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LARCH CASEBEARER, Coleophora laricella (Hübner) -- Coleophoridae

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The larch casebearer is native to central Europe and is relatively innocuous in the alpine area on its normal host, Larix decidua Mill. (Jagsch 1973). A rich complex of parasitoids is thought to maintain the casebearer at lower densities in its endemic region (Ryan et al. 1987). It is a defoliator of Larix species and becomes a pest in Europe and Asia wherever larch is planted. This insect was probably introduced on nursery stock into North America from Europe and was first found at Northampton, Massachusetts in 1896 and in Canada at Ottawa in 1905 (Otvos & Quednau 1981). They spread rapidly on tamarack, Larix laricina (Du Roi) K. Koch, in eastern Canada so that by 1947 it was in Newfoundland, the Maritimes, and Ontario and in the United States, Maine, Michigan and Wisconsin (McGugan & Coppel 1962). It is currently widely distributed in the eastern United States and Canada. In 1957 the casebearer was discovered on western larch, Larix occidentalis Nutt, in Idaho (Denton 1958) and in 1966 in British Columbia (Moinar et al. 1967). It is now widely distributed over the range of western larch including British Columbia, Montana, Idaho, Washington and Oregon (Clausen 1978).

The casebearer has one generation per year. The adults begin appearing in late May and lay eggs on either side of the needles. The larvae hatch and burrow directly down into the needles. In the late summer the larvae emerge from the mined needles and form overwintering cases. They feed for a while and then move to branches and twigs to pass the winter. In the early spring the larvae with their cases move and begin feeding on the young buds and foliage. Pupation occurs within the enlarge case, which is commonly attached to a branch on a leaf whorl. The larval feeding, when extensive, causes a loss of growth that is its greatest impact on larch (Ryan et al. 1987).

A biological control program began in 1928 in western Canada with a request to the Farnham House Laboratory of CIBC for information on the parasitoid complex of the casebearer in Europe (McGugan & Coppel 1962). Importation and field releases of 5 species of parasitoids occurred in eastern Canada between 1931 and 1939 as follows: 1,037 Agathis pumila (Ratz.)--Braconidae, 29,664 Chrysocharis laricinellae (Ratz.)--Eulophidae, 506 Cirrospilus pictus (Nees)--Eulophidae, 3,283 Dicladocerus westwoodii Steph.--Eulophidae, and 97 Diadegma laricinellum (Strobl)--Ichneumonidae (Clausen 1978). All species were subsequently recovered at release sites in Ontario but only two became well established and spread rapidly, A. pumila and C. laricinellae. Between 1942 and 1947 large scale redistribution releases were made at a number of sites in eastern Canada. The parasitoids were obtained at established colony sites at Millbridge, Ontario (Clausen 1978). By 1948 populations of the casebearer were low on the original release sites. The parasitoids followed the spread of the casebearer to the west assisted by occasional releases (Ryan et al. 1987). This is definitely an example of a successful biological control program (Webb & Quednau 1971).

A separate, extensive parasitoid importation program was also conducted between 1932 and 1936 in the eastern United States in New England and New York (Clausen 1978). Four of the same parasitoids as released in Canada were used in the U.S. (Clausen 1978) as follows: 8,141 A. pumila, 24,671 C. laricinellae, 231 D. westwoodii, and 3,580 D. laricinellum (Strobl). Although there is little information, the results were apparently the same in the eastern United States with the establishment of A. pumila and C. laricinellae followed by high parasitization rates particularly by A. pumila (Dowden 1962). Releases of the two established parasitoids were also made in 1937, 1950 and 1952 in Michigan and Wisconsin.

In the western United States, the first releases of A. pumila were made in 1960 with 2,360 adult parasitoids that were collected in Rhode Island (Clausen 1978). These were released at 5 locations in Idaho. Recoveries were made at 3 sites in 1962. Between 1964 and 1969 field rearing of A. pumila in whole tree cloth cages permitted the release of this parasitoid at 400 sites in Idaho, Montana, Washington and British Columbia (Ryan et al. 1987). The parasitoid became established and built up at some sites but at other sites it either didn't become established or it didn't build up. In addition, significant defoliation still occurred throughout much of the area by 1970 and the program was rated as a failure (Turnock et al. 1976, Ryan et al. 1987).

Between 1971 and 1983 a new strategy was used as C. laricinellae and five other species of parasitoids from Europe and Japan were released over a period of several years. C. laricinellae became widely established but the other species don't appear to be very important for control of the casebearer though isolated recoveries have been made (Ryan et al. 1987). In an effort to properly evaluate the effect of the parasitoids, the larch casebearer was sampled at sites in Oregon where the casebearer had recently invaded. The populations were followed to the point of severe defoliation from 1972 to 1978 and then parasitoids were released between 1979 and 1985 (Ryan 1983, 1986; Ryan et al. 1987). The first parasitoid to be released was C. laricinellae followed by A. pumila. Parasitoids increased and the casebearer steadily declined and this trend has continued in all plots through 1987 (R. B. Ryan, personal communication). Although the prospects are good for a complete success, Ryan et al. (1987) feel it is too soon to make the claim.

In British Columbia the larch casebearer biological control program was reviewed in 1974 due to the successes in eastern Canada (Otvos & Quednau 1981). Four parasitoids have been released: A. pumila, C. larcinellae, Diadegma laricinellum, and Dicladocerus japonicus Yshm. The story is much the same as with the other release programs--A. pumila and C. laricinellae have become well established and the other two have not been recovered. It is too early to evaluate the effects of the two parasitoids but C. laricinellae is fairly common in British Columbia and may be responsible for the reduction of larch casebearer and less tree mortality (Otvos & Quednau 1981).

The larch casebearer is a successful biological control program in eastern Canada and may shortly be successful in the northwestern United States. It is an example of a classic introduction program with the subsequent redistribution of the parasitoids from areas of establishment to new areas. It is interesting because the two parasitoids complement one another in their action against the casebearer. Agathis is extrinsically superior at low host densities and Chrysocharis is effective at high host densities. Quednau (1970) hypothesized that Agathis can only give partial control on its own and that success is only possible through cooperative interaction with Chrysocharis. Ryan (1985) hypothesized that Agathis may not be detected in successive samples since parasitized larvae commonly descend to understory vegetation. Samples could be biased toward Chrysocharis due to the absence of Agathis in the foliate that is sampled. There has been no success in establishing other parasitoid species. This program also is an example of one where there was a rigorous attempt to evaluate efficacy of the parasitoids (Ryan 1986, Ryan et al. 1987).

For further details on biological control effort and biologies of host and natural enemies, please also see the following (Herrick 1912, Thorpe 1933, Graham 1944, 1949, 1958; Turnbull & Chant 1961, Dowden 1962).

REFERENCES: [Additional references may be found at: MELVYL Library ]

Clausen, C. P. 1978. Coleophoridae. In: C. P. Clausen (ed.), Introduced parasites and predators of arthropod pests and weeds: a world review. U. S. Dept. Agric. Handbook No. 480. 545 p.

Denton, R. E. 1958. The larch casebearer in Idaho--a new defoliator for western forests. USDA, Forest Service, Intermountain Forest and Range Experiment Station, Res. Note 51: 6 p.

Dowden, P. B. 1962. Parasites and predators of forest insects liberated in the United States through 1960. U. S. Dept. Agric. Agric. Handb. 226. 70 p.

Graham, A. R. 1944. The establishment of some imported parasites of the larch casebearer, Haplotilia laricella Hbn. in Ontario. Ent. Soc. Ontario 74th Ann. Rept. 1943: 48-52.

Graham, A. R. 1949. Developments in the control of the larch casebearer, Coleophora laricella (Hbn.). Ent. Soc. Ontario 79th Ann. Rept. 1948: 45-50.

Graham, A. R. 1958. Effectiveness of two introduced parasites of the larch casebearer, Coleophora laricella (Hbn.) (Lepidoptera: Coleophoridae) in Ontario. Ent. Soc. Ontario 88th Ann. Rept. 1957: 37-41.

Herrick, G. W. 1912. The larch case-bearer. New York Agric. Expt. Sta. Bull. 322: 29-54.

Jagsch, A. 1973. Populationdynamik und Parasitenkomplex der Larchenminiermotte, Coleophora laricella Hbn., in naturlichen Verbreitungsgebiet der Europaischen Larche, Larix decidua Mill. Zeit. ang. Ent. 73: 1-42.

McGugan, B. M. & H. C. Coppel. 1962. A review of the biological control attempts against insects and weeds in Canada. II. Biological control of forest insects, 1910-1958. Commonwealth Inst. Biol. Control Tech. Comm. No. 2: 35-216.

Otvos, I. S. & F. W. Quednau. 1981. Chapter 49. Coleophorea laricella (Hübner), larch casebearer (Lepidoptera: Coleophoridae), p. 281-84. In: J. S. Kelleher & M. A. Hulme (eds.), Biological Control Programmes Against Insects and Weeds in Canada, 1969-1980. Commonwealth Agricultural Bureau, London, England. 410 p.

Ryan, R. B. 1983. Population density and dynamics of larch casebearer (Lepidoptera: Coleophoridae) in the Blue Mountains of Oregon and Washington before the build-up of exotic parasites. Canad. Ent. 115: 1095-1102.

Ryan, R. B. 1985. A hypothesis for decreasing parasitization of larch casebearer (Lepidoptera: Coleophoridae) on larch foliage by Agathis pumila. Canad. Ent. 117: 1573-74.

Ryan, R. B. 1986. Analysis of life tables for the larch casebearer (Lepidoptera: Coleophoreidae) in Oregon. Canad. Ent. 118: 1255-63.

Ryan, R. B. 1987. Classical biological control: an overview. J. Forestry 85(7): 29-31.

Ryan, R. B., S. Tunnock & F. W. Ebel. 1987. The larch casebearer in North America. J. Forestry 83(7): 33-39.

Thorpe, W. H. 1933. Notes on the natural control of Coleophora laricella, the larch case-bearer. Bull. Ent. Res. 24: 271-91.

Turnbull, A. L. & D. A. Chant. 1961. The practice and theory of biological control of insects in Canada. Canad. J. Zool. 39: 697-753.

Turnock, W. J., K. L. Taylor, D. Schroder & D. L. Dahlsten. 1976. Biological control of pests of coniferous forests, p. 289-311. In: C. B. Huffaker & P. S. Messenger (eds.), Theory and Practice of Biological Control. Academic Press, New York. 788 p.

Webb, F. E., & F. W. Quednau. 1971. Chapter 38. Coleophora laricella (Hübner), larch casebearer (Lepidoptera: Coleophoridae), p. 131-36. In: Biological Control Programmes Against Insects and Weeds in Canada, 1959-1968. CAB, Commonwealth Inst. of Biol. Control, Tech. Comm. No. 4. 266 p.