Oecologia (1991) 87:135-145 Oecologia 9 Springer-Verlag 1991 Differences in foliage quality of young jack pine (Pinus banksiana Lamb.) on burned and clearcut sites: effects on jack pine budworm (Choristoneura pinus pinus Freeman) Deborah G. McCullough and Herbert M. Kulman Department of Entomology, Hodson Hall, University of Minnesota, St. Paul, MN 55108, USA Received September 25, 1990 / Accepted in revised form February 6, 1991 Summary. Suitability of young jack pine as a host for jack pine budworm was examined on similarly-aged trees growing on two areas previously burned in wildfires and on two previously clearcut areas in northwest Wisconsin. Nitrogen, monoterpenes, and moisture levels of foliage, and xylem water potential were measured and related to larval survival and pupal weight of caged jack pine bud- worm larvae. Nitrogen, monoterpenes, needle weight, and needle moisture were higher in trees growing on clearcut sites than on burned area trees. Survival of budworms to early and late instar, pupation, and adult eclosion was greater for larvae caged on clearcut-area trees than on burned-area trees. Female pupal weight differed between older (ca 10 years old) and younger (ca 8 years old) trees, but not between clearcut and burned areas. Mean female pupal weight was greatest on low- nitrogen trees, where larval survival was lowest. Foliar nitrogen was consistently included as a significant predic- tor in budworm survival regressions. Regressions in- dicated larval survival and pupal weight may be asso- ciated with different tree- and foliage-related traits. Re- sults suggest long-lasting effects of previous forest distur- bance may subsequently affect herbivorous insects such as jack pine budworm. Key words: Nitrogen Monoterpenes - Herbivory - Resource availability - Fire - Clearcutting Jack pine (Pinus banksiana Lamb.) is a commercially important species widely distributed across Canada and the Lake States (Yeatman 1967). It is shade intolerant, and typically found on sandy, nutrient-poor soil, where other forest species do poorly (Rudolf 1958 ; Wilde et al. 1964; Benzie 1977; Rudolph 1984). Jack pine produces serotinous cones throughout much of its range, reflecting Offprint requests to." D.G. McCullough the importance of fire in the jack pine ecosystem (Eyre 1938; Beaufait 1960; Roe 1963; Cayford 1970; Heinsel- man 1973). Large-scale regeneration of jack pine usually occurs only after fire or clearcutting. Jack pine budworm (Choristoneura pinus pinus Freeman) is the primary defo- liator of jack pine. Budworm outbreaks generally occur at 8- to 10-year intervals, and can result in serious growth loss, top-kill and tree mortality (Kulman et al. 1963; Kulman I971; Howse 1984). However, control measures can seldom be economically justified (Nyrop et al. 1983). Identification of factors affecting the jack pine-jack pine budworm interaction may enable resource managers to predict impacts of disturbance or silvicultural treatments on stand resistance to defoliation. Results of disturbances such as fire and clearcutting on subsequent interactions between plants and insect herbivores are not well-documented. Fire and other per- turbations can have long-lasting effects on availability of nitrogen (N) and other nutrients to regenerating vegeta- tion (Ahlgren and Ahlgren 1960; Sims 1976; DeBano et al. 1979; Ohmann and Grigal 1979; Wells et al. 1979; Raison et al. 1985). Feeding behavior of herbivorous birds and mammals has been altered by fire-induced changes in vegetation (Beck and Vogl 1972; Vogl 1973; Goldberg et al. 1980; Smith and Kadlec 1985). However, most studies of fire and insects have examined fire pri- marily in the context of pest control (Komarek 1970; Miller 1979). Defoliating insects are often closely attuned to host plant condition and should presumably be affect- ed by even subtle changes in foliage quality. Differences in insect abundance or general herbivory rates have been observed shortly after fires (Rice 1932; Lilly and Hobbs 1960; Hurst 1970; Knutson and Campbell 1974), but long-term impacts on phytophagous insects are relatively unknown. We hypothesized that suitability of jack pine as a host for jack pine budworm differed between areas that had been burned in wildfires and areas that had been clearcut. Tree water status, and foliage N, moisture and monoter- pene levels of jack pine were compared between trees that regenerated after clearcutting and those that regenerated