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.
One-year-old needles from 20 silver fir trees in the Tisovik Reserve (Belarus) were characterized in respect to 12 morphological and anatomical traits, and the data were analyzed statistically to determine variability between trees. Individuals within the population generally were homogenous for those traits. Needle length was the most variable trait within the studied population. The width/height ratio of the hypodermic cell exerted the weakest differentiating effect between trees. The results indicated that the Tisovik Reserve population is weakly differentiated.
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.
Effects of elevated temperature and soil pollution with fluorine on host-pathogen relations were studied in seedlings of the pedunculate oak (Quercus robur L.) inoculated with oak powdery mildew (Microsphaera alphitoides Griff. et Maubl.) and control seedlings. The plants were grown for 1month in elevated temperature (on average by 1.6°C) and soil pollution with sodium fluoride (330 ppm F). The above factors did not have any significant effect on nitrogen content of leaves or on concentrations of metabolites favourable to growth and development of the fungal pathogen (total non-structural carbohydrates, including soluble carbohydrates and starch) and those unfavourable to fungi (soluble phenols, condensed tannins and lignins). The elevated temperature and fluorine pollution did not affect the leaf infection rate. However, a significant temperature × pollution interaction was observed in inoculated seedlings. At the elevated temperature, fluorine caused a less severe infection by powdery mildew. This could be due to a direct toxic effect of fluorine on the pathogen or by an indirect influence, resulting from changes in levels of other metabolites, which were not analysed in this study. The inoculation of oak seedlings with powdery mildew caused a decline in the carbohydrate content of leaves but did not have any significant effect on levels of other analysed metabolites. However, it significantly affected the distribution of phenols and lignins in oak leaves. Those compounds accumulated within necrotic lesions and in adjacent cells. Our results do not enable drawing definite conclusions on effects of a slight rise in temperature and a relatively low level of fluorine pollution of the soil on relations between the pedunculate oak and oak powdery mildew. Lower values of the leaf infection rate in seedlings growing in elevated temperature and fluorine pollution suggest that in warmer years a lower level of infection by M. alphitoides may be expected in areas affected by fluorine pollution.