676 ability to recognize and respond to slight differences in relative humidity enables an insect to move into a region of preferred humidity. Not only does this have immediate survival value, but because other individuals of the species will tend to respond similarly it may also increase the chances for perpetuation of the species. Some insects seek out sites with a preferred humidity, in which to enter diapause. Though this behavior is of no immediate value to the insect, it increases the chances of survival of the dormant stage. Similarly, female grasshoppers about to oviposit dig "test holes" with their ovipositor to determine the moisture content (and probably other physical and chemical features) of the soil. Eggs are normally laid in moist soil, and a female may retain the eggs in the oviducts for some time if she does not immediately find a suitable site. Again, this behavior has no immediate value to the female but certainly increases the eggs' chances of survival.

Thus far, the discussion has emphasized the harmful effects of too little water and the mechanisms by which terrestrial insects avoid this problem. On occasions, however, too much moisture may be equally detrimental to insects' survival. The effects of excessive moisture may be direct (namely, causing drowning) but more often are indirect. For example, insects that normally develop cold-hardiness partially as a result of dehydration may be less cold-hardy and therefore less capable of surviving low temperatures of winter if this has been preceded by a wet fall. Wet conditions may also affect a species' food supply. However, the most important way in which excessive moisture affects insect populations is by stimulating the development and spread of pathogenic microorganisms (bacteria, protozoa, fungi, and viruses). For example, in the summer of 1963 in Saskatchewan (Canada) the weather was abnormally humid, with above-average rainfall in some areas of the province. These conditions appeared ideal for the fungus Entomophthora grylli, which underwent a widespread epizootic, causing high mortality in populations of several species of grasshoppers, especially Camnula pellucida, the clear-winged grasshopper, and to a lesser extent Melanoplus bivittatus (two-striped grasshopper) and M. packardii (Packard's grasshopper). Such was the effect of the fungus on C. pellucida that by the fall of 1963 its proportion in the grasshopper species complex had fallen to 7% compared with 64% the previous year (Pickford and Riegert, 1964).

Finally, the beneficial effects of snow on the survival of insects must be noted. Snow is an excellent insulator and in extremely cold climates serves to reduce considerably the rate of heat loss from the substrate. Thus, the substrate remains considerably warmer than the air above the snow. For example, with an air temperature of -30°C and a snow depth of 10 cm, the temperature of soil about 3 cm below its surface is about -9°C. In the absence of snow the soil temperature at this depth is only a degree or two higher than that of the air. This means that species with only limited cold-hardiness may be able to survive the winter in cold climates provided that there is ample snow cover. In other words, because of snow a species may be able to extend its geographical range into areas with low winter temperatures. In Saskatchewan, for example, the damselflies Lestes disjunctus and L. unguiculatus overwinter as eggs (in diapause) laid in emergent stems of Scirpus. The eggs can tolerate exposure to temperatures as low as -20°C and remain viable. Below this temperature mortality increases significantly (Sawchyn and Gillott, 1974b). At Saskatoon, where this study was carried out, the mean temperature for January is, however, about-22° C, though the temperature frequently falls well below this value (the record low being about -48°C!). Field collection of eggs throughout the winter showed that, whereas the viability of eggs from beneath the snow remained near 100%, no eggs collected from exposed stems survived. Thus, the insulating effect of snow is essential to the survival of these species in this region of Canada. In addition, the snow cover may also prevent desiccation.

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

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