University of Michigan Biological Station

Biology 442 - Biology of Insects

Lecture Notes - Reproduction

1. Structure and function of reproductive systems.
   1. Male.
      1. Testis. Sperm producing structure.
      2. Spermatic tube or follicle. Contain germ cells to produce spermatogonia to spermatocytes to spermatids to spermatozoa. Usually contained in cysts with several cells in each.
      3. Vas efferens. Tube from follicle to vas deferens.
      4. Vas deferens. Collecting tube to ductus ejaculatorius. Often contain seminal vesicles.
      5. Ductus ejaculatorius. Ectodermal, cuticle lined, muscular, leads to aedeagus.
      6. Accessory glands. Sometimes include seminal vesicles. Also include glands to produce spermatophores.
      7. Phallomeres. External structures including claspers and aedeagus (intromittent organ) on segment 9.
   2. Female.
      1. Ovary. Egg producing structure.
         1. Ovariole. Make up ovary. Contain germ line cells. Divided into germarium with oogonia and early oocytes and vitellarium with mature and growing oocytes.
            1. Panoistic. Oocytes supplied with nutrients by follicle cells. Found in Thysanura, Odonata, Plecoptera, Orthoptera, Isoptera, Siphonaptera.
            2. Meroistic. Oocytes supplied by special nurse cells.
               1. Telotrophic. All nurse cells remain in germarium. Connected to oocytes by nutritive cord. Found in Hemiptera, Homoptera, some Coleoptera.
               2. Polytrophic. Nurse cells accompany oocytes inside follicle cells. Found in Psocoptera, Dermaptera, Diptera, Lepidoptera, Hymenoptera, some Coleoptera.
            3. Egg formation.
               1. Vitellogenesis. After oocyte is mature. Deposition of yolk mainly from hemolymph but also some from follicle cells.
               2. Vitelline membrane. Surrounds oocyte. Formed after yolking by follicle cells and oocyte.
               3. Egg shell (Chorion). Primarily protein produced by follicle cells. Contains micropyle to allow fertilization and often cap for escape of immature.
               4. Eggs may be resorbed by females if they become nutrient starved.
         2. Pedicel and egg calyx. Collecting tubes for follicles (consist of oocyte plus surrounding follicle cells).
         3. Ligaments. Each ovariole has a terminal ligament which unite to form the ovarial ligament to anchor the ovary.
      2. Lateral oviduct. Ovulation occurs into this. Muscular.
      3. Common oviduct. Tube into which lateral oviducts empty. Ectodermal, muscular.
      4. Vagina. Distal chamber also known as bursa copulatrix. Marked by entrance of spermatheca.
      5. Spermatheca. Sperm storage stucture. Ectodermal and cuticle lined. May have gland to provide nutrients for sperm.
      6. Accessory glands. Often associated with vagina. May secrete glue for egg attachment, substances for construction of ootheca in Periplaneta, frothy secretions in grasshoppers, silk in Hydrophilus, poison in Hymenoptera, pheromones in ants.
      7. External organs. Include ovipositor or sting. Derived from coxae and appendages of segments 8 and 9. Ovipositor consists of 2 halves (1 from 8th, 1 from 9th) covered by sheathes (both from 9th).
      8. Modification in Lepidoptera. 2 external openings. 1 to bursa copulatrix on 8 and egg pore on 9.
2. Mating behaviors.
   1. Indirect sperm transfer. Male leaves sperm packages in environment and female finds them. Not efficient for males. Would be strong selection for contact with female. Much sperm would be wasted.
      1. Collembola. Male deposits sperm on stalked spermatophore and female finds it. Sometimes produced in aggregations. Some use antennae to grasp female and guide her to it. Spermatophores may survive 2 days and males may produce 200.
      2. Thysanura. Also deposit spermatophores on ground but guide females by spinning silk girdle over female.
      3. Microcoryphia. Males place sperm droplets on thread and twists body around female and guides her to sperm with cerci and antennae.
   2. Odonata. Sperm produced at end of abdomen, transfered to 2nd segment, female is grasped, she picks up sperm by bending abdomen forward.
   3. Spermatophores with male/female contact.
      1. Orthoptera. Male produces large spermatophore and places in external pouch. Female may eat part and part may fertilize. Males may be choosy, spermatophore may be up to 40% of body weight.
      2. Most others. Insert spermatophore into bursa copulatrix and sperm then migrate to spermatheca for storage.
   4. Direct insemination. In some Hemiptera, Homoptera, Mecoptera, Trichoptera, Hymenoptera, Coleoptera, and Diptera free sperm are placed either into bursa copulatrix or into spermatheca.
   5. Male guarding. Common. Last male fertilizes 60-80% of eggs laid immediately after so favors guarding. Some Odonata hold on or guard. Many others stick around during oviposition. Some deposit structures that prevent further mating.
   6. Hoemocoelic insemination. Puncturing body cavity to deposit sperm.
      1. Alloeorhynchus (Nabidae). Copulate normally but male pierces vagina and release sperm into hemolymph. Collects around ovariole and pass into ovariole to fertilize eggs.
      2. Primicimex (Cimicidae). Male pierces abdomen between tergites. Sperm collects in heart and circulates with hemolymph. Collects in pouches at base of oviducts.
      3. Cimix and Xylocoris. Females have special structure in wall of abdomen (mesospermalege, organ of Ribaga, organ or Berlese). Males still pierce but place sperm in this organ. From here it migrates to hemolymph and then to pouches at base of oviducts.
      4. Stricticimix and others. Females have external opening in abdomen into which sperm is placed and tubes connect to oviducts through storage spermalege.
3. Specialized reproduction.
   1. Ovoviviparity. Egg retained in body. No special nutrition, all provided in egg. Occurs in many orders including Ephemeroptera, Blatteria, Psocoptera, Homoptera, Thysanoptera, Lepidoptera, Coleoptera, and especially Diptera. Larviposition occurs.
   2. Viviparity. Eggs retained but nutrients provided by parent in addition to or instead of those in the yolk.
      1. Pseudoplacental viviparity. Follicle cells serve as nutritive tissue for eggs with no yolk or chorion. Occurs in Dermaptera.
      2. Adenotrophic viviparity. Eggs with chorion and yolk. Larvae hatches and stays in uterus nurished by maternal glands. Develops completely to pupation in mother. Only in Diptera (see diagram of Glossina).
      3. Hemocoelic viviparity. Development occurs in hemocoel of female. No oviducts so oocytes are released into hemocoel. Nutrients provided by hemolymph. Occurs in Strepsiptera and some Diptera. Female wall ruptures when larvae are mature.
   3. Polyembryony. One egg produces more than one larvae. Occurs in some Acridoids but most commonly in Hymenoptera.
   4. Parthenogenesis. Development of eggs without fertilzation. Occurs extensively.
      1. Arrhenotoky. Males produced by unfertilized eggs. Usually haplo-diploidy in Hymenoptera, Thysanoptera, some Coccids and Micromalthus.
      2. Thelytoky. Female to female. May have no reduction division so to produce clones, or may have meiosis followed by fusion of nuclei or chromosome doubling. Occurs in some Thysanoptera, Coccidae, Lepidoptera, Coleoptera.
      3. Alternation of generations. Parthenogenesis combined with sexual generations. Aphids and Cynipids.
   5. Paedogenesis. Precocious maturation. Usually associated with parthenogenesis and viviparity. Larvae give birth to larvae or lay eggs in Micromalthus (Coleoptera) and Miastor (Diptera). Aphids may be developing before the parent is born but not be released until parent is adult.

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