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Effectiveness of Bacillus thuringiensis exotoxin on Tetranychus telarius (Acarina: Tetranychidae)
478
NOTES
Effectiveness
of Bacillus thuringiensis Exotoxin telarius ( Acarina: Tetranychidae
It is well known that the effectiveness of the thermostable exotoxin produced by “active strains” of different varieties of Bacillus thuringiensis is not limited to demonstration in Lepidoptera. Thus, the range of susceptible hosts is larger than that of the thermo-instable endotoxin of “crystalliferous strains.” It was shown by several workers that, after peroral administration, exotoxin can be effective against different species of Lepidoptera, Diptera, Hymenoptera, Coleoptera, Isoptera, and Orthoptera. Susceptibility of arthropods other than insects against exotoxin, however, has not been reported so far. The effectiveness of sediments and supernatants of submerged cultures of two different crystalliferous strains of B. thuringiensis has been tested on the carmine spider mite (two-spotted spider mite), Tetranychus telarius ( = Tetranychus urticae). One strain (No. 11) belongs to serotype HI (var. thuringiensis); it produces crystals toxic for such lepidopterous larvae as those of Plutella maculipennis and, in addition, exotoxin which is toxic for such dipterous larvae as those of Drosophila melunogaster. The other strain (No. 26) belongs to serotype Hz (var. finitimus) ; it produces crystals nontoxic for insects and no exotoxin. After sporulation, the culture media of submerged cultures were centrifuged (at 5000 rpm). Supematants were autoclaved and sediments were resuspended in saline to the original volume. For experiments, about 15 ml of such a preparation were sprayed on both surfaces of the leaves of a young bean plant (Phasaeohs vulgaris). About 250 individuals of active instars were placed on each of the treated plants. Then the test plants were held at room temperature (15”
on Tetranychus )
to W’C) and mean relative humidity (50% to 80%). Application of sediments containing spores and crystals of both strains had no effect on the mites. After 35 days the treated mite population had increased similarly to that of the untreated control. Up to 100 individuals of active instars and more than 100 eggs per cm2 of leaves were present. Also no mortality of the mites occurred on plants treated with supematant of the var. finitimus strain (which does not contain exotoxin). In contrast, the supematant of the exotoxin-positive var. thuringiensis strain induced 100% mortality after 35 days. After this period, all new leaves produced by the test plants were heavily infested by the mites in the untreated control and in all experiments with the exception of such plants which were treated with supematant containing exotoxin. These preliminary results showing the effectiveness of exotoxin, but not of spores and crystals, of B. thuringiensis to Tetranychus telarius may explain some observations on the toxicity of some commercial preparations of B. thuringiensis on populations of other mites in the field. In addition, these results may encourage further study on the effectiveness of B. thuringiensis exotoxin on arthropods other than insects. ALOYSIUS
Biologische Bundesanstalt Forstwirtschaft Institut fiir biologische Schiidlingsbekiimpfung Darmstadt, Germany Received July 23,1968
fiir Land-
KRIEG
und
NOTES
Effectiveness
of Bacillus thuringiensis Exotoxin telarius ( Acarina: Tetranychidae
It is well known that the effectiveness of the thermostable exotoxin produced by “active strains” of different varieties of Bacillus thuringiensis is not limited to demonstration in Lepidoptera. Thus, the range of susceptible hosts is larger than that of the thermo-instable endotoxin of “crystalliferous strains.” It was shown by several workers that, after peroral administration, exotoxin can be effective against different species of Lepidoptera, Diptera, Hymenoptera, Coleoptera, Isoptera, and Orthoptera. Susceptibility of arthropods other than insects against exotoxin, however, has not been reported so far. The effectiveness of sediments and supernatants of submerged cultures of two different crystalliferous strains of B. thuringiensis has been tested on the carmine spider mite (two-spotted spider mite), Tetranychus telarius ( = Tetranychus urticae). One strain (No. 11) belongs to serotype HI (var. thuringiensis); it produces crystals toxic for such lepidopterous larvae as those of Plutella maculipennis and, in addition, exotoxin which is toxic for such dipterous larvae as those of Drosophila melunogaster. The other strain (No. 26) belongs to serotype Hz (var. finitimus) ; it produces crystals nontoxic for insects and no exotoxin. After sporulation, the culture media of submerged cultures were centrifuged (at 5000 rpm). Supematants were autoclaved and sediments were resuspended in saline to the original volume. For experiments, about 15 ml of such a preparation were sprayed on both surfaces of the leaves of a young bean plant (Phasaeohs vulgaris). About 250 individuals of active instars were placed on each of the treated plants. Then the test plants were held at room temperature (15”
on Tetranychus )
to W’C) and mean relative humidity (50% to 80%). Application of sediments containing spores and crystals of both strains had no effect on the mites. After 35 days the treated mite population had increased similarly to that of the untreated control. Up to 100 individuals of active instars and more than 100 eggs per cm2 of leaves were present. Also no mortality of the mites occurred on plants treated with supematant of the var. finitimus strain (which does not contain exotoxin). In contrast, the supematant of the exotoxin-positive var. thuringiensis strain induced 100% mortality after 35 days. After this period, all new leaves produced by the test plants were heavily infested by the mites in the untreated control and in all experiments with the exception of such plants which were treated with supematant containing exotoxin. These preliminary results showing the effectiveness of exotoxin, but not of spores and crystals, of B. thuringiensis to Tetranychus telarius may explain some observations on the toxicity of some commercial preparations of B. thuringiensis on populations of other mites in the field. In addition, these results may encourage further study on the effectiveness of B. thuringiensis exotoxin on arthropods other than insects. ALOYSIUS
Biologische Bundesanstalt Forstwirtschaft Institut fiir biologische Schiidlingsbekiimpfung Darmstadt, Germany Received July 23,1968
fiir Land-
KRIEG
und