Sawfly

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This article is about the hymenopteran. For the moth, see Symphyta (moth genus).
Sawfly
Temporal range: Triassic–Recent
XN Tenthredo mesomela.jpg
Tenthredo mesomela
Scientific classification e
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Suborder: Symphyta
Gerstäcker 1867[1]
Superfamilies[2]

Sawflies are insects belonging to suborder Symphyta of the order Hymenoptera. The name sawfly is associated especially with the Tenthredinoidea, by far the largest superfamily, with about 7,000 of the 8,000 known species of Symphyta.

Sawflies are distinguishable from most other hymenopterans by the broad connection between the abdomen and the thorax instead of a wasp waist, and by their caterpillar-like larvae. The common name comes from the saw-like appearance of the ovipositor, which the females use to cut into the plants where they lay their eggs. The great majority of sawfly species and families are plant-eating, though the youngest superfamily, the Orussoidea, is parasitic.

The sawflies consist of several basal groups within the Hymenoptera, which also contains the Apocrita (wasps, ants, and bees): its sister clade is the Orussoidea. The Apocrita are not considered sawflies, so the sawflies as a whole do not form a separate clade of their own, but are paraphyletic. Sawflies first appeared 250 million years ago in the Triassic. The oldest superfamily, the Xyeloidea, has existed from that time to this.

Large populations of species such as the pine sawfly can cause substantial damage to economic forestry, while others such as the iris sawfly are important pests in horticulture.

Etymology[edit]

Sawfly laying eggs in a plant, using the serrated saw-like ovipositor for which the group is named

The suborder name Symphyta derives from the Greek word symphyton, meaning "grown together", referring to the group's distinctive lack of a wasp waist between prostomium and peristomium.[3] Its common name, "sawfly", derives from the saw-like ovipositor that is used for egg-laying, in which a female makes a slit in either a stem or plant leaf to deposit the eggs.[4] The first known use of this name was in 1773.[5] Sawflies are also known as wood-wasps.[6]

Description[edit]

Adults[edit]

Adult sawflies, except for those in the family Cephidae, have structures that latch onto the underside of the fore wings to help hold the wings in place when the insect is at rest. These "cenchri", which are absent in the suborder Apocrita, are located behind the scutellum on the thorax. Adults of some species are carnivorous, eating other insects, but many also feed on nectar. Adults also have stronger antennae. Among the largest sawflies ever discovered was Hoplitolyda duolunica from the Mesozoic, with a body length of 55 millimetres (2.2 in) and a wingspan of 92 millimetres (3.6 in).[7]

Larvae[edit]

Sawfly larvae feeding on leaves

Some larvae look like caterpillars (the larvae of moths and butterflies), with some notable differences; (1) they have six or more pairs of prolegs (sometimes greatly reduced and difficult to see) on the abdomen, while caterpillars have five pairs or fewer, (2) they have two stemmata instead of a caterpillar's six, (3) caterpillars (except for a tiny minority) always have the two first abdominal segments legless, and (4) sawfly larvae have an invariably smooth head capsule with no cleavage lines, while lepidopterous caterpillars bear an inverted "Y" or "V" (adfrontal suture). Typical sawfly larvae are herbivorous, the group feeding on a wide range of plants. Individual species, however, are often quite specific in their choice of plants used for food. The larvae of various species exhibit leaf-mining, leaf "rolling", or gall formation. Three families are strictly xylophagous, and called "wood wasps", and one family is parasitic. The larvae that do not feed externally on plants are grub-like, without prolegs. When harassed, many sawfly larvae are able to squirt a foul liquid from their last segment.

Phylogeny[edit]

Carl Gerstäcker established the suborder Symphyta

In his original description of Hymenoptera in 1863, Carl Gerstäcker divided them into three groups, Hymenoptera aculeata, Hymenoptera apocrita and Hymenoptera phytophaga.[8] But four years later in 1867, he described just two groups, H. apocrita syn. genuina and H. symphyta syn. phytophaga.[1] Consequently the name Symphyta is given to Gerstäcker as the zoological authority. In his description Gerstäcker distinguished the two groups by the transfer of the first abdominal segment to the thorax in the Apocrita, compared to the Symphyta. Consequently there are only eight dorsal half segments in the Apocrita, against nine in the Symphyta. The larvae are distinguished in a similar way.[9]

The Symphyta have therefore traditionally been considered, alongside the Apocrita, to form one of two suborders of Hymenoptera.[10][11] Symphyta are the more primitive group,[12] with comparatively complete venation, larvae that are largely phytophagous, and without a "wasp-waist", a symplesiomorphic feature. Together, the Symphyta make up less than 10% of hymenopteran species.[12] While the terms sawfly and Symphyta have been used synonymously, the Symphyta have also been divided into three groups, true sawflies (phyllophaga), woodwasps or xylophaga (Siricidae), and Orussidae. The three groupings have been distinguished by the true sawflies' ventral serrated or saw-like ovipositor for sawing holes in vegetation to deposit eggs, while the woodwasp ovipositor penetrates wood and the Orussidae behave as external parasitoids of wood-boring beetles. The woodwasps themselves are a paraphyletic ancestral grade. Despite these limitations, the terms have utility and are common in the literature.[11]

While most hymenopteran superfamilies are monophyletic, as is Hymenoptera, the Symphyta has long been seen to be paraphyletic.[13][14] Cladistic methods[15] and molecular phylogenetics are improving the understanding of relationships between the superfamilies, resulting in revisions at the level of superfamily and family. The Symphyta are the most primitive (basal) taxa within the Hymenoptera[14][12] (some going back 250 million years), and one of the taxa within the Symphyta gave rise to the monophyletic suborder Apocrita (wasps, bees, and ants). In cladistic analyses the Orussoidea are consistently the sister group to the Apocrita.[11][12]

The oldest unambiguous sawfly fossils date back to the Middle or Late Triassic. These fossils, from the family Xyelidae, are the oldest of all Hymenoptera.[16] One fossil, Archexyela ipswichensis from Queensland is between 205.6 to 221.5 million years of age, making it among the oldest of all sawfly fossils.[17] More Xyelid fossils have been discovered from the Middle Jurassic and the Cretaceous, but the family was less diverse then than during the Mesozoic and Tertiary. The subfamily Xyelinae were plentiful during these time periods, in which Tertiary faunas were dominated by the tribe Xyelini; these statements indicate a humid and warm climate.[18][19][20]

The cladogram is based on Schulmeister 2003.[21][22]

Symphyta within Hymenoptera
Hymenoptera, 250mya

 Xyeloidea (Triassic-present) Xyelapusilla.jpg 




 Tenthredinoidea Diprionpini crop.jpg




 Pamphilioidea Caenolyda reticulata.jpg




 Cephoidea (stem sawflies) Hartigia linearis.jpg




 Siricoidea (horntails or wood wasps) Hymenoptera Vielfalt Horntail.jpg




 Xiphydrioidea (wood wasps) Xiphydria prolongata crop.jpg


parasitism

 Orussoidea (parasitic wood wasps) Orussus coronatus.jpg 


wasp waist 200mya

 APOCRITA (ants, bees, wasps) Specimen of Podalonia tydei (Le Guillou, 1841).jpg









Symphyta
Symphyta (red bar) are paraphyletic as Apocrita are excluded.

Taxonomy[edit]

There are approximately 8,000 species of sawfly in more than 800 genera,[23] although new species continue to be discovered.[24][25] Early phylogenies, based on morphology and behaviour, such as that of Alexandr Rasnitsyn[26] identified nine clades though these did not reflect historical division into superfamilies and families. Such classifications were replaced by those using molecular methods, following the work of Dowton and Austin (1994).[27] As of 2013 these are treated as nine superfamilies (one extinct) and 25 families. Most sawflies belong to the Tenthredinoidea superfamily, with about 7,000 species worldwide. Tenthredinoidea has six families, of which Tenthredinidae is by far the largest with some 5,500 species.[10][2]

Distribution[edit]

Sawflies are widely distributed throughout the world.[28] The largest family, the Tenthredinidae, with some 5,000 species, are found on all continents except Antarctica, though they are most abundant and diverse in the temperate regions of the northern hemisphere; they are absent from New Zealand and there are few of them in Australia. The next largest family, the Argidae, with some 800 species, is also worldwide, but is commonest in the neotropics, especially in Africa, where they feed on woody and herbaceous angiosperms. Of the other families, the Blasticotomidae and Megalodontidae are Palearctic; the Xyelidae, Pamphilidae, Diprionidae, Cimbicidae, and Cephidae are Holarctic, while the Siricidae are mainly Holarctic with some tropical species. The parasitic Orussidae are found worldwide, mostly in tropical and subtropical regions. The wood-boring Xiphydriidae are worldwide, but most species live in the subtropical parts of Asia.[29]

Ecology[edit]

Sawflies are herbivores, feeding on plants that have a high concentration of chemical defences. These insects are either resistant to the chemical substances, or they avoid areas of the plant that have high concentrations of chemicals.[30] The larvae primarily feed in groups; they are folivores, eating plants and fruits on native trees and shrubs, though some are parasitic.[31][4][32] However, this is not always the case; Monterey pine sawfly (Itycorsia) larvae are solitary web-spinners that feed on Monterey pine trees inside a silken web.[33] The adults feed on pollen and nectar.[31]

Anti-predator adaptation: spitfire sawfly larvae grouped together for safety in numbers

Sawflies are eaten by a wide variety of predators. While many birds find the larvae distasteful, some such as the currawong and stonechats (Saxicola) eat both adults and larvae.[34][35] The larvae are an important food source for the chicks of several birds, including partridges.[36] Sawfly and moth larvae formed one third of the diet of nestling corn buntings (Emberiza calandra), with sawfly larvae being eaten more frequently on cool days.[37] Black grouse (Tetrao tetrix) chicks show a strong preference for sawfly larvae.[38][39] Sawfly larvae formed 43% of the diet of chestnut-backed chickadees (Poecile rufescens).[33] Small carnivorous mammals such as the masked shrew (Sorex cinereus), the northern short-tailed shrew (Blarina brevicauda) and the deer mouse (Peromyscus maniculatus) predate heavily on sawfly cocoons.[40] Insects such as ants and certain species of predatory wasps (Vespula vulgaris) eat adult sawflies and the larvae, as well as lizards and frogs.[41][42] Pardalotes, honeyeaters and fantails occasionally consume laid eggs, and several species of beetle larvae prey on the pupae.[35]

The larvae have several anti-predator adaptations. While adults are unable to sting, the larvae regurgitate a liquid from their mouths which is distasteful and irritating to potential predators, which makes them avoid the larvae.[4] The larvae also cluster together which reduces their chances of getting killed, and in some cases, a group of larvae will form together with their heads pointing outwards or tap their abdomens up and down.[35] Depending on how much is regurgitated, an insect (such as an ant) will either walk away and clean itself or become fatally affected by it.[43]

Parasites[edit]

Sawflies are hosts to many parasitoids, most of which are parasitic Hymenoptera; more than 40 species known to attack them. However, fewer than 10 of these species actually cause a significant impact on sawfly populations.[44]

Relationship with humans[edit]

The pine sawfly Diprion pini is a serious pest of forestry.

Sawflies are important economic pests of forestry, where species in the Diprionidae such as the pine sawflies, Diprion pini and Neodiprion sertifer cause serious damage to pines in regions such as Scandinavia. D. pini larvae defoliated 500,000 hectares (1,200,000 acres) in the largest outbreak in Finland, between 1998 and 2001. Up to 75% of the trees may die after such outbreaks, as D. pini can remove all the leaves late in the growing season, leaving the trees too weak to survive the winter.[45] Little damage to trees only occurs when the tree is large or when there is minimal presence of larvae. Eucalyptus trees can regenerate quickly from damage inflicted by the larvae; however, they can be substantially damaged from outbreaks, especially if they are young. The trees can be defoliated completely and may cause "dieback", stunting or even death.[35]

Caterpillar-like larvae of Iris sawfly on yellow flag, showing damage to host plant

Sawflies are serious pests in horticulture. Different species prefer different host plants, often being specific to a family or genus of hosts. For example, Iris sawfly larvae, emerging in summer, can quickly defoliate species of Iris including the yellow flag and other freshwater species.[46] Similarly the rose sawflies Arge pagana and A. ochropus defoliate rose bushes.[47]

The giant woodwasp or horntail, Urocerus gigas, has a long ovipositor, which with its black and yellow coloration make it a good mimic of a hornet. Despite the alarming appearance, the insect cannot sting.[48] The eggs are laid in the wood of conifers such as Douglas fir, pine, spruce, and larch. The larvae eat tunnels in the wood, causing economic damage.[49]

See also[edit]

Notes[edit]

  1. ^ a b †: extinct
  2. ^ spp.: species

References[edit]

  1. ^ a b Gerstaecker 1867.
  2. ^ a b Aguiar et al 2013.
  3. ^ "Symphyta". Merriam-Webster. Retrieved 2 December 2016. 
  4. ^ a b c Australian Museum (20 October 2009). "Animal Species:Sawflies". Retrieved 11 August 2015. 
  5. ^ "Sawfly". Merriam-Webster Online Dictionary. Retrieved 29 November 2016. 
  6. ^ Gordh, G.; Headrick, D.H. (2009). A Dictionary of Entomology (2nd ed.). Wallingford: CABI. p. 1344. ISBN 978-1-84593-542-9. 
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  23. ^ Asaro 2008.
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  27. ^ Dowton & Austin 1994.
  28. ^ Looney et al 2016.
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  32. ^ Bandeili, Babak; Müller, Caroline (2009). "Folivory versus florivory—adaptiveness of flower feeding". Naturwissenschaften. 97 (1): 79–88. Bibcode:2010NW.....97...79B. doi:10.1007/s00114-009-0615-9. PMID 19826770. 
  33. ^ a b Kleintjes, P. K.; Dahlsten, D. L. (1994). "Foraging Behavior and Nestling Diet of Chestnut-Backed Chickadees in Monterey Pine" (PDF). The Condor. 96 (3): 647–653. doi:10.2307/1369468. JSTOR 1369468. 
  34. ^ Cummins, S.; O'Halloran, J. (2002). "An assessment of the diet of nestling Stonechats using compositional analysis: Coleoptera (beetles), Hymenoptera (sawflies, ichneumon flies, bees, wasps and ants), terrestrial larvae (moth, sawfly and beetle) and Arachnida (spiders and harvestmen) accounted for 81% of Stonechat nestling diet". Bird Study. 49 (2): 139–145. doi:10.1080/00063650209461258. 
  35. ^ a b c d Phillips, Charlma (December 1992). "Spitfires – Defoliating Sawflies" (PDF). Department of Primary Industries and Resources. Government of South Australia. Retrieved 11 August 2015. 
  36. ^ Campbell, L.H.; Avery, M.I.; Donald, P.; Evans, A.D.; Green, R.E.; Wilson, J.D. (1997). A Review of the Indirect Effects of Pesticides on Birds (PDF) (Report). Peterborough, UK: Joint Nature Conservation Committee, Report. no 227. p. 27. ISSN 0963-8091. 
  37. ^ Brickle, N. W.; Harper, D. G. C. (1999). "Diet of nestling Corn Buntings Miliaria calandra in southern England examined by compositional analysis of faeces". Bird Study. 46 (3): 319–329. doi:10.1080/00063659909461145. 
  38. ^ Starling-Westerberg, A. (2001). "The habitat use and diet of Black Grouse Tetrao tetrix in the Pennine hills of northern England". Bird Study. 48 (1): 76–89. doi:10.1080/00063650109461205. 
  39. ^ Cayford, J.T. (1990). "Distribution and habitat preferences of Black Grouse in commercial forests in Wales: conservation and management implications". Proceedings of the International Union Game of Biologists Congress. 19: 435–447. 
  40. ^ Holling, C. S. (1959). "The Components of Predation as Revealed by a Study of Small-Mammal Predation of the European Pine Sawfly" (PDF). The Canadian Entomologist. 91 (5): 293–320. doi:10.4039/Ent91293-5. 
  41. ^ Müller, Caroline; Brakefield, Paul M. (2003). "Analysis of a Chemical Defense in Sawfly Larvae: Easy Bleeding Targets Predatory Wasps in Late Summer". Journal of Chemical Ecology. 29 (12): 2683–2694. doi:10.1023/B:JOEC.0000008012.73092.01. ISSN 1573-1561. PMID 14969355. 
  42. ^ Petre, Charles-Albert; Detrain, Claire; Boevé, Jean-Luc (2007). "Anti-predator defence mechanisms in sawfly larvae of Arge (Hymenoptera, Argidae)". Journal of Insect Physiology. 53 (7): 668–675. doi:10.1016/j.jinsphys.2007.04.007. PMID 17540402. 
  43. ^ Hairston, N.G. (1989). Ecological Experiments: Purpose, Design and Execution. Cambridge, Massachusetts: Cambridge University Press. p. 96. ISBN 978-0-521-34692-4. 
  44. ^ Capinera 2008, p. 1827.
  45. ^ Krokene, Paal (6 December 2014). "The common pine sawfly – a troublesome relative". Science Nordic. Retrieved 28 November 2016. 
  46. ^ "Iris sawfly". Royal Horticultural Society. Retrieved 28 November 2016. 
  47. ^ "Large rose sawfly". Royal Horticultural Society. Retrieved 28 November 2016. 
  48. ^ "Great Wood Wasps". UK Safari. Retrieved 28 November 2016. 
  49. ^ "Giant Woodwasp". Massachussetts Introduced Pests Outreach Project. Retrieved 28 November 2016. 

Bibliography[edit]

Books and chapters[edit]

Articles[edit]

Catalogue of Symphyta[edit]

External links[edit]