A hypothesis to explain outbreaks of looper caterpillars, with special reference to populations of Selidosema suavis in a plantation of Pinus radiata in New Zealand

Abstract

A hypothesis originally postulated to explain changes in abundance of sapsucking insects is here extended to an interpretation of changes in abundance of populations of geometrid defoliators.The hypothesis states that most herbivorous insects usually remain at a low level of abundance relative to the apparent abundance of their food because most of them die when very young from a relative shortage of nitrogen in their food.Only occasionally do their food plants become a sufficient source of nitrogen to allow a high proportion of the young insects to survive, and the population to increase to outbreak levels.The plants become a richer source of nitrogen when they are stressed by random fluctuations in the summer and winter rainfall, although other factors such as soil type and topography may contribute to this stress.The hypothesis may well have wider application to population fluctuations of other herbivores-both invertebrate and vertebrate.

Does a vascular fungus of tomato induce a defence response or a change in host plant quality that also affects the oviposition of spider mites?

“…The lower drought levels did not cause significant changes in mite oviposition. Thus, our results are not in agreement with White (1969White ( , 1974White ( , 1976White ( , 1984, Lewis (1979) and Hollingworth and Berry (1982) who reported a stimulation of insect outbreaks on droughtstressed plants nor with English-Loeb (1989, 1990) who found a non-linear response of drought stress on mite performance. Such a non-linear relationship was postulated earlier by White (1984) and Mattson and Haack (1987a,b) in extreme stress situations, in which the plant is so badly damaged that it has become unsuitable for herbivores.…”

The effect of ozone fumigation and different Brassica rapa lines on the feeding behaviour of Pieris brassicae larvae

“…This reduced development and expansion of new leaves causes a decreasing demand for starch and other carbohydrates in these leaves, which leads to an accumulation of carbohydrates in the fully developed leaves (Robinson & Rowland, 1996;Barnes et al, 1999;Herold, 1980). Stressed plants are believed to become more vulnerable to herbivory when biochemical changes lead to increases in the nutritional value or decreases in plant chemical defences (White, 1974(White, , 1984). An increase in nutritional value is often due to the breakdown of protein and mobilization of soluble nitrogen in stressed leaves (White, 1984).…”

Predictions of Southern Pine Beetle Populations Using a Forest Ecosystem Model

“…This type of model could be used to alert forest managers to present areas of heavy SPB infestation or future areas that are susceptible to infestation given changing climate. White (1974) hypothesized that insect performance is favored in stressed plants because consumed tissues have higher nitrogen concentrations, and Rhoades ( 1979) linked increased stress with reduced synthesis of defensive compounds. It has long been recognized that climatic effects, especially drought can weaken host trees and increase SPB populations (Wyman, 1924;Craighead, 1925;St.…”