Erichsonii

A number of diterpenes are known to be active against herbivores ( ). The diterpenes abietic, dehydroabietic, 12-methoxy-abietic, sandaracopimaric, and isopimaric acid serve as feeding deterrents for the larch sawfly, Pristiphora erichsonii in single needles from new shoots of tamarack (Larix laricina) (133). The larvae of this insect do eat tufted needles on short shoots of the same trees. 

Ohigashi, H., M. R. Wagner, F. Matsumura, and D. M. Benjamin, Chemical basis of differential feeding behavior of the larch sawfly, Pristiphora erichsonii (Hartig), J. Chem. Ecol., 7, 599-614 (1981). 

The most destructive insect pest of tamarack is the larch sawfly (Pristiphora erichsonii). Periodic epidemics of this defoliator occur across Canada and the northern United States. Another serious defoliator of tamarack is the larch casebearer Coleophora laricella). Severe outbreaks have caused extensive mortality of trees of all ages (Johnston, 1990). 

Spectral and X-ray crystallographic analysis has established the structure of the major alkaloid (0.11%) of S. erichsonii stem bark from French Guiana, erichsonine, as (13). It is a vobasine-type base, evidently related to 16- pi-affinine, and is of a type that has not previously been found in Strychnos species (338). 

Information about the pharmacology (and/or the chemistry) of most of the remaining species employed is inadequate. In the case of S. erichsonii, one of the more frequently exploited species, the activity appears to be due primarily to diaboline and its derivatives erichsonine (13) (Section 1.4.5.2), the only other alkaloid isolated from it, is without pharmacological effects. S.jobertiana, a species reported to have only weak activity, may similarly rely on diaboline and related compounds (Section 1.5.3). 

In some species, pharmacological effects other than muscle-relaxation may dominate. Thus, as already seen, the activity of S. erichsonii extracts appears to be due primarily to the presence of diaboline derivatives. Leaf extracts have analgesic properties, while stem-bark extracts have spasmolytic properties and augment the activity of the central nervous system (50). The bark alkaloids of S. glabra are reported to have central rather than peripheral effects (Table 1.4, footnote j). Sublethal doses of aqueous extracts from S. castelnaeana cause hypertension, tachycardia, and slight respiratory stimulation enhancement of the hypertension by atropine and its reduction by hexamethonium (mecamylamine) show that the extract has nicotinic activity. Evidently, the toxicity of the plant must be partly due to the tertiary bases it contains (314). 

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