Geographic Range
Melittobia australica
was first discovered by A.A. Girault in Queensland, Australia. It has since been
discovered in the lower part of the Nearctic region (certain regions of the United
States and Mexico), and the upper part of the Neotropical region (Central America,
the Carribbean, and parts of South America). It has been postulated that this relatively
recent expansion in the range of
Melittobia australica
is related to human commercialism.
- Biogeographic Regions
- nearctic
- neotropical
- australian
Habitat
Broadly speaking,
Melittobia australica
selects habitat in tropical rainforests that contain the high humidity and temperature
to which it is adapted. Specifically,
Melittobia australica
is a parasitoid wasp and as such, lives most of its life in the nests of its hymenopteran
hosts. As an egg and through all developmental stages, both males and females spend
their lives inside the pupa of the prepupal and pupal stages of their host. Adult
males stay in the nest cell of the previously parasitized hosts and mate with the
females. Adult females either become crawlers that stay within the nest cell and look
for other, later developing hosts to lay their eggs on, or become fliers that leave
in search of another nest cell.
- Habitat Regions
- temperate
- tropical
- terrestrial
- Terrestrial Biomes
- forest
- rainforest
Physical Description
Melittobia australica
has a body length ranging from 1.1 to 1.4 mm which is very small for hymenoptera.
It contains the typical head, thorax, abdomen body structure with the constriction
of the first abdominal segment found in many wasps (wasp waist). Sexual dimorphism
is displayed in size and coloration. The male is typically larger than the female
(1.2 to 1.4 mm versus 1.1 to 1.3 mm) with a wider head. The wings are smaller in males
and the antennal scape is broadened significantly. The males are also a honey brown
color whereas the females are dark brown.
Melittobia australica
females exhibit polymorphism. Whether there exists two or three different subgroups
is up for debate, but the key differences are the abdominal size, wing development,
and eye size of the two (or three) different subgroups. 'Crawlers' have a normally
sized abdomen, shorter wings, and small eyes. 'Fliers' (which may or may not be made
up of traditional fliers and another sub group 'jumpers' which have intermediate wing
sizes) have much longer wings, large eyes, and a smaller abdomen. These differences
are clear adaptations to the differing lifestyles of the crawler (stay within the
nest cell) and the flier (leave the nest cell and fly to another nest cell) after
development.
- Other Physical Features
- ectothermic
- bilateral symmetry
- polymorphic
- Sexual Dimorphism
- male larger
- sexes colored or patterned differently
Development
The life cycle of
Melittobia australica
begins when a fertilized adult female locates a juvenile solitary wasp or bee host
in its prepupal stage. Once on the host, the female feeds from it and deposits eggs
inside its pupal coverine at a rate of 10 to 50 eggs per day for two weeks, with fertilized
eggs becoming female and unfertilized eggs male. One interesting pattern to note is
that unlike many other related species that lay eggs on many hosts,
Melittobia
species are often observed to lay eggs on only one host and in fact many females
will share a host as an oviposition site. Because of this, a prepupal host becomes
virtually covered by larva (which hatch a few days after being laid) in differing
stages of development. During this period, the larva feed on the tissue of the host
and females begin the process of differentiating into the various polymorphs that
are observed in nature. Which polymorph a larva will develop into is ultimately decided
by the density of larva present on the host during the critical stages of its development
(which in turn is determined by when the egg was laid). Low density values result
in ‘crawlers’ that search the immediate vicinity for other hosts. Medium density values
result in ‘jumpers’ that are capable of short flight and search the nest site for
other nests. Finally, high density values result in ‘fliers’ that are capable of long
rang flight and venture out in search of new, distant, nest cells.
- Development - Life Cycle
- metamorphosis
Reproduction
Mating in
Melittobia australica
takes place within the host pupa following maturation, and involves the males attracting
the females. Males are known to excrete a very powerful attractive pheremone that
attracts any females inside the cocoon. The sex ratio is heavily skewed in the direction
of females and so males must mate with many females once they reach maturity. Males
mate with their sisters who, having been laid as eggs at the same time, reach maturity
at the same time. Breeding occurs only once in each wasps lifetime and males never
leave their place of birth. Males die shortly after mating.
- Mating System
- polygynous
Reproduction in
Melittobia australica
begins with males attracting females via a very powerful pheromone. During this time,
many of the males will fight each other in often fatal encounters. The purpose of
fighting is currently unknown as there can be as many as 40 to 50 females per male.
Once a male and female have come into contact, a courtship ritual follows. If the
female is receptive, mating takes place and the male internally fertilizes the eggs
of the female. Each male fertilizes many females in this way. Once the female finds
a new host, she lays the newly fertilized eggs inside it. Females lay an average of
10.9 eggs, which hatch into larvae within 2 to 3 days. Larvae fully develop into adults
in 20 to 30 days depending on conditions, with an average of 25.5 days under ideal
conditions. The newly mature adults mate with their siblings and begin the cycle again.
- Key Reproductive Features
- semelparous
- year-round breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- fertilization
- oviparous
The only parental involvement in
Melittobia australica
is shown by the females, who seek out an appropriate host in which to lay their eggs.
In doing so, they provide the food and developmental environment that the larvae will
need to survive to adulthood.
- Parental Investment
- no parental involvement
-
pre-fertilization
- provisioning
Lifespan/Longevity
There has been very little published on the exact lifespans of
Melittobia australica
. One experiment showed that without finding a host, the average adult female will
live from 6 to 9 days following adult development. The same study found that developmental
time was anywhere from 25 to 28 days depending on the amount of other
M. australica
females that also parasitize on the same host. This results in a range of anywhere
from 31 to 37 days for the longevity of this species.
Behavior
Melittobia australica
may complete it's entire life cycle on and around a host larva. As the larvae of
this species develop, they kill and consume the juvenile host. The species is social
in the developmental period in the sense that all the offspring of a single mating
develop together in the same pupa. Also, new adult females (sisters) often will work
together to chew their way out of the protective pupa covering that traps them by
forming a chewing circle and working together to exit their birth place. One female
will pierce the pupa with her ovipositor, releasing an attractive pheromone. Other
females will then flock to the site of the small piercing and will begin working in
a circle to create a hole large enough to escape. However, once the juveniles have
matured into adults and mated, they become solitary as they either die post-mating
(males) or go off in search of new hosts in which to lay their eggs (females).
Home Range
The exact home range size for Melittobia australica is unknown, however many individuals will complete their entire life cycle within or around a single larval host.
Communication and Perception
Courtship and mating is the only major area of communication between members of Melittobia australica . The males perform a complex mating dance in which they raise and lower their legs and rub the females with their antennae and legs. Within this ritual, chemical, tactile, and auditory forms of communication are being utilized. The males elicit a strong pheromone from their abdominal region that is a very strong attractant to females. Also, the existence of a large gland in the male antennae suggests that pheremones are also emitted from the antennae as they are rubbed against the female. Tactile communication obviously occurs through the rubbing of the female with leg and antennal segments. Finally, during the mating dance, the males beat their wings in distinct patterns. Since the wings rarely touch the females, it is thought that these patterns of wing beating are a form of auditory communication.
The only other form of "communication" comes in the form of a pheremone that is released
by a newly mature female when she has inserted her ovipositor into the pupal covering.
This pheremone acts as an attractant to other females, and they will form a chewing
circle around the pheremone site and attempt to chew their way out of their birth
place.
The methods by which
Melittobia australica
perceives its environment are largely unstudied, fortunately there are some areas
that have at least been given a cursory examination. Location of a nest cell, for
example, seems to be through a form of chemical arrestant as females do not travel
preferentially towards a nest cell (attractant) but once in an area containing nest
cells, will not leave. Also, the two different kinds of females both exhibit visual
phototaxis of some kind. The crawlers exhibit negative phototaxis in order to stay
within the nest cell of the nadal host. Fliers on the other hand, exhibit positive
phototaxis to achieve their goal of exiting the nest cell and finding another in which
to lay their eggs.
Food Habits
Melittobia australica , being a parasitoid wasp, gets all of its food from the tissues of its host. As a larva, it feeds entirely on its natal host, killing it in the process. Then as adults, the females will feed on the host that it has chosen to oviposit on.
As far as what insects
Melittobia australica
parasitizes, primarily it is the solitary (non social) members of the order Hymenoptera
(bees, wasps, ants, etc.). However,
Melittobia australica
has also been known to parasitize inquilines (nest dwelling insects) of their typical
wasp hosts and seem to show adaptability when it comes to host choice.
- Primary Diet
- carnivore
- Animal Foods
- insects
Predation
Melittobia australica
has no confirmed predators or parasites. There has been a single parasite observed
but not confirmed. In general, possible predators of parasitic wasps include birds,
bats, amphibians, reptiles, or other invertebrates.
Ecosystem Roles
Melittobia australica
, like all other members of the genus
Melittobia
are parasitoids of other wasps. In many cases, these small wasps will be the biggest
mortality-causing agent in the ecosystem for non social hymenopterans. Mortality is
caused primarily through the devouring of the juvenile stages of the host as the
Melittobia australica
larvae develop. Because of the high mortality caused by
Melittobia australica
, many common host species have developed defenses such as physical barriers, chemical
defenses, behavioral modification, and nest location strategies as a direct result
of their association with
Melittobia australica
. To date, there have been no recorded accounts of natural predators of any of the
Melittobia
species. Only one parasite (
Pteratomus putnamii
, an egg parasite) has been recorded and is, as of yet, unconfirmed. Because of their
importance in the mortality of solitary wasps, many of which are pollinators,
Melittobia australica
also can inhibit the reproduction and dispersal of many plant species. Bumblebees
have also been shown to be parasitized by
M. australica
.
- Ecosystem Impact
- parasite
- solitary wasps ( Hymenoptera )
- bumblebees ( Bombus )
Economic Importance for Humans: Positive
The only positive economic impact of
Melittobia australica
seems to be the fact that their small generation time, low amount of effort required
to culture, and ability to thrive on many different hosts make them a useful organism
for research or educational uses. Under ideal conditions, several generations can
be cultured and studied in a given year.
- Positive Impacts
- research and education
Economic Importance for Humans: Negative
The primary economic impact of
Melittobia
species, including
M. australica
, is that they parisitize pollinators that are cultured for use in agricultural pollination.
Many important pollinators including bumblebees can be parasitized by
Melittobia australica
. This can severely damage pollination, thereby inhibiting fruit and seed production
of agricultural plants. One of the major reasons that
Melittobia
species are so dangerous in this regard is that they have the ability to chew right
through the normally effective protective nests made by many pollinating species.
Conservation Status
Melittobia australica is not listed as threatened or endangered on any of the major worldwide conservation classification systems.
Additional Links
Contributors
Andrew Wood (author), University of Michigan-Ann Arbor, Heidi Liere (editor), University of Michigan-Ann Arbor, John Marino (editor), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor, Rachelle Sterling (editor), Special Projects.
- Nearctic
-
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
- introduced
-
referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.
- Neotropical
-
living in the southern part of the New World. In other words, Central and South America.
- introduced
-
referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.
- Australian
-
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- temperate
-
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
- tropical
-
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
- terrestrial
-
Living on the ground.
- forest
-
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
- rainforest
-
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
- ectothermic
-
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
- bilateral symmetry
-
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
- polymorphic
-
"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.
- metamorphosis
-
A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
- polygynous
-
having more than one female as a mate at one time
- semelparous
-
offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.
- year-round breeding
-
breeding takes place throughout the year
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- fertilization
-
union of egg and spermatozoan
- internal fertilization
-
fertilization takes place within the female's body
- oviparous
-
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
- parasite
-
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
- motile
-
having the capacity to move from one place to another.
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
- visual
-
uses sight to communicate
- chemical
-
uses smells or other chemicals to communicate
- parasite
-
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
- carnivore
-
an animal that mainly eats meat
- insectivore
-
An animal that eats mainly insects or spiders.
References
Abe, J., M. Shimada, N. Kondo, Y. Kamimura. 2003. Extremely female-biased sex ratio and lethal male-male combat in a parasitoid wasp, Melittobia australica (Eulophidae). Behavioral Ecology , 14/1: 34-39.
Dahms, E. 1984. Revision of the Genus Melittobia Chalcidoidea Eulophidae with the Description of 7 New Species. Memoirs of the Queensland Museum , 21/2: 271-336.
Freeman, B., K. Ittyeipe. 1993. The Natural Dynamics of the Eulophid Parasitoid Melittobia-Australica. Ecological Entomology , 18/2: 129-140.
Girault, A. 1912. A New Melittobia from Queensland. Psyche , 19: 203-205.
Gonzalez, J., J. Genaro, R. Matthews. 2004. Species of Melittobia (Hymenoptera:Eulophidae) Established in Bahamas, Costa Rica, Cuba, Hispaniola, Puerto Rico and Trinidad.. Florida Entomologist , 87/4: 619-620.
Gonzalez, J., R. Matthews, J. Matthews. 1985. A Sex-Pheromone in Males of Melittobia-Australica and Melittoba-Femorata (Hymenoptera, Eulophidae). The Florida entomologist , 68/2: 279-286.
Gonzalez, J., R. Matthews, J. Teran. 1996. Courtship in parasitoid wasps: Melittobia acasta and Melittobia australica (Hymenoptera: Eulophidae). Revista de biologÃa tropical , 44/2B: 687-695.
Gonzalez, J., R. Matthews, S. Vinson. 2008. Distribution and host records of Melittobia (Hymenoptera: Eulophidae) from Mexico. Distribution and host records of Melittobia (Hymenoptera: Eulophidae) from Mexico , 79/2: 529-531.
Matthews, R., J. Gonzalez, J. Matthews, L. Deyrup. 2009. Biology of the Parasitoid Melittobia (Hymenoptera: Eulophidae). Annual Review of Entomology , 54/1: 251-266.
Matthews, R., J. Gonzalez. 2002. Development and sex ratio of Melittobia australica and M-digitata (Hymenoptera : Eulophidae) on Megachile rotundata (Hymenoptera : Megachilidae) and Trypoxylon politum (Hymenoptera : Sphecidae). The Great Lakes entomologist , 35/1: 85-91.
Matthews, R. 1997. Weird Wonderful WOWbugs. Carolina Tips , 60/2: 9-11.
Silva-Torres, C., R. Matthews. 2003. Development of Melittobia australica Girault and M. digitata Dahms (Parker) (Hymenoptera: Eulophidae) parasitizing Neobellieria bullata (Parker) (Diptera: Sarcophagidae) puparia.. Neoptropical Entomology , 32/4: 531-536.
Woodward, D. 1994. Predators and Parasitoids of Megachile-Rotundata (F) (Hymenoptera, Megachilidae), in South Australia. Journal of the Australian Entomological Society , 33/13: 13-15.