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Parasitoids
are predators that feed on host organisms that causes the host’s death. Parasites are predators that infect and feed on host organism but do not cause the death of the host. There are four main parasitoids that infect butterflies and moths. These are: Trichogramma wasps, Chalcid wasps, Brachnoid wasps, and Tachinid flies
1) Trichogramma wasp
Butterfly and moth eggs turn dark all over and never hatch? That’s trichogramma wasp infection, the miniature (almost microscopic to microscopic) parasitoid.
First, let’s look at a normal egg so we have a standard in our minds. Before a butterfly or moth egg hatches, it normally (depending on species) turns dark in one spot first. That spot is the head of the caterpillar.
Monarch butterfly egg about to hatch
But sometimes eggs turn all dark and never hatch. They aren’t infertile. Infertile eggs collapse upon themselves. No, the problem wasn’t a predator. Predators either eat the entire egg or drain it, leaving an empty shell. It’s trichogramma wasps, a parasitoid.
Giant Swallowtail butterfly egg with trichogramma wasps inside
Trichogramma wasps are tiny, sometimes microscopic.
Trichogramma wasp laying eggs in a Brazilian Skipper Butterfly egg
Trichogramma wasps often ride around on female butterfly’s body. When she lays eggs, they hop off and lay eggs in her eggs. We’ve photographed (not a good photo by any stretch of the imagination) a trichogramma wasp on the antenna of a Gulf Fritillary butterfly. We brought in Eastern Tiger Swallowtails for a few of their eggs. (Females can be released again after they lay a few eggs.) As we photographed the eggs laid, we found trichogramma wasps with them. They rode in on the female. We spoke with a Lepidopterist who collected butterflies for science. He found as many as 31 trichogramma wasps on one female butterfly.
Trichogramma wasp on the antenna of a Gulf Fritillary butterfly
The only way to totally avoid trichogramma wasps is to emerge adults away from eggs, in a closed room. Allow the adults to pair indoors and lay eggs indoors. Once they are outdoors, trichogramma wasps can find them and infect the eggs.
If you suspect that butterfly eggs may be infected by trichogramma wasps, place them in a clear SEALED container and date it with the date the eggs were laid. If you aren’t sure when the eggs were laid, date the container with the date you bring in the eggs. If a caterpillar emerges from any of the eggs, remove it and place it on a host plant. Before opening the container to remove hatchling caterpillars, hold the cup under a bright light, checking the lid for trichogramma wasps underneath it, crawling around on the underside of the lid. After a week in cooler weather or five days for warmer weather, destroy the contents by freezing for a week, flushing the eggs, or throwing away the sealed container in the garbage. Trichogramma wasps take a week to ten days to emerge.
The fine mesh popup habitats that are sold by Butterflygrower.com / ButterflyConservationSupplies.com and Shady Oak Butterfly Farm have a mesh so fine that most trichogramma wasps cannot fit through the screen. Check out this photo that has trichogramma and chalcid wasps as well as a tachinid fly lying on top of both window screen and the fine mesh used by Butterflygrower.com..
Trichogramma wasps are available from many beneficial insect companies. Although butterfly enthusiasts consider them an enemy, farmers and (non-butterfly) gardeners consider them beneficial. To farmers and most gardeners, caterpillars are considered ‘worms’ that eat their plants. They are the most used biological control agent. Farmers began using trichogramma wasps as biological control agents in the early 1900’s. There are over 200 species of trichogramma wasps.
Some of our photos were taken with a phone camera and are not good quality. Without a good camera in hand, photographing these miniature critters is difficult to impossible.
2)Chalcid wasps
“What happened to my chrysalis?” “Why didn’t my butterfly come out and why is there a tiny hole in the chrysalis?” People often ask about butterfly chrysalises and chalcid wasps.
When given Monarch chrysalises from a person who was not experienced with chalcid wasps, we knew immediately that there were serious issues with them. They were off-color and softer than normal.
We isolated them from the good chrysalises from the same person.
Instead of Monarch butterflies emerging, chalcid wasps emerged. When one chrysalis was broken open, we could see the chalcid wasp larvae inside.
We have experimented with chalcid wasps, primarily to be able to detect an infected chrysalis that we may find when we buy plants from nurseries that grow their plants outdoors. Many people write to ask us about their empty chrysalis shells that have a tiny hole in them but a butterfly never emerges. We needed photos and detailed personal answers, drawn from our own experiences.
We allowed some of the wasps to emerge in a mesh popup in a sealed room. A video camera was placed in the popup focused on the chrysalis. When the wasps began emerging, the video camera was turned on.
Two of our videos are on YouTube. You can watch the males emerge first by clicking on this sentence. You can watch the females emerge by clicking on this sentence.
Male chalcid wasps are smaller than female chalcid wasps. Male chalcid wasps emerged first. When most male wasps had emerged, a female tried to emerge. Because males are ready to pair as soon as they emerge, they gathered around the opening in the chrysalis, waiting for the females to emerge. When a female approached the opening, males began to bite at the opening to enlarge it. It was too small for a female wasp. As each female emerged, a male would crawl upon her back and begin to touch her antennae, a courtship ritual.
The chalcid wasps that emerged from these chrysalises were moved to another area. Two Monarch caterpillars were placed into the popup with the wasps. One caterpillar was ready to find a place to pupate. The other was two days younger and still wanted to eat. A few milkweed leaves were placed in the bottom of the popup. This was done in a room without other caterpillars.
The older caterpillar immediately headed to the top of the popup and wandered to select a spot to attach itself to pupate. The younger caterpillar crawled to the milkweed leaves and began eating.
Within a few minutes, the wasps were gathering around and on the caterpillar at the top of the popup. Everywhere it crawled, they followed. They totally ignored the younger caterpillar at the bottom of the popup.
The older caterpillar selected its spot, laid its mat of silk, and hung in a J. The wasps stayed on and around it. When it pupated, they began laying eggs in the chrysalis. So many eggs were laid that the chrysalis died within a few days.
It was immediately clear that:
3) Tachinid Flies
A white maggot emerges from a dead or dying caterpillar or chrysalis. The maggot moves to a dark corner or under whatever is around and changes into a small brown capsule shaped pupa. In a week or two, an adult fly emerges. Yes, that is a Tachinid fly!
Flies around caterpillars can be deadly. Tachinid flies lay eggs on young caterpillars. The eggs hatch and the fly larvae (maggots) begin to drink the hemolymph (blood) of the caterpillar. Just before it pupates, the maggot eats it way out of the caterpillar or pupa. It finds leaf litter, and moves underneath the leaves and twigs. Hidden, it pupates into a small brown pupa.
There are different species of Tachinid flies. Some kill the caterpillars and they fall to the ground. When the butterfly or moth caterpillar is lying on the ground, the fly larvae emerge from the caterpillar and move away to become pupae.
Other species will leave the caterpillar while it is J’ing or after the caterpillar changes into a chrysalis. The fly larvae lower themselves about three or four inches on a mucus string before dropping to the ground.
A caterpillar may have one to six fly larvae growing inside it.
If you are raising caterpillars indoors, keep them safe from flies. It just may NOT be a housefly!
We wild collected butterfly and moth caterpillars to raise and photograph their life cycle. We collected some species to raise indoors and re-release outdoors. Every tachinid fly we have seen on our property has come from wild-collected caterpillars because our caterpillars are raised in a closed room in closed rearing containers. Flies cannot fit through the mesh into the rearing containers.
From the wild, we find about a 25 – 50 percent infection rate in some species.
When you find a caterpillar, you can’t always tell that it has a Tachinid fly larva inside its body. You can see eggs. When the fly larva hatches, it bends the shell of the egg outward, into the caterpillar.
In some cases, you can see that the caterpillar is infected with Tachinid fly larvae.
Butterfly chrysalises and moth pupae are discolored before the fly larva emerges. You can compare the Tawny Emperor butterfly chrysalis photos to the left and below. One is healthy with its wings showing through the chrysalis. The other is dark in the abdominal area. A Tachinid fly larva (at least one) is inside the chrysalis and will soon emerge.
4) Brachnoid wasps
One of the greatest parasitoids, responsible for many moth and butterfly deaths, is the braconid wasp.
This sight is one that most people recognize.
What most of us don’t realize is that these are not eggs. These are cocoons. We never see the eggs that begin this process.
Braconid wasps lay eggs in or on the caterpillar.
The eggs hatch and the young wasp larvae drink the blood/hemolymph as well as non-essential organs of the caterpillar while the caterpillar is still eating and growing.
As the caterpillar grows, so do the wasp larvae. The wasp larvae do not take as long to mature as the moth/butterfly caterpillar.
Before the caterpillar is ready to pupate, braconid wasp larvae will leave the caterpillar by eating holes in the caterpillar’s skin/cuticle. They work their way out of the body, to the outside of the caterpillar. At that point, the larvae immediately begin making their cocoons.
There are two basic types of braconid wasps that parasitize butterfly and moth caterpillars.
1) One type attaches its cocoons on the caterpillar itself.
2) The second creates ‘zombie caterpillars‘, having made a chemical change in the brain of the caterpillar, causing it to live the rest of its life protecting the wasp cocoons.
Depending upon which type of braconid wasp is emerging, the cocoons are made either on the caterpillar or by the caterpillar.
1) The braconid wasps that attach themselves, stay on the caterpillar. The make their cocoons attached to the caterpillar, at the holes where they emerged. The caterpillar continues to live for a few days, sometimes moving about a little, but not eating and growing. It is now dying.
2) The braconid wasps that cause caterpillars to protect the wasp’s cocoons will make their cocoons either jumbled and/or under the caterpillar. Some make a stack of cocoons, one on top of the other.
Some of these wasps have made chemical changes in the brains of the caterpillar that causes the caterpillar to cover the stack with its own silk after the wasp larvae have made their cocoons. The caterpillar then sits on top of the stack of cocoons and protects them, the best that they can, from anything that approaches the stack of cocoons. They strike at intruders with their heads or abdomens. The caterpillar never eats again. It continues to protect the wasp cocoons until it dies. (See the photo captioned, “Moth Caterpillar Protecting
Braconid Wasp Cocoon Stack”.)
On occasion, the caterpillar is linked to the cocoons with a bit of silk and hangs below the cocoon stack. (See the photo captioned, “Dead Unicorn Moth Caterpillar Protected Braconid Wasp Cocoons”.)
Some wasp larvae make a loose stack of cocoons and the caterpillar climbs on top of it and sits, protecting the cocoons, until it dies. Once again, these caterpillars no longer eat after the wasp larvae emerge. (See the photo captioned, “Duskywing Butterfly Protecting Braconid Wasp Cocoons”.)
As you walk along, you may see these tiny cocoons in the grass or on plants. (See photo captioned, “Braconid Wasp
Empty Cocoons”.) This is due to the fact that, after the caterpillar dies, it normally falls to the ground and isn’t noticed. The braconid wasp cocoons are attached to the item and do not fall, even after the wasps emerge from their cocoons.
If the wasps have emerged from their cocoons, the end of each cocoon has a hatch-type opening. (See photo captioned, “Braconid Wasp
Empty Cocoons”.)
There are predators for braconid wasps.
Ants will empty braconid wasp cocoons. (See photo captioned, “Ants Eating Braconid Wasps in Cocoons”.)
Another predator is a hyperparasitoid. There are species of chalcid wasps that parasitize braconid wasps, inside their cocoons. These wasps tend to exit from the side of a braconid wasp cocoon while braconid wasps emerge from the end of their cocoons.
Farmers and gardeners consider these to be beneficial insects.
They are responsible for the deaths of many Tomato Hornworm and Tobacco Hornworm caterpillars, enemies of tomato plants.
