The Importance of Conifer Seed in British Columbia

Reforestation is an important business in British Columbia. Currently, around 250 million trees are planted annually in the province. The bulk of these plantings are grown from seed (the rest are produced from rooted cuttings and embryogenesis) collected from conifers in natural stands or grown in seed orchards. Seed from orchards currently accounts for 25% of all seedlings produced and the Province has established a goal of producing fully 75% of all plantings from orchard seed by the year 2007. Clearly, conifer seed is an important commodity in the BC forest industry.

Much effort goes into ensuring that seedlings are appropriately adapted to the environmental conditions they will be exposed to once they are outplanted and that they will produce more lumber of higher quality than naturally regenerated trees of the same species growing under the same conditions. Extensive tree selection and breeding programs for most of the major conifer species in BC produce the parents of the seedlings.

The parents resulting from the tree selection and breeding program are planted in seed orchards. Each orchard is comprised of clones (or occasionally seedlings) of up to 100 or more parents of a single species. Clones are produced by grafting cuttings (scion material) from the parents onto selected rootstock. The trees in one orchard are adapted for a particular set of biogeoclimatic conditions (a Seed Planning Zone or SPZ) from within the range of the species. For example, there are three SPZ's for Douglas-fir on the coast of BC and different orchards address these needs. Seed orchards are similar to tree fruit orchards - both are intensively managed agroecosystems. Seed orchards are irrigated, fertilized, heavily pruned, and treated in various ways to produce cone crops on a regular basis. Because of the high value of orchard trees and seed produced by them, insect and disease management are a high priority for orchard managers.

The Importance of Cone and Seed Insects

Insects are a natural and very important component of forest ecosystems. Without them (and fungi) forests would be unable to cycle properly. However, because of the human need for wood products, many species of insects become our major competitors in utilizing forest resources. Understanding the biology of these insects and learning how to live and deal with them is the major challenge of forest insect pest management.

A small but determined group of insects (conophytes) is in direct competition with us in the exploitation of conifer cones and seeds. Only about100 of the 50,000 species of insects known in Canada are conophytes, but they are very good at their business as, for many of them (obligate conophytes), their lives depend on cones and/or seeds. Conophytes can destroy entire cone crops in some years, particularly when crops are small. For example, the redcedar cone midge (Mayetiola thujae) regularly consumes all redcedar seeds in some areas; Ponderosa pine cone moth (Cydia piperana) has been credited with destroying 50% of total seeds per cone; and an average of one Douglas-fir cone moth larva (Barbara colfaxiana) per cone will result in a 65% reduction in seed. The low species richness and diversity of conophytes suggest stable host associations developed through a very long co-evolutionary history -- i.e., in natural stands, conifer hosts and their conophyte populations coexist peacefully and natural regeneration proceeds apace.

Those insect species that must complete some part of their lifecycle within cones or seeds are termed "obligate conophyte." A good example of an obligate conophyte is the Douglas-fir cone gall midge (Contarinia oregonensis), the most important cone and seed insect in coastal populations of Douglas-fir. In contrast, facultative conophytes are not dependent upon cones or seeds but can survive on other plant parts such as foliage or cambial tissue. The western spruce budworm is the most important facultative conophyte in British Columbia.

Facultative Conophytes

General characteristics of facultative conophytes are:

Populations are cyclic but relatively stable.
Populations of facultative conophytes such as western spruce budworm may fluctuate cyclically but rarely disappear.
Not dependent upon cones or seeds.
Many facultative conophytes are better known as forest defoliators but feed upon cones and seeds preferentially when they are available.
Low host species and cone tissue specificity.
Facultative conophytes are not usually particular about what species or part of a cone they feed upon. When populations are high, western spruce budworm can be found feeding on cones of most conifers in BC.
Many lay large numbers of eggs in clusters.
Because facultative conophytes can survive upon a variety of resources, females may produce large numbers of eggs and deposit them in clusters. There is little benefit in carefully selecting optimal sites for offspring survival.

Obligate Conophytes

General characteristics of obligate conophytes are:

Populations are apparently unstable.
In years when there are no cones, obligate conophytes seem to disappear only to reappear the next time cones are produced.
Dependent upon ephemeral resources and have therefore developed specialized techniques to help them survive cone droughts
Natural stands of conifers often bear large cone crops in one year, then grow for several years with few or no cones produced. During these periods of cone drought, obligate conophytes enter extended diapause, an inactive resting state, until such time as cones are again available. Extended diapause can be of two types: risk spreading or predictive. In risk spreading diapause, the offspring of one female are genetically programmed to diapause for lengths of time varying from one to two or more years. Progeny emerging in years of poor cone crops may not survive or be able to reproduce. Based on sizes of mid-1990's spruce cone crops and associated population levels of the spruce cone moth (Cydia strobilella), this moth is likely a good example of an insect with risk spreading diapause. Predictive diapause is apparently ended by the environmental conditions that initiate cone production. Thus, most of the progeny will emerge to find abundant resources for feeding or reproduction. The Douglas-fir cone moth (Barbara colfaxiana) is a good example of an insect with predictive diapause.
Often host species and cone tissue specific and have developed specialized techniques to maximize their use of the resource.
Many obligate conophyte species feed in the cones of only one conifer species and are often very specific about which cone tissues they are exploiting. For instance, the Douglas-fir seed chalcid (Megastigmus spermotrophus) larvae are associated only with seeds of Douglas-fir. Most obligate conophytes have complex host and conspecific recognition techniques to aid them in targeting a particular resource (cones of the correct species) and to avoid over consumption of the resource. These techniques usually involve visual and/or chemical cues. Thus, adult flies of the spiral spruce cone maggot (Strobilomyia neanthracina) apparently select spruce based on a combination of visual (tree form, conelet colour) and chemical (volatile chemicals emitted by spruce conelets) cues. Females chemically mark the cones after laying eggs to deter egg-laying by other cone maggot flies.
Many lay eggs singly.
Because of their resource specialization, most obligate conophytes lay relatively few eggs, singly, and in such a manner as to maximize the chances of successful development of the progeny. Seed chalcids (Megastigmus spp.) are adept at drilling tiny, inconspicuous holes through cone tissue and directly into individual developing seeds. One egg is laid within each seed.

Dealing with Cone and Seed Insects

The British Columbia Ministry of Forests and Range maintains a "Seed Pest Management Program" to serve the needs of the seed production community.

For more information on cone and seed insects and their management see:

de Groot, P., J.J. Turgeon, and G.E. Miller. 1994. Status of cone and seed insect pest management in Canadian seed orchards. The Forestry Chronicle. Vol. 70, No. 6. p 745-761.

Turgeon, J.J., A. Roques, and P. de Groot. 1994. Insect fauna of coniferous seed cones: diversity, host plant interaction, and management. Annu. Rev. Entomol. Vol. 39. p. 179-212.

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