Environmental effects on forensic entomology

Forensic Entomology encompasses any aspect of certain arthropods involved in legal proceedings. Forensic Entomology is divided into three branches: urban, stored products, and medicocriminal. Various environmental factors, such as climate and geographical location are responsible for certain athropodal behavior.

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.

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.

Temperature

Temperature has an influential affect on what species of insects are present on a carcass during decay. If it is too cold certain insects they simply will not come out to eat. Inversely, if it is too hot, they will not be out and about either. There are two insects that are the most relevant to forensic entomology in the United States. The blowfly and the Staphylinidae (Rove beetles) are the two insects discussed in this article.

The Calliphoridae otherwise known as Blowfly or Harry Maggot Blowfly are of small build and green in color. They are the very first insects to arrive at a carcass and begin feeding. The average life cycle of the blowfly is very important to entomologists when they are found at a crime scene. They have such a precise interval of growth that when found at any stage of development, it can be accurately calculated the approximate time of birth of the larvae, which usually is very close to the time of death of the victim.

The Rove Beetle or Staphylinidae is the largest known family of beetles on the planet with over 45,000 different species. Most adults are about 7mm long, and have short elytra. They are very skinny and flexible, allowing them to gain access to many cramped spots to find shelter and food. They feed on just about anything they can find in or near a carcass, including maggots. They are much less submissive to temperature then the blowfly due to their existence almost everywhere on the planet. This is something important to entomologists because if there the temperature is right, but there are no blowfly maggots present, there might have been several days of weather that was actually too cold for the fly allowing the beetle to come in and take over.

Insects are the single most important source for gathering information. There are many factors that must be taken into account when a forensic entomologist enters a crime scene. Location, weather, humidity, etc all affect an insects ability to participate in the feeding. Without the correct conditions, it is very difficult for insects to go about their normal lives.

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.

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