Polyembryony, the development of more than one embryo from one egg, is known to be a normal occurrence in about 30 species of parasitic Hymenoptera (mostly Encyrtidae, Platygasteridae, and Braconidae) and one species of Strepsiptera (Ivanova-Kasas, 1972). In these insects it is always associated with either parasitism or viviparity and is presumed to have evolved in conjunction with the abundance of food offered by these two modes of life. Characteristically, the eggs of polyembryonic species are minute and devoid of yolk. Because they depend on an external (host or maternal) source of nutrients the chorion, which is initially thin and permeable, soon disappears. Further, in Hymenoptera, the serosa becomes modified for the uptake of nutrients and is known as a "trophamnion."

Both the number of embryos formed and the point in development at which they become discernible vary. In Platygaster hiemalis, a parasite of Hessian fly larvae, for example, at the four-cell stage, the cells may separate into two groups so that twin embryos are formed. In contrast, in the chalcidid Litomastix truncatellus, which parasitizes larvae of the moth genus Plusia, formation of embryos does not begin until the 220- to 225-blastomere stage. At this stage, certain of the blastomeres become spindle-shaped and fuse to form a syncytial sheath that divides the remaining blastomeres into groups, the primary embryonic masses. In due course, secondary, tertiary, etc., embryonic masses form so that the final number of potential embryos may exceed 1000. The early development of Litomastix is summarized in Figure 20.13. Eventually the polygerm (the total embryonic mass within the trophamnion) disintegrates, and each embryo develops into a larva. The larvae feed within a host until all the usable parts are consumed and then pupate. At this point the host is nothing more than a cuticular bag full of parasites (Figure 20.14).

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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