[The developmental capacities of partially UV-irradiated eggs of the bean WeevilBruchidius obtectus SAY (Coleoptera)]

1. Eggs of the bean weevilBruchidius obtectus were irradiated regionally with UV-light of 270-330 nm wave length. The irradiated area extends transversally across the egg and covers 10 or 20% of the egg's length. Irradiation was done either from a single side ("QB") or from 4 sides each after a 90°-rotation of the egg ("RB"): the latter treatment affects the egg more strongly. The 3 different irradiation periods used, one, two or three minutes, produced similar results. Of the incident irradiation energy, 75-85% is absorbed by the egg's envelope. 2. UV-irradiation before preblastoderm formation does not visibly injure any egg component. Normal embryos develop as a rule even after UV-irradiation of the whole ventral face of the egg. There is, however, a considerable retardation of development which indicates primary or secondary influences of the irradiation procedure on developmental reactions of the ooplasmic system. 3. Irradiation after preblastoderm formation is followed by visible damage early in development. The effects, accumulation of ectoplasm and pycnosis of nuclei, decrease from the center towards the margins of the irradiated area; the underlying yolk-entoplasm appears unaffected. Early damage produced by irradiation of preblastoderm eggs leads to defects in the germ band only if the irradiated area includes at least partially a "critical region for definable segment defects" ("KBS") between 35 and 65% of the egg's length. Damage in front of or behind this critical region can be regulated. 4. Early damage observed after irradiation of blastoderm, however, is always, and irrespective of its location, followed by formation of a disturbed metameric pattern. It is concluded that between preblastoderm and blastoderm stages the functional condition of the superficial egg materials must have changed towards the egg poles so that the capacity to regulate is lost. 5. Late defects may become manifest in any region of the embryonic body. They may in accordance with the longitudinal extent of the irradiated area involve one or several body segments. QB-irradiation affects one lateral half of each segment involved, RB-irradiation eliminates both halves. Irradiation of a whole lateral Vorkeimanlage is followed by formation of a half-embryo from the remaining lateral Vorkeimanlage. 6. Segmental defects produced by irradiation of preblastoderm or blastoderm stages correlate with the same positions of irradiated area for any particular segment. To affect the same segment by irradiation of the Vorkeimanlage, a more posterior area of irradiation is required. 7. The "critical zone for bipartite development" ("KBB") revealed by earlier ligation experiments of blastoderm eggs is congruent in position and extent with the "critical region for definable segment defects" from UV-irradiation (see 3). In contrast to ligation experiments, the loss of germ band segments after early irradiation is not more extensive than after late irradiation. From this and from the formation of complete segment patterns by UV irradiated eggs it is concluded that the bipolar reaction system revealed by ligation experiments cannot be confined to the superficial egg regions affected by UV. 8. It is pointed out that in order to be able to compare different insect egg types these have to be studied by identical methods.