A description of the external morphogenesis of male and female embryos of X. ferrugineus, derived from in vivo observation, is presented here. The embryogenesis of this beetle is typical of the Coleoptera, and is also similar in most respects to the generalized insect plan. Observed unusual aspects of X. ferrugineus embryogenesis include the precocious formation of primordial g/rm cells and their temporary exclusion from somatic blastoderm; the precocious in situ delineation of gnathal metameres, the closing of the gastral groove beginning at both ends and proceeding towards its middle, the formation of several paired lateral amnio-serosal folds, the formation of cellular processes between the amnion and serosa, and the absorption of the thoracic limbs to produce an apodous larva. The embryonic developmental picture provided here, and the previously established means of rearing X. ferrugineus in controlled laboratory culture jointly provide a promising basis for the further use of this insect in developmental studies.
The developmental rates of male and female embryos of Xyleborus ferrugineus were compared by charting for each sex the mean age for each of ten discrete morphological stages of embryogenesis from pole cell exclusion to eclosion male and female embryos developed synchronously from stage 1 (which begins with pole cell exclusion) through stage 4 (which ends with the completion of germ band extension and metamerization). After stage 4 and throughout the remainder of embryogenesis, the mean ages per morphological stage of male embryos were significantly greater than those for female embryos. The expected physiological consequences of a haploid genome in the male embryo as compared to a diploid condition in the female embryo are discussed as the possible basis for the persistent lag observed in male developmental rate after stage 4.
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