Dermestid beetles: Feeding behavior and relationships with post-mortem interval determination WONG SOOK YEN School of Natural Sciences and Psychology Liverpool John Moores University James Parsons Building, Byrom Street, Liverpool L3 3AF, United Kingdom
AbstractBackground: The use of beetles (Coleoptra) in determining post-mortem interval isextensively reported. Dermestid beetles (Family Dermestidae) are one of the last groups ofarthropods that feed on the carcasses, particularly with reference to dry skeletonised remainsin the final stage of decomposition process. This study aims to investigate the feedingpreference of Dermestid beetles and their ability in locating buried remains.Methodology; Larvae and adult Dermestid beetles were reared for 48 hours in containerscontaining dry and wet bacons; and fat and lean meat. Parameter that determines feeding isthe distribution of the beetles of different food type coupled with the percentage change inweight of the food presented to them. Adult beetles were reared above and under soil withfood buried for 48 hours.Principal findings: Significant reduction in weight of wet bacon was observed which is incontrary to the initial expectation that reduction in weight of dry bacon would occur. Thereduction in mass of lean meat was observed as expected. Majority of adult beetles werefound to remain underground at most of the time.Conclusion: Dermestid beetles generally prefer dried bacon than wet bacon although theexperimental data does not support the statement. Also, lean meat is preferred than fat. Thebeetles are able to locate food presented under 2 cm thick soils, indicating their ability inlocating buried remains.Significance: The use of larval Dermestid beetles in post-mortem interval determination is tobe confirmed.
IntroductionDecomposition is a process that involves the return of organic matter in dead organisms backto the environment. This process is divided into several stages: fresh, bloated, active decay,advanced decay and dry decomposition. Carrion, or dead animal matter, represents atemporary and changing food source for a varied and distinct community of organisms(Kocarek, 2002). The sequence of insect colonisation of body remains had been established(Anderson, 2001). The use of these invertebrates in post-mortem interval investigation iswidely reported (Ozdemir and Sert, 2009; Kocarek, 2002; Eberhardt and Elliot, 2008). Due togeographical isolation and social disengagement of the deceased may lead to the discovery ofthe body remain in mummified, partially or fully skeletonised condition after months or yearsafter death (Archer et al., 2005). This adds to the difficulty in identifying the deceased, andestablishing the cause and circumstances surrounding death (Archer et al., 2005). Thedetermination of the time since death of skeletonised as well as mummified body hasremained a challenge to forensic investigator and results in extensive study (Kulshrestha andSatpathy, 2001).Dermestidae, a group of beetles belonging to the order Coleoptra, is involved in the dry stageof decomposition process, responsible for the skeletonisation of the dead body (Archer et al.,2005). Dermestes beetles are common domestic pest that normally feed on dry substancessuch as hair, feathers, skin, dried beef etc (Martin and West, 1994; Vijay Veer et al., 1995).The common types of Dermestidae involve in the succession of body remain includesDermestes ater, Dermestes caninus, Dermestes maculates and Dermestes Frass (Bryd andCastner, 2001). Since human corpse is one of the food sources of these beetles, carriondecomposition and succession as well as the biology, phenology, biogeography or habitatpreference of Dermestes insect communities need to be known. According to Anderson
(2001), Dermestid beetles are rarely found in the fresh and bloat stage of decay, and morecommonly found during the advanced stage of decay, depending on geographical differences.Factors associating with the attractiveness of the body remain and the ability of the beetles tolocate and colonise the body is also important for the determination of time since death.Information that have been known are: Dermestes beetles commonly feed on dry food sourceand are involved in the colonisation of body remains during the dry stage of decomposition(Bryd and Castner, 2001). However, the effect of feeding behaviour and preference ofDermestid beetles towards fat and moist meat has not been determined by previous researches.In the present study, I would like to investigate the preference of food type of Dermestidbeetles, attractiveness of fat towards these beetles as well as the ability of these beetles tolocate buried remains.
Materials and MethodAll parts of experiment were done in duplicates.Section A: Effect of Moisture ContentThe combinations of bacons and different stages of Dermestid beetles were left in containerswith measurements of 25.7 x 9.5 x 5.2 cm for 48 hours. Figure 1 illustrates the relativepositions of the beetles and bacons.Location 1 Location 2 Location 3 Location 4 Location 5 Moist paperFigure 1. Experimental set up – container measuring 25.7 x 9.5 x 5.2 cmThe combinations of experimental set up that were prepared to investigate the effect ofmoisture content on the feeding behaviour of Dermestid beetles are shown in Table 1.Table 1. Relative positions of bacons and Dermestid beetlesTreatment Location 1 Location 3 Location 51 Wet bacon 10 adults Dry bacon2 Wet bacon + 10 adults Dry bacon3 Wet bacon 10 larvae Dry bacon4 Wet bacon + 10 larvae Dry bacon5 Wet bacon Dry bacon + 10 adults6 Wet bacon Dry bacon + 10 larvae7 Wet bacon + 10 adults Wet bacon8 Wet bacon + 10 larvae Wet bacon9 Dry bacon + 10 adults Dry bacon10 Dry bacon + 10 larvae Dry bacon
Section B: Attractiveness of fatUsing similar set up of experiment, the attractiveness of fatty food products on Dermestidbeetles were investigation. The fat and lean meats that were cut in similar sizes originatedfrom pork chop purchased from Tesco. Table 2 shows the distribution of fat, lean meat andrat pellets in the similar container used in Section A.Table 2. Relative positions of fat, lean meat and Dermestid beetlesTreatment Location 1 Location 2 Location 3 Location 4 Location 51 Fat 5 adults Lean 5 adults Rat pellets2 Fat + 10 adults Lean Rat pellets3 Fat Lean + 10 adults Rat pellets4 Fat Lean Rat pellets + 10 adults5 Fat Lean Rat pelletsSection C: Colonisation of buried remainsThe capability of adults and larvae of Dermestid beetles in locating buried remains is beinginvestigated. Five containers filled with 10 cm of John Innes number 2 compost were set upand placed into a container measuring 10.2 x 7.2 x 27.2 cm. The components in eachcontainer were tabulated in Table 3.Table 3. Relative positions of rat pellets, larvae and adult beetlesTreatment Content1 Rat pellets + 10 adults and topped up with 2 cm layer of soil2 Rat pellets + 10 larvae and topped up with 2 cm layer of soil3 Rat pellets buried under a layer of 2 cm soil with 10 adult beetles on the surface4 Rat pellets buried under a layer of 2 cm soil with 10 larvae on the surface5 Dry bacon buried under a layer of 2 cm soil with 10 adult beetles on the surface6 Dry bacon buried under a layer of 2 cm soil with 10 larvae on the surface
ResultsFor all the three sections, the number of beetles present on the meats, bacons, fats as well asthe difference between initial weight and final weight of bacons after 48 hours were used asan indication of feeding preference of Dermestid beetles. The results for Section A, B and Care tabulated in Table 4, 5 and 6 respectively.Section ATable 4. Effect of moisture on the distribution of Dermestid beetles and percentage change in weight of baconTreatment Organism Duplicate Distribution of Percentage change Percantage change Dermestid in weight of bacon in weight of bacon beetles at location 1 at location 5 (%) (%)1 Adult 1 M - 100% -8.46* +55.5 2 M - 100% -5.17* +25.662 Adult 1 M - 100% -6.83* +53.6 2 M - 100% -4.35 +29.393 Larvae 1 D - 50% -10.19* +46 W - 10% 2 M – 100% -4.61 +30.064 Larvae 1 D- 40% -9.05* +44.55 W - 30% 2 D – 20% -5.85* +26.78 W – 20% M – 60%5 Adult 1 M - 100% -8.11* +41.83 2 M - 100% -6.97* +30.116 Larvae 1 D – 100% -5.60* +36.31 2 W – 40% -7.22* +38.33 M – 60%7 Adult 1 M – 100% -3.92 -1.75 2 M - 100% -2.62 -1.688 Larvae 1 W – 20% 20.15 -1.64 2 W – 10% -5.21* -3.459 Adult 1 M - 100% -29.68* -34.50* 2 M - 100% +27.97 +27.7710 Larvae 1 D– 100% +21.37 +24.95 2 D – 30% +25.57 +26.64 M – 70%D indicates dry bacon; W indicates wet bacon; M indicates moving around*Indication of feeding - Reduction in weight greater than 5% for wet bacon; any degree fordry bacon
Wet bacon acting as control showed a decrement in weight of 3.59% whereas control drybacon showed an increment of weight by 0.15% (not shown in Table 4). Therefore, reductionin weight of dry bacon to any extent and that of wet bacon by more than 5% is taken as thestandard that indicates feeding. It was also noticed that all adult Dermestid beetles tend tomove around in the beginning of the investigation rather than staying at a particular site offood. Even after being exposed to the food for 48 hours, they showed no preference to any ofthe meat. Majority of the time greater proportion of the larvae were found resting on the pieceof moist paper. When the adult beetles are free to move about as in Treatment 1, reduction ofweight of wet bacon is greater than 5% are observed in both duplicates. Similar observationresults when the adults were placed on wet bacon (Treatment 2) and on dry bacon (Treatment5). No matter in which initial conditions the adult beetles were placed (Treatment 1, 2 and 5),increment in weight was observed on dry bacon, ranging from 25% to 55%. When adultbeetles were placed in environment that contains only wet bacons (Treatment 7), both baconsshowed the relatively similar reduction in weight, but in a reduced manner compared toTreatment 1, 2 and 5. In duplicate 1 of Treatment 9 (adult beetle placed in environment withonly dry bacon), significant reduction in weight was observed. However in duplicate 2 ofsimilar treatment, a contradicted condition occurred, i.e. increment in weight was observed.When larvae are free to move about to search for food (Treatment 3), 50% of them tend tostay at dry bacon. When they were initially placed at wet bacon, those that discovered stayingat wet bacon were 30% and 20% respectively in duplicate 1 and 2 of Treatment 4. Some otherlarvae (40% in duplicate 1 and 20% in duplicate 2) dislocate to dry bacon. On the other hand,when the larvae were initially placed on dry bacon, all of them remained on the dry bacon.However, the duplicate set of similar experiment does not produce similar finding. Only 40%of the larvae remained on the dry bacon in this case, others were moving about freely. In thecase when both bacons were wet, 10 to 20% of the larvae stayed on the wet bacon.
Interestingly, the bacon in location 5 showed a greater reduction in weight than the bacon inlocation 1 where the larvae were initially placed. Last but not least, no reduction in weightwas observed when the larvae were placed in environment consisting of only dry bacons.Section BTable 5. Effect of fat on distribution of Dermestid beetles and percentage change in weight of fat and lean meatTreatment Organism Duplicate Distribution Percentage Percantage Percantage of Dermestid change in change in weight change in weight beetles weight of fat of lean meat at of rat pellets at at location 1 location 3 location 5 (%) (%) (%)1 Adult 1 P - 100% -4.90 -7.18 10.05 2 P - 100% -3.83 -6.85 9.312 Adult 1 L - 10% -8.95 -13.75* 10.95 P - 90% 2 P - 100% -3.63 -9.43 11.693 Adults 1 P - 100% -6.13 -10.56* 12.84 2 P - 100% -3.20 -7.96 12.404 Adults 1 P - 100% -6.15 -8.72 13.66 2 P - 100% -3.20 -7.26 12.02Control - 1 - -6.09 -8.07 13.94 2 - -3.53 -7.57 18.19F indicates fat; L indicates lean meat; P indicates rat pellet (*indicates significant reduction inweight)It was observed that at all times, adult Dermestid beetles tend to stay at rat pellets. Allportions of fat and lean meat showed reduction in weight while increment in weight wasobserved for all rat pellets. The percentage drop of weight of lean meat were always higherthat of fat. When the adult beetles were exposed to fat at the beginning, a great reduction inweight of lean meat was observed. Also, when the adults were placed on lean meat in thebeginning, a great reduction in weight of lean meat was observed.
Section CTable 6. Percentage distribution of Dermestid beetles and their ability in locating buried foodTreatment Organism Duplicate Percentage Distribution of Dermestid beetles On surface Below ground1 Adult 1 10 90 2 - 1002 Larvae 1 - 80 2 90 -3 Adult 1 90 10 2 - 1004 Larvae 1 - 90 2 - 605 Adult 1 100 - 2 - 1006 Larvae 1 20 60 2 - 90Certain beetles were found missing after being left in the experimental set up after 48 hours.It was observed that majority of the time both adult beetles and larvae tend to stay below thesoil. When the adults were placed below a layer of 2cm soil, they moved about freely andtend to stay underneath the ground most of the time. Similarly, when the beetles were placedabove ground in the start of the experiment, they found their way downwards into the soil.DiscussionUnder natural condition of decay without involving Dermestid beetles, raw flesh of anyorganism will undergo dehydration and results in the reduction in weight observed in control.Dry meat and rat pellets however, have deliquescence properties whereby water will beabsorbed by the material under natural conditions and thus results in the increment of weightobserved in the control. This is an important property for the development of Dermesteslarvae. Food with too high moisture content is not preferable for development (Fraenkel et al.,1941). The initial observation after placing the Dermestid beetles onto different locationswere that the beetles tend to move towards the edges and the wall of the containers. This is anatural behaviour of Dermestid beetles. In most of the treatment sets, majority of the beetles
tend to be found on moist paper. This property is common in most insects where they preferto stay at a closed and moist environment. However it does not illustrate the feedingbehaviour of Dermestid beetles in detail. The percentage change in weight provides anindication in the preference of food type by the beetles rather than just relying on the spatialdistribution of the beetles itself.Reduction in bacon/fat/lean meat weight is mainly contributed by the natural dryingmechanism of tissue decomposition as observed in Section A and B. Majority of the drybacons and rat pellets showed an increment in weight rather than decrement as expected, butit doesn’t mean that there was no feeding of adult beetles or larvae on the dry bacons, becausethose are their natural food sources.Dermestid beetles are equipped with sensory system that allows them to identify the locationof food source. Placing the beetles at the food initially allow them to know the location offood. It is the matter of preference of food that decides the movement of these beetles andsubsequent colonisation of food. Based on the reduction in weight, adult beetles showedgreater preference towards wet bacon than that of dry bacon. When adult beetles are neitherplaced on dry bacon nor wet bacon, they showed greater preference towards wet than dryfood. It doesn’t matter whether the adult beetles were exposed to wet or dry food initially; wetfood is still preferred compared to dry food. This is in contrast to the information obtainedfrom numerous literatures stating that the natural food sources of these beetles are normallydry (Ozdemir and Sert, 2009; Kocarek, 2002; Eberhardt and Elliot, 2008). This is probablycaused by higher rate of water uptake by dry bacon which masks the reduction in mass due tofeeding.Another possible explanation is that the beetles need to ensure that there is suitable andsufficient food for egg and larval development. So adult beetles tend to move about in
searching for “good” food that provides suitable criteria for growth and development of theiroffspring. It was found that increment in weight of dry bacon always coincides with thedecrement in weight of wet bacon. I think that this is a mechanism for the adult to ensuresurvival of their offspring. The adult beetles choose to eat non-preferable wet food andreserve the “good” dry food for the development of egg and larvae. This is further confirmedby the finding that when wet food is present solely in an enclosed environment, reduction inweight is not in as high. Insect has lost their appetite when there is no suitable environmentfor breeding. Since there is no stimulus for breeding to take place, their food intake is reducedin the similar manner. Both bacons in Treatment 7 showed reduction in weight indicated thatthe beetles move from one site to another in searching for better food. A great reduction inweight of dry bacon was observed in Treatment 9 when adult beetles were placed in enclosedenvironment with their favourite dry food. The high percentage of weight reduction mightdue to increased appetite of the beetles as well as the presence of suitable environment for theinsects to prepare for breeding. Based on Anderson and Vanlaerhoven (cited in Kulsherathaand Satpathy, 2001), Dermestidae larvae are commonly found 21 days after death in the earlystage of advanced decay, but more were collected after 43 days post-mortem interval (duringthe dry decomposition stage). This statement is supported by a case study (Kulsheratha andSatpathy, 2001) on male corpse found on a sandy beach revealed a post-mortem interval of 34– 46 days. Another case study reported by the similar researchers indicated that adults, pupaeand larvae of D. maculatus were present on female human remains with a post-morteminterval of 4 months 13 days. It is unsure for both the findings to which extent the corpse hasdried. Thus in my opinion adult Dermestid beetles showed preference to dry food if there areenough amounts for breeding process, otherwise will reserve the food which is essential forthe development of their offspring. Dermestid beetles cannot use a completely dry carcassunder the controlled environment in museum as food source (Martin and West, 1994).
According to Coombs (1978), successful development of Dermestes sp. larva at 65% relativehumidity should occur between a little above 15°C and at least to 32.5˚C. Increasing therelative humidity to 80% will speed up rate of larval development (Armes, 1989). Larvaeshowed greater proportion of feeding on dry bacons compared to adult beetles and there wasindication for movement as well when they were placed on wet food, they did move about tosearch for dry food. When the larvae were placed on dry bacon initially they would ratherstaying on the dry bacon than moving about to search for other food sources. This importantproperty of feeding preference of larvae allows it to be useful in the determination of timesince death in forensic point of view. This indicates that once the eggs were laid on thecarcass and the environment is favourable for development, larvae tend to stay at the siterather than moving about. Then the post-mortem interval could be calculated based on thisbasis.In the next part of the current study, Dermestid beetles prefer lean meat rather that fats. It isobserved that the difference between the type of food initially presented and the food inneighbouring area influences which type of food is preferred. When they were not exposed toany of the food type, they would explore the food in the surrounding and choose to eat leanmeat rather than fats. However once they were exposed to fat in the beginning, a greaterreduction in weight of lean meat was observed indicating that the difference in odour wouldsignificantly enhance the preference to lean meat. This supported with the significantreduction in weight of lean meat once the beetles were initially exposed to it. However in thestudy of dried fish, Osuji (1974) (cited in Rajendran and Hajiran Peravan, 2005) found apositive correlation between the lipid content of fish and the level of infestation by Dermestesmaculatus. Further experiments with D. maculates by Osuji reported that development ofadult and larvae of this species needed cholesterol and the observation was well supported
with the finding that the larval developmental period of D. maculates was shorter in fishhaving a higher lipid content. Study by Armes (1991) on Dermestid beetle diets stressed theimportance of including both sugar and protein in increasing their mean lifetime fecundity.Perhaps this characteristic will determine the attractiveness of meat products presented to thebeetles. The main food types of Dermestid beetles contain cholesterol as the majorcomponent. It was found that cholesterol is essential for growth of Dermestid beetles(Fraenkel et al., 1941), other types of sterols introduced in their diet is fatal to them.According to Smith (1986), Dermestid beetles are attracted to the corpse when fats are rancid.This explains the observation that the beetles seem not interested to the fat in theexperimental set up. Therefore there must be certain physiological and behaviouralmechanism that determines the direction to which the beetles will be attracted to. Furtherstudy is required to determine the linkage between these factors.According to Bryd and Castner (2001), the adult beetles are cannibalistic and will eat younglarvae and pupae; sometimes eating one another as well. Therefore the missing beetles mighthave been eaten by the other insects. Moving and hiding underneath the soil is naturalbehaviour of invertebrates in avoiding sunlight and predators. This well explains the findingthat the beetles tend to move about in soil. The beetles when placed underneath the soil withtheir natural food (rat pellets) tend to stay underneath the ground. These adult beetles werealso found on the surface of the soil, but in a lesser proportion. These beetles therefore areable to live underground for at least 48 hours, and are useful for the determination of post-mortem interval. A way of disposing dead bodies is by burial underground (Galloway et al.,2001). The movement of the beetles in and out of soil greatly influences the ability of them inlocating buried remains. Dermestid beetles are able to locate food buried for at least 2 cmunderneath the soil as shown in the present study. Ability to locate the buried remain is not
sufficient enough to be used as forensic indicator of post-mortem interval. It is important toknow till which extent the beetles will stay underground colonising the remains and otherfactors associating with the succession process. But according to Martin and West (1994)Dermestid activity does not occur on submerged material and rapid burial will also prevent it.Study on another species of Dermestes beetles revealed that these beetles were found oncarcasses buried approximately 30 cm deep in soil (Anderson, 2001). As shown in the presentstudy, adult beetles tend to move about rather than staying on the food substance presented tothem. If this is the case Dermestid beetles are not useful for the determination of post-morteminterval of buried remains. It is not sure whether the adult beetles are feeding on the foodburied in this study as the percentage changes of weight were not determined. It is also notsure whether larvae of Dermestid beetles laid on the food stuff would remain on the food untilit is exhausted. If it is possible, then the use of larvae instead of adult would be useful for thedetermination of time since death. The determination of time since death using Demestes sp.is usually done based on the development of Dermestidae larvae which, according to Hinton(cited in Arnaldos et al., 2005) takes about 22 days at 28–30 ˚C and 40–50 days at lowertemperatures. Dermestes sp. were additionally active in early spring (April) and late autumn(November), but not during the winter months (Schroeder et al., 2003). Due to the distinctseasonal pattern of the early colonizing blowfly species it becomes possible to determine thetime of death even in cases of long post-mortem intervals (i.e. several months or years) ifempty puparia or frass of these insects are found (Schroeder et al., 2003).
ConclusionIn summary, there was a definite succession pattern among the carrion fauna, and each stageof decay was characterized by groups of arthropods occupying particular niches. Dermestidbeetles, a member of the order Coleoptra arrive and feed on carcasses during the later stage ofdecay. It is the matter of taste that determines the preference of food type of Dermestidbeetles. Dermestid beetles prefer to colonise dried and lean meat products. When thesebeetles were presented with unsatisfactory food, they will move about and search for betterfood for survival. This implies that when Dermestes arrive at a corpse in the early stage ofdevelopment, they would not colonise the corpse until it reaches a suitable stage that favourstheir succession. Upon succession, the developmental stage of larvae will allow for thecalculation of post-mortem interval. Calculation of post-mortem interval could not be done byusing adult Dermestes because they are not constantly feeding on the same food source all thetimes. The calculation is based on the assumption that the feeding larvae instars remain on thecorpse until they are developed into adults. Since each section of experimental set up wasdone in duplicates, no statistical test was employed to verify the difference between the data.More duplicates are needed to further evaluate the results of the present study. The baconsand pork meat were used as simulator that mimics the decomposition process of humanremains. This study can be extended to greater number of days. In this way, a greaterdifference between the weights would results and would be able to give a clearer idea on thefeeding preference of Dermestid beetles. The changes in weight of Dermestid beetles in theinvestigation of buried remains were not obtained and thus no conclusion can be made aboutthe degree to which Dermestid beetles are able to colonise buried remains. Also, study needto be done to determine whether larvae developed from the eggs laid on corpse will remain onthe corpse until there were no more material left as their food. This is important feature thatallow post-mortem interval to be estimated correctly.
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