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.
Communication Channels: tactile ; acoustic ; chemical
Perception Channels: visual ; chemical
Melittobia australica is not listed as threatened or endangered on any of the major worldwide conservation classification systems.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
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
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.
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
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.
Ecosystem Impact: parasite
Species Used as Host:
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.
Animal Foods: insects
Primary Diet: carnivore (Insectivore )
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 (Introduced ); neotropical (Introduced ); australian (Native )
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
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.
Typical lifespan
Status: wild: 31 to 37 days.
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.
Range length: 1.1 to 1.4 mm.
Other Physical Features: ectothermic ; bilateral symmetry ; polymorphic
Sexual Dimorphism: male larger; sexes colored or patterned differently
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.
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.
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.
Key Reproductive Features: semelparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); 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)
Melittobia australica is a species of chalcid wasp from the family Eulophidae which is a gregarious ecto-parasitoid of acuealate Hymenoptera.
Melittobia australica is a small wasp between 1.1 and 1.4 mm in length but has the typical wasp body plan of a head, thorax, abdomen body structure with the "wasp waist". It is sexually dimorphic with males is normally being larger than females, males are 1.2 to 1.4 mm in length while females are 1.1 to 1.3 mm. Males also have a with a wider head and smaller wings are smaller and their antennal scape is significantly broader. The colour difference is that the males are also a honey brown whereas the females are coloured dark brown.[1]
There are at least two morphs of females in M. australica which differ in the size of the abdomen, the size of the eyes and the extent of wing development. The "crawler" morph have a normal abdomen, small eyes and underdeveloped wings. The "flier" and possibly the "jumper" morphs have larger eyes and wings and a smaller abdomen. The "crawlers" remain within the host nest for the whole of their life cycle while the other morphs disperse as adults.[1]
Melittobia australica was first described by the American entomologist Alexandre Arsène Girault in 1912 from Australia but it has since been recorded from North America, Central America, northern South America, the Caribbean, Africa, eastern Asia, Europe (Sicily) and New Zealand.[2][3] Some authorities believe that it is indigenous to Australia but that human commercial activity has allowed it to spread and become cosmopolitan.[1]
In Australia Melittobia australica was original reared from the nest of the sphecid wasp Pison spinolae by Girault[3] and rainforest was the original habitat.[1]
Melittobia australica is a parasitoid and its primary hosts are solitary bees and wasps. Its life cycle starts with the female finding the nest of a suitable host where the progeny are in the prepupal stage. The female feeds on the prepupa, she punctures it with the ovipositor and feeds on the exuded body fluids, using the proteins in the ingested fluid for ovogenesis.[4] She lays 10–50 eggs per day under the pupal covering of the host. Fertilised eggs develop into female wasps and unfertilised eggs into males, a behaviour known as arrhenotoky. The eggs are normally laid on a single host within the nest and many females may lay eggs on the same host which can be completely covered in larval M. australica of different ages which emerge from the eggs a few days after oviposition. The larvae feed on the tissue of the host and their development of the fames into the differing morphs is determined by the density of larvae feeding on the host. Where there is a low density of larvae the females will mainly be "crawlers" whereas intermediate densities will result in "jumpers" or and high densities of larvae will cause mostly "fliers" to develop.[1] Where the host larvae are small the female may lay her eggs on more than one host.[4]
Male M. australica produce a very powerful pheromone to attract females. As they have been laid on the same host at the same time the males mature at the same time as their sisters and often mate with them. If males encounter other males they will fight, often resulting in the death of the losing male.[1] It has also been observed that the first male to emerge will often decapitate any other males either before the merge or immediately after emergence and I another observation the first male to emerge stopped the development of the other males by touching them with his antennae.[4] There are up to 50 females per male and it is not known why the males fight when there are so many females. Once the male finds a receptive female they start a courtship ritual which involves tactile, chemical and auditory signals including the release of pheromone from the abdomen, the raising and lowering of the male's legs and the male rubbing the female with his antennae which also have a large gland which may produce pheromones too. The males hold the female's head in their mandibles, just below the ocelli and maintain antennal contact throughout the ritual which usually lasts 15 minutes.[4] The ritual is followed by mating which fertilises the females eggs. The female then finds a new host, in the same nest if she is a "crawler" or in a new nest if she is a "jumper" or a "flier" and begins to lay eggs on the new host. Each female lays a mean of 10.9 eggs on a host and these take 2–3 days to hatch, the larvae take 20–30 days to develop into adults, depending on conditions, and begin the life cycle again. Under laboratory conditions females live up to 9 days as adults and the total livespan is between 31 and 37 days.[1] The female will normally mate only once while the males are polygynous. If no males are present or an inseminated female has used up all of the sperm from mating she may lay a few unfertilised eggs to produce males, often mating with her own son.[4]
M. australica is a gregarious ectoparasitoid and when the female oviposits on a host she releases a pheromone which attracts other females to that site. All of the progeny resulting form a mating are laid on the same host and they develop together, consuming the host's tissues and eventually killing it. The newly mature females move to the original oviposition site and release a pheromone which induces nearby females to co-operate in forming a group, called a "chewing circle", which chews through the cuticle of the host allowing the adult wasps to escape. The adults, however are solitary and after mating the males die and the females move to a new host.[1]
Females seem to detect the cells of the hosts by chemical means and once a nest is detected the female remains in its vicinity but they do not appear to be attracted to the cells, rather they are "chemically arrested".[1] Female M. australica have been observed excavating access holes through the mud walls of the nests of Pison sp. with their mandibles, just one hole per cell was excavated and several females were observed working on each hole. Only a single female at a time worked on the digging, each taking turns.[4] Adult females are responsive to light, phototaxis, with the crawlers being negatively phototaxic and the fliers positively phototaxic, i.e. attracted to light, so that they leave the host nest after mating.[1] The females can delay feeding and egg laying for several weeks until the host reaches an appropriate developmental stage, they will even wait in empty cells until the host uses them.[4]
M. australica is totally dependent on the host wasps for food, the females feed on the host before oviposition and the larvae consume the host. Adult males probably do not feed.[4] The primary hosts are solitary wasps and bees but it will also parasitise inquilines of other insect orders where these are present in the host's nest. Bumblebees have also been found to be hosts of this wasp. Where populations of M. australica are high it can have a noticeable effect on the populations of host species and many of the host species have evolved defences against M. australica including nest location, chemical defences, physical barriers and defensive behaviours. Where M. autralica is common there can be a high mortality of its host species, which are often pollinators, and so M. australica parasitism can lead to an inhibition in the reproductive and dispersal capabilities of many plants. There is very little information about predators and parasites of M. australica, although an egg hyperparasitoid, Anagrus putnamii, has been recorded it has not been confirmed that it was using M. australica as its host.[1] In addition, there have been observations of parasitic mites which feed on larvae of the sphecid wasp Sceliphron spp. competing with M. australica larvae and even feeding upon them.[4]
The first recorded host of Melittoboa australica was Pison spinolae;[3] however, the primary hosts are leaf cutting bees Megachile spp, mason wasps and mud dauber wasps but it is wide-ranging in its choice of hosts. There are no indigenous social wasps in Australia but in New Zealand and North America it has been recorded in the nests of Vespula species, as well as nests of Polistes, Bombus and honeybees Apis mellifera.[5][4] The bombyliid fly Anthrax angularis and the ichneumonid Stenarella victoriae are parasites in the nests of Sceliphron spp. and have been recorded as being viable hosts for M. australica. In addition, M. australica were found on dipteran puparia found in the nests of Sceliphron which are thought to be parasites on the spiders stocked in empty cells by the wasps.[4]
Melittobia australica is a species of chalcid wasp from the family Eulophidae which is a gregarious ecto-parasitoid of acuealate Hymenoptera.
Melittobia australica is een vliesvleugelig insect uit de familie Eulophidae. De wetenschappelijke naam is voor het eerst geldig gepubliceerd in 1912 door Girault.
Bronnen, noten en/of referenties
