Fieldwork was
performed at the experimental field of the Institut of Forage Crops, Pleven,
Bulgaria during the period 2006-2009. To measure the abundance and sex ratio of
Empoasca pteridis moving in alfalfa stand, net sweeping was carried out weekly
during the growing season. Samples were taken along the diagonals of a crop
from the plant growth to the harvest of each regrowth in the flowering stage.
It was found that the population growth of leafhoppers in alfalfa reached a
peak just before harvest, and the peaks increased from the first to the third
harvest. The sex ratios of E. pteridis successively decreased from the first to
the fourth growth cycle. In addition, the first, second and third growth cycles
were initially strongly female-biased, and the sex ratio decreased over time
successively and occupied the lowest value immediately before cutting. In the
fourth growth cycle, the sex proportion was equalized. Significant impact on
female density had the temperature factor and the predominance of females was a
consequence of the higher temperature and negligible amount of rainfall. It was
found also that the sex ratio of E. pteridis in the third growth cycle was
characterized by a high homeostaticity and stress resistance and is the most
stable in relation to the changing environment.
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