The Ash Content of Insects

Abstract

In the case of silica, there appears to be a definite variation of SiO2 content with different species. The difference between yellow locusts (6·27 per cent.) and red locusts (14·7 per cent.) is especially marked. It may be attributed to the fact that red locusts are actively feeding, sexually immature adults, and in consequence they consume large amounts of food with a high silica content. The fact that museum specimens of yellow locusts contain a higher percentage of silica than intact yellow specimens indicates that the majority of the silica is not concentrated in the digestive tract. The same appears to apply to the iron content. Copper was found in appreciable quantities in all the insects examined, but no definite conclusion can be drawn from the numerical results, as the variation from batch to batch was too great. The results for manganese are not satisfactory, as in several cases negative evidence was obtained. This is inconsistent with the work of Vinogradov, who obtained conclusive evidence of manganese in insects. In the case of Agonoscelis, however, the manganese content was found to be extraordinarily high (0·47 per cent.), suggesting that it may play a definite physiological part. The presence of a respiratory pigment, pinnaglobin, containing manganese, has been shown in the tropical mussel, but there is as yet no evidence for the presence of this pigment in the insect world.It is impossible, however, to draw any such conclusions from ash analysis results of entire insects only, and systematic analyses of the blood of numerous species will be necessary to establish the presence of the metals iron, copper and manganese, in their respiratory pigments.Definite evidence of nickel (in almost negligible amounts) was shown by the large-scale analysis, but apart from this no element was detected which had not been previously reported.