Treesearch

The term "guild" describes a group of organisms that exploit the same class of resources in a similar manner (Root 1967, Mattson et al. 1988). This study focuses on six members of the folivore guild of subalpine larch, Larix deciduas, in Switzerland--five lepidopterans and one hymenopteran. From 1949 to 1979, Auer (1977) sampled populations of the larch bud moth, Zeiraphera diniana L., and at the same time collected associated larvae. I have analyzed these 30 years of insect sample data for the six different species and now offer it to the scientific literature. In spite of some methodologi...

The gypsy moth, Lymantria dispar L., was introduced from Europe into North America near Boston, Massachusetts, in 1869, and is now well established as a serious defoliator of forest, shade, and fruit trees over much of the eastern United States. Despite substantial efforts to eradicate, contain, or control this pest, the gypsy moth has persisted and continues to extend its range. The generally infested area currently extends from the northeast corner of North Carolina along a diagonal line that extends through Virginia, West Virginia, and the northeast corner of Ohio into Michigan. These...

It has been suggested that the enormous diversity of phytochemicals within the plant kingdom makes it impossible for one and the same insect species to exploit all plant species (Dethier 1954, Fraenkel 1959). Not surprisingly, the number and diversity of host plants utilized by different phytophagous insects are highly variable, and the specific selective pressures acting on them are still poorly understood (Bemays and Graham 1988, Strong 1988). Many hypotheses have been proposed to explain variations in host specificity among phytophagous insects. For example, there are those based on...

Patterns that occur in nature are the result of a complex set of current and historical factors that interact with one another and the adaptive plasticity of plants. Scientists are forced to assess such processes on the basis of series of "snapshots" over a relatively short time that represent only part of the grand pattern. In the case of insects interacting with forest trees, there are dozens of environmental and host plant factors that could be the key factor responsible for the patterns we observe. Because of the high experimental standards of research and the many potentially important...

It is widely believed that plants facilitated the evolution of terrestrial insects (Southwood 1973). However, the mechanisms by which this evolution occurred are not yet fully understood. I therefore propose a hypothesis about one possible mode of formation of terrestrial insects and fauna. The soil, warm shallow lagoons, tidal zones, and accumulations of detritus are assumed by many authors to be the "bridges" for the transition of aquatic organisms to terrestrial existence.

A general principle of adaptive allocation was proposed by Cody (1966) who hypothesized that 1) all living organisms have finite resources to partition among growth and competing physiological processes such as reproduction and defense; and 2) natural selection results in the evolution of unique resource allocation patterns that maximize fitness in different environments. Today, it is well established that plants have limited resources to allocate among these processes (Bazzaz et al. 1987), and theories of life-history strategy rests on the assumption that there are fitness trade-offs...

In North America, about 85 species of free feeding and leafmining folivorous insects in the orders Lepidoptera and Hymenoptera periodically cause serious and widespread defoliation of forest trees (Appendix 1). We call these insects expansive outbreak folivores based on the following criteria: 1) population eruptions occur two or more times per 100 years, 2) severe host defoliation (> 50 percent) occurs for 2 or more years per eruption, and 3) the area of each individual outbreak exceeds 1,000 contiguous ha. There are about 20 other insects whose populations meet criteria one and two, but...

Numerous investigations have shown that forest insect outbreaks usually occur in specific habitats. Frequently these outbreaks do not generally extend to other territories occupied by these same host trees. Moreover, in every stand subjected to an outbreak, both slightly undamaged plots and heavily damaged plots are found. Perhaps some plots are initially more resistant to insect attack, and insect distribution within forest ecosystems may have a mosaic pattern. Therefore investigation of the relation between dendrophagous insect distributions and initial heterogeneity of ecosystems may...