Module 5 - Insects as Decomposers Flashcards
Evaluate and summarize the roles insects play in nutrient cycling
- When an organism releases metabolic waste or dies, the molecules are released back into the ecosystem; many molecules are in a form that cannot be absorbed by producers so they first must be broken down into simpler compounds by DECOMPOSERS (organisms that break down organic material)
Decomposers have an important role to play in replenishing the pool of chemicals available for use by primary producers
- ex. silverfish, cockroaches, termites, ants, juvenile and adult beetles, larval flies, moth larvae
Detrivores
- animals that consume dead organic material and wastes through oral ingestion rather than external digestion
- insects and other anthropod detrivores are important in accelerating the process of decomposition; they do so by phsically and chemically breaking down plant material, animal corpses, and organic waster
- activity affected by temp and moisture which also affect decomposition rates
- ex. millipedes, mites, springtail
Nutrient cycling
The circulation of chemical resources in the environment
- Key elements that are important building blocks in complex organic molecules: C, N, P
- Elements exist in many different forms in the atmosphere, soil, and water
Identify insect detrivores in different insect orders and feeding guilds
Detritivore Feeding Guilds:
1. Xylophagy
- bark beetles feed on stems of live trees
- termites feed on dead and decaying trees
- Coprophagy
- dung beetles (particularly the larvae)
- mites
- adult dung flies
- house flies
- blowflies - Necrophagy
- carrion beetles
- ecological succession
Xylophagy
- Xylophages: animals that consume wood tissue; wood is composed mostly of cellulose
- have symbiotic gut microbes that help digest the complex polysaccharides (cellulose) into forms the insects can use
- In termites, endosymbionts are housed in the hindgut which; since the cuticular lining of the hindgut is shed with each moult, the symbionts are lost. To replenish, insects transfer microbes between nest-mates. This occurs via mouth-to-mouth feeding on specialized fluids or by TROPHALLAXIS, feeding on hindgut secretions.
Coprophagy
Coprophages: dung feeding insects, they help circulate nutrients back into the soil when they feed on dung, so that plants can take up the nutrients efficiently.
- adult dung flies, house flies, and blowflies are the first to colonize a dung patty bc they are strong fliers and well adapted with many sensory receptors to locate fresh piles of excrement to oviposit.
- important to colonize when dun is fresh so juveniles can obtain enough nutrients to complete development before it dries out
- mites and dung flies are too small to locate dung so they hitch a ride on larger coprophagous insects
- Dung beetle offspring have a taste for animal waste. Adults provide access by excavating a burrow that they fill with a supply of dung for their larvae to feed on with little competition from other coprophages. Dung ball is buried in the burrow to protect it and female oviposits onto it. Not all dung beetles form dung balls, some burrow directly into dung patties. Others may be KLEPTOPARASITES that steal the burrows prepared by other dung beetles.
-Coprophages have a significant role in the maintenance of healthy pasture ecosystems; movement of nutrients back to the soil can promote plant growth. Consumption by coprophages also prevent the dung being consumed by harmful species.
Necrophagy
Necrophages: animals that feed on the corpses of other animals, called carrion.
- Carrion is a nutrient-rich resource that supports a wide diversity of organisms, many of which are arthropods
- important in nutrient cycling bc they break down the complex organic molecules into simpler compounds that can be taken up by plants or further broken down by microbes
- carrion is a short-lived resource, like dung
Carrion Beetles
- both larval and adult carrion beetles feed on vertebrate carrion
- Carrion is rare but nutrient rich; to help their offspring compete with other insects adult carrion beetles may carry symbiotic mites with them to the carrion. Mites feed on maggots that colonize the corpse prior to the arrival of carrion beetles, reducing the number of competitors for the beetle offspring.
- larvae take several days to reach maturity; adult beetles cover the carrion in oral and anal secretions containing symbiotic microbes that compete with colonizing bacteria and fungi for space but don’t digest the corpse; allows the beetle larvae to complete development and digest the carrion
- Biparental care is common in carrion beetles that specialize on small vertebrate carrion; mating pair of beetles excavate a chamber to bury a carrion resource; drag the whole corpse to the burrow; parents remain with their larvae, regurgitating food for the offspring and defending the nest
Ecological Succession
Ecological succession: when the species composition in an ecological community changes over time
- waves of colonizer appear, and while they consume the resources they physically alter the carrion, making it attractive to other organisms.
- species that make up these waves of colonizers depend on the geographical area and enviro conditions of a region, but the broad taxonomic categories of carrion specialists remain similar around the world.
Discuss the effect of temperature on insect postembryonic development and calculate degree-day accumulations
Temperature affects the growth rate, size, fecundity, and activity rates of arthropod decomposers since they are ectothermic. influences rates of decomposition.
Moulting
- Insects must grow in stages (instars) since their exoskeleton is limited in its ability to stretch and does not grow; each insta is separated by a moult.
- Stadium: the duration of the instar btw successive moults; affected by external factors (temp and moisture) as well as the mass or size of the insect.
Voltinism: the number of generations per year
- Due to the strong influence of temperature on insect development, some insect species experience different numbers of generations across their geographical range
- univoltine, bivoltine, multivoltine
- variation occurs in insects that occupy a large geographical range (high temps = more generations)
- Semivoltine: beetles are high elevations who move through 1 generation every 2 years
Degree-Days: measures of heat units accumulated over time; the number of degrees above a given ‘lower temperature threshold’ that accumulate over a 24-hr period
- The lower threshold is the minimum temp at which growth and development occurs for a specific insect
- The upper threshold to insect development is the highest temp at which development still occurs
- Insect development can continue at all temperatures btw these 2 threshold, though there is an optimal temp btw the 2 at which the greatest rate of development occurs
- Given the lower threshold, we can approximate the amount of degree days experienced by an insect over the course of a day using the formula: average daily temperature - lower developmental threshold
Degree Day Models
Degree-Day Models: the relationship btw temp and insect development can be used to develop these mathematical models that track insect development based on the temperature it experiences
- developed for each species of insect by rearing at multiple temps and tracking development.
- USED IN pest management programs to determine the best timing for implementation of control methods it fhtye must target a specific stage of the insect, or to predict when pest damage may be the most severe. Also extensively used in forensic entomology, which is the use of insects to provide info in forensic investigations.
Demonstrate applications of insect biology, behaviour and development to forensic investigations
Medicolegal forensic entomology
- most widely used and recognized form of forensic entomology
- the use of insects in criminal investigations involving injury or ailments, especially homicides
- Studying the arthropods present on a corpse helps investigators determine the amount of time elapsed since the victim dies, known as the postmortem interval
- Knowledge of the type of arthropods present, their species-specific development rates, and records of temperatures at the crime scene are all revelvant pieces of infor that enable investigators to estimate TOD
- 2 methods to estimate PMI: 1) degree day models for the first generation of insects to colonize the corpse, and 2) the concept of insect succession when more than one generation has occurred on the corpse
Forensic Entomology
The use of insects and other arthropods in legal investigations. It is a multidisciplinary approach to forensics that involves applied biology, ecology, criminology, and entomology.
Estimating PMI with degree-day models
Degree-day models can be applied when the first generation of colonizers are present on a corpse to determine the age of the insects, which are often present on the cadaver during the first month after death. Since many flies can locate a cadaver within hours or even minutes after death, determining the age of these insects can give a good approximation of the postmortem interval. 5 step process:
- Collect arthropod colonizers from the corpse
- Usually blow flies, in the family Calliphoridae
- All stages of these insects present should be collected since the age of different individuals can be difficult to determine in a field setting; the oldest stage is likely to be the first colonizers
- The length of time required to complete development is strongly influenced by temperature and can be predicted by degree-day models. If multiple generations of insects are found on the body, the cadaver is likely too old for degree day models to be used along in estimating the PMI, and the concept of insect succession must be used. - Species identification of the initial colonizers
- Accurate identification is necessary to ensure that the correct degree-day models are used to calculate development time of the insects
- Accurate species identification of maggots can be challenging since there are often few morphological indicators; a portion of the maggots are reared to adulthood to identify the species based on adult morphological traits
- high-throughput sequencing allows investigators to accurately identify a large number of specimens of different specieis in a short amount of time, but this is a more costly approach - Estimate the developmental stage at which the insects were collected
- some of the insects collected are preserved to determine the stage they were collected by applying the associated species-specific degree-day models. In some cases the body length or dry wt of maggots may be used to estimate the developmental stage. - Collect short-term climatic data
- Once the species and developmental stage of an insect colonizer have been determined, the degree day model for the insect is compared to climate data for the site where the body was found.
- Climatic data includes info about everything from temp to rainfall to cloud cover, which all affect the number of degree days experienced at the site - Estimate the postmortem interval (PMI)
- Once the number of degree days required to reach the specific instar of the collected larvae has been identified, this info is combined with the climatic data to estimate how long it took for the insect to experience this number of degree days
- standard assumption that eggs were laid on the body soon after death, this calculation yield the PMI
- when manually calculating degree days we can simplify calculations using average daily temp
Estimating PMI using insect succession
In forensic entomology, insect succession refers to the changes in the species composition associated with a decomposing body over time. Waves of colonizers also include non-insect arthropods.
- After the first generation of insects has left the body, it becomes necessary to estimate the postmortem interval based on the stage of insect colonization.
- predictable waves of insect colonization on a cadaver can help inform investigators about the time of death
- the patterns of colonization are referred to as INSECT SUCCESSION, and can be combined with climatic data and degree-day models to estimate a postmortem interval
The colonizers can be categorized into 3 main feeding groups: necrophages, predators, and incidental species (these appear at different stages of decomposition).
- initially a body will begin to decay due to the activity of microbes (bacteria and fungi); odours released that attract necrophages; different species appear depending on what art of the cadaver they exploit to match the resources available
- predatory and parasitic insects arrive to feed on the necrophagous insects, and sometimes predators will feed on the corpse
- with large vertebrate carrion it is common to find INCIDENTAL ORGANISMS that do not feed on the cadaver but use resources on and around it
- waves in which arthropods arrive follow the STAGES OF DECOMPOSITION
Stages of Decomposition
Stages of Decomposition: allow us to determine the age of a cadaver based on the species present
1. Fresh
- begins at the moment of death
- decomposition initiated by microorganisms within and around the body’ release VOCs that are olfactory cues for the first wave of necrophagous insects. First wave of colonizers often includes female blow flies, flesh flies, house flies
- feed on bodily fluids and deposit their eggs; eggs hatch into maggots that feed on the dead tissue, attracting carnivorous arthropods
2. Putrefaction
- occurs when the corpse begins to bloat due to gases produced by anaerobic bacteria within it
- this stage marks the arrival of the second wave of arthropods; other fly species such as cheese flies and faniid flies
- predatory insects continue to arrive as well, attracted by the maggots; many beeetles
3. Black Putrefaction
- sometimes called active decay
- characterized by a discolouration of the body and the escape of gasses from the body as a result of bacterial decomposition
- maggots of flies that initially colonized the body exit to pupate in the soil
- adult flies begin to dimish in number as the corpse becomes unsuitable for offspring development
- beetle species dominate
4. Butyric Fermentation
- also known as advanced decay
- named for the butyric acid produced by microbes during this pase
- butyric acid has a characteristic smell that attracts a new suite of arthropods
- little flesh remains; beetles remain dominant and are joined by predatory mites
5. Dry decay
- hair, bones, cartilage, and some dry skin is left
- most necrophagous arthropods are gone except for the keratin-feeding beetles in the family Dermestidae
- Dermestid beetles are scavengers that feed on animal proteins that few others can digest such as skin, hair, and feather
- incidental species join by chance
