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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Applied Ecology. SUMMARY(1) The dynamics of the seed bank of the tropical weed Mimosa pigra were investigated in two regions of northern Australia by monitoring changes in the seed populations beneath mature stands, by a seed burial experiment, and by measuring the seed output of populations.(2) Seed populations were generally very high compared to the range expected for secondary tropical vegetation. For example, in 1986 they varied from 8500 m-2 in one region to nearly 12 000 m-2 in another.(3) In the seed burial experiment, viability declined with time. The rate of loss declined with increasing depth of burial, and differed between the two regions, with exponential half-lives ranging from 99 weeks at 10 cm depth in a light clay to 9 weeks at 1 cm depth in a heavier black cracking clay. These seed loss rates were within the range reported in the literature.(4) The measured seed banks broadly agreed with the values predicted by a simple model based on the rates of seed loss found in the burial experiment.(5) Although the decline in viability of M. pigra seeds can be fairly rapid, it is argued that, because of the large soil seed population, rigorous control of seedlings would have to be maintained for some years after the eradication of mature plants.

Observations were made over a two-year period on the growth and natural enemies of Lantana tiliaefolia and L. glutinosa growing naturally at nine sites covering different climatic areas of Parana State, south Brazil. Lantana was found to be subjected to continuous attack by insects and/or fungi throughout the year, with different species causing damage at different times. Temperate-climate sites had a more diverse complex of insects and a greater intensity of attack than warmer-climate sites. Shrubs in sites which suffered severe insect attack, especially during the previous season, flowered and fruited significantly less than those which had suffered only light attack. Differential weighting of the principal phytophagous insects demonstrated that feeding by insects of some groups may be more damaging than that by others. The relevance of the results to the search for biological agents for control of lantana in Australia is discussed.

An investigation of the effects of 20 secondary plant chemicals on the survival, development, and feeding behavior of a polyphagous insect, Melanoplus bivittatus (Say), was made using chemically defined synthetic diets.When added to the basic diet, only one chemical, tigogenin, showed unqualified stimulatory effects on growths. Nornicotine dipicrate, solanine, tomatine, digitonin, and saponin caused all nymphs to die before they attained the adult stage, and santonine, indican, diosgenin, hecogenin, and lupinine produced leas severe toxic effects. Very few of the chemicals which permitted survival affected adult weight.Feeding preference experiments showed that some chemicals reduced feeding but none increased it. If it is assumed that the role of secondary plant chemicals in the feeding behavior of M. bivittatus is to indicate to the insect which diets to discriminate against, anomalies existed in that diets containing innocuous chemicals were sometimes discriminated against, whereas diets containing some chemicals producing lethal effects were accepted.Steroid chemicals exhibited the greatest effects on feeding behavior, survival, and growth, and it is postulated that the distribution of plant steroids may provide an insect – food plant association mechanism.

No abstract