Entomology

1
Entomology

• 3 larval stages
• 1st instar
• 2nd instar
• 3rd instar

2
Larval Development

• ELMO for parts of a larva
• One larva (maggot) is produced from each egg.
• The body is tapered from the anterior (front) end
  to the posterior (back) end
• Anterior end has mouth and hooks
• Posterior end has breathing apparatus (spiracles)
• Entomologists can distinguish different species
  by the shape of the spiracles, as well as body
  size and shape.

3
Further Development

• Larvae feed off the corpse.
• After 3rd instar stage, larvae crawl away from
  the corpse and burrow into nearby soil to
  transform into the pupal stage.
• Larva emerge from pupal case as an adult fly.

4
Species Identification
House fly
Blow fly
Flesh fly
5
Larval Identification

• Based primarily on spiracular openings
• Maggots have 2 sets of openings for respiration
• One set is on the lateral side of the 3rd body
  segment.
• One set is on the posterior end. (This is the one
  mainly used for species identification.)

6
Larval Identification, continued.

• Refer to your drawings of larvae.
• 2 dark circles on the posterior end are called
  spiracular plates.
• Spiracular plates contain the spiracles
  (openings) for breathing.
• Pattern of spiracular plates and openings are
  unique to each species.
• The dark ring surrounding the spiracular plate is
  called the ____________, and it regulates the
  opening of the spiracles.
• The peritreme may be a complete circle or
  slightly incomplete.

7
Larval Identification, continued.

• Within each peritreme may be 0-3 spiracular slits
  (openings), which may be straight or S-shaped
• 1st instar 0-1 openings
• 2nd instar 2 openings
• 3rd instar ???

8
Life Stage Identification

• Most flies deposit eggs, but Sarcophagidae (flesh
  flies) lay living larvae.
• Eggs incubate a few hours to several days.
• 1st instar larva stage lasts less than 36 hours.
• 2nd instar stage usually lasts the same amount of
  time as 1st instar.
• 3rd instar stage lasts longest.
• Maggots get larger with each stage, but the
  posterior spiracles change each time. (HOW?)
• What happens after 3rd instar stage?

9
Thermal History

• Logically thinking, how would you expect
  temperature at the scene to affect the life
  stages of insects?
• Once you have identified the species and instar
  stage, you can research the literature to find
  how long it takes the insect to reach that stage
  at the scenes average temperature.

10
Thermal History, continued.

• Example You have 3rd instar maggots of Phormia
  regina, and the mean temperature from the scene
  was 22 C.
• You find that P. regina takes 70 hours to reach
  3rd instar at that temperature.
• Using the accumulated degree hour method, 70
  hours x 22 C 1540 accumulated degree hours
  (ADH)

11
Thermal History, continued.

• We will use the daily maximum and minimum
  temperatures to determine average daily
  temperature, so we will have to subtract 6 C
  from our average.
• ELMO for example of Cochliomyia macellaria.
• Demonstrate use of dichotomous key for tomorrows
  lab.