Insecticidal activity against silkworms

The acetone extract of okara fermented with Penicillium expansum Link MK-57 was found to exhibit the insecticidal activity against silkworms. The acetone extract of okara fermented with this strain was purified by solvent extractions, column chromatography, HPLC, and crystallization to yield five active compounds—i.e., two known compounds, communesins A (70) and B (71), and three new ones, communesins D (72), E (73), and F (74) [48]. The structures of the known compounds, 70 and 71, were assigned by comparing their physicochemical properties and spectral data with those reported in the literature [49]. 

The hint, which led us to this finding, was the accidental observation of paralytic syndrome in silkworms that had digested an extract of a certain isolate. We had been screening numerous soil isolates for their insecticidal activity against silkworms upon oral administration in the usual manner. It was of great interest that the strain Aspergillus japonicus Saito JV-23 resulted in paralysis in silkworms. 

In the 1980s, our group began to screen microbes for insecticidal compounds that could be used in practice, or become lead compounds for the generation of new carbon skeletons. As a result, various strains were found to exhibit insecticidal, convulsive and paralytic activities against silkworms. This chapter deals with the procedures used for isolation of bioactive strains and their active principles. An overview of their chemical structures, activities, synthesis, and structurally related compounds is also given. 

Table 1. Insecticidal Activity of Okaramines against Silkworms.

In their review of lignans MacRae and Towers [9] cited the activity of kobusin and sesamin against silkworm larvae, sesamin and sesamolin against juvenile hormone activity in the milkweed bug, and podophyllotoxins against insect larval growth. On the other hand, sesamin, asarinin, savinin and hinokinin enhanced the toxicity of a wide variety of insecticides. 

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