Biological Control of Pests in Forests of Eastern United States



WOOD WASP (Sirex noctilio)-in progress

Roy Van Driesche, University of Massachusetts, Amherst ( and Nathan Schiff, USDA Forest Service, Stoneville, MS (

Range in North American and other Invaded Areas

Steel blue wood wasp, Sirex noctilio (Fabricius) (Hymenoptera: Siricidae), is a European species (Chrystal, 1928) that has invaded many countires, including New Zealand (Tillyard, 1927), Australia (Bedding and Akhurst, 1974), Brazil (Iede et al., 1988), Argentina (Aguilar and Lanfranco, 1988), Chile (ref?), South Africa (right?, ref?), and most recently the northeastern United States (in 2004, ref?).


In general, damage from species of Sirex is minor because most species attack damaged, suppressed or dying trees (Morgan, 1968). However, in areas outside its native European range, S. noctilio attacks and kills healthy trees. In the southern hemisphere, S. noctilio outbreaks have killed large numbers of healthy pines, such as Pinus radiata, grown in plantations (Bedding, 1993).

The ability of S. noctilio to kill healthy trees is based on its production of large amounts of a phytotoxic mucus, which is injected into the sapwood by ovipositing wood wasps and which interferes with the transport of water and starch (Coutts, 1969). In addition, the wasp inoculates the tree with a symbiotic fungus (Amylostereum areolatum [Fries] Boidin) (Coutts, 1969).

Known Natural Enemies

Following the invasion of S. noctilio of New Zealand in the early 20th century, surveys were conducted in Europe, the United States, and the Himalaya Mts. to locate parasitoids of this species. Several larval parasitoids were discovered and imported, including the ichneumonid Rhyssa persuasoria (L.) (from Germany and the United Kingdom) and the ibaliid Ibalia leucospoides Hochenwald (from the United Kingdom) (Scheidter, 1923; Chrystal and Myers, 1928; Taylor, 1976; Nuttal, 1989). The species that established in New Zealand and caused the most mortality were I. leucospoides and the ichneumonid Megarhyssa nortoni nortoni (Nuttall, 1989). In Tasmania the parasitoids causing the most mortality were M. nortoni and R. persuasoria (Taylor, 1978). Parasitoids, however, have not proven the agents controlling the pest. Rather, a nematode of uncertain origin was found associated with S. noctilio populations in New Zealand (Zondag, 1965) and was later linked to population collapses of the wasp in parts of New Zealand.

Fig. 2. Rhyssa sp. parasitoid of Sirex wood wasp (Photo courtesy of Kevin Dodds, USDA Forest Service)

The life cycle of this nematode, later named Beddingia siricidicola (Bedding (earlier placed in the genus Deladenus), is complex with nematodes able to either develop by feeding on the wood wasp's associated fungus or as a parasite in the wood wasps themselves (Bedding, 1968, 1993). Nematodes penetrate wood wasp larvae but do not kill them. Rather, they allow larvae to mature to adults and then nematodes invade the ovaries of adult wood wasps, sterlizing them and causing a loss of up to 92% of the potential reproduction at the population level (Morgan, 1989). This nematode appears to have been accidentally introduced to New Zealand either with its host or the parasitoids that were introduced against it.

Biological Control Efforts Against the Pest, Worldwide

The first program attempting to control S. noctilio occurred in New Zealand, where this wood wasp had become a damaging invasive pest by the 1920s. This effort was based on importation of the parasitoids R. persuasoria and I. leucospoides from Europe, India, and the United States (Chrystal and Myers, 1928; see Clausen, 1978 and Nuttall, 1989 for program reviews). Evaluations of the outcome of these importations are limited. Levels of parasitism by I. leucospoides are usually 25-30%. Total parasitism by all species combined can reach 70% in local areas (Nuttall, 1989). By 1963, wood wasps were noted to be infected with a nematode (later recognized as B. siricidicola) and pest populations declined. However the impact of this nematode on the pest in New Zealand has not been evaluated.

In the early 1950s, S. noctilio invaded Tasmania and reached the mainland of Australia by the 1960s (Bedding, 1993), where it caused extensive damage in plantations of exotic pines. A number of parasitoid species were introduced and five established (I. leucospoides, M. nortoni, R. persuasoria, Ibalia rufipes sbsp. drewseni Borries and Schlettererius cinctipes (Cresson) (Talyor, 1976). Spradberry and Kirk (1978) summarize information on European species of Sirex and their associated parasitoids. The nematode B. siricidicola was also introduced (Bedding and Akhurst, 1974). Historical summaries of work in Australia are provided by Taylor (1976), Morgan (1989) and Bedding (1993).

The impact of parasitoids in Tasmania before the introduction of the nematode is discussed by Taylor (1980), who found them to provide some control. However in Australia, most control was attributed to the inoculation of susceptible pine stands with the nematode B. siricidicola, which was mass processed and widely distributed. To support inoculations of forest stands with the nematode, methods to mass rear it on the wood wasps' fungal symbiont (A. areolatum) were developed. Using this system, the nematode was propagated in its fungal-feeding phase (Bedding, 1993). Herbicides were used to kill trees to provide sample points to detect wood wasps in forest stands (Neumann et al., 1982). The abundance of the nematode in particular plantations could be assessed by cutting wood chips from 20 Sirex-infested trees and the number of nematodes in such samples be used to estimate the percentage parasitism in Sirex larvae, using a a predictive equation developed by Haugen and Underdown (1991). This system of suppression remained effective for several decades. However, eventually, the infectivity of the laboratory nematode colony delcined after over 20 years of rearing in its non-parasitic form. This loss of infectivity allowed damaging populations fo S. noctilio to reemerge in some parts of Australia (Bedding, 1993). To suppress the wood wasp, it was necessary to again isolate from nature an effective parasitic strain of the nematode and use it to reinoculate areas that no longer had effective nematode populations. To prevent a reoccurrence of loss of infectivity in the mass rearing colony, an effective parasitic strain (currently, the Kamona strain) was frozen and production batches have since been initiated with this matieral on a yearly basis.

Subsequently, S. noctilio invaded other southern hemisphere areas with plantations of exotic pines (Chile, Brazil, Argentina, Uraguay, South Africa) and introductions of the nematode employed in Australia were made. These provided effective control in (insert refs and discuss results).

South Africa was invaded by this pest in 1994 in the Western Cape. Both the nematode B. siridicola and several parasitoids (I. leucospoides and M. nortoni) were introduced (Anon., 2007). I. leucospoides established but the fate of M. nortoni is still uncertain. In the winter rainfall areas of the Western Cape the pest has been completely controlled, but in the summer rainfall areas of the Eastern Cape and KwaZulu-Natal, the pest remains damaging. No clear explanation exists as to the reason for this difference in outcome, but it may be rooted in poor synchrony of the parasitoids to their hosts in the summer rainfall region. Work on this problem continues. This experience indicates both that the nematode alone may not be a complete control package and that the local climate and ecology of newly invaded areas can affect the outcomes of releases. Thus how well the nematode will work in North America and whether or not parasitoids should also be introduced remain to be determined.

Current Status of Biological Control Efforts in the United States

In 2004, S. noctilio was detected in Oswego County, New York, in the eastern United States. This has led to the initiation of a nematode-based biological control program. However, unlike previously invaded areas, pine in this region consists of predominately native pines, in native forests (in the northeast) or plantations and native forests (in the southeast). Compared to Australia, little acreage is devoted to plantations of exotic pines in the United States. These differences bring up several important, as yet unanswered, questions:

1. Will the nematode spread well in native forests without regular and repeated reinoculations as is done with newly planted stands in Australia?

2. Will any native insects, especially native Sirex and their associates, be at risk? An assumption concerning analysis of this risk is the the nematode will be able only to come into contract with species using the same fungal species as S. noctilio. There are 20 siricid species and subspecies in North America, in five genera (Sirex, Urocerus, Xeris, Eriotremex, and Tremex). In North America, only the Holarctic species in these groups are likely to be adapted to utilize Amylostereum areolatum, the fungal associate of S. noctilio. Xeris morrisoni indecisus (MacGillivaray), Xeris spectrum spectrum (L.) and Xeris spectrum townesi Maa attack trees already under attack by a variety of other siricids, and thus may be exposed to the nematode if they attack trees previously attacked by S. noctilio. In addition, two Sirex species, S. Juvencus juvencus (L.) and S. cyaneus F., may use both Amylostereum areolatum and the fungus typical of North American siricids, Amylostereum Chailletii (Pers. ex Fries) Boidin (Williams, unpublished).

3. Is the fungus to be introduced into the United States with the nematode already present (having been introduced along with the wood wasp) or is the fungus present a different strain?


References Cited

Aguilar, A. M. and D. M. Lanfranco. 1988. Aspects of the biology and symptoms of attack by Sirex noctilio: a review. Bosque 9: 87-91 (in Spanish).

Anon. 2007. Control of the Sirex woodwasps, pp. 40-41. Research and Technology Report 2005/2006. Plant Protectoin Research Institute, Pretoria, South Africa

Bedding, R. A. 1968. Deladenus wilsoni n. sp. and D. siricidicola n. sp. (Neotylenchidae), entomophagous-mycetophagous nematodes parasitic in siricid woodwasps. Nematologica 14: 515-525.

Bedding, R. A. 1993. Biological control of Sirex noctilio using the nematode Deladenus siricidicola, pp. 11-20. In: Bedding, R., R. Akhurst, and H. Kaya (eds.). Nematodes and the Biological Control of Insect Pests. CSIRO Publications, East Melbourne, Victoria, Australia.

Bedding, R. A. and R. J. Akhurst. 1974. Use of the nematode Deladenus siricidicola in the biological control of Sirex noctilio in Australia. Journal of the Australian Entomological Society 13: 129-135.

Chrystal, R. N. 1928. The Sirex wood-wasps and their importance in forestry. Bulletin of Entomological Research 19: 219-247.

Chrystal, R. N. and J. G. 1928. Natural enemies of Sirex cyaneus Fabr., in England and their life-history. Bulletin of Entomological Research 19: 67-77.

Clausen, C. P. 1978. Introduced Parasites and Predators of Arthropod Pests and Weeds: a World Review. Agricultural Handbook No. 480. United States Department of Agriculture, Washington, DC.

Coutts, M. P. 1969. The mechanisms of pathogenicity of Sirex noctilio on Pinus radiata. II. Effects of S. noctilio mucus. Australian Journal of Biological Science 22: 1153-1161.

Haugen, D. A. and M. G. Underdown. 1991. Woodchip sampling for the nematode Deladenus siricidicola and the relationship with the percentage of Sirex noctilio infected. Australian Forestry 54: 3-8.

Iede, E. T., S. Do R. C. Penteado, and J. C. Bisol. 1988. First record of Sirex noctilio attacking Pinus taeda in Brazil. Circular Tecnica Centro Nacional de Pesquisa de Florestas No. 20 (in Portuguese).

Morgan, F. D. 1968. Bionomics of Siricidae. Annual Review of Entomology 13: 239-256.

Morgan, F. D. 1989. Forty years of Sirex noctilio and Ips grandicollis in Australia. New Zealand Journal of Forestry Science 19: 198-209.

Neumann, F. G., J. A. Harris, F. Y. Kassaby, and G. Minko. 1982. An improved technique for early detection and control of the Sirex wood wasp in radiata pine plantations. Australia Forestry 45: 117-124.

Nuttall, M. J. 1989. Sirex noctilio F., sirex wood wasp (Hymenoptera: Siricidae), pp. 299-306. In: Cameron, P.J., R. L. Hill, J. Bain, and W. P. Thomas. A Review of Biological Control of Invertebrate Pests and Weeds in New Zealand 1874 to 1987. Commonwealth Agricultural Bureaux Institute of Biological Control, Technical Communication No. 10, Wallingford, United Kingdom.

Scheidter, F. 1923. On the life-history of our wood wasps. Zeitschr. Schadlingsbekampfung 1: 89-98 (in German)

Williams, D. W. Potential non-target effects of Beddingia siricidicola when used as a biological control agent of Sirex noctilio in North America (unpublished White Paper, USDA, APHIS, Otis, ANCB, Massachusetts, 25, Janurary, 2007).

Spradbery, J. P. and A. A. Kirk. 1978. Aspects of the ecology of siricid woodwasps (Hymenoptera: Siricidae) in Europe, North Africa, and Turkey with special reference to the biological control of Sirex noctilio F. in Australia. Bulletin of Entomological Research 68: 341-359.

Taylor, K. L. 1976. The introduction and establishment of insect parasitoids to control Sirex noctilio in Australia. Entomophaga 21: 429-440.

Taylor, K. L. 1978. Evaluation of the insect parasitoids of Sirex noctilio (Hymenoptera: Siricidae) in Tasmania. Oecologia 32: 1-10.

Taylor, K. L. 1980. Studies with Sirex noctilio (Hymenoptera: Siricidae) and its parasites that illustrate the importance of evaluating biological control attemps. Acta Oecologia, Oecologia Applicata 1: 181-187.

Tillyard, R. J. 1927. The giant horntail. A serious menace to pine plantations. Nelson Evening Mail, 9th February 1927, p. 6. Nelson, New Zealand.

Zondag, R. 1965. Entomology. Report of Forestry Research Institute of New Zealand for 1964, pp. 53-62.