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The aim of this investigation was to survey the occurrence, biodiversity, and toxicity of Bacillus thuringiensis strains originating from dead caterpillars of the forest pest, Lymantria dispar (Lepidoptera). Morphological, biochemical, and microscopic identification of isolates from the insects showed the presence of five different Bacillus species, including 2% of B. thuringiensis. Based on the biochemical profiles, the B. thuringiensis were determined to be B. thuringiensis finitimus-like and B. thuringiensis alesti-like bacilli. Both produced spherical inclusions composed of three or five protoxins. The molecular weights of these proteins varied from 20 to ca. 64 kDa. Mixtures of spores/inclusions of the B. thuringiensis were tested for their toxicity against larvae of Drosophila melanogaster. The mortality levels of the larvae caused by these spores and crystalline inclusions varied from 5 to 15%. The lethal doses (LD₅₀) of these isolates against D. melanogaster were 8.8 x 10¹² spores/ml for B. thuringiensisfinitimus and 1.3 x 10¹⁸ spores/ml for B. thuringiensis alesti.
Future climatic warming may modifyinsect development, sex ratio, quantitative changes in populations that could affect the frequency of outbreaks. Here we analyzed the influence of temperature on larval growth and development in the gypsy moth (Lymantria dispar L.). The larvae were reared at three constant temperatures: 15, 20 or 25°C, and fed with leaves of the English oak (Quercus robur L.). Larval mortality, duration of development (DD), relative growth rate (RGR), total mass of food eaten (TFE), and pupal mass (PM) were estimated. Larval mortality was lowest at 20°C, higher at 25°C, and highest at 15°C. DD significantly decreased with increasing temperature and depended on sex. The influence of temperature on the shortening of DD was stronger in males than in females. RGR significantly depended on temperature and was the highest at 25°C, and lowest at 15°C. At 15°C, RGR did not change markedly with time. In contrast, RGR at 20°C was characterized bya continuous decreasing trend. At 25°C, RGR was very high for 2 weeks but quickly declined afterwards. Temperature did not affect the TFE. PM was significantly correlated with temperature and sex. PM of females was higher at 20°C than at 15 and 25°C, in contrast to that of males, which was similar at 20 and 25°C, and higher than at 15°C. For larval growth and development, the most favourable was the medium temperature (20°C). The least favourable temperature for females was 25°C, for males 15°C. The results suggest that global warming may modifythe future sex ratio of gypsy moths that may affect insect development and outbreaks.
This study assessed the effects of temperature on survival rate and duration of development (DD), i.e., time needed by larvae to reach the pupal stage, in nun moth (Lymantria monacha L.) and gypsy moth (L. dispar L.). The larvae were raised at 15, 20 or 25°C, and fed with current-year-needles of Scots pine (Pinus sylvestris L.) and leaves of English oak (Quercus robur L.), respectively. With increasing temperature 15, 20 and 25°C, larval survival rate (LSR) declined in L. monacha (for 35th day LSR was 0.44, 0.31 and 0.21, respectively), but increased in L. dispar (0.50, 1.00 and 0.94). In contrast, the duration of development decreased with increasing temperature in larvae of both moth species (67, 52 and 39 days for L. monacha, and 66, 43 and 33 days for L. dispar, respectively). The differences in larval survival rate between those species at higher temperatures can affect significantly their growth and development in warmer years. Therefore, it is possible that under global climate change these differences may lead to changes in distribution of both insect species.
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