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A REVIEW OF THE LITERATURE
AND
IDENTIFICATION OF FUTURE OPPORTUNITIES
R. G. Van Driesche
University of Massachusetts
Fernal Hall, Department of Entomology
Amherst, MA 01003
and
S. Healy, and R. Reardon
Abstract
The literature on 94 species of arthropod forest pests was reviewed with the objective of summarizing current knowledge about the role of biological control in the population dynamics of these pests. This was done for the purpose of identifying which species were the best candidates as future, new or reopened, projects of biological control. The report, to be published by the Forest Service in 1997, identified species for which opportunities for use of biological control existed through natural enemy importation, conservation or augmentation. Other species reviewed were felt to not be suitable as biological control targets. This information is summarized as follows
(Tables 1-4).
Summary of Recommendations
Ninety four species of forest arthropods have been reviewed in this report. Other species, not reviewed, may be important pests from the perspective of more particular geographic areas or tree species. Consideration of application of biological control in such cases will require further review.
Of the species reviewed, 58 (62%) are believed to be native to North America. Of the remainder, the origins of two species (2%) (spruce mite and larch sawfly) are uncertain or disputed. The remainder include 29 species (31%) of non-native origin currently found in North America and three species (3%) not yet present in North America, but of concern (Ips typographus, Sirex noctilio, and Lymantria monacha). Finally, three species (Cooley spruce gall adelgid, Nantucket pine tip moth, and tuliptree aphid) are native to North America, but have spread into regions of North America outside their original ranges, and thus occur as non-native species in some areas.
Detailed recommendations of how biological control might be employed for the control of these pests are given as the concluding paragraphs in each species' section. These recommendations have been grouped into the following categories that correspond to the ways in which biological control can be employed:
Some species listed in this category have already been successfully controlled through natural enemy introductions (e.g., larch casebearer, European spruce sawfly, introduced pine sawfly, and Nantucket pine tip moth in California).
Most of the pests listed in this category have invaded North America from other continents. A few, however, are native species (e.g., Cooley spruce gall adelgid, tuliptree aphid, Nantucket pine tip moth) that have invaded parts of the continent outside their historical ranges and become non-native pests locally.
For the species that have invaded North America from abroad, it is important to identify the native homeland, which may be different from the area from which the pest came to North America. Many species, for example, appear to have moved from Russia or Asia to Europe and then to North America. In such cases, the species may lack important natural enemies in Europe as well as North America and Europe would thus be an inappropriate location in which to seek natural enemies able to suppress the pest.
A small number of native species have been considered as possible targets for natural enemy introductions, using species collected from European or Asian species related to the pest at the generic level. Examples include spruce budworm and white pine weevil.
Of the 29 species of non-native pests reviewed, 27 were judged to provide opportunities for their control via natural enemy introductions (Table 1). In some cases, these species have never been targets of natural enemy importations (e.g., beech scale, mimosa webworm, eastern spruce gall adelgid) or present opportunities for work additional to that which was done in the past. An example of the later would be searching new regions not considered or accessible in the past, e.g., the Caucasus Mts. for predators of the balsam woolly adelgid.
For pests of high value sites (forest nurseries, shade trees, Christmas tree plantations), use of more expensive biological control products such as nematodes, predacious mites, or formulated pathogens is possible. Fourteen species were identified for which studies on the effectiveness of augmentative biological control seem useful (Table 2). Examples include the development of nematodes for the control of white grubs in forest nurseries, the use of Bacillus thuringiensis for control of defoliating Lepidoptera, and the use of nuclear polyhedrosis viruses for control of some species of sawflies.
For some pests, insufficient information was found to judge the importance of natural enemies in the population dynamics of the species. In some cases there were needs to compare the importance of natural enemies between habitats (such as natural stands versus managed plantations) or locations (in North America versus the native range). A need for population dynamics studies of these sorts was identified for 17 species (Table 3). Examples include the need to clarify the importance of pipinculid parasitoids attacking the Saratoga spittlebug, a need to study the effect of different slash management practices on natural enemies of pine engraver beetle and larger pine shoot beetle, and studies of effects of vegetation diversity on various shoot borers.
For 29 species (Table 4) no role for biological control was identified. These species were predominantly native (27) insects, for which natural enemy introductions were not likely to be relevant and for which augmentativebiological control methods were too expensive in view of the nature and distribution of the damage. While natural control by unmanipulated natural enemies is undoubtedly a factor to some degree in the population dynamics of these species, opportunities to intentionally employ silvicultural practices to increase biological control were not identified.
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