Melittobia australica facts for kids

Quick facts for kids Melittobia australica
male Melittobia acasta (right) male Melittobia australica (left)
Scientific classification

Melittobia australica is a tiny wasp that belongs to a group called chalcid wasps. It's a special kind of wasp known as a parasitoid. This means it lives on or in another insect, called a host, and gets its food from it. These wasps often live in groups and attack other wasps and bees.

About the Melittobia australica Wasp

Melittobia australica is a very small wasp, usually between 1.1 and 1.4 millimeters long. That's about the size of a pinhead! Like most wasps, it has a body divided into three main parts: a head, a middle section called the thorax, and a back section called the abdomen. It also has a thin "wasp waist."

Male and Female Differences

Male and female Melittobia australica wasps look a bit different. This is called being sexually dimorphic.

• Males are usually a little bigger than females, measuring 1.2 to 1.4 mm.
• Females are slightly smaller, from 1.1 to 1.3 mm.
• Males have wider heads and smaller wings. Their antennae are also much broader.
• Males are a honey-brown color, while females are dark brown.

Different Types of Females

There are at least two different forms, or morphs, of female M. australica. These forms differ in their abdomen size, eye size, and how developed their wings are.

• The "crawler" females have normal abdomens, small eyes, and wings that aren't fully grown. These crawlers usually stay inside the host's nest for their entire life.
• The "flier" and possibly "jumper" females have larger eyes, bigger wings, and smaller abdomens. These types of females can fly or jump away from the host nest when they become adults.

Where Melittobia australica Lives

This tiny wasp was first found in Australia in 1912 by an American scientist named Alexandre Arsène Girault. Since then, it has been found all over the world! You can find it in North America, Central America, northern South America, the Caribbean, Africa, eastern Asia, Europe (specifically Sicily), and New Zealand.

Some experts believe that M. australica originally came from Australia. They think that human activities, like trade and travel, helped these wasps spread to many other parts of the world.

Natural Homes

In Australia, Melittobia australica was first discovered living in the nest of a type of sphecid wasp called Pison spinolae. Its natural home, or habitat, was originally in rainforests.

Life Cycle and Reproduction

Melittobia australica is a parasitoid, which means it uses other insects as hosts to grow and develop. Its main hosts are solitary bees and wasps.

Finding a Host and Laying Eggs

The life cycle of M. australica begins when a female wasp finds a suitable host. She looks for hosts that are in their prepupal stage (a stage before they become adults).

• The female wasp feeds on the host by making a small hole with her ovipositor (a tube for laying eggs). She then drinks the host's body fluids, which are rich in protein. This protein helps her produce her own eggs, a process called ovogenesis.
• She lays between 10 and 50 eggs each day. These eggs are usually placed under the host's outer skin.
• Fertilized eggs will develop into female wasps, while unfertilized eggs will become males. This is a special way of reproduction called arrhenotoky.
• Often, many female M. australica wasps will lay their eggs on the same host. The host can become completely covered with wasp larvae of different ages.

Wasp Larvae and Their Development

A few days after the eggs are laid, the larvae (young wasps) hatch. They feed on the host's tissues, which eventually kills the host.

• How many larvae are feeding on a host can affect what type of female wasp develops.
• If there are only a few larvae on a host, most of the females will become "crawlers."
• If there's a medium number of larvae, "jumpers" or "fliers" will develop.
• If there are many larvae, most of the females will become "fliers."
• If the host larvae are small, the female wasp might lay her eggs on more than one host.

Male Wasp Behavior

Male M. australica wasps produce a very strong pheromone (a chemical scent) to attract females. Since they are often laid on the same host at the same time, males usually mature at the same time as their sisters and often mate with them.

• If males meet other males, they will fight. The losing male often dies.
• Scientists have seen that the first male to hatch might even cut off the heads of other males before or right after they hatch. In another case, the first male stopped other males from developing by touching them with his antennae.
• There can be up to 50 females for every male, so it's a bit of a mystery why the males fight so much.

Courtship and Mating

When a male finds a female ready to mate, they perform a courtship ritual. This involves touching, chemical signals, and sounds.

• The male releases pheromones from his abdomen.
• He raises and lowers his legs.
• He rubs the female with his antennae, which might also release pheromones.
• The male holds the female's head with his mouthparts, just below her ocelli (simple eyes). They keep their antennae touching throughout the ritual, which usually lasts about 15 minutes.
• After the ritual, they mate, and the female's eggs are fertilized.

After Mating

Once fertilized, the female wasp looks for a new host.

• If she is a "crawler," she will find another host within the same nest.
• If she is a "jumper" or "flier," she will leave to find a new nest with hosts.
• Each female lays an average of about 11 eggs on a host.
• These eggs hatch in 2–3 days.
• The larvae take 20–30 days to grow into adult wasps, depending on conditions. Then, the life cycle starts again.
• In a lab, adult females live up to 9 days, and their total lifespan is between 31 and 37 days.
• Females usually mate only once, but males can mate with many females (this is called being polygynous).
• If no males are around, or if a female has used up all the sperm from mating, she might lay a few unfertilized eggs to produce males. She might even mate with her own son.

Group Behavior

M. australica is a gregarious ectoparasitoid, meaning many individuals live and feed together on the outside of one host.

• When a female lays eggs on a host, she releases a pheromone that attracts other females to that spot.
• All the young wasps from one mating develop together on the same host, eating its tissues until it dies.
• When the new adult females are ready to leave, they move to the spot where the eggs were first laid. They release another pheromone that makes nearby females work together to form a "chewing circle." This group chews through the host's outer skin, allowing the adult wasps to escape.
• However, once they are out, the adult wasps are solitary. After mating, the males die, and the females go off to find new hosts.

Finding Host Nests

Female M. australica seem to find host cells using chemical signals. Once they find a nest, they stay nearby. They aren't necessarily attracted to the cells themselves, but rather "chemically arrested" by them.

• Female M. australica have been seen digging holes through the mud walls of Pison wasp nests using their mouthparts. They usually make only one hole per cell, and several females might work on the same hole. Only one female digs at a time, taking turns.
• Adult females react to light, a behavior called phototaxis. "Crawlers" move away from light (negatively phototaxic), while "fliers" are attracted to light (positively phototaxic). This helps the fliers leave the host nest after mating.
• Females can wait for several weeks before feeding and laying eggs until the host reaches the right stage of development. They will even wait in empty cells until a host uses them.

Impact on Hosts

M. australica wasps depend completely on their host wasps for food. The females feed on the host before laying eggs, and the larvae eat the host as they grow. Adult males likely don't eat at all.

• Their main hosts are solitary wasps and bees. However, they can also parasitize other insects that live in the host's nest.
• Bumblebees have also been found to be hosts for this wasp.
• When there are many M. australica wasps, they can significantly reduce the number of host species. Many host species have developed ways to protect themselves, such as choosing different nest locations, using chemical defenses, building physical barriers, or showing defensive behaviors.
• Where M. australica is common, many host species can die. Since many of these host species are important pollinators, a lot of M. australica can make it harder for many plants to reproduce and spread their seeds.

Who Eats Melittobia australica?

There isn't much information about what animals or parasites prey on M. australica.

• One type of egg hyperparasitoid (a parasite that preys on another parasite's eggs) called Anagrus putnamii has been recorded. However, it's not confirmed if it was actually using M. australica as its host.
• Also, tiny parasitic mites have been seen feeding on the larvae of Sceliphron wasps. These mites sometimes compete with M. australica larvae and even feed on them.

Known Hosts of Melittobia australica

The first recorded host for Melittobia australica was Pison spinolae. However, it can parasitize many different insects.

• Its main hosts include leaf-cutting bees (like Megachile species), mason wasps, and mud dauber wasps.
• While there are no native social wasps in Australia, M. australica has been found in the nests of Vespula species in New Zealand and North America. It has also been found in nests of Polistes, Bombus (bumblebees), and honeybees (like Apis mellifera).
• Other insects found in Sceliphron wasp nests, such as the bombyliid fly Anthrax angularis and the ichneumonid wasp Stenarella victoriae, have also been recorded as hosts for M. australica.
• Additionally, M. australica has been found on fly pupae (the resting stage before becoming an adult fly) in Sceliphron nests. These flies are thought to be parasites on spiders that the wasps store in their empty cells.