Possible dual roles of an allelopathic compound, cis-dehydromatricaria ester
The aqueous extract of the root ofSolidago altissima was lethal to nematodes. The major compound isolated from the toxic fraction wascis-dehydromatricaria ester (methyl 2-decene-4,6,8-triynoate), which is already known as an allelopathic compound of a composite showing growth-inhibition to a rice seedling. This compound showed high toxicity to plant-parasite nematodes. A composite exudes one defending substance against both competitive plants and plant-parasite nematodes.
IDENTIFICATION OF ASPARAGUSIC ACID AS A NEMATICIDE OCCURRING NATURALLY IN THE ROOTS OF ASPARAGUS
A nematicidal constituent, present at least at 35 ppm, was isolated from the roots of asparagus and identified as asparagusic acid, which has also been reported to exist in the edible part of the plant. The acid was toxic to several plant parasitic nematodes and would be a major factor in resistance of asparagus.
HOST PLANT SELECTION IN THE COLORADO BEETLE LARVA
In the food finding behaviour of the Colorado beetle larva, random searching and random biting are two apparently spontaneous behaviour elements belonging to different motor systems. Locomotion is directed by light and by host odour, biting is slightly inhibited by indifferent substrates like glass and filter paper. Initiation and maintenance of feeding are partly dependent upon different stimuli, as shown by the behaviour of the larva on Solanum demissum Lindl. Substances inhibiting the ingestion of food do not necessarily interfere with locomotory responses causing the insect to remain on the plant, nor do they prevent the feeding action from being released. This may lead to the cyclic process represented in fig. 6. The factors regulating intensity of motivation and threshold releasing stimulus are discussed.