doesn't kill its host. Most of the time, ladybugs that are infected live their lives almost normally, though bad infections might make it harder to move their wings or mate. The fungus uses a type of parasitism called commensal ectoparasitism—where it benefits, and the host has minor or unnoticeable problems.
Observations show that infected ladybirds eat and move normally, but some insect experts think that many fungi might weaken their immune systems or make them more likely to get other diseases. For the fungus, the goal is to live and spread—not to kill.
Fungus Spreads Through Mating and Grouping
Ladybug behavior greatly increases how beetle hangers spread. When ladybugs mate—adults join bodies for a while—this helps the fungus move directly from one to another. Infected males can spread spores to many females during mating periods. Also, ladybugs often group together for warmth in protected places when it’s cold. These groups are crowded, which is perfect for spores to spread.
Research has shown that infection levels in groups that stay together over winter can rise a lot. In one study by Nalepa and Weir [2007], infections went up by over 40% in groups that were just exposed to a few infected ladybugs. Spores can also spread by just touching dead, infected bodies, which shows how persistent these fungi are.
The Biological Bodyguard: Microsporidia
Beetle hangers are parasites you can see that don't do much harm, but microsporidia—fungi inside cells—are more complex. These tiny fungi live inside the blood and tissues of Harmonia axyridis. But they don't hurt their host. They actually protect it, acting more like bodyguards than attackers. But their protection comes with a cost—they attack other insects that are a threat.
Invasion by Fungi Used as Weapons
Microsporidia are old types of fungi. They don’t have many common fungal features, but they do have structures and ways of reproducing that show they are fungi. Unlike mushrooms, which are made of many cells, microsporidia are single-celled. Their main weapon is a coiled polar filament—a tiny harpoon that shoots their infectious stuff right into the cell it targets.
In Harmonia axyridis, these fungi are calm and seem to have adapted together with the ladybug. But things get interesting when local beetles—like the two-spotted ladybird—eat eggs laid by H. axyridis. These eggs, without knowing it, are full of microsporidia, and they act like timebombs. Once inside the local beetle, the microsporidia quickly grow in numbers, making it weak or even killing it [Williams, 2013].
Bioweapon or Helper?
This way of working lets Harmonia axyridis stop possible rivals indirectly—a clear example of biological war built into a reproductive cycle. Researchers say this might be why H. axyridis has become so dominant in North America and Europe.
Chemical tests by Vilcinskas et al. [2013] showed that the blood of infected harlequin ladybirds has a lot of antimicrobial peptides. These might be made or increased by microsporidian genes or enzymes. These peptides do two things—they fight off other infections and weaken predators that eat their host.
Origins and Behavior of Microsporidia
Looking back in time, microsporidia are among the oldest parasitic fungi. They might have developed together with arthropods for hundreds of millions of years. Even though they are very small and have small genomes, they are very good at infecting hosts from fish and insects to humans.
With ladybugs, their close relationship shows a developing area of microbial co-development. What was once only seen as infection now seems to help the ladybug move into new areas, suggesting a back-and-forth between the host’s success and the fungi’s survival.
The Killer Fungus: Beauveria
One of the most aggressive fungi that attack ladybugs is Beauveria—a type of fungus that makes white spores and kills insects. Beauveria bassiana is not only for ladybugs. It has been studied a lot because it is good at wiping out insect pests—from beetles to caterpillars to rootworms. This fungus is a great example of biological control.
How Does Beauveria Kill?
The killing starts with a tiny spore that lands on the outer shell of an insect. Once it sticks, it sends out substances that break down the shell and let it get inside. Inside, the fungus quickly takes over the insect's blood, breaking down tissues as it grows. Infected insects usually die in 3–7 days. After death, the fungus comes out—thin white threads burst out of the joints and openings, forming groups that release new spores [Roy et al., 2008].
The fungal kill is often so complete that the insect doesn't seem to fight back at all. It’s a clean, effective end—both scary and amazing.
Beauveria in Biocontrol and Farming
Because it is so deadly, Beauveria bassiana was one of the first fungi sold to be used in managing pests in a joined-up way (IPM). Biopesticide products now give choices that are better for the environment than man-made chemicals. In vineyards and greenhouses, Beauveria sprays can stop mites, aphids, and weevils while not harming helpful pollinators much.
For ladybugs that have moved into new areas, some farmers are thinking about using Beauveria types that are specific—types that target Harmonia axyridis but don't hurt local types. This is still being tested, but making specific types might one day make this a good way to control beetle problems in homes, farms, and even wineries [Roy et al., 2008].
Understanding Fungal-Insect Relationships
Why is this important? Because fungi adapt to insects in big and small ways. What look like tiny spots on a beetle’s back or invisible cells in its gut can actually decide which species becomes dominant, what happens to crops, and even patterns of variety in nature.
Understanding these connections lets researchers and growers:
- Make targeted fungal biocontrol products.
- Fight back against insects that move into new areas.
- Improve farming methods that are good for the environment.
- See fungi as powerful forces in nature—not just things that break down dead stuff.
What This Means for Fungal Variety
Fungal life in and on ladybugs is a small picture of bigger biological ideas: co-development, helpful partnerships, competition, and fighting in nature. If one kind of ladybug can be home to three different fungi with such different effects, how much complexity is hidden in other insects?
People who are interested in nature, growers, and fungus researchers could find new kinds of fungi, discover new antimicrobial substances, or even follow evolutionary changes through parasitic co-adaptation. Fungi might be under our feet—but they are also right in front of us, under wings, and doing well under outer shells.
Why Growers and Mycologists Should Care
At Zombie Mushrooms, this is exactly the kind of tiny living world we are excited about. Whether you're growing lion’s mane for its brain benefits or shiitake for tasty meals, understanding fungi like Hesperomyces or Beauveria adds depth to how we see fungi.
These insect fungi teach us about strength, how to adapt, and biological cleverness. They show how fungi can be tools, threats, and helpers—depending on the situation. This information is very valuable for:
- Organic farmers managing pests.
- Mycologists interested in fungus shapes.
- Ecologists studying species that move into new areas.
- Everyday mushroom fans discovering unique lifeforms.
Friend or Foe? The Fungi That Live With Ladybugs
In the end, fungi linked to ladybugs are not bad or good—they just work. Some stay without hurting their hosts (Hesperomyces), others protect them (microsporidia), and some just kill them (Beauveria). This three-part relationship shows the amazing range of things fungi can do—even in very specific situations.
So next time you see a ladybug, look closer—it might be carrying fungi that are living, breeding, and fighting silently.
