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Fertility and Climatic Adaptations in Siberian Grasshoppers
Published online by Cambridge University Press: 10 July 2009
Summary
1. The number of egg-tubes and the number of eggs in each tube varies in accordance with the food and the climatic and microclimatic conditions of each habitat. The majority of Siberian grasshoppers have adaptations in the ovaries which enable them to take full advantage of the available heat.
2. In the species possessing 10 or more egg-tubes, their number varies in different parts of the distribution area. It decreases towards the centre of the area with increasing warmth and dryness, and increases towards the colder and more humid margins of that area (e.g., in the Far East and in Western Europe).
3. The potential fertility is more or less stable in different species of grasshoppers, and in the species studied it fluctuates between 84 and 388 eggs per female.
4. There is no correlation between the potential fertility and the abundance of the species in nature, for the greatest fertility is met with in those species which occur but rarely. The injurious (i.e., very numerous) grasshoppers have a medium, or somewhat less than a medium, potential fertility.
5. The actual fertility is greatly dependent on the environment and has a wide range of fluctuation.
6. Lack of food in reservations was observed to lower the fertility of grasshoppers by 30–40 per cent. The parasites (Blaesoxipha spp., Mermis spp.) greatly reduce the degree of fertility of the Siberian grasshoppers. However, the percentage of infestation by these parasites is low, but in the reservations it is somewhat higher than outside. Thus, the actual fertility in reservations is rather lower than outside.
7. The outbreaks of the Siberian grasshoppers are determined by the climatic and microclimatic conditions. The fluctuations in fertility never have any real importance in causing the outbreaks. Lack of food, parasites, predators and diseases are of minor importance; among the latter the main factors are the diseases of the egg-pods, which again depend on the microclimate.
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