Environmental effects on forensic entomology

Forensic Entomology encompasses any aspect of certain arthropods involved in legal proceedings. There are many external effects that forensic entmologists have to consider when evaluating data.

Climate

In determining degree days, forensic entomologists address and observe weather conditions that may have contributed to the alteration of the standard time for an insect to develop. Temperature, moisture, sun exposure all effect insect development leading to accurate post mortem interval determination. "Because insects are cold-blooded animals, their rate of development is more or less dependent on ambient temperature."

Moisture Levels

Rain and humidity levels can affects the time for insect development depending on the amount of rain fall and humidity in the area where the body is found. If there are large amounts of rain, slower development occurs due to drop in temperature in most species, but there exceptional species that prefer these conditions. Light rain or a very humid environment will result in faster development. In a humid environment, the maggot mass heats up by the humid air trapping the heat in a localized area where the maggots are leaving a smaller number of degree days.

Sun Exposure

Sun exposure can increase or decrease time of insect development. Bodies found in open areas with large amounts of sun being exposed, the body will heat up giving the insects a warmer area to develop increasing there development time. Vice-versa, in shaded areas the bodies will be cooler leaving longer degree days. If the body or area of infestation has been rained on or been made moist the insect populations will increase more rapidly.

Degree Days

Degree day is a quantitative index demonstrated to reflect demand for energy to heat or cool houses and businesses. This index is derived from daily temperature observations at nearly 200 major weather stations in the contiguous United States. The "heating year" during which heating degree days are accumulated extends from July 1st to June 30th and the "cooling year" during which cooling degree data are accumulated extends from January 1st to December 31st. A mean daily temperature (average of the daily maximum and minimum temperatures) of 65°F is the base for both heating and cooling degree day computations. Heating degree days are summations of negative differences between the mean daily temperature and the 65°F base; cooling degree days are summations of positive differences from the same base. For example, cooling degree days for a station with daily mean temperatures during a seven-day period of 67,65,70,74,78,65 and 68, are 2,0,5,9,13,0,and 3, for a total for the week of 32 cooling degree days.

Development of many organisms is dependent on temperature. All farmers know that crops and pests develop faster in warmer than in cooler years. However, there is not necessarily a yield or quality benefit in cool or warm seasons. Organisms simply grow or develop faster when the air temperature is warmer. When temperatures are higher, organisms develop faster. However, they are exposed to the greater heat for fewer days and the net accumulation of heat required for development is about the same as for organisms grown under cooler conditions for more days. This accumulation of heat is called “physiological time” and ºD are a measure of physiological time. One oD is defined as one degree above a threshold temperature (TL) during 24 hours. There are no oD when the threshold temperature is higher than the daily maximum temperature. When the lower threshold temperature is lower than the daily minimum temperature, the number of oD is estimated as the mean of the maximum and minimum temperatures minus the lower threshold. When the threshold falls between the maximum and minimum temperature, calculation of oD is more difficult and the method will be explained later.

With integrated pest management (IPM), degree day accumulations are used to predict important events in the life of an insect. Examples include egg laying, egg hatch, scale crawler movement, or appearance of symptoms. These biological events are in turn used to schedule particular activities such as scouting and synchronizing insecticide sprays. The easiest way to calculate degree days for a specific date is to add the daily high and low temperature and divide by two. Then, subtract the threshold temperature for the particular insect. For example, if the min/max thermometer indicates a low of 45 degrees F and a high of 75 degrees F, then the average temperature for the day was (45+75)/2 = 60 degrees F. If the threshold temperature was 50 degrees F, then 10 degree days would have accumulated. Formula: (max T + min T/2)-threshold=degree days Check your thermometer and make this calculation each day. Add the daily value to the total from all the previous days.

Geographic Distribution

According to Jean Pierre Mégnin’s book entitled La Faune des Cadavres there are eight distinct faunal successions attracted to a corpse. While most beetles and flies of forensic importance can be found worldwide, a portion of them are limited to a specific range of habitat. It is forensically important to know the geographical distribution of these insects is order to determine valuable information such as post mortem intervals or if a body has been moved from its original place of death.

Calliphoridae is arguably the most important family concerning forensic entomology given that they are the first to arrive on the corpse. The family’s habitat ranges into the southern portion of the United States. However, while Chrysonoma rufifaces, the hairy maggot blow fly, is part of the Calliphoridae family and is widespread it is not prevalent in the Southern California, Arizona, New Mexico, Louisiana, Florida, or Illinois regions.

Beetles are representative of the order Coleoptera which accounts for the largest of the insect orders. Beetles are very adaptive and can be found in mostly all environments with the exception of Antarctica and high mountainous regions. The most diverse beetle fauna can be found in the tropics. In addition, beetles are less submissive to temperatures. Thus, if a carcass has been found in cold temperatures, the beetle will be prevalent over Calliphoridae.

All geographic locations have a temperature range linked to that area. Temperature has an influential effect on what species of insects are present on a carcass during decay. When conditions are extremely hot or cold, certain insects are less active.

Utilizing Environment Factors for Pest Control

Pest control experts and agencies put environmental information to practical use everyday so as to predict insect behavior and location. Pest control is a multi-million dollar operation enforced worldwide.

Weather Factors

Various weather conditions in a given amount of time cause certain pests to invade your household. Reasoning is because the insects are in search of food, water, and shelter. Damp weather causes reproduction and growth enhancement in many insect types, especially when coupled with warm temperatures. Most pests concerned at this time are ants, spiders, crickets, cockroaches, ladybugs, yellow jackets, hornets, mice, and rats. When conditions are dry, the deprivation of moisture outside drives many pests inside searching for water. While the rainy weather increases the numbers of insects, this dry weather causes pest invasions to increase. The pests most commonly known during dry conditions are scorpions, ants, pillbugs, millipedes, crickets, and spiders. Extreme drought does kill many populations of insects, but also drives surviving insects to invade more often. Cold temperatures outside will cause invasions beginning in the late summer months and early fall. Box elder bugs, cluster flies, ladybugs, and silverfish are noticed more often, seeking the warm indoors.

Precautions

There are a few measures homeowners can implement in preventing serious pest breakouts. Sealing any cracks/holes outside the home is extremely helpful, especially on the south and west areas of the home because the sun will heat those walls, creating a nice habitat for pests. Utilizing information about insect behavior due to outside influences enables humans to take the necessary steps for pest control.

IPM

IPM is a well-known Integrated Pest Management program designed to undertake pest problems, using a strong background of information about each pest in order to choose the best course of action. the overall goal of IPM is to reduce harmful effects from insects on crops, houses, and livestock while avoiding any unnecessary harm on the surrounding environment. The program utilizes and enhances any natural control methods on pests, as a priority, to avoid using pesticides if possible. A general technique is outlined with regard to formulating an active plan and evaluating the best policy.

External Links

http://www.clt.uwa.edu.au/__data/page/112507/fse07_forensic_entomology.pdf

http://www.blackwell-synergy.com/doi/abs/10.1111/j.1556-4029.2006.00217.x