Ovaries

Polistes bellicosus

Colony 114 Colony 64 Colony 155

Polistes carolinus

Colony 14 Colony 35 Colony 39

Determination of Reproductive Status

Because queens are not physically distinct from workers, determination of an individual's reproductive status requires the dissection of the wasp in order to observe the condition of the ovaries. Social wasps have two ovaries t hat are each divided into three ovarioles in which the eggs develop. While workers have undeveloped, long, stringy ovaries, queens have visibly developed eggs.

After dissection, there are several methods used to assess ovarian development:

  1. Count all mature eggs in the ovary.
  2. Count the nearly mature eggs.
  3. Measure the most developed oocyte in the ovary.

Though the size of the most developed ovary is not used in this project, this measurement is often used to assess the relative development of ovaries that are not entirely developed.

Image of Developed Ovaries, Dissection Under a Stereomicroscope

Polistes females have three ovarioles in each of their two ovaries. With the use of a steromicrosope, the stage of development within the ovarioles can be determined. Mature eggs are identifiable due to their large size and well developed, h ighly reflective chorionic membrane. Eggs and immature oocytes are arranged linearly in each ovariole. Those eggs closest to the ovaries, where the ovarioles come together, are most mature. If these mature eggs are not laid within a certain period of time , they will degenerate, and the ovaries will again appear small and undeveloped.



Detail of a Compound Microscope Slide Preparation (stained with Periodic Acid (PAS))

Preparation with a compound microscope reveals the DNA within the eggs. The dark dots within the oval spaces are the nuclei of the nurse cells, which provide nourishment to the developing oocytes.








Fertilization and Egg Laying
Mated females store sperm in a cavity called the spermatheca. The spermatheca is connected to the vaginal duct by a small channel. At the time when eggs are laid, the female may fertilize them as they move down the vaginal duct and pass by the spermathecal opening. Eggs that are fertilized mature into females. Eggs that are not fertilized become males. This is true for all species of Hymenoptera.



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© Joan E. Strassmann, reproduction by permission only
updated 13 September 1996, strassm@rice.edu