Studies on antifungal effect of mite alarm pheromone citral : 2. Antifungal effect of the hexane extracts of the grain mites and some analogues of citral

Abstract

The antifungal effect of the following 3 groups of volatile materials on Aspergillus fumigatus (Asp. fumi.) were investigated by "the modified gas method" (Okamoto et al., 1978) : (1) hexane extract of the 5 species of the grain mites : Carpoglyphus lactis (C. lactis), Lardoglyphus konoi (L. konoi), Aleuroglyphus ovatus (A. ovatus), Tyrophagus putrescentiae (T. putrescentiae) and Dermatophagoides farinae (D. farinae), (2) four analogues of citral : geraniol, nerol, neryl formate and citronellal, (3) some volatile alkanes and alkens identified from T. putrescentiae by gas liquid chromatography (G.L.C.) (Kuwahara et al., 1976) : tridecane, tetradecane, pentadecane, tridecene, tetradecene and pentadecene. As the result, it was revealed that the hexane extracts of 4 species of the grain mites (20g) and T. putrescentiae (40g) inhibited the growth of Asp. fumi. Comparing the citral equivalence based on the relation between the dose of citral and the growth inhibition of fungi with the quantity of citral in each extract of the mites measured by G.L.C. (Table 1), it was supposed that the antifungal effects of hexane extracts of C. lactis and L. konoi were almost due to citral but those of D. farinae and A. ovatus might also be affected by other volatile substances. All analogues of citral were less effective than citral. The order of the inhibitory activity of them was citral > geraniol ≑ nerol > citronellal > neryl formate (Fig. 2). Six kinds of alkanes and alkens gave no inhibitory effect on Asp. fumi. Following the sieving method of Kobayashi et al. (1979), colonies of C. lactis and L. konoi isolated from the culture medium were separated into three developmental stages, adult, nymph, and larva. The quantity of citral in each stage of mites was evaluated with G.L.C., and it was shown that as the mites grow the quantity of citral per weight of mites increased (Table 2).