Insect Reproduction

Question 1

General points about reproduction

Answer 1

• M and F systems consist of paired gonads which are connected to a median duct leading to a gonopore
• glands in system will secrete compounds into the tract serving a variety of functions
• accessory glands
• adults won’t have active gonads upon imaginal eclosion (adult emergence)

Question 2

The male system

Answer 2

• pair of testes connected to paired seminal vesicles by ejaculatory duct
• accessory glands in charge of secreting seminal fluid (complexity and function is variable)
• some M produce spermatophores (accessory involved in secreting the coatings and compounds of it)
• teste contains 1-100 testicular follicles where sperm produced

Question 3

Spermatogenesis

Answer 3

•distal end of follicle (to outside of body) leads to tube
•follicle’s apical end is blind-ending where spermatogonium found
•germ cells divide and grow pushing down developing cells to follicle end
=gradient of aged sperm
•sperm grouped in cysts where meiotic division, then lots of mitotic
-can take up to 20days but varies

Question 4

Female system

Answer 4

•ovaries attached to oviducts into common oviduct and genital tract
•spermathecae branches off where sperm stored (Q honey bees 6-7yrs)
•ovaries have ovarioles where oogenesis occurs
•genital tract lined with cuticle till oviducts then not
-median oviduct and vagina lined
•bursa-copulatrix accommodates the males aedeagus during copulation
-some this has evolved into sperm store

Question 5

Oogenesis

Answer 5

•top apical end where germanium found
•apical cell splits and divides, pushing cells through system til functional egg forms
•some division takes place, but only 1 cell makes through as egg (all Ms make it)
-more sophistication = more derived forms of supplying nutrients to egg
Eventually leaving with bigger and fewer eggs

Question 6

Different ovary types

Answer 6

1. Panoistic ovaries - most basal types, apical divides, 2 divisions, 4 cells = 1 becomes egg and others die.
   - absorbs nutrients from haemolymph
2. Polytrophic ovaries - other cells don’t die, provide nutrients to egg
3. Acroptrophic - whole clusters of cells who’s sole function is to provide nutrients to the egg

Question 7

Spermatophores

Answer 7

Apterygotes will deposit spermatophore on ground, F picks up and deposits in genital tract
•some have courtship displays - live silverfish
•some are very remote from each other - collembola
•consistent with moving from aquatic E to terrestrial via bridging habitat
•can have nuptial gift attached - high nutrient value, F eats distracted for longer in mating
•can be more complex than free sperm

Question 8

Aedeagus

Answer 8

M pterygotes - like a penis
•derived from paired appendages of 9th segment which fuse and form intermittent organ
•is sclerotised tube designed for transferring sperm
•basal insects (mayflies) have a pair of aedeagi and F paired genital tract
Pterygotes use either spermatophore or free sperm

Question 9

Aedeagus modifications and diversity

Answer 9

Rarely used for just sperm transfer
•dragonflies displaces rival sperm, then inseminates
-Ae inflates with haemolymph and deflates several times per sec - flagella moved by this removing sperm with hooked spines on it
•bed bugs - F evolved a spermalege with immune cells where will be hypodermically inseminated
•bean weevil - males top modified with sclerotised spines for causing damage, prevents remating

Question 10

Oviposition

Answer 10

F gonopore modified into ovipositor - eggs exit here
•can be highly modified…
-sawflies - F ovipositor formed by fusion of two valves like saw, to deposit eggs in hole
-F dragonfly punctures hole into aquatic vegetation for laying
•covered in sensory receptors - to make sure its right
•eggs take different forms for laying site