This book begins with the physical and biological characterization of the four North American deserts and a description of the primary adaptations of plants to environmental stress. In the following chapters the authors present case studies of key species representing dominant growth forms of the North American deserts, and provide an up-to-date and comprehensive review of the major patterns of adaptations in desert plants. One chapter is devoted to several important exotic plants that have invaded North American deserts. The book ends with a synthesis of the adaptations and resource requirements of North American desert plants. Further, it addresses how desert plants may respond to global climate change.

Physiological Ecology of North American Desert Plants

Literature data were collected on the floristic distribution and toxicity of phytochemicals to herbivores and on herbivore specialization in order to test phytochemical coevolution theory. The theory makes four predictions that can be tested with this information. Herbivores can adapt to novel, more toxic chemicals by becoming specialists, or they can become generalists but at the cost of lower feeding success on any particular host. Thus, the first two predictions are as follows: herbivores should do better on chemicals that are present in their normal host, and this pattern should be stronger for specialists than for generalists. The "escape and radiation" aspect of the theory holds that if a plant taxon with a novel defense chemical diversifies, the chemical will become widespread. Eventually, herbivores will adapt to and disarm it. So the third prediction is that more widespread chemicals are less toxic than more narrowly distributed ones. Because generalists should not do as well as specialists on chemicals disarmed by the latter, the fourth prediction is that the third prediction should be more true for generalists than specialists and should depend on presence/absence of the chemical in the normal host. Multiple regressions of toxicity (herbivore mortality and final weight) on three predictor variables (chemical presence/absence in the normal host, specialism, and chemical floristic distribution) and relevant interactions were used to test these predictions. Chemical presence/absence in the normal host, the interaction between this variable and specialism, and chemical floristic distribution had significant effects on both measures of toxicity, supporting the first three predictions of the model. Support for the fourth prediction (a three-way interaction among all predictor variables) was evident for final weight but not mortality, perhaps because growth is more responsive to toxicity differences than survival. In short, the phytochemistry literature provides broad support for the phytochemical coevolution model.

https://www.jstor.org/stable/10.1086/368346

Herbivore responses to plant secondary compounds: a test of phytochemical coevolution theory.

Chitosan, the N-deacetylated derivative of chitin, is a potential biopolysaccharide owing to its specific structure and properties In this paper, we report on the synthesis of 24 new chitosan derivatives, N-alkyl chitosans (NAC) and N-benzyl chitosans (NBC), that are soluble in dilute aqueous acetic acid The different derivatives were synthesized by reductive amination and analyzed by 1H NMR spectroscopy A high degree of substitution (DS) was obtained with N-(butyl)chitosan (DS 036) at a 1:1 mole ratio for NAC derivatives and N-(2,4-dichlorobenzyl)chitosan (DS 052) for NBC derivatives Their insecticidal and fungicidal activities were tested against larvae of the cotton leafworm Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae), the grey mould Botrytis cinerea Pers (Leotiales: Sclerotiniaceae) and the rice leaf blast Pyricularia grisea Cavara (Teleomorph: Magnaporthe grisea (Hebert) Barr) The oral feeding bioassay indicated that all the derivatives had significant insecticidal activity at 5 g kg(-1) in artificial diet The most active was N-(2-chloro-6-fluorobenzyl)chitosan, which caused 100% mortality at 0625 g kg(-1), with an estimated LC50 of 032 g kg(-1) Treated larvae ceased feeding after 2-3 days; the mechanism of action remains unknown In a radial hyphal growth bioassay with both plant pathogens, all derivatives showed a higher fungicidal action than chitosan N-Dodecylchitosan, N-(p-isopropylbenzyl)chitosan and N-(2,6-dichlorobenzyl)chitosan were the most active against B cinerea, with EC50 values of 057, 057 and 052 g litre(-1), respectively Against P grisea, N-(m-nitrobenzyl)chitosan was the most active, with 77% inhibition at 5 g litre(-1) The effect of different substitutions is discussed in relation to insecticidal and fungicidal activity

Rajesh P. Srivastava

Papers

Toxicity and antifeedant activity of a sesquiterpene lactone from Encelia against Spodoptera littoralis

Contact toxicity and feeding inhibitory activity of chromenes from Asteraceae against Spodoptera littoralis (Lepidoptera : Noctuidae)