entomology Flashcards
what is forensic biology
the use of biological knowledge in legal investigations
how can forensic entomology identify an individual
human DNA can be extracted from maggots as they will have fed off the body and ingested the DNA
how can forensic entomology tell us how a person died
distribution of maggots - go for easy access to food (open wounds)
maggots may have consumed drugs from the cadaver which we can test for
how can forensic entomology tell us when a person died
presence/ development stage of maggots - requires a knowledge of life cycle
how can forensic entomology determine where a person died
the presence of specific species of invertebrates that are only found in specific locations can tell us if a body was moved after death
what is the famous ancient story regarding forensic entomology
Sung Tz’u and the bloody sickle
what is the most commonly used organism in forensic entomology
blowflies
what are the two main problems with calculating the PMI from species composition
- no stage has fixed duration and different regions of the body may decay at different rates
- Season and weather affect sequence of colonisation e.g. blowflies may not be active during the winter period in the UK
in regards to entomology what occurs during the fresh stage of decomposition
first insects to arrive are usually blowflies such as Calliphora Vicina and Lucilia sericata - entomology isn’t studied here as the fresh stage is obvious death wasn’t long ago
in regards to entomology what occurs during the bloat stage of decomposition
the gases released during the bloat stage attract blowflies, as well as predators that feed on blowfly eggs/ larvae
maggot masses will also change the temperature of the body and disarticulate the body depending on where the flesh is eaten from
in regards to entomology what occurs during the active decay stage of decomposition
as putrefaction continues and more ammoniacal fermentation products are produced other species of insects are attracted to the cadaver e.g. histerid beetles and muscid fly Hydrotaea capensis
in regards to entomology what occurs during the post/ advanced decay stage of decomposition
blowfly larvae are usually absent or departing as there is no more soft tissue to be eaten, but beetles remain
in regards to entomology what occurs in the skeletonisation stage of decomposition
few insect species are found as little to no organic matter remains
what 3 factors do we have to consider before estimating time of death from species composition
- Time of year
- The temperature
- The species of insect found on the body
what does one require in order to calculate the PMI from invertebrate development rates
- biology + development times of an invertebrate
- how these are affecrted by temperature and other environmental conditions
- can back calculate to determine when egg from a specimen developed was laid
what is meant by the term minimum time since death and why is it used
it reflects the least time it would take for invertebrate to reach a particular stage of development - person may have been dead longer, but very unlikely that initial infestation took place after the calculated date
what is meant by the term blowfly
blow = mass of eggs, therefore blowfly = a fly that produces a mass of eggs
describe the typical blowfly life cycle in 6 stages
- Gravid female chooses natural openings and under body in which to lay up to 180 eggs
- Eggs hatch to release 1st instar larva which begin feeding on tissues and bacteria - tend to be very small
- Larva moults to 2nd instar after around 24-48 hours
- Larva moults to 3rd instar after another 24-48 hours getting bigger each time
- 3rd instar larva continue to feed voraciously and dramatically increase in size over the next 3-4 days until maximum size is reach
- They then move away from the cadaver and burrow themselves into soft ground of hide in order to pupate until an adult fly emerges
overall how do we use the blowfly life cycle to estimate the minimum time since death
compare stage development of ‘field’ maggot with the time taken for a lab maggot to reach the same stage, however we also use the ADD to account for temperature changes between field and lab
how can the presence of maggot infestation be a sign of neglect
wound myiasis is easily avoided with proper care of wounds like bandages and cleanings
how can entomology be used to determine the source of drugs in drug trafficking
the presence of a foreign species indicates the cannabis is imported
