Insect Reproduction

Most insects reproduce sexually, by the joining of male and female gametes or sex cells. Gametes are produced by a special kind of cellular reproduction. Some insects reproduce asexually, without the joining of male and female gametes.

DEFINITIONS

Mitosis	-	process by which most cells of an organism reproduce themselves. During cell division the chromosomes containing the genetic material of the cell are duplicated and each new cell contains a complete set of the original chromosomes.
Meiosis	-	the process by which sex cell (gametes, eggs and sperm) are reproduced. Because a new individual has genetic material contributed from both of its parents, the eggs and sperm have to undergo a reduction in the number of chromosomes they contain to half. This condition is called haploid (1n). When the 2 sex cells fuse the diploid, 2x, condition is restored. Serves to keep the chromosome number constant.
Ovum	-	(pl. ova) = the female sex cell, sometimes limited to the sex cell before fertilization. Covered by an exoskeleton or chorion. Pores called micropyles allow entry of sperm.
Sperm	-	male sex cell, consisting of a head region containing the nucleus and a slender body terminated in a short end piece  (flagellum) or are aflagellate.
Spermatheca	-	sperm storage reservoir, some insects store sperm for years.
Spermatophores	-	sperm packet enclosed and protected by a gelatinous membrane in a specialized sac.

Cell Division: two types, cell duplication and reproduction division

Types of cell division

• Mitosis - cell duplication, produces identical copies
• Meiosis - reproduction division, produce cells with half the original genetic material (1N, haploid cells)

Although these examples have only two chromosomes, most organisms have more than two.

Insect Egg

Insect Sperm

Insect eggs and sperm are typical of land animals.

What changes were needed when insect ancestors were making the transition from aquatic to land animals?

For insects, sexual reproduction is the normal situation but not the only method of reproduction.

Female Reproductive System. Two roles.

1. To receive and store sperm
2. To produce ova

Diagrammatic Representations of Female and Male Reproductive Systems

Types of Embryonic Development

Oviparous: The usual case in insects, occurs in most insects.

• Egg is produced with sufficient yolk to complete embryonic development
• Fertilization occurs as the egg passes the spermatheca
• Egg is oviposited by the female in the environment
  • female behavior important
  • single or groups
  • may be fused together into capsule, ootheca

Ovoviviparous:

• Eggs are normally developed
• Fertilized
• Retained in the female's body until they hatch

Viviparous: (live birth):

• Eggs are normally fertilized
• An egg shell (chorion) does not develop
• Development takes place in the females body
  • supplemental nourishment from female
  • live birth
  • ex. many aphids, tsetse fly

Other Types of Reproduction

In some species males are absent or rare.

Parthenogenesis: Reproduction without fertilization, reproduction without the joining of female and male gametes or sex cells. Common in aphids.

Polyembryony: The reproduction of several embryos from a single egg. Two types:

• Type 1 - Early dividing cells separate and give rise to separate individuals.
• Type 2 - Later dividing cells give rise to separate individuals.

Paedogenesis: Reproduction by immatures.

Return to:

top of page

Entomology  home page

Entomology  topics list

Last updated Dec. 30, 2000
Gary Brewer