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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)
