396 Calculations show that even for large insects such as dragonflies the maximum distance for depth perception using binocular vision is about 20 cm. Thus, fast-moving insects employ other methods for estimating longer distances, notably motion parallax and peering (Jarvilehto, 1985; Kral and Poteser, 1997). When an insect peers (Section 7.1.1), both the distance and the angle between an object and each compound eye will change. The object will move faster and by a greater angle over the nearer eye than over the farther eye. These differences are analyzed within the central nervous system to obtain a measure of the object's distance. The same technique also allows an insect to differentiate between the object and the background.

7.1.3. Spectral Sensitivity and Color Vision

Light-sensitive cells do not respond equally to all wavelengths of light; rather, they are particularly sensitive to certain parts of the spectrum. This differential sensitivity may be related to the presence in the cells of either a single visual pigment that has peak absorption at two or more wavelengths, or two or more visual pigments, each with a characteristic peak of absorption. Though the range of the spectrum to which insects are sensitive is about the same as in humans, it is shifted toward the shorter wavelengths. Many species, representative of most orders, have been shown to be very sensitive to ultraviolet light (300-400 nm) (UV) and some very significant phototaxes (behavioral responses to light) are initiated by it. For example, ants are negatively phototactic to UV and when given a choice will always congregate in a region not illuminated by UV. Many other insects are attracted by UV. Worker bees are attracted to yellow and red flowers by the pattern of UV that the latter reflect. In many species of butterflies the members of one sex have a characteristic pattern of UV-reflecting scales on the wings, invisible to would-be vertebrate predators, which facilitates intraspecific recognition and mating.

In addition to UV, the compound eye is sensitive to other wavelengths of light, though the peaks of sensitivity differ among species and even among regions of the same eye. The fly Calliphora, for example, shows maximum sensitivity at 470 nm (blue), 490 nm (blue-green), and 520 nm (yellow). The honey bee drone has peaks at 447 and 530 nm. All butterfly eyes have at least three distinct rhodopsins, sensitive to UV (360 nm), blue (470 nm), and green (530 nm) (White, 1985; Briscoe etal., 2003). Though most insects see poorly at long wavelengths, behavioral and electrophysiological studies indicate that the eyes of some papilionid butterflies are red-sensitive (585-610 nm), in addition to having receptors sensitive to UV, blue, and green.

Although, as noted above, an insect's eye may show peaks of sensitivity to different wavelengths of light, this in itself does not constitute color vision. The latter requires that the insect has the ability to discriminate between wavelengths to which it is sensitive. Field observations and behavioral experiments have demonstrated that representatives of many orders are able to distinguish between colors. Clearly, the ability to discriminate requires at least two types of receptors (retinular cells), each of which responds to light of a particular wavelength. Further, it seems that in the insect eye, as in the human eye, the varied response of the color receptors is achieved through the possession of different visual pigments. In the rhabdom of the worker bee, each rhabdomere appears to be especially sensitive to either UV, blue, or green (Figure l2.l5A). Furthermore, the bee appears to have a trichromatic color vision system similar to that ofhumans; that is, it can be described by a color triangle (Figure l2.l5B) whose corners represent the three primary colors with points along each side being the relative stimulation of each primary color. Like vertebrates, most insects lose their ability ultraviolet (360nm)

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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