The European pine sawfly Neodiprion sertifer is an important pest species on different species of Pinus. In certain areas of Europe, populations of N.sertifer undergo pronounced, sometimes more or less cyclical fluctuations. Outbreaks usually last 2-3 years before the density drops again to below 1% of the peak level.

The origin of N. sertifer was North America from where it migrated (or its ancestral form) via the Bering land bridge to North Asia and then over the hole northern Eurasia.

About 70 years ago it was reintroduced to North America (first records 1925 (?, unknown sawfly larvae) in New Jersey and 1939 in Windsor/Ontario), where it became especially in the southeast of Canada and especially in the north-easth of the USA an important pest of European and American Pinus-species.

Synonyms

Diprion sertifer , Lophyrus rufus Panz , Pteronus sertifer , Tenthredo sertifera (Geoffroy 1785).

Distribution

In Europe it occurs from southern Italy to northern Finland, in the European Alps up to elevations of 6.500 feet. North America, North Asia, Japan. In the European Alps it is distributed as an alpine form characterised by a smaller body size.

Wirtspflanzen

N. sertifer attacks most species of two-needled pines. However, in Europe Scots pine (Pinus sylvestris) is the preferred host plant.
In general, all age classes may be attacked. In Germany and Belgium younger trees (20-25 years) and stands not yet closed are preferred. A preference for older trees was reported from Austria and Finland.

Pinus sylvestris, Pinus radiata, Pinus nigra austriaca, Pinus montana, Pinus pumila in the Japanese Alps, Pinus strobus under lab conditions.

Occasional feeding on spruce has been recorded where these trees grow in close proximity to pines.

Merkmale

Adults

Males: 7-9.5 mm, black, abdomen ventral total or in part redish-brown, sometimes dorsal redish. Legs yellow-brown, coxae black. Antenna with 25-31 Segments. Females: 8-10.5 mm, body brown-redish-yellow, base of tibia whitish, sometimes black marks on the mesonotum. Antenna with 19-25 segments.

Development

In Central Europe 1 generation/year, in mountain areas and Central Norway 2 years for one generation. Development in general depending latitude:

Adults: emergence in northern Europe occurs August - October and in Italy October - December;

Eggs: hibernate;

Larvae: in late May - June in the north and in April in the south. Larval development time under 500 m NN 5-7 weeks, in mountain areas 8-11 weeks).

Prolonged Diapause

In warmer areas usually low (0-10%), in colder areas up to 50%.

Biologie

Like other species of diprionids, males of N. sertifer are strongly attracted by pheromones. In case of N. sertifer the active compound is (2S,3S,7S)-diprionyl acetate or propionate.

Outbreaks

Factors causing outbreaks are not fully understood yet. There are different hypotheses:

Climatic factors, especially dry and hot years

Suboptimal side conditions, like water deficit and nitrogen-deficit.

Factors which are responsible for the collapse are:

increase of egg mortality (caused by egg parasitoids, eg. Dipriocampe diprioni),

increase of larval mortality (caused by parasitoids),

climatic conditions, like frost in April/May,

pathogens, which may be the most important factor.

Damage

Usually older needles are fed, current year needles remain untouched. Therefore, even after severe damage only weak trees will dy. However, there may be an increment loss of 40% in 10 years.

Economic Importance

Finland: primary pest on scots pine.

Germany: Less important. Outbreaks usually occur in young plantations, but collapse after 1-2 years.

Italy: most important diprionid pest species.

Sweden: most important diprionid pest species.

Natural enemies

Predators

Birds like starlings, crows, and wild fowl have been reported. Usually they are of minor importance. In the case of tits it was shown that larval defence (unpalatability and colonial behaviour) is effective. Reduviidae, Elateridae, and spiders are of minor importance. Ants can cause high mortalities in some areas of Europe. However, effectivity of ants is limited by their range. Small mammals may have a large impact on cocoons. It is suggested that at times of low host density small mammals may be a regulating factor.

Parasitoids

More than 30 parasitoid species are recorded, about 6 species of ichneumonids and 2 tachinids are dominating. The host specific species are perfectly synchronised with N. sertifer, they also are univoltine.

Pathogens

A polyhedrosis-virus (Borrelinavirus diprionis) is an important mortality factor, especially at times of high population densities.

Literatur

Good summaries about the biology, ecology, and pest status of N. sertifer can be find in:

Lyons, L.A. 1964: The European pine sawfly, Neodiprion sertifer (Geoffr.) (Hymenoptera: Diprionidae). A review with emphasis on studies in Ontario. Proc. Entomol. Soc. Ont. 94: 5-37.

Pschorn-Walcher, H. 1982: Unterord. Symphyta, Pflanzenwespen. In: Die Forstschädlinge Europas (ed.: W. Schwenke). Parey, Hamburg & Berlin. Vol. 4: 4-234 (in German).

For pheromone biology and physiology see Pheromones of Sawflies