[MUSIC] Detritivores feed on many kinds of organic material from plant fragments to animal matter such as skin, feathers, and even dumb. When different types of arthropods feed on similar organic material, they can be grouped into what is known as a feeding guild. Let's examine some of the detritivore of or feeding guilds, including xylophages, coprophages, and necrophages. Cellulose is a large complex polysaccharide or sugar molecule found in the cell walls of plants. It is an important structural component plants and is the most abundant carbohydrate on Earth. It is therefore not surprising that many insects have evolved the capacity to use cellulose through the consumption of wood, a substance relatively low in nutrients other than cellulose and lignin. These insects are collectively called xylophages. While some insects feed on and damage live trees, many wood feeder specialize on dead and decaying trees. Wood feeding insects such as carpenter ants, termites, and many beetles play an important role in breaking down dead wood in forest ecosystems. However, the same insects that are important nutrient recyclers in forests can also feed on man-made wood instructors potentially causing major damage. But how exactly do these insects feed on wood? Most xylophagus insects have closed symbiotic interactions with gut microbes to help them digest the tough cellulose. Termites, for example, have particularly well-developed endosymbiotic fauna in their hind guts. That being said some insects including many termite species and certain cockroaches can produce cellulose degrading enzymes of their own. [MUSIC] Microbes in the hind gut of many termites break down the complex sugars found in wood into simpler sugars that can be metabolized by the termite host. Cellulose in particular is broken down to short-chain fatty acids that the termites use for nourishment. The endosymbiotic community is complex and includes bacteria, archaea, and protists, all housed in the termite hind gut. Because the cuticular lining of the hind gut is shed at each molt, the symbionts are lost when the insect molts. To deal with this termites transfer microbes between nest mates through a process known as trophallaxis. This microbe exchange occurs between individuals in the colony either through mouth to mouth feeding on specialized fluids or by feeding on hind gut secretions. Termites use the ladder method for symbiont exchange. Take note though that termite trophallaxis axis is an exchange of special hind gut secretions and should not be confused with dung feeding or coprophagy which we will discuss next. Vertebrate dung is a rich source of nutrients for insect detritivores. Insects that consume dung are called coprophages and include species such as dung beetles and many flies. By consuming organic waste copropahgus detritivores help move nutrients back into the soil where they can be taken up by plants. Maggots of dung flies, house flies, and blowflies commonly feed on dung. The adult flies of these groups are particularly well adapted to locate fresh piles of excrement that are suitable over position substrates. Eggs or larvae are deposited onto the freshly laid dung. Rapid colonization of the dung while it is still fresh is particularly important for juveniles so that they obtain enough nutrients from it to complete development before the dung dries out. In some cases, small faradic fly species such as the lesser dung flies will take advantage of another species ability to locate and access dung piles by hitching a ride on a larger copropahgus insect. There are several groups of beetles that feed on dung. Though the most well-known are probably the dung beetles in the family scarabaeidae. You may be familiar with these beetles from their prominence in Egyptian mythology or their starring role in some movies. We will learn more about the place of insects and mythologies and pop culture in module 12. Some adult dung beetles gather the excrement and form it into a ball sometimes working in pairs. The ball is rolled to a suitable location where it is buried and used as a deposition site for the females eggs. The larvae that hatch feed on the dung supplied by the parents in the nest chamber. Some adult dung beetles will also feed on fecal material, but only on the fluids and finest particulate matter or on associated microbes. The dung burying behavior of these beetles protects their food from competitors, predators, and unfavorable climatic conditions. Rather than making a nest, some dung beetle species will burrow directly into the dung pile to lay their eggs. Many species of dung beetle also exhibit bi-parental cooperation as both male and female beetles work together to build a nest and provide food and protection for the offspring. For some dung rolling species, the production of the dung ball can even serve as a sexual display to attract mates looking for a big pile of poop. Some species of dung beetles have evolved an alternative strategy. Rather than gathering and preparing their own dung, these beetles are kleptoparasites. They take advantage of nests prepared by other dung beetles. Coprophages are important recyclers of the nutrients in fecal material. They are particularly important in the management of pastoral farming ecosystems where the dung of cattle and other livestock needs to be rapidly transformed into usable nutrients. If dung is left on the ground too long, it can impede plant growth through lack of light or nutrients and seriously deteriorate pasture land. This in turn limits the available grazing area. Some researchers have suggested that dung beetles may help reduce parasite infestations and livestock by removing fecal material that could otherwise incubate parasitic worms. Furthermore, dung beetle activity may also suppress the breeding success of pestiferous flies due to interspecific competition for resources. Let's hear from Dr. Kevin Floate, an expert from Agriculture and Agri-Foods Canada on the decomposition of dung and other fecal factoids. So I'm a research scientist with Agriculture and Agri-Food Canada. And I study different topics of entomology. Insects can play a very large role in dung decomposition, but overall there's other factors that are equally or more important. For example, if you have fresh cattle manure on a pasture and a sudden rainstorm that can essentially wash the pad away in a matter of hours. Birds will forage in dung looking for insects or seeds and they will shred a cow pie very quickly. You can imagine a dung pat which gets deposited in the where time, it may persist for years. So most of the insect colonization occurs within the first hours maybe the first two weeks after the dung is deposited. And if nothing's colonized during that period, probably nothing will colonize. So it depends a lot on when the dung pat is deposited on the pasture. It depends on what the animal might have been treated with. So most livestock or cattle, for example, are treated with some sort of a parasiticide product. Depending on what parasiticide is used residues appear in the dung which can affect activity of the dung insect. And consequently have implications for how quickly those insects can break down the dung. Any factors affecting insect activity. So if the pie is deposited at night time versus daytime, in the shade versus full sun, again time of the year. It also would depend on what insect species are present where the dung pie is deposited. So one of these groups we call detritivores. And these are beetles that are attracted to fresh dung to feed, but they don't actually lay their eggs in dung. They come and they feed they disappear. Their larvae will develop in crop land or rich organic soils. And then we have another group I refer to these as a dwellers. So these are dung beetles. The adults will arrive at a fresh pie. They'll dig and tunnel into the fresh pie made, lay an egg. And that egg will hatch into larvae and the larvae will develop in the pie as it sits on the surface of the soil. We have another group called the rollers down here. And as you might expect from the name, these adults will come into a fresh pie and the adults will actually remove a bit of the manure and form it into a ball. And then working as a pair of male and female, they'll push that ball of away from the pie some distance. It could be a matter of centimeters or a meter or more and then buried underground. And in the tunnel where they bury the manure, they'll lay an egg. So that when that egg hatches into a larva, the larva has already food supply and it'll feed on the bird manure. And then we have another group called tunnelers here in the bottom. And the tunnelers are very similar to the rollers. It's the adults that arrives at the fresh dung pie. And adults will rip apart the pie and and make it into small balls manure. And then they tunnel directly beneath where the pie is sitting into the ground. They'll bury them in your in the tunnels and then lay an egg. Now when the egg hatches, the larva has something to eat. They can rip apart a pie and spread it within a matter of hours or days whereas you can have a lot of dwellers coming in, but degradation from dwellers because it's larval feeding can take months. So you got the little head up here. You have the three pair of legs at all insects have up here. But then the rest of this is the abdomen. And like the rumen of a cow the the gut of dung beetles have specialized microorganisms designed to break down plant fiber. So different bacteria than you'd find in a cow, but the same function. And that's why dung beetle take so long to develop from egg to adult because the quality of their diet plant fiber is not very nutritious. Other insects, for example, like flies that are feeding on bacteria for the life cycle can go from egg to adult in a week or last depending on temperatures. If you have a fresh cow pie on a pasture, the grass beneath that pie cannot be grazed. So it's immediately taken out of grazing as far as a cow is concerned. And then the nutrients from that manure will leach out into the surrounding area and fertilize the grass. But because it's so much nitrogen now surrounding the pie, that grass comes up not as healthy but is almost on nitrogen rich almost rank. There's like a green halo surrounding the pie. Cows don't like that grass. So they avoid it. So if you look at the amount of dung deposited by one cow on a pasture during a day and assume the pies don't overlap each other, they remove about a meter of folage out of that pasture per cow per day. We do a lot of our research on native grassland in Southern Alberta. And there are species associate native grassland that we don't find on tame pastures. So pastures in which the line has been plowed up and planted to grasses. I have species, tunnelers or rollers. I love because they have a lot of very high level of paternal care and maternal care for their offspring. Animal corpses also called carrion are nutrient rich resources that can support a wide diversity of organisms many of which are insects. Carrion feeding insects called necrophages convert complex organic molecules within the carrion into simpler compounds and release them into the ecosystem. Carrion, like dung, is a short-lived resource, which is only available for brief periods of time. Therefore, necrophagous insects such as flies and carrion beetles have evolved to be highly sensitive to odors of decay and can quickly find carrion in the immediate area. A good example of necrophagous insects are the carrion beetles in the family. In most carrion beetles, the larvae and adults feed on vertebrate carrion. However, adult beetles may also feed on carrion associated fauna such as maggots and other beetles. Many carrion beetles have to compete with other necrophagous insects such as blowflies and flesh flies for resources on large carrion. Carrion beetle larvae may have a key advantage though. In some cases, symbiotic mites that are transported by the carrion beetle adults feed on maggots already present on the corpse reducing competition for the beetles. Carrion beetle larvae don't just have to compete with other insects. Since the beetle larvae takes several days to reach maturity, they must get all their nutrition from the corpse before colonizing bacteria and fungi digested since carrion is very susceptible to microbial decomposition. To deal with this, carrion beetle adults remove the fur or feathers of their prize and cover the skin of the animal in oral and anal secretions that contain their own cocktail of symbiotic bacteria and fungi. These microbes compete with other colonizing microbes for a place on the cadaver, but do not digest it as actively as the other species. Instead by taking up space that other microbes could colonize, the protective layer of the beatles microbes prevents other species from consuming the dead body, helping to preserve the carrion for long enough for the developing larvae to mature. The beatle's fluids also contain antimicrobial compounds that can further stunt the growth of unwanted bacteria and fungi. There are some species of carrion beetles that specialize on smaller corpses like dead rodents. These species tend to exhibit bi-parental care, which is extremely uncommon in insects. The beetle pair bury the carrion resource where the offspring have exclusive access to the food. A corpse may be 200 times the beetle size. Yet they can drag it to an excavated chamber up to a meter away. The parents remain with the larvae as they grow, fending off potential predators and feeding on the carrion to regurgitate food for the offspring. The parent beetles also practice a behavior known as filial cannibalism in which the parents kill and consume their larvae in order to regulate brood size. This ensures that surviving offspring grow and develop successfully as they receive the lion's share of the nutrients. Parenting can be tough, but in this case, it may be even tougher for the kids. Depending on the state of decay and the type of carrion, the composition of detritivores species changes as different species colonize or finish development on the carrion. This is known as ecological succession, which is the change in species composition of a community over time. While this concept applies to any ecosystem, it is particularly predictable in the decay of carrion. As waves of colonizers appear, they consume their favored resources and physically alter the habitat making it attractive to other organisms. The species present on a dead body at each stage of decomposition differs depending on geographical area and environmental conditions, because each region has its own carrion fauna. Nonetheless, the broad taxonomic categories of carrion specialists are similar across the world. We will discuss the phenomenon of succession in more detail in a future lesson as we explore its applications in forensic entomology.
