Color production

The diverse colors of insects are produced by the interaction of light with cuticle and/or underlying cells or fluid by two different mechanisms. Physical (structural) colors result from light scattering, interference, and diffraction, whereas pigmentary colors are due to the absorption of visible light by a range of chemicals. Often both mechanisms occur together to produce a color different from either alone.

All physical colors derive from the cuticle and its protuberances. Interference colors, such as iridescence and ultraviolet, are produced by refraction from varyingly spaced, close reflective layers produced by microfibrillar orientation within the exocuticle, or, in

Fig. 2.5 (opposite) The cuticular pores and ducts on the venter of an adult female of the citrus mealybug, Planococcus citri (Hemiptera: Pseudococcidae). Enlargements depict the ultrastructure of the wax glands and the various wax secretions (arrowed) associated with three types of cuticular structure: (a) a trilocular pore; (b) a tubular duct; and (c) a multilocular pore. Curled filaments of wax from the trilocular pores form a protective body-covering and prevent contamination with their own sugary excreta, or honeydew; long, hollow, and shorter curled filaments from the tubular ducts and multilocular pores, respectively, form the ovisac. (After Foldi 1983; Cox 1987.)

some beetles, the epicuticle, and by diffraction from regularly textured surfaces such as on many scales. Colors produced by light scattering depend on the size of surface irregularities relative to the wavelength of light. Thus, whites are produced by structures larger than the wavelength of light, such that all light is reflected, whereas blues are produced by irregularities that reflect only short wavelengths. The black color on the wings of some butterflies, such as Papilio ulysses (Lepidoptera: Papilionidae), is produced by the absorption of most light by a combination of light-absorbing pigments and specially structured wing scales that prevent light being scattered or reflected.

Insect pigments are produced in three ways:

1 by the insect's own metabolism;

2 by sequestering from a plant source;

3 rarely, by microbial endosymbionts.

Pigments may be located in the cuticle, epidermis, hemolymph, or fat body. Cuticular darkening is the most ubiquitous insect color. This may be due to either sclerotization (unrelated to pigmentation) or the exocuticular deposition of melanins, a heterogeneous group of polymers that may give a black, brown, yellow, or red color. Carotenoids, ommochromes, papiliochromes, and pteridines (pterins) mostly produce yellows to reds, flavonoids give yellow, and tetra-pyrroles (including breakdown products of porphyrins such as chlorophyll and hemoglobin) create reds, blues, and greens. Quinone pigments occur in scale insects as red and yellow anthraquinones (e.g. carmine from cochineal insects), and in aphids as yellow to red to dark blue-green aphins.

Colors have an array of functions in addition to the obvious roles of color patterns in sexual and defensive display. For example, the ommochromes are the main visual pigments of insect eyes, whereas black melanin, an effective screen for possibly harmful light rays, can convert light energy into heat, and may act as a sink for free radicals that could otherwise damage cells. The red hemoglobins which are widespread respiratory pigments in vertebrates occur in a few insects, notably in some midge larvae and a few aquatic bugs, in which they have a similar respiratory function.

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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