Observations of density effects on the German cockroaches, Blattella germanica (L.)

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  • KOMIYAMA Motoko
    Department of Environmental Biology, Japan Environmental Sanitation Center
  • OGATA Kazuki
    Department of Environmental Biology, Japan Environmental Sanitation Center

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  • チャバネゴキブリにおける密度効果実験
  • チャバネゴキブリ ニ オケル ミツド コウカ ジッケン

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Abstract

In order to know the most efficient density for rearing of German cockroaches Blattella germanica (L.) to obtain a number of favorable test insects as possible for insecticide test, dencity effect was examined. Cockroaches were reared in plastic containers (10×16×15.5cm), provided two boads (10×5cm) as a shelter, under laboratory conditions of 25±1℃, 50-60% R.H. and 15 hours illumination a day. 1,2,10,50,100,500 and 1,000 newly hatched nymphs were admitted to each container. The susceptibilities of the emerged adults to fenttrothion were examined by the topical application method. Results were as follows : Generally, the nymphal period was slightly prolonged and adult emergence decreased in accordance with increasing density. The body weight and the length of hide tibia showed the maximum values in the moderate density. The adult life span and the reproductivity were remarkably influenced by densityssize. The female adults, bred in 2 individuals during nymphal stage, survived for 226.0 days and produced 193.8 nymphs per female in average. On the other hand, the female bred in 1,000 individuals, was most inferior surviving only for 107.7 days and producing only 30.0 nymphs per female in average. Due to high density, individuals with damaged wings and antennae increased significantly. There was no significant difference on the susceptibility to fenitrothion among different densities. But insects which were reared under the high densities were slightly smaller in size, and slightly susceptible than others. The number of offsprings per rearing container was the biggest in the container contained 500 individuals, producing 15,737 offsprings. It seemed that taking account of insecticide susceptibility not depending on density, the most preferable rearing density for insecticide test, is 1-2 individuals per 1(cm)^2 of available space in container.

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