Melangyna novaezelandiae, commonly referred to as the large hover fly, is a hoverflyendemic to New Zealand. It is a generalized pollinator of a large range of plants that are both native and exotic to the New Zealand flora. M. novaezelandiae is widespread throughout New Zealand, including in agricultural environments. The larvae of this species feeds on other arthropods and may have uses as a biocontrol agent.
This species was first described as Syrphus novaezelandiae in 1855 by French entomologist Pierre-Justin-Marie Macquart.[1] However, the species was actually first described as Syrphus ortas in 1849 by Walker.[2] Although in principle this should be the correct specific name for the species, it has been discarded due to the former spelling being widely used.[3] In 1875, it was described yet again as Syrphus rectus by Polish zoologist Maksymilian Nowicki.[4][3] In 1969, it was transferred to the genus Melangyna, and placed in the newly erected subgenus Austrosyrphus.[5] In some literature, it has been incorrectly misspelled as Melangyna novaezealandiae, with this error originating in an 1881 publication.[6][3] In 2008, Christian Thompson recognized M. novaezelandiae, S. ortas, and S. rectus as being the same species.[3] This species is commonly referred to as "large hover fly", although it should be noted this name is likely shared with other species.[7] One study has suggested that M. novaezelandiae likely evolved after dispersing over from Australia.[3]
Description
Adult female
These flies are 9-12mm in length. At the top of the head are three ocelli, simple light detectors.[8] Males and females are mostly identical, but can be distinguished by whether the eyes are touching dorsally (male) or not (female).[9] The legs are slender and are covered in black hairs. The thorax is oval in shape and coloured shiny black. It is also covered in fine hairs. The male abdomen is coloured shiny black with three pairs of creamy yellow bands on the upper surface. In the female there are four pairs, with the last pair of markings being reduced. The abdomen is covered in small fine hairs, although they are not easily seen.[8] As the flies age, their wings become increasingly worn out from flight and foraging activities.[9] The larvae are coloured green and resemble a wrinkled slug.[10] The eggs are typical for diptera and have hexagonal patterning on their surface.[8]
Distribution and habitat
Melangyna novaezelandiae are widespread throughout New Zealand and can even be found on offshore islands such as the Chatham Islands.[11][12] They occur in a wide range of habitats including subalpine zones, tussock and agricultural habitats.[13][14][15] In agricultural habitats, they are one of the two most common species of hoverfly present, with the other species being Melanostoma fasciatum.[16]
Life history
Adults are abundant from September to May (the warmer months in the southern hemisphere), but may be found all year round.[10][9][8] After being laid, the eggs takes roughly three days to hatch. Like many other hover-flies, Melangyna novaezelandiae have three larval instars. The first instar usually takes 3-4 days, but can potentially take up to 14 days. At the end of this stage, fatty tissue begins to accumulate. The second instar takes roughly 3-10 days and the third instar takes 4-20 days. Upon completion of the third instar, the larvae begin pupation, lasts 8-15 days depending on the time of year. Adults can live between 19-45 days.[8]
Once the larvae are fully grown, they begin to shrink and turn into pupae. When pupating they lay among the remains of their prey at the base of plant stems.[10]Egg production also occur from spring to autumn.[17] The eggs of the flies are laid in close proximity to aphid colonies, which the larvae feed on once they hatch.[9]
Diet
Larva feeding on aphids
As larvae, they are predators that often feed on aphids, but have also been observed feeding on other arthropods such as scale insects and moth larvae.[16][18] In one study, Melangyna novaezelandiae and Melanostoma fasciatum accounted for 32.6% of Pieris rapae caterpillar mortality.[18] New Zealand has very few native aphids, with most of the aphid fauna being introduced species. Because of this, it presumed they had to rely on other prey groups for food. Before the introduction of additional aphid species, M. novaezelandiae may have been far less common.[8] To catch aphid prey, the larvae lay in the middle of a groups of aphids and wait for an aphid to walk within reach. Upon feeling an aphid, the larvae then strike it with their pointed head, which are covered in sticky mucus. The larvae then retracts their head (with the prey) and consumes it.[10] Because of this diet, the larvae have been considered for use as biocontrol agents to manage aphids and other pests that damage crops.[9] In laboratory settings, the larvae have been observed performing cannibalism, usually by older larvae preying upon younger ones.[8]
Floral feeding
M. novaezelandiae visiting a flower
As adults, they are herbivores that feed on pollen and nectar, which may make them a useful pollinator.[17] They are known to be frequent flower visitors in both agricultural and natural settings, including subalpine zones.[13][15] In one study of pollination in subalpine zones, it was found that M. novaezelandiae visited more species of flower than any other pollinator observed.[13] In agricultural areas, it was found that M. novaezelandiae were the second most common visitor of crop flowers, so they may have a role in pollination.[19] In one study of bok choy crop pollinators, M. novaezelandiae transferred roughly 13 pollen grains between flowers per hour, indicating that it is ineffective as a pollinator of this crop. For contrast, the bumble bee Bombus terrestris transferred around 2247 grains per hour.[20] Like many syrphids, they are very generalized and will visit many species of flower. Some of the flowers that they are known to visit include Trifolium pratense, Raoulia grandiflora, Leptospermum scoparium,Celmisia spectabilis and Melicytus species, but many more are known.[13][21] One study found that they are most attracted to yellow colours, which may be an important cue in finding floral resources.[16]
A previous study that linked gut fullness with egg production has suggested that pollen is essential for the development of eggs.[17] Because of this, females tend to feed on pollen more frequently than males.[9] Studies of the gut contents of M. novaezelandiae found that pollen grain sizes varied from 19μm to 47μm.[22]
Parasites
Diplazon laetatorius, an Ichneumonidae wasp introduced to New Zealand, lay their eggs in the larvae of Melangyna novaezelandiae, as well as other hoverflies. The wasps develop in the larvae, maturing into adults and bursting out when the larvae pupates.[23] In one study, 5 larvae out of 60 were found to be parasitised by D. laetatorius.[8]
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