Sawfly

This article is about the hymenopteran. For the moth, see Symphyta (moth genus).

Sawfly Temporal range: Triassic - Recent
Large rose sawfly Arge pagana stephensii
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Suborder:	Symphyta
Superfamilies and families
Superfamily Cephoidea    Family Cephidae Superfamily Megalodontoidea    Family Megalodontesidae    Family Pamphiliidae Superfamily Orussoidea    Family Orussidae Superfamily Siricoidea    Family Anaxyelidae    Family Siricidae Superfamily Tenthredinoidea    Family Argidae    Family Blasticotomidae    Family Cimbicidae    Family Diprionidae    Family Pergidae    Family Tenthredinidae Superfamily Xyeloidea    Family Xyelidae    Family Xiphydriidae

Sawfly is the common name for insects belonging to suborder Symphyta of the order Hymenoptera. Sawflies are distinguishable from most other hymenopterans by the broad connection between the abdomen and the thorax, 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. Large populations of certain sawfly species can cause substantial economic damage to forests and cultivated plants.

Taxonomy

Sawfly ovipositing

Sawflies are a group of largely phytophagous insects. The overall group is paraphyletic, but the name is still in common use, and treated as a suborder, though it likely will be phased out in future classifications. These superfamilies are regarded as the most primitive taxa within the Hymenoptera (some going back 200 million years), and one of the taxa within the Symphyta gave rise to the suborder Apocrita (wasps, bees, and ants - this group is considered monophyletic). In the opinion of many experts, the most likely sister taxon to the Apocrita is the family Orussidae, the only symphytan group which is parasitic.

Fossils in the family Xyelidae are regarded as the oldest of all insects known in Hymenoptera, dating back to the Lower Triassic from rocks collected in the Soviet Union.

Description

Larvae

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.

Adults

File:Sawfly 0906.jpg

Bristly rose sawfly Cladius difformis, above millimeter scale

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 sawfly 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).

Ecology

Group of sawfly larvae feeding on leaves

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. The larvae primarily feed in groups; they are folivores, consuming plants and fruits on native trees and shrubs, though some are parasitic. 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. The adults feed on pollen and nectar.

Schematic preview of the sawflies found in the regions of Pijanec and Maleš in Macedonia (with legends on Macedonian and English)

Sawflies are eaten by a wide variety of predators. Both adults and larvae, along with other insects, are an essential food source for stonechat (Saxicola) birds. The larvae are also important for partridge chicks. Based on a study, the diet of nestling corn buntings (Emberiza calandra), the larvae of sawflies and moths compromised one third of their diet, although sawfly larvae would be eaten more frequently on cool days in comparison in warm temperatures. The larvae are not regarded as important to the diet of corn buntings. Black grouse (Tetrao tetrix) chicks show a preference for sawfly larvae which makes them one of the most consumed invertebrates by them. Even if there are high populations of other insects, the chicks still predominately feed on the larvae. Sawfly larvae comprised 43% of the diet of chestnut-backed chickadees (Poecile rufescens). Small mammals prey on sawfly cocoons, causing high mortality rates among them. These predators include the masked shrew (Sorex cinereus), the northern short-tailed shrew (Blarina brevicauda) and the deer mouse (Peromyscus maniculatus). Insects such as ants and certain species of predatory wasps (Vespula vulgaris) eat sawflies.

Spitfire sawfly in a group together on a tree: Larvae that group together are less likely to die from predators.

The larvae have several defensive tactics against predators. 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. 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.

Parasites

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.

See also

• Spitfire sawfly

External links

• ECatSym - Electronic World Catalog of Symphyta
• Alder-feeding Sawflies of Alaska United States Forest Service
• A sawfly injurious to young pines hosted by the UNT Government Documents Department