Invasive Species Compendium

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Abstract

Mode of reproduction and development of the reproductive system of Helicotylenchus dihystera.

Abstract

The adult female reproductive system in Helicotylenchus dihystera and H. digonicus comprises the following: ovary (8.7 to 21.2 oogonia and oocytes in anterior gonad, 7.6 to 18.3 in posterior gonad of H. dihystera), narrow constriction (4 cells), tubular oviduct (16 cells), constriction (8 cells), dorsally bulging nonfunctional spermatheca (12 cells), glandular tricolumella (12 cells) and uterus proper. The final number of cells making up the spermatheca is determined during the last moult, no cell divisions take place later in the adult. No spermatozoa could be demonstrated in the spermatheca or in any other part of the gonoducts and reproduction was by mitotic parthenogenesis. The cells of the tricolumella have a secretory function and the material they produce appears to be deposited on the surface of the eggs. The post-embryonic development of H. dihystera comprises 4 larval stages and the adult. The first moult takes place within the egg. The 3 larval stages outside the egg can be recognized on the basis of the degree of the development of the reproductive system. The reproductive system of each larval stage has a constant number of nuclei. Nuclear divisions in the reproductive system occur only during moulting, whereas cell enlargement takes place mainly during the larval stages. The reproductive system consists of 4 nuclei in the 2nd larval stage, 14 nuclei in the 3rd and 108 nuclei in the 4th. The final differentiation of the various gonadal parts takes place during the 4th moult. Specialized ventral cord nuclei and some other nuclei outside the gonad whose origin could not be determined take part in the formation of the vagina. One of the central nuclei of the gonad proper appears to function as vaginal organizer ("I" nucleus). [A.S.] S.W.A.