and circulation of vital mineral nutrients needed 

 for plant growth. Insects are an energy and nu- 

 trient-rich food source for the plethora of animals 

 that feed on them. Research on energy flow or 

 nutrient cycling can often supply tools to deter- 

 mine when pest action has a net benefit on the 

 forest and should not be controlled. 



Research on the forest tent caterpillar and other 

 defoliating insects in the aspen-birch ecosystem of 

 the Lake States has featured investigations into 

 nutrient cycling and energy flow. This approach 

 has brought new understanding of the roles of 

 insects in forest communities. Of significance is 

 the discovery that defoliating insects tend to op- 

 timize plant productivity of particular sites over 

 the long term. In general, site factors that ad- 

 versely aff'ect tree hosts ultimately enhance the 

 success of the infesting insects. This research 

 promises to bring about a better understanding of 

 the complex nutrient factors and interactions 

 which are important for plant vigor and resistance 

 to disease and which can signal the release of 

 endemic insect populations into an epidemic 

 phase. 



Mattson. W. J. and N. D. Addy. 1975. Phytophagous insects 

 as regulators of forest primary production. Science. 190:515- 



522. 



Population Ecology of Forest Insects 



Population ecology research usually focuses on 

 insects assumed or proven to be forest pests. This 

 basic research involves: (I) Developing methods 

 describing quantitatively the populations of target 

 insects and their associates including natural 

 enemies; (2) evaluating the roles of natural ene- 

 mies — parasites, predators, pathogens — and other 

 associates, physical factors, and host relationships 

 in determining population changes; and (3) devel- 

 oping methods to predict population changes in 

 time and place and the effects of such changes on 

 trees, stands, and forest ecosystems. Investiga- 

 tions have included the mountain pine beetle, 

 western pine beetle, spruce budworms, and forest 

 tent caterpillar. As a result, a broad base of knowl- 

 edge is available on a wide variety of forest pests. 

 Technology was developed, applied, and improved 

 for sampling insect populations to gather quantita- 

 tive data both in research and operational control 

 programs. Life history and population dynamics 

 studies have identified key life stages most suscep- 

 tible to direct control actions and pointed the way 

 toward utilizing biological control agents — paras- 

 ites, predators, pathogens — as well as conventional 

 control approaches for forest resource protection. 



In recent years, eff'orts have intensified to de- 

 velop pest management systems for the southern 



14 AGRICULTURE 



pine beetle, gypsy moth, and Douglas-fir tussock 

 moth. New approaches are being used to develop 

 models for pest populations, their efl'ects on for- 

 est stand parameters, treatment techniques ap- 

 plied singly and in combinations, and interacting 

 social and economic criteria that influence pest 

 and forest management decisions. 



Campbell, R. W. 1967. An analysis of numerical change in 

 gypsy moth populations. Forest Sci. Monograph 15:3.^pp. 



Cole. W. E., G. D. Amman and C. E. Jensen. 1976. 

 Mathematical models for the mountain pine beetle-lodgepole 

 pine interaction. Environ. Entomol. 5:11-19. 



McKnight. M. E. 1971. Natural mortality of the western spruce 

 hudwomi. Choristoneunt occidentials. in Colorado. USDA For- 

 est Serv. Res. Paper RM-81. 12 p. Rocky Mt. Forest and 

 Range Exp. Sta.. Fort Collins. Colorado. 



Witter. J. A.. W. J. Mattson, and H. M. Kulman. 1975. 

 Numerical analysis of a forest tent caterpillar (l.epidoptera: 

 Easiocampidae) outbreak in northern Minnesota. Can. Ento- 

 mol, 107:837-854. 



Insect Pathology 



Forest insects pests are hosts of many patho- 

 genic mircoorganisms, and disease is known to be 

 an important factor in the population dynamics of 

 some of the major pests which have been studied 

 most intensively. Broad knowledge of the occur- 

 rence and distribution of naturally occurring dis- 

 eases, their effects on individuals and populations, 

 and their modes of transmission and persistence 

 in forest ecosystems suggests that certain patho- 

 gens of forest insects can be manipulated by man. 

 Our experience in developing microbial insecti- 

 cides has shown the essentiality of basic biologi- 

 cal, chemical, and physical characterization of 

 specific pathogens to establish their environmental 

 safety. With these prerequisites fulfilled, registra- 

 tion of the Douglas-fir tussock moth nuclear poly- 

 hedrosis virus (NPV) has been granted (the first 

 forest insect virus approved for operational use) 

 by the Environmental Protection Agency (EPA), 

 and registration of the gypsy moth NPV is expect- 

 ed soon. Forest Service research on NPV's and 

 on formulations of commercially available Bacil- 

 lus thuringiensis has provided forest managers 

 with biological control agents for two of the most 

 important forest insect pests of North America. 

 With protocols for registration now established, 

 research should move aggressively to provide 

 mote knowled;,e to support operational use of a 

 variety of pathogens — viruses, bacteria, fungi, 

 protozoa, nematodes — known to be effective 

 against important forest insects. 



Campbell, R. W. and J. D. Podgwaite. 1971. The disease com- 

 plex of the gypsy moth. J. Invertebrate Path, 18:101-107. 



Hughes. K. M. and R. B. Addison. 1970. Two nuclear poly- 

 hedrosis viruses of the Douglas-fir tussock moth. J. Inverte- 

 brate Path. 16:196-204. 



