Calliphora vicinia larvae grow at different rates on different body tissues
The problem which was approached in this experiment is to measure the growth rate of the blowfly ( Calliphora vicinia) on different body tissues which inhabit a dead body. The main aim of approaching this problem is even though much work is done by many scientists to measure the growth rate of this fly on various tissues that is how the growth is affected when it is provided with different body parts like in liver the work has been done by the Levot et al 1979, in pork it is studied and documented by Ames and Turner in 2003 and many more, but when such data's are collected to write the review articles the feeding substrates are not recorded and are not considered relevant.
The question which arises is to what extent these studies which are done earlier represents correctly the model of feeding and growth and how accurate it is to be followed as post-mortem interval determination? So this paper which was authored by G. Kaneshrajah and Bryan Turner discuss uses the variability of growth rates of blowfly on different tissues on a single animal.
The methods which were followed were done by a biostatistics analysis and by software named SAS package stat view v 5. The samples are the tissues of liver, brain, heart muscle; lung and kidney of pig were collected from butcher or local abattoir available locally. Then they were subjected to freezing after which they are thawed and are used for carrying out experiments in which the samples taken are of 30 gms, and 10 larvae are allowed to grown on each group. And daily 10 larvae from each group were taken washed in distilled water, dried individually weighed and killed in hot water and measured from 1st instar larvae to pupariation which occurs between 9th and 10th days from oviposition.And this experiments are carried in 3 replicates.
The data's which are generated by observing or measuring the growth of that larvae on various tissues are plotted in a graph in which the first graph depicts the growth rate in various tissues measured in length taken along y axis and the number of days in which growth have occurred in x axis. Where error bar is of +/- 1 standard deviation. The second graph shows the same readings except here growth has been measured in terms of the weight gained.
Now coming to the outcomes there was not much difference in length and weight in 3 replicates since ANNOVA test for weight gave F= 0.496, p= 0.609 and for length F= 0.435, p= 0.648 on same substrate for three triplicates. This test is mostly done to know the variance of a particular thing on a groups of things and mostly done when groups is greater than two. This result was observed when we the variation in length and weight against day's are taken collectively.
Later the result was plotted for every individual tissue and the effect of it on the growth of the organism and was found that there was a significant difference in annova test for weight and length studies for individual tissue and also the post feeding development is low in both weight and length but there is a variation in these also weight variation is much when feeded on different substrates but there is a very little variation of the length.
So from the results and outcomes it is concluded that the substrates does not appear to be a factor which affects the development of larvae since there is no definitive pattern which can be used as a model for future reference.
REFERENCE 2
In this paper the problem which is approached is to know the relation between the temperature and other factors which affects the growth of the L.sericata on various tissues of animal and to know whether there is any effect on growth by the change in structure of a tissue as a substrate or any intrinsic property of tissue are responsible for it.
The paper authors have hypothesized that many factors are responsible for the growth of the larvae which could be range from fluctuations in ambient temperature, prolonged low temperature, production of metabolic heat by aggregation of larvae, clothing, burial or ingested drugs may affect the growth and development pattern.
The adult L.seratica is maintained in rearing cages which are maintained at 25 degree Celsius and the adults are fed with water sugar and libidum. After 3 days they were fed with beef liver so that there will be development of ovaries. And when eggs are required 70 Gms of sliced fresh beef liver was placed for oviposition.And and were removed after three hour. The eggs were analysed until they were hatched and when hatched were removed and placed in treatment group.
The experimental methods followed are forty pots which have some pig and cow tissues in both liquid and solid quantity are arranged with definite quantity and dimensions. Then 20 larvae were placed in each pots within 1 hour of hatching and these pots are kept in beakers which contain 2 cm deep layer of the sawdust at bottom covered with the cotton mesh. The beakers were kept in the incubator at 25 degree Celsius at 70% humidity and 14:10 h L:D. Half of the pots were left till larvae complete its feeding and wandered from the meat to sawdust and another group till adult flies emerged. Total 240 pots were taken and 10 replicates for each combination of of cow/pig liver/heart/lung, chunked/liquidised, larvae/adult measurements were done.
After the larvae finish its feeding its goes to wandering stage where it leave the pots and goes to the sawdust in the beaker where they are pupariated. All the beakers are checked for the larvae for the first 2 days and after that after 4 hours of interval till the larvae wandered and time taken by the 50% of larvae to wander was recorded.
Larvae in the groups which are in wandering stage were measured after being killed by the immersion in boiling water, and the measurements of adults in groups were done by the transference of adults to the beaker with the sawdust and allowed to pupate. The counting was done for min 12 days and then after every 4 hours. The time taken for flies to emerge was also recorded. Different measurements were done for the different parts like the posterior cross vein was measured.
The data's are analysed by the Anderson-darling normality tests. Multiple analysis of variance are used to consider the differences in size and time between the various treatment groups.
The results or data's which are obtained by these experimental set up is there was no much difference in the wandering, larval length, time from wandering to emergence or adult wing vein length.
The structure of the substrates has no effect on the time of wandering .It was found that larvae which were allowed to feed on pig were developed faster than those who were given cow to eat.
The time taken for the larvae to reach the wandering stage is significantly varied for different tissues
.Larvae which is fed on lung and heart wander on an average of 31 and 29.2 hr earlier than larvae reared on liver. Larvae were significantly larger who reared on pig rather than on cow even though the difference in the detransformed means was only 0.63mm.Those who are reared on lung and heart are larger than the larvae that are reared on liver.
No significant effect of the animal species, organ type or structure has effect on the time taken from 50% wandering to 505 emergences. But the adults who were reared on the liver are significantly smaller when compared to lung and heart.
The authors of this paper have concluded that mostly there is no effect of the structure of the substrates or feed on the larval growth and development and how different tissues have different effect on the growth of larvae.
What is the rationale for each of the studies and how do the authors use these rationales to justify the aims of these studies???
Ans :- Main rationale for each of the studies was to find out or designing of a model which will be standard for determination of the PMI ( Post Mortem Interval ) and further research on the forensic entomology so that analysis of corpse will be easier for them.
And how these rationales are used to justify the aims in these two studies are discussed below-
In the first study the growth of the Calliphora vicina how is affected by different tissues are studied which will throw some light that do different organs or body parts have effect on the growth and development of the flies or organisms which feed upon them. And if we can devise a definitive model regarding this that is pattern of development and growth when feeded upon different tissues it will be easier for the forensic department to go to the root of a particular case. So they have checked the larval growth on different tissues and the time period and which part grows so that they will know about the post mortem interval.
In the second study their main aim was to find out the reason which mainly affects the development of L.seratica when feeds upon the corpse and do the tissue structure have any effect on the growth and development of the organism. For that they have favoured a bit sophisticated method where they have recorded the wandering and emergence timing and also feeded them both liquidised and non liquidised solid food. And the result obtained was there is no much effect of the structure of organ on the development and growth of the larvae.
Even though both the authors have tried to justify their rationales but the question which was to be put here is do doing experiments on the pig and other animal tissue will help the forensic officials where they mostly come across human corpse. In the second paper where the L.seratica has taken into consideration the author has told that much research has to be done in this regard that is with relation to the human beings because since they have shown that different tissues of different animal have different effect on the larvae so what result they got from pigs and cows may vary when they will conduct research on human bodies, So to have a real world relevance the study has to be done with the human bodies.
List the two most important limitations of each study briefly and state why?
Study1: Growth rates of the blowfly, Lucilia sericata, on different body tissues
1. The authors had reported the growth and development of the experimenting samples at a constant temperature of 25°C which may not be the condition at the actual site, growth and development is affected with fluctuation in temperatures. Therefore result that has been concluded by the authors may not be applicable or true in all conditions.
2. Although the pig tissue is closely related to human tissue, but still there is chances for differences in the concluding results in the two cases, since there is a considerable difference in growth of larvae between pig and cow tissues so the results obtained in this paper should have to be further quantified for any differences between pig and human tissues.
Study2 : Gajen Kaneshrajah · Bryan Turner
Calliphora vicina larvae grow at different rates on different body tissues
1. A group of larvae were fed on the provided substrate and in few cases reduced growth rate and loss of weight was observed, this could be due to over-crowding ,because due to overcrowding competition takes place that reduces growth rate and hence size.
2.This paper shows the effect of different substrates from the same animal on the growth rate of the larvae under study, but these results cannot be taken as standard for all other substrates from other animals too because since if growth rate of larvae can differ in the substrate from the same animal then the results for different animals can also be different.
List the two most important strengths of each study and state why?
Study1: Growth rates of the blowfly, Lucilia sericata, on different body tissues
1. Blowflies such as Lucilia sericata are the first one to arrive to a body after death so knowing the age of the oldest larvae on the body helps to a great deal to the forensics entomologists, but since the growth rate of these larvae depends on the kind of tissues it feeds on, so it can create a problem to identify the correct larvae, the present study solves this problem as the authors have conducted the study of growth and development of these blowflies on different substrates, hence providing information that which are the substrate on which growth rate of these blowflies are higher.
2.The present study also showed that the structure of the substrate does not affect the growth rate of these flies as there was no significant change in the growth rate in the chunk of the tissues or liquidized tissues.
Study 2
Calliphora vicina larvae grow at different rates on different body tissues
1. The present study confirms the conclusions of the study1 and it is confirmed by taking size and weight of the larvae into account and not on the basis of convenience or low odour.
2. In this paper authors have also demonstrated the effect of growth rates of these blowflies on the tissues of brain and kidney too, as brain tissues are soft and are more likely to be targeted first by these blowflies.
Compare and contrast the results of each paper
In the study1, tissues from, heart, lung and kidney of pig and cow were taken and the different growth rate of blowflies on these tissues were demonstrated but in the study2, tissues from brain and kidney were taken as well as because brain comprises of soft tissues which is targeted first by larvae of these flies. A comparitve study for growth curve was done in study2, to give more accurate calculation of postmortem interval.
Based on the results are the discussions and conclusions of each papers are justified?
The growth and development of larvae is not only substrate dependent but also temperature dependent, in both the studies only one temperature condition was considered which is not enough to prove the same results as shown in the studies to be true for all other temperature conditions.
Though tissues form the models used for study relates to human tissues but since differences occurs between pig and cow, so possibly there will be difference in the growth rate of larvae when compared with condition of human tissues, so a further study should be done to adjust the results shown in these studies with that of human tissues.