1. Team Maggot: Designing a Better Bait Cup
Jordan Corsolini, Chris Henning, Tori Tamburrino, Kristi Bugajski
Department of Biology, Valparaiso University
Abstract
Methods
Forensic entomology is the application of data from arthropods for investigative purposes in the criminal justice system. This study examined blow fly (Diptera: Calliphoridae) oviposition (egg laying) rates on chicken liver. The purpose of this experiment was to create a more effective bait cup for a higher percent yield in oviposition. The three main questions studied were: “does the weight of the liver affect oviposition?”, “does the location of the bait cup affect the occurrence of oviposition?” and, “is a foil or a plastic cup more attractive for oviposition?”. A one way ANOVA showed a significant difference in the amount of oviposition using different liver weights (F=4.5, df=27, p=0.012). Tukey post hoc tests revealed significant differences between the 15g and 60g weights, and between the 30g and 60g weights. A one way ANOVA found no significant difference in the number of trials with oviposition in different locations (F=2.283, df=34, p=0.084). An independent samples t-test found a significant difference in the number of trials with oviposition using foil vs. plastic cups (T=-2.61, df=12, p=0.023). These results will help to create an ideal bait cup for studying larger diurnal oviposition questions.
Research was conducted from May-July 2015 at Valparaiso University in Valparaiso, Indiana. To answer the three study questions, bait cups consisting of a ~500 g Styrofoam cup with 6 mm of vermiculite in the bottom and aged chicken liver, were placed in the field for a period of five hours to document the timing and frequency of blow fly oviposition.
The first experiment examined four different liver weights, 15g, 30g, 45g and 60g. Four replicates of each weight were used in nine separate trials, all occurring in the stair wells behind Neils Science Center (Fig. 1, stairwell site).
The second set of trials used 60 g of chicken liver placed in either small foil or plastic cups within a Styrofoam cup (Figure 2). One foil and one plastic replicate were placed in each of five different locations around Neils Science Center, for a total of five foil and plastic replicates per trial (Fig. 1, Sites 1-5). The experiment was repeated 10 times.
Cups were checked hourly for the presence of eggs and blow fly activity (Fig. 3). After oviposition was found, the cups were brought into the laboratory and eggs masses were weighed (Fig. 4) before being placed into a fume hood. The eggs were reared to the third larval instar stage for species identification.
Data analysis was done using SPSS® software. One way ANOVAs examined differences in oviposition frequency between liver weights and location of the bait cups. Tukey post hoc tests were used to determine which treatments were significant from each other. An independent samples t-test was used to determine significance in oviposition frequency between foil and plastic cups.
Discussion
An effective bait cup is essential for conducting accurate forensic entomology studies.
The results of this research suggest that the bait cup most likely to yield oviposition will contain 60 g of chicken liver in a foil cup, which supports the alternative hypotheses that higher weights and foil will yield higher oviposition.
A statistical significance was not found between site locations, which supports the alternative hypothesis that location does not affect oviposition. However, there was a higher rate of oviposition at sites 1 and 2, so moving research from the stairwells to these locations should increase the rate of oviposition.
Future work will include identifying the insects collected and examining liver weights larger than 60 g.
It is possible that the odor of the liver gets stronger as the weight increases, which would increase the attraction of blow flies. Collaboration with the chemistry department to quantify the odor of liver at differing weights is being considered.
In conclusion, a bait cup with 60 g of chicken liver, in a foil cup, at site 1 or 2, is recommended to achieve the highest rate of oviposition.
Introduction
Forensic entomology uses data collected from insects to assist with criminal investigations1. Blow flies (Diptera: Calliphoridae) are usually the first to arrive on carrion, and have been found to oviposit (lay eggs) within minutes2. Forensic entomologists use weather and insect development data to provide estimations of the post mortem interval (PMI), or time between death and corpse discovery. Any factors that influence oviposition are critical to provide accurate PMI estimations.
Forensic entomologists use different tissues as bait in experiments, with liver being the most common2. The literature lacks information on the design of the most effective bait cup.
This study tested the following hypotheses:
Ho: The amount of liver does not affect the frequency of oviposition
Ha: Higher liver weights will yield more oviposition
Ho: Location of the bait cups will not affect oviposition frequency
Ha: Sites near vegetation will have higher oviposition frequency
Ho: There will be no difference in foil vs plastic cups in total amount of oviposition
Ha: Foil cups will yield higher amounts of oviposition because they are reflective
Figure 2. Foil and plastic bait cups
Figure 3. Blow fly eggs on liver
inside of bait cup
Figure 4. Blow fly egg masses
before weighing
Results
Liver Weights: Table 1. The ANOVA showed a significant difference in the amount of oviposition using different liver weights (F=4.5, df=27, p=0.012). Tukey post hoc tests revealed significant differences between the 15g and 60g weights, and between the 30g and 60g weights.
Location: Table 2. A one way ANOVA found no significant difference in the number of trials with oviposition in different locations (F=2.283, df=34, p=0.084).
Foil vs. Plastic: Table 3. An independent samples t-test found a significant difference in the number of trials with oviposition using foil vs. plastic cups (T=-2.61, df=12, p=0.023).
*Trials with no recorded oviposition were excluded from analysis.
Table 2. Total percent oviposition for 5 site locations with 35 replicates
Table 1. Percent oviposition for 4 liver weights with 28 replicates
Table 3. Total percent oviposition for foil vs plastic cups with 35 replicates
Site Number
% of Trials with Oviposition 1
50% 2 3
20% 4 5
10%
Literature Cited
Liver Weights
Percent Oviposition
15 g
3.5%
30 g
45 g
17.8%
60 g
32.1%
Cup Type
% of Trials with Oviposition
Foil
31%
Plastic
17%
Byrd, J. & J. Castner.  2010.  Forensic Entomology:  The Utility of Arthropods in Legal Investigations, 2nd ed.  CRC Press, Inc., Boca Raton, Florida. 681 pages.
Haskell, N. & R. Williams Entomology and Death: A Procedural Guide, 2nd ed. Forensic Entomology Partners, Clemson, South Carolina. 182 pages.
This research was supported by the Valparaiso University
College of Arts and Sciences and the Mathematics and Science Education Enrollment and Development Program (NSF Grant No )