STUDIES ON THE ANTIMICROBIAL FUNCTION OF INSECT LIPIDS : VI. DIFFERENCE IN SUSCEPTIBILITY OF FIELD INSECTS TO FUNGAL DISEASES

Abstract

1. The percentage of infection in the artificial inoculation and the antifungal actions of lipids, especially of volatile ones which are assumed to be a mixture of free short-chain saturated fatty acids obtained from the entire bodies were compared with each other to two species of pathogenic fungi, Isaria farinosa(DICKS)and Spicaria pracina(MAUBL.)between two groups of insects, i.e., between larvae of Chilo simplex BUTLER(Lepidoptera), imagines of Coccinella bruckii MULSANT(Coleoptera), larvae of Dendrolimus spectabilis BUTLER (Lepidoptera) and imagines of Agonum magnus BATES (Coleoptera) all of which are proved in nature to be highly susceptible to the infection of Isaria farinosa but resistant to Spicaria pracina and larvae of Barathra brassicae L.(Lepidoptera), larvae of Hemerophila atrilineata BUTLER (Lepidoptera) and Locusta danica L. (Orthoptera) which possess equally a marked degree of natural resistance to the infection of Isaria but succumb readily to the disease by Spicaria. 2. Artificial inoculation experiments show that the percentages of infection to Spicaria pracina are exceedingly low but high to Isaria farinosa in all anti-Spicaria insects which were proved so in the field in constrast to the results of anti-Isaria insects in which the percentages are high to Spicaria but low to Isaria except in the case of Locusta danica which is more resistant to Spicaria than to Isaria differing from the results of field observation. 3. The antifungal actions of lipids, especially of volatile ones obtained from the entire bodies of the anti-Spicaria insects are more powerful to the development of Spicaria pracina than to that of Isaria farinosa, while the substances from the anti-Isaria species act more vigorously to Isaria than to Spicaria except in the case of Locusta which shows the same relation with the anti-Spicaria insects. 4. The phenomenon of the species-specificity between the pathogenic fungi and the host insects in the field may be explained in part by the antifungal activities of body lipids of the related insects. 5. The fact that the results of the artificial inoculation and the antifungal actions of insect lipids are in good agreement with those observed in nature will conversely tell the fact that some species of insects may be susceptible to a particular infecting fungus, but not even to those of a closely related genus.