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Melittobia australica

By Andrew Wood

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. (Girault, 1912; Gonzalez, et al., 2004; Matthews, et al., 2009)

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. (Freeman and Ittyeipe, 1993; Matthews and Gonzalez, 2002; Matthews, et al., 2009)

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. (Dahms, 1984; Freeman and Ittyeipe, 1993; Girault, 1912; Matthews and Gonzalez, 2002; Matthews, et al., 2009; Silva-Torres and Matthews, 2003)

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. (Dahms, 1984; Freeman and Ittyeipe, 1993; Girault, 1912; Gonzalez, et al., 2008; Matthews and Gonzalez, 2002; Matthews, et al., 2009; Silva-Torres and Matthews, 2003)

  • Sexual Dimorphism
  • male larger
  • sexes colored or patterned differently
  • Range length
    1.1 to 1.4 mm
    0.04 to 0.06 in

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. (Freeman and Ittyeipe, 1993; Matthews and Gonzalez, 2002; Matthews, et al., 2009; Silva-Torres and Matthews, 2003)

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. (Freeman and Ittyeipe, 1993; Gonzalez, et al., 1985; Matthews and Gonzalez, 2002; Matthews, et al., 2009)

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. (Freeman and Ittyeipe, 1993; Gonzalez, et al., 1996; Matthews, et al., 2009; Silva-Torres and Matthews, 2003)

  • Breeding interval
    Melittobia australica breeds only once in their lives.
  • Breeding season
    Melittobia australica may breed year round.
  • Average eggs per season
    10.9
  • Average age at sexual or reproductive maturity (female)
    25.5 days
  • Average age at sexual or reproductive maturity (male)
    25.5 days

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. (Matthews, et al., 2009)

  • 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. (Silva-Torres and Matthews, 2003)

  • Typical lifespan
    Status: wild
    31 to 37 days

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). (Matthews, et al., 2009)

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. (Freeman and Ittyeipe, 1993; Matthews, et al., 2009)

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. (Freeman and Ittyeipe, 1993; Matthews, et al., 2009)

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. (Freeman and Ittyeipe, 1993; Matthews, et al., 2009)

  • 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. (Matthews, et al., 2009)

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 (Anagrus 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. (Matthews, et al., 2009)

Species Used as Host

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. (Matthews, et al., 2009)

  • 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. (Matthews, et al., 2009)

Conservation Status

Melittobia australica is not listed as threatened or endangered on any of the major worldwide conservation classification systems.

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.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

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.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

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.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

insectivore

An animal that eats mainly insects or spiders.

internal fertilization

fertilization takes place within the female's body

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

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.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

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

polygynous

having more than one female as a mate at one time

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.

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.

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.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

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).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

year-round breeding

breeding takes place throughout the year

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 biología 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. 1997. Weird Wonderful WOWbugs. Carolina Tips, 60/2: 9-11.

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., J. Gonzalez, J. Matthews, L. Deyrup. 2009. Biology of the Parasitoid Melittobia (Hymenoptera: Eulophidae). Annual Review of Entomology, 54/1: 251-266.

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.

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