So far I have mainly discussed the
social insects in the suborder Apocrita (wasps, ants and bees) from which most
of Hymenoptera belong to. But there is another suborder of the Hymenoptera –
the Symphyta - which contains the sawflies, horntails and parasitic wood wasps.
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| Image 1: Paperbark or Melaleuca Sawfly (Lophyrotoma zonalis) |
The Symphyta are believed to be the most primitive of the order based on their
morphology and being that they are the first hymenopterans found in fossils – the earliest being Xyelidae found in Middle Triassic
fossil records from Central Asia (Wang et al, 2014). The Xyelidae are
considered to be the basal group from which all other hymenopterans evolved and some of the members of this superfamily have primitive features that have been abandoned
by other hymenoptera (Gauld & Bolton, 1988).
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Image 2: Dorsal view of Sawfly (Cathayxyela extensa sp.) fossil found in China (Wang et al, 2014).
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One of the distinctions between
Symphyta and Apocrita is the ovipositor – on Symphyta it is saw-like (hence the
name sawflies) which allows the female to make slits or borings in the host
plant in which to lay her eggs (Gauld & Bolton, 1988). Morphologically the
Symphyta also lack the tapered typical wasp-waist and a stinger as seen on the Apocrita and hold
their wings flat over the body (The University of Edinburgh, 2001). Although not
social, there is evidence of group pupation and some mother Symphyta will
provide defence to young and will viciously attack predators (Costa, 2007).
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| Image 3: Sawfly (Perga sp.) mother defends her offspring, photo courtesy of Kristi Ellingsen. |
The larvae of Symphyta feed on host
plants completely exposed, in leaf rolls/webs or concealed within parts of the
plant such as the fruit; however there are some species (from the Orussidae
superfamily) that are parasitic (Gauld & Bolton, 1988). Adult sawflies feed
from flowers, on parts of the flower and some species are carnivorous (Gauld
& Bolton, 1988). The majority of Symphyta larva
are caterpillar-like but have at least six pairs of prolegs compared to the
caterpillars maximum of five and lack the hooks that caterpillars have on their
prolegs (Barnard, 2011).
Having a similar life to the caterpillar, Symphyta larvae
are subject to similar selective pressures as butterfly larva and they have
developed similar chemical and communicative defence mechanisms (Costa, 2007).
Communication has been observed in Australian species Perga affinis and Perga
dorsalis in the form of substrate borne vibrational cues made by a hardened
cover on the tip of the abdomen being tapped on surfaces to signal group
members to reunite (Costa, 2007). The North American red-headed pine sawfly, Neodiprion
lecontei, has been found to use
chemical cues to communicate with other members of the group (Costa, 2007).
Below is a video showing the “tapping” communication in a Perga sp.
in Australia.
The best example of chemical
defence in the Symphyta larvae comes from the Australian Steel-blue sawflies (Perga sp.) found around South Eastern
Australia - they are commonly known as ‘spit-fires’ as they eject an irritating
fluid from their mouths as a defence against predation (Australian Museum,
2015). Below is a video showing the defensive behaviour of spit-fires.
References:
Barnard, P 2011, Royal
Entomological Society Book of British Insects, Wiley-Blackwell, Hoboken NJ.
pp. 226-267.
Costa, JT 2007, Social Sawflies, Department of
Biology Western
Carolina University, viewed 19 April 2015, <http://web.cortland.edu/fitzgerald/sawflies.html>
Gould, I & Bolton, B 1988, The hymenoptera, Oxford University
Press, Oxford.
Wang, M, Rasnitsyn, AP & Ren, D 2014, ‘Two new fossil
sawflies (Hymenoptera, Xyelidae, Xyelinae) from the Middle Jurassic of China’, Acta Geologica Sinica (English Edition), vol. 88, no. 4, pp.
1027-1033.
Steel-blue sawflies, Australian
Museum, viewed 19 April 2015, <http://australianmuseum.net.au/steel-blue-sawflies>
Image 1: Melaleuca Sawfly (Lophyrotoma zonalis),
viewed 19 April 2015, <http://www.ozanimals.com/image/albums/australia/Insect/Melaleuca-sawfly-1.jpg>
Image 2: Wang, M,
Rasnitsyn, AP & Ren, D 2014, ‘Two new fossil sawflies (Hymenoptera,
Xyelidae, Xyelinae) from the Middle Jurassic of China’, Acta Geologica Sinica (English
Edition), vol. 88, no. 4, pp. 1027-1033.
Image 3: Only a mother could
love them - Kristi Ellingsen, Australian Museum, viewed 19 April 2015, <http://australianmuseum.net.au/Uploads/Images/10229/OP105_Only%20a%20mother%20could%20l.jpg>
Video 1: Spitfires, youtube,
viewed 19 April 2015 <https://www.youtube.com/watch?v=oNos7PDWjkg>
Video 2: Sawflies and spitfire
grubs, youtube, viewed 19 April 2015 <https://www.youtube.com/watch?v=MB_oapTpIQk>
On the origin of Symphyta, there seems to be a little inconsistency in your info: In the text you say the earliest fossils are from the Middle Triassic but in your references the title of the journal article referenced says "Middle Jurassic". Is there a typo somewhere here?
ReplyDeleteIn any case, a Triassic origin for hymenopterans would make sense as there were heaps of new groups evolving in the Triassic due the Permian-Triassic Mass Extinction having wiped out almost every creature that previously lived on Earth and thus leaving lots of vacant niches to be filled.
Interesting how sawfly mothers defend their larva. Wasn't really expecting that from any of the non-eusocial insects that have larva. Seeing as how one of the main points of larva seems to be to allow niche partitioning between adults and young.
No, according to Wang et al., the earliest fossil records of hymenoptera have been recorded from the mid or late triassic - that particular journal article was about specific fossils of 2 new species found in china from the mid jurassic. Thank you for the observation.
DeleteThere are other insects that provide care for their young but do not behave eusocially per se - such as tree hoppers and lace wings - perhaps the parental care is a necessary evil for solitary species. The risk of defending the young would be high, but if they produce clutches rather than continuous laying defence might be necessary to ensure offspring survive to adulthood.
Very enlightening. I found this post really interesting as didn’t realise the sawflies were actually hymenopterans :) I also agree with Leon that it is really interesting that sawfly mothers defend their larvae. What is the major difference between the three groups of Symphyta? I think the name “horntail” is a fantastic one :) Nice post.
ReplyDeleteIt begs the question (well to me anyway), that if some of the most primitive form of hymenoptera show parental care and aggregation of larvae, could this be the contributing factor to why there are more eusocial species in the hymenoptera than any other order? has this "kin help" gene been around longer than the evolution of completely eusocial species?
DeleteFrom what I can gather the differences between the sawflies, horntails and wood wasps are:
*sawflies make a slit in vegetation with their saw-like ovipositor and deposit eggs in which the larvae then consume
*horntails have a spiral shape on their ovipositor (not visible to naked eye) and females use this to bore holes into wood in which to lay their eggs, the larvae then feed on the wood.
*parasitic wood wasps and wood wasps are different in that wood wasps feed on the wood and parasitic wood wasps will feed on the insects who feed on the wood - including other hymenoptera.