Plant-Insect Coevolution The Role of Alkaloids

The causes for replacement of the paleophytic flora of the Pennsylvanian (Carboniferous) by the mesophytic flora of the Permian period are reasonably self-evident, because the cryptogam plants are inferior in reproductive capacity to the Gymnospermeae. The second replacement, which occurred in the Jurassic and Cretaceous periods, is less easily understood. Indeed, the Gymnospermeae have persisted up to the present time and are, 

Leptinotarsa decemlineata, the common Colorado potato beetle, is encountered on a number of Solanaceae. But the development of the larvae can be observed only on some plants. All plants containing nicotine are 

The occurrence of specialized predators indicates the role of alkaloids as plant-protecting agents when the alkaloid becomes in the last resort useless agaist the plant predators, it even in some cases provides immunity for the alkaloid-rich insects from predation by birds and mammals. 

The process of coevolution of the plant and the predatory insect may be either simple or complicated. A rather simple case would be as follows A species of plant is broadly distributed, it has a spectrum of predators, and a balanced system exists. The number of herbivorous insects developed on 

The chemical arms race is continually leading to deadlocks, increasing only the chemical diversity of plants and simultaneously the devices the insects develop to enable them to live on food unusable by other species. The larvae of the blue butterfly, Plebeius icarioides, are restricted in feeding habits to various species of the plant genus Lupims (Downey and Dunn, 1964), which are rich in alkaloids. In all laboratory tests so far conducted the insect readily feeds on any species of lupine including paleoarctic and neotropical species with which extinct insect populations have never been associated. The larvae will not accept other types of plants and will succumb without lupines. 

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