Forensic Entomology. Insect Life Cycles & Development

Transcription

1 Forensic Entomology Insect Life Cycles & Development

2 Basic Insect Development Metamorphosis = change in form over time Ametabolous without metamorphosis Hemimetabolous incomplete metamorphosis Holometabolous complete metamorphosis

3 Ametabolous No larvae stage go from egg to smaller looking adult (juvenile), then adult E.g. Silverfish

4 Hemimetabolous Egg Nymph Adult E.g. Milkweed Bug

5 Holometabolous Egg Larvae Pupa Adult E.g. Butterflies, Blow Flies, and Beetles

6 Terminology: Oviposition egg laying Eclosion egg hatching Molting shedding outermost skin Instar period between molts Prepupa inactive stage just before pupa Pupation the process of becoming a pupa Puparium/Puparia outer skin forming pupa casing Emergence when the adult leaves the puparium

7 Oviposition Eclosion 1 st molt 2 nd molt Emergence

8 Temperature, Temperature, Temperature! Insects have no internal mechanism for regulating body temperature Ways animals regulate body temperature: Endothermic generates own body heat (humans) Ectothermic exchanges heat with surroundings Poikilothermic body heat varies with surroundings **Insects**

9 Physiological Time The rate of growth and development of insects is proportional to ambient temperature There is a min. and max. for each stage of development

10 Typical Blowfly Development constant temp of 70 C Oviposition Eclosion 23h 27h (50) 1 st molt 22h (72) 2 nd molt 130h (202) 143h (345) Emergence

11 Typical Blowfly Development constant temp of 70 C Oviposition Eclosion 23h 27h (50) 1 st molt 22h (72) 2 nd molt 130h (202) 143h (345) Emergence

12 What does this mean????? From egg to adult takes about 2 weeks at 70 C

13 Forensic Entomology Decomposition and Insect Succession

14 Insect Succession on Pig Carcasses 1960s Jerry Payne identified more than 500 species that colonized decomposing pig carcasses We will focus on the most COMMON and PREDICTABLE!

15 Don t Forget Those That Colonize the Living! Insects that may be present prior to death, may remain on the corpse through the fresh stages of decomposition E.g. The rate of algor mortis (body temp lower) will influence the presence or absence of body lice

16 Fresh Stages: 1-2 days Insects may appear minutes after death to feed, mate and reproduce They are attracted to odors associated with decay and insect activity Common Insects: Blow flies, Flesh flies, and some predators

17 Fresh Stages: 1-2 Days In the absence of wounds, blow flies colonize the mucus membranes (eyes, nose, mouth)

18 Bloat Stages: 2-6 Days Adult blow flies and flesh flies may still be arriving, but as the body odors change, the flies will seek fresh remains Early bloat early instars will be present Late bloat late instars will be present

19 Active Decay Stages: 5-11 Days Adult blow flies leave Maggot mass is present Some maggots beginning to wander and pupate Common insects arriving: secondary flies, predators, beetles

20 Post Decay Stages: Days Blow flies complete life-cycle and do not return As body starts to dry out more beetles arrive Mature beetle larvae start to appear around 2 week mark 80% biomass loss due to maggot feeding

21 Post Decay Stages: Days Secondary flies continue to arrive E.g. adult Cheese skippers (Piophilidae) Some larvae may be present How do these flies know when to arrive? Butyric acid (what make feet stink and some cheeses smell) is a byproduct of fermenting bodies

22 Dry, skeletal Remains: 25+ Days Some predators Early beetles are pupating Secondary flies and their larvae Dermestid beetles colonize the dry remains

23 How Can Insect Succession Estimate PMI? How it can work (scenario): species are collected from corpse 2. All are identified and stage of development recorded 3. Stage of decomposition, location, and temperatures noted 4. This assemblage is compared to an occurance matrix 5. PMI is estimated based on where the assemblage falls *Basically you compare your evidence data with a reference data table

24 Groups of 4 Each person read one section of the paper Intro Methods Results Discussion That person should report to the group what that section was about Answer questions together on 1 sheet to turn in

25 Gruner et al article questions 1. What is succession? 2. Besides PMI, what other factors can be concluded based on entomological evidence? 3. Why are there not very many studies on insect succession? 4. What is the purpose of this study? 5. How were the pig carcasses protected from predators during the study? 6. Why were temperatures near the surface recorded? 7. How many fly species were collected during the 16 trials? 8. During most of the study (except for the coldest days) how long did it take for the first flies to appear? 9. Compare Figure 2 with Figure 3 (Spring vs. Summer), why do you think the abundance of each type of species changes from Spring to Summer? 10. Refer to Figure 5 (Winter), why do you think there is such a low abundance of C. rufifaces compared with other seasons? (Hint: think about rate of decomposition) 11. How would the heavy rain in the Summer months impact the study? 12. What were the results in terms of aerial samples versus larval samples? Why is this important?