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Plantwise Technical Factsheet

European pine sawfly (Neodiprion sertifer)

Host plants / species affected
Picea abies (common spruce)
Pinus banksiana (jack pine)
Pinus cembra (arolla pine)
Pinus contorta (lodgepole pine)
Pinus densiflora (Japanese umbrella pine)
Pinus echinata (shortleaf pine)
Pinus mugo (mountain pine)
Pinus nigra (black pine)
Pinus nigra austriaca
Pinus ponderosa (ponderosa pine)
Pinus pumila (Dwarf Siberian pine)
Pinus pungens (tabel Mountain pine)
Pinus radiata (radiata pine)
Pinus resinosa (red pine)
Pinus rigida (pitch pine)
Pinus sibirica (Siberian stone pine)
Pinus strobus (eastern white pine)
Pinus sylvestris (Scots pine)
Pinus thunbergii (Japanese black pine)
List of symptoms/signs
Leaves  -  external feeding
Leaves  -  frass visible
Stems  -  external feeding
Stems  -  visible frass
Whole plant  -  plant dead; dieback
Symptoms
Large larval colonies feed on needles from spring to mid-summer. The older needles are fed on down to the needle sheath and the newly developing needles are mainly untouched. The older larvae may also consume bark from the older, thin branches. Heavy outbreaks may result in the complete removal of the old foliage. Normally the trees recover later in the summer when the new shoots and needles reach their full size. Lyons (1964) has published illustrative photos of the stages in the defoliation of one tree. Heavy defoliations in subsequent years may kill buds and twigs. Although extensive mortality seldom occurs, repeated defoliation weakens the trees and increases their susceptibility to attack from secondary pests (e.g. bark beetles).

The frass of diprionid larvae can be easily distinguished from lepidopteran frass (Escherich, 1942). The shape of the diprionid excrement pellets is rhomboid. They are initially green and later turn brownish. During heavy larval infestations, a light patter caused by the dropping frass can be heard in quiet forests and a thin layer of frass can be detected on the ground.
Prevention and control

Biological control

One of the best examples of the successful development of biological control methods in forest protection is the nuclear polyhedrosis virus of N. sertifer (NsNPV). The virus was discovered in Germany (Escherich, 1913). Bird (1953, 1955, 1961) developed a supply of the virus from a few dead larvae of N. sertifer from Sweden in 1949. This was used for experimental purposes and eventually for release as a control agent. Due to the intensive studies in America and Europe (e.g. Bird and Whalen, 1953; Franz and Niklas, 1954; Benjamin et al., 1955; Krieg, 1955; Rivers and Crooke, 1962; Nuorteva, 1972; Donaubauer, 1973; Cunningham and Entwistle, 1981; Juutinen, 1982; Podgwaite et al., 1984), the NsNPV became the most widely used baculovirus in several countries (Pschorn-Walcher, 1982; Morris et al., 1986). It has been registered under different names in the USA, UK, Finland and the Czech Republic. In Ontario, N. sertifer was a major pest of Christmas tree plantations but since the 1970s it has only been a minor pest due to the use of the NsNPV and parasitoid introductions (Griffiths et al., 1984; Morris et al., 1986).

The incubation time of NsNPV is 1-2 weeks. The virus should be applied on early instars (L1, L2) to be effective and cause over 90% mortality. According to the critical review by Olofsson (1988a), the virus plays a minor role in the population dynamics of N. sertifer; often a smaller role than other biotic mortality factors. Therefore, virus treatment should be resorted to in exceptional cases only, when there are specific indications that a treatment is required. For example, when severe damage by secondary forest insects, e.g. bark beetles, can be expected. See van Frankenhuyzen (2002) for an assesssment of the successful control of N. sertifer in Canada with the NPV.

In the laboratory and field tests performed by Heimpel and Angus (1963), Bacillus cereus was pathogenic (25% mortality) to larvae of N. sertifer, but the Bacillus thuringiensis var. sotto Ishiwata toxin was ineffective (Angus, 1956). Sezen et al. (2001) investigated the insecticidal potential of the bacterium, Serratia marcescens Bn10, which was isolated from Balaninus nucum. Mortality of the N. sertifer larvae was 88% within 5 days.

The rhabditid nematode, Heterorhabditis heliothidis, caused 100% mortality of N. sertifer larvae within 120 hours at 15°C in the laboratory. The intact cocoons were not susceptible and only 11% mortality in 168 hours was observed. However, the pupae that were dissected out of the cocoons were all parasitized in 48 hours (Finney and Bennett, 1983).

In small ornamental trees or in pine plantations of small acreage, N. sertifer can be controlled simply by hand-picking and destroying the larval colonies. A mere knocking down of the larvae is useless, because the larvae climb back into the trees within a few hours (Teräs, 1982).

Host-Plant Resistance

Different pine species, provenances and varieties have been shown to vary in their susceptibility to N. sertifer (refer to Notes on host range). Where possible, less susceptible alternatives should be used in forestry programs.

The larvae of N. sertifer normally reject the young foliage of the Scots pines. This feeding pattern is mainly caused by a deterrent compound identified as 13-keto-8(14)-podocarpen-18-oic acid (Niemelä et al., 1982). This substance was mainly found in the young foliage of pines, and the highest concentrations were found in the trees whose needles had been badly damaged by the N. sertifer larvae.

Pheromonal control

Like many other species of diprionids, the males of N. sertifer are strongly attracted by the female sex pheromones. The investigation of the diprionid sex pheromones started in the late 1950s (Coppel et al., 1960), and the first pheromone was identified 16 years later (Jewett et al., 1976). Anderbrant (1993, 1999) thoroughly reviewed the literature since then and up to 1999.

The inactive precursor of the N. sertifer pheromone is 3,7-dimethyl-2-pentadecanol (diprionol) and the active compound is (2S,3S,7S)-diprionyl acetate or propionate, which has proved to be attractive in Europe, North America and Japan (Anderbrant, 1993, 1999). Traps baited with synthetic pheromone can be used for many purposes. The flight period can be determined (Simandl, 1993; Schedl, 1994), the abiotic factors important for flight can be investigated (Jönsson and Anderbrant, 1993), and the behaviour of the sawflies can be studied (Östrand, 2001). The first attempts to use pheromone monitoring traps for determining population densities or population trends of N. sertifer showed either significant relationships (Baldassari et al., 2000), only weak relationships (Lyytikäinen-Saarenmaa et al., 1999, 2001) or no significant correlation (Herz et al., 2000) between the trap catch and the sawfly density or defoliation.

The use of sex pheromones in the mating disruption technique to control populations resulted in the suppression of the N. sertifer population in isolated pine stands in Italy (Martini et al., 2002). It was ineffective in larger areas of pine forests in Sweden (Anderbrant et al., 1995).

Chemical Control

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:


Impact
N. sertifer is a univoltine, early season defoliator. The larvae feed on older needles and leave the new growing needles mainly untouched. Hence tree mortality is normally modest, even after heavy infestations. In North American Christmas tree plantations, N. sertifer has been a serious problem and control applications have been widely used, because even a light defoliation renders the trees unmarketable (Lyons, 1964; Wilson, 1971).

Relatively little is known about the effect of defoliation on tree growth. In Michigan, 20, 65, 85, and 100% defoliation before new foliage developed, caused 14, 23, 37, and 63% loss in terminal shoot elongation and 18, 47, 53, and 71% reduction in radial increment, respectively. The 100% defoliation was simulated and trees survived 3 years of complete defoliation (Wilson, 1966).

In Hungary, heavy defoliation caused 30-45% reduction in annual growth (Kolonits, 1965). In Sweden, Forsslund (1945) found the height growth loss to vary between 25% and 60% in young Scots pine stands defoliated for two consecutive years. Eklund (1964) recorded a reduction of 52% in the diameter growth of old pine stands due to defoliation. The measurements were made 1-2 years after the infestation, therefore they do not cover the whole recovery period, which may be as long as 9 years (Austarå et al., 1987).

In Finland, the mortality of Scots pine after 1 years defoliation was recorded as approximately 4%, and a reduction in the volume increment for the following 5 years was 20% corresponding to one normal annual increment (Juutinen, 1967; Tiihonen, 1970). Most of the killed trees were suppressed or weakened before the infestation. In Norway, a heavy defoliation of Scots pine for 2 years in 90-120-year-old forests caused a volume loss of 33% during 9 years. This loss corresponds to three normal annual increments (Austarå et al., 1987). The economic consequences of the growth loss and mortality have been calculated by Austarå et al. (1987), and Lyytikäinen-Saarenmaa and Tomppo (2002).
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