DECOMPOSER INSECTS Eduardo Galante and Mª Angeles Marcos-Garcia Centro Iberoamericano

8/14/2019 DECOMPOSER INSECTS Eduardo Galante and M Angeles Marcos-Garcia Centro Iberoamericano

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DECOMPOSER INSECTS

Eduardo Galante and M Angeles Marcos-GarciaCentro Iberoamericano de la Biodiversidad

Alicante, Spain

In any natural or semi-naturalhabitat, three types of organisms exist:producers, consumers anddecomposers. Good functioning of theecosystem will depend on their suitableaction and interaction. Organismscapable of catching energy andsynthesizing organic matter frominorganic compounds constitute theproducers. Though chemosynthetic

bacteria exist, most producers areplants. Green plants use solar energyand fix CO 2, producing organiccompounds rich in energy. Most of thisaccumulated energy will get used in theecosystem by respiratory processes andother vital functions, whereas someorganisms of the community such as theconsumers and decomposers will usethe energy accumulated by otherorganisms.

The consumers are heterotrophicorganisms that obtain food fromproducers or from other consumers, withthe possibility of several levels ofcomplexity inside an ecosystem.Primary consumers feed directly on theproducers. Secondary consumers feedon primary consumers, etc. Finally, wehave the decomposers, saprophyticorganisms feeding on dead matter ordecaying remains derived fromproducers and consumers. Thus, theorganic matter synthesized byproducers goes on to other levels oforganisms across the trophic chains,though much of the energy will be usedin respiratory processes at all levels.

In these trophic processes, animportant element to take into account is

that the decomposers operate at all thelevels. Thus, all energy not used by theconsumers and producers, as well asthat accumulated in excretory products,is used by the decomposers andrecycled into the ecosystem. Thisprocess constitutes the energy cycle ,and good functioning and subsistence ofthe ecosystems depends on effectiveenergy cycling.

In a terrestrial ecosystem, morethan 90% of the organic mattersynthesized by the green plants remainsunconsumed, and it passes to the levelof decomposers as plant materialdecaying on soil, together with theremains of animal corpses, and theexcretory products of all levels.

The process of decomposition isone of the most important events in thefunctioning of ecosystems.

Decomposition can be defined as theprocess by means of which a deadorganism or its remains are brokendown into the parts or elements thatcomprise it, and at the end of theprocess the animal or plant remains willhave gradually disintegrated until theirstructures cannot be recognized, andtheir complex organic molecules willhave fragmented. This involves acomplex process in which biotic andabiotic agents interact within theecosystem. To sum up, thedecomposition processes cause theliberation of energy and mineralizationof chemical nutrients, turning theorganic matter into inorganic elements.

In the process of decomposition,there are two phases, sometimes


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difficult to distinguish, that we could calldestruction and degradation of theorganic matter. The process ofdestruction refers to the initial phase ofthe decomposition cycle and is

characterized by breaking down theorganic remains by mechanical meansso that at the end of this process small-sized particles are obtained. During thisinitial phase both abiotic (rain, wind,temperature, etc.) and biotic elements(decomposer fauna) play an importantrole. In the second phase, degradationof the organic matter occurs, resulting inthe disintegration of the small particlesinto molecules, producing CO 2, H2O and

mineral salts as final products.The destruction phase alsoresults in dispersion of the organicmatter, because the small resultingparticles can be taken by means ofdiverse mechanisms out of the initialsource (dragging by wind and water, ordirect action of animals such as burial,ingestion, movement, etc.). It isimportant to note that nutrients releasedby decomposers constitute a foodsource for numerous animal species,extending the cycle by means ofincorporation of the nutrients intotissues, and eventually constituting newcorpses and excrements.

The groups of arthropodsinvolved in the processes ofdecomposition of animals and plantsremains belong to many taxa (Fig. 1).They are considered to be mesofaunawhen their size ranges between 100 and200 mm (such as mites (Acari),springtails (Collembola) and smallinsects), or macrofauna when they arelarger, such as some beetles (e.g.,Scarabaeidae, Geotrupidae orSilphidae), Diptera larvae (e.g.,Muscidae, Sarcophagidae,Scatophagidae or Calliphoridae),

centipedes (Diplopoda), woodlice(Isopoda), etc. All these groups areresponsible for the fragmentation ofplant or animal remains, contributing tothe destruction phase. They contribute

both to the redistribution of the organicremains and formation of soil elements.These groups of arthropoddecomposers are present in nearly allterrestrial habitats, and generally in veryhigh numbers. In some cases, millionsof individuals belonging to hundreds ofspecies have been identified in just onesquare meter. Especially in temperateareas, arthropods are the majordecomposers, playing a very important

role in degradation of waste. Thanks tothe action of the arthropods during theinitial phase of fragmentation, organicremains can be degraded, andeliminated from the soil surface.

When a suitable community ofdecomposers exists, it prevents theappearance of potential bottlenecks inthe recycling of basic elements in theecosystem. Thus, when entomofaunacapable of acting effectively on plantand animal remains does not exist in aterrestrial ecosystem, serious alterationsin the ecosystem arise, with a reductionin energy flow and great loss ofbiodiversity.

Decomposers of plant remains Arthropods play an important role

in degradation processes of plantremains. Nevertheless, most lack theability to develop enzymatic processesfor degrading the fundamentalcomponents of any plant: lignin andcellulose. Degradation of celluloserequires the presence of the enzymecellulase, which most arthropods lack.Many insects have solved this problemby means of mutualistic relations withmicro-organisms, having bacteria or


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symbiotic protozoa in the intestinal tract.Others take advantage the cellulaseproduced by external microflora. Amongthe well-known insect decomposers aretermites (Isoptera) and cockroaches

(Blattodea). The termites possesssymbiotic bacteria and protozoa, and intheir absence wood cannot beassimilated by these insects.

In many ecosystems millipedes(Diplopoda) have special importance asdecomposers. These arthropods, whichspecialize in leaf litter consumption,sometimes are abundant, concentratedin relatively small areas, and activeduring a great part of the year.

Another important group in thedegradation of plant remains is woodlice(Isopoda), which also possess symbioticmicroorganisms in their intestine thatallows them to degrade cellulose.

Not all arthropods assimilatecellulose by means of symbioticbacteria, but they make use of woodymaterials that are pre-digested byextraintestinal microorganisms. Includedin this group are some species ofspringtails such as Tomocerus (Collembola), ambrosia beetles(Coleoptera: Scolitydae), ants of thegenera Atta (Hymenoptera: Formicidae)and termites (Isoptera) that cultivatefungi.

All plant remains do not alwayspresent the same difficulty of digestionfor arthropods. Fruits are extensivelyexploited by arthropods, thanks to theexistence of yeasts that enhance fruitdecomposition, allowing manyarthropods such as flies ( Drosophila isprobably the best known example) andwasps (Hymenoptera: Vespidae) to feedinto the product resulting from thefermentation. Nevertheless, a fact thatmust be remembered is that therelationship between micro-organisms

(bacteria, fungi and protozoa) and plantremains is very close, and therefore, inmost cases it is inevitable that thearthropods consume both resourcessimultaneously. In some cases, the

ingested biomass of micro-organisms ismore important nutritionally than theingested plant remains.

The entomofauna of excrement andcorpses

The studies of ecosystems havegenerally paid preferential attention tothe decomposition processes ofvegetative remains, due to theimportance that litter has in the

composition of the soil and thecontribution of its nutrients. The processof decomposition of carrion and dung,though sometimes not well known andlittle studied in many ecosystems, isalso important.

To understand the processes ofdegradation of corpses and excrements,and the attractiveness of this decayingmatter to arthropods, we must considerthat they are very rich resources oforganic components that have veryspecial microclimatic conditions. Dungand carrion represent not only a richsource of energy, but also a veryspecialized habitat that is exploited, inmost cases, by very specificentomological fauna. This fauna obtainsfood either directly, such as in the caseof the coprophages and carrion-eatingarthropods, or indirectly, such as in thecase of the predators that feed on thedecomposers.

It is generally difficult to establishthe limits of an arthropod community,but when we study carrion or dung wemeet a perfectly defined ecological unit,limited in both space and time. Carrion(Fig. 2) and dung present many specialcharacteristics that influence the


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composition and dynamics of the set ofspecies using them. These resourcesconstitute isolated microhabitats insidean ecosystem in which they aredeposed, forming a patchy system.

These microhabitats are relatively smallin size (except for corpses of largevertebrates), rich in nutrients, and with ashort existence (generally not more thanone insect generation). Carrion anddung are special microhabitatscharacterized fundamentally by theirrapid ecological successions, beingextremely ephemeral micro-ecosystemsthat are rapidly destroyed by the actionof the arthropods that colonize them.

Arthropod species are sometimes veryabundant in these resources, andthousands of individuals belonging to aset of arthropod decomposers may beattracted to an isolated unit. Forexample, more than 100 species ofarthropods belonging to 16 orders and48 families have been found in just onerabbit corpse, or 16,000 dung beetlesfound in elephant dung.

The arthropods involved insuccession vary according togeographical areas, even in places withsimilar climates. Also, the number ofindividuals and the species colonizingthese microhabitats vary enormouslyfrom one patch to another, and alsothrough time. Typically, these speciesare more or less aggregated in theselimited resources, with interspecificdifferences in foraging and breedingbehavior. The aggregated spatialdistribution and resource partitioningallow a great number of decomposerspecies to coexist in an ecosystem, butgreat differences in numbers ofindividuals and species composition aregenerally found among similar amountsof carrion or dung. However, the broad

taxonomic categories of carrion or dungspecialists are similar worldwide.

Sometimes it is difficult to discernwhether the arthropod fauna involved indecomposition processes contributes

directly to the recycling of organic matteror, as in leaf debris systems, they makethe substrate more available to themicroorganisms (bacteria and fungi)considered by some authors to be thetrue decomposers. The action of thelarvae of flies and other insects, forexample, produces liquefaction ofcorpse tissues, preparing thesubstratum for the intervention ofmicrobial decomposers. On the other

hand, the mechanical action associatedwith removal of excrement by beetles,and in making tunnels by both beetlesand fly larvae, enhances microbialactivity. The existing studies show thatthe action of decomposer species ofarthropods and microorganisms iscomplementary, but not purely additive.

Vertebrates are often consideredto be important scavengers, and manyspecies feed on carrion. Vertebratesmay not distinguish between freshlykilled prey and a freshly dead animal,and many predators eat both of them. Itis not easy to know how much organicmatter is recycled in this manner, butdepending on the period of the year,many of the small animal corpses canbe totally destroyed by scavengers.However, during summer and autumn intemperate regions, and in the rainyperiod in tropical areas, corpses arerapidly colonized by arthropods. As aresult, rapid decay is observed, with thevast majority of carrion being consumedby various arthropod species, principallyfly larvae.

The process of decompositionamong excrement and corpse systemsvaries as a result of the particular


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composition of the remains, whichattracts its own specialist community ofarthropod decomposers. Likewise,differences between the entomologicalfauna of excrement are found,

especially between the excrement ofcarnivores and those of herbivores. Thisoccurs because the composition ofnutrients is totally different betweencarnivore and herbivore excrement.While the excrement of herbivorescontains a great number of vegetativecomponents that are little changed fromthe plants ingested (80-75% of theingested weight), the digestive systemof carnivores is much more efficient and

the excrements contain less organicmatter suitable for exploitation byarthropod species. The fauna feeding onthe carnivore excrement is generallydepauperate, and decay often resultsexclusively from the actions ofmicroorganisms.

Decomposers of corpses Arthropod species attracted to

corpses change according to theecosystem and environmentalconditions. The importance ofnecrophagous arthropods is not only theingestion of carrion, but also in makingthe carrion available to microorganisms.Many insects, principally fly larvae,secret enzymes directly into the carrion,producing liquefaction of the tissues.Likewise, adult and larval beetles, andfly larvae, make tunnels through thecarrion, increasing aeration andmicrobial activity. The dominant groups,both in number of individuals anddiversity, are dipterous andcoleopterous species. Also, ingeographic areas where ants areabundant, the corpses are removedrapidly by these insects, specially thecorpses of invertebrates. Nevertheless,

the arthropods involved in thisprocesses, and the intensity of theaction of these animals, vary accordingthe spatial location of the corpse, type ofsoil and depth of burial. The number of

insects living in carrion diminishes withdepth of burial.The arthropods colonizing

corpses form a sequential succession ofgroups and species that depends on thesize of the carrion, and on the climaticand edaphic conditions of the areawhere they live. Very few species arewidespread throughout the world, andeach geographical area and ecosystemhas its specialist species feeding on

carrion.The colonization of a corpse is asequence of arthropods arriving assuccessive waves at the carrion. Theform, nature and timing of thesuccession depend on the geographicarea, the surrounding non-biologicalenvironment, and the size of the carrion.The first waves involve blow flies(Diptera: Calliphoridae) and house flies(Diptera: Muscidae) arriving for a fewhours to oviposit or drop live larvae.Later, there is a second wave ofsarcophagid flies (Diptera:Sarcophagidae) that together withspecies of calliphorid and muscid flies,deposit their eggs or live larvae on thecorpse. The larvae of these flies are, inturn, consumed by larvae and adults ofpredatory beetles living in corpses.Staphylinids (Coleoptera:Staphylinidae), histerids (Coleoptera:Histeridae) and silphids (Coleoptera:Silphidae), all are predators of flies,though they also feed on carrion. Whenthe viscera decompose and the fat ofthe corpse turns rancid, a third wave ofinsects starts, with some species ofphorids (Diptera: Phoridae), drosophilids(Diptera: Drosophilidae) and hover flies


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of the subfamily Eristalinae (Diptera:Syrphidae) arriving. The fourth waveconsists of cheese skipper species(Diptera: Piophilidae) and relatedfamilies of flies. Finally, a fifth wave

occurs, the larvae and adults from somegroups of beetles such as dermestids(Coleoptera: Dermestidae), trogids(Coleoptera: Scarabaeoidea: Trogidae)and clerids (Coleoptera: Cleridae) andtineid caterpillars (Lepidoptera:Tineidae) that eat keratin and feed onthe remaining hair and feathers.

Diptera are among the mostimportant decomposers, especiallysome of the Calliphoridae (e.g., Lucilia ,

Calliphora , Chrysomyia , etc.), followedby some Muscidae (e.g., Fannia ), andSarcophagidae (e.g., Sarcophaga ).Though the adults feed on the fluids ofthe corpse, the larvae are the truedecomposer organisms, secretingenzymes directly into the carrion andhelping with the liquefaction of thecorpse tissues while assisting theincrease of microbial activity. Thesefamilies of Diptera are more abundantfrom early summer to mid autumn intemperate regions, and also in the rainyseason in tropical areas.

The biology of all the Dipteraspecies is similar. Females of blow fliesand house flies lay eggs or drop livelarvae on to the surface of the freshcorpses, generally at the base of thehairs or near to the natural holes. Suchnatural openings facilitate thepenetration of larvae into the innerregions of the corpse. The ovoviparousfemales of sarcophagids are less fecundthan blow flies and house flies, and donot deposit all their larvae in the samecarrion, rather distributing them evenlyamong several corpses. Development offly larvae is normally very fast (3 to 6days during the favorable periods of the

year) and pupation takes place awayfrom the corpse, in the soil surroundingit. Sometimes the mature larvae maymigrate more than one meter from thecarrion. Ten to 30 days after pupation,

the new adults emerge and fly off tosearch for new corpses, starting a newlife cycle.

Among Coleoptera, a principalgroup in many temperate ecosystems isSilphidae (e.g., Nicrophorus , Silpha ). Itis a group specifically adapted to livingin carrion and its action is comparable tothat of the Diptera. The adults ofNicrophorus species show a veryspecial biology. When a species of this

genus arrives at the fresh corpse, themale and female bury the carrionunderground (Fig. 3), thereby reducingthe risk of colonization by other insects.Once the carrion is safe in the burialchamber, and the beetles havecopulated, they make the corpse into aball. The eggs are deposited into a shortchamber above the carrion ball. Thefemale makes a conical depression onthe top of the ball, and defecates andregurgitates droplets of partiallydigested food, and stridulates, attractingthe larvae to the depression in thecarrion. The female, and sometimes themale, give parental care and providefood by regurgitating into thisdepression. Thus, they ensure thesurvival of the offspring and avoidpredation and competition.

In tropical forests, many speciesof Scarabaeinae are attracted to bothcarrion and dung. Availability ofresources for dung beetles in mostNeotropical forests is low because of thelow density of large mammals and thelow availability of any particular type ofdung. This absence can probably beattributed to the absence of suitablenumbers of large herbivores in the


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forests of Central and South America,and the few natural pastures of thisregion (except where cattle have beenintroduced). In African forests, wherelarge herbivores are present in relatively

large numbers, many dung beetlesspecialized in the use of excrement maybe found.

Forensic entomology Knowledge of the succession of

species taking place in a corpsefollowing death has been used instudies of forensic entomology. Thisrather consistent succession has beenused for medical legal analyses to

estimate the time elapsed since death ofan animal. The study of arthropodspecies from a cadaver gives usinformation about the location, time, andconditions to which the corpse wasexposed before being found. Thegeneralized sequence of fly colonizationis most frequently used. The firstcolonizing species are the bigger fliesbelonging to the blow fly family(Calliphoridae) followed bysarcophagids (Sarcophagidae) andhouse flies (Muscidae). The adults ofthe lesser-sized families such asPsychodidae, Scatopsidae, Sciaridae,Phoridae, Sepsidae andSphaeroceridae come to the corpse inthe last phase of decomposition, afterthe corpse has been abandoned by thelarvae of the first colonizing flies. Theirlarvae leave the corpse to pupate awayfrom the larval site, normally in theground or substrate below carrion. Thedevelopment of larvae is temperaturedependent, and knowledge of the larvalcycle and its relationships at differenttemperatures, can be used to estimateof age a cadaver. Forensic entomologyis an important instrument in criminalinvestigation; however, we must take

into account that each succession willconsist of different species in differentgeographical regions. This is true evenin sites with similar climatic conditions,because few species are widespread in

distribution, and each area may have itsown carrion-feeding species.Nevertheless, the broad taxonomiclevels of decomposers of carrion areconstant worldwide. Also, somedifferences may be found as a result ofvariation in ambient temperatures thatmay speed the process (sunlight andhigh temperatures) or retard it (shelterand cold conditions), variation inexposure of the carrion, possible burial

of the corpse, cause of death, etc.Some carrion-feeding flies cancause myiasis, an infestation of livevertebrates by larvae of Diptera,particularly blow flies of the generaLucilia , Chrysomyia , Cochlyomyia , etc.,that feed on live or dead tissues of thehost. This infestation causes problemsin some farming areas, and may be ofconsiderable economic importance.Probably one of the best knownexamples of myiasis is with Cochliomyia hominivorax (Diptera: Calliphoridae), aspecies living in neotropical regions.Larvae of C. hominivorax develop onwounded animals and humans, and canprovoke the death of the host.

Decomposers of excrement The excrement of vertebrates

generally is a rich source of nutrients,and insects play an important role in therapid recycling processes of feces.However, carnivorous excrementcontains little material useable byinsects because of their efficientdigestive process. In contrast, thedigestive system of herbivores is lessefficient, and the dung produced is quitesimilar to the original leaf material. More


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than half the food consumed byherbivorous animals is returned to theground in the form of unassimilatedmaterial, i.e., dung. Because it isabundant in organic matter and moist,

herbivore dung is an ideal medium forestablishment of a specific, richentomofauna involved in the process ofdecomposition and elimination of feces.Quantitatively, large herbivore dung patsare the most important resource fordung beetles in most regions, and thisfauna is especially abundant in historicgrazing areas.

Excrement is a very specialhabitat for coprophagous species, and

the spatial distribution of dung increasesthe tendency of these insects toconcentrate in a limited space. Theprocess of colonization of excrementtypically consists of three waves ofinsects. The first wave of colonizersinvolves certain flies arriving withinhours to lay eggs or larviposit on thedung before a crust is formed on thepat. The second wave is several familiesof beetles. Lastly, mites becomeabundant.

The main groups of flies areMuscidae and Scatophagidae, followedby Fanniidae and Calliphoridae. Mostadults and larvae of flies arecoprophagous, but feeding also on themicro-organisms present in the dung.Others are facultative or obligatepredator species. Many species areattracted to any decaying matter, butothers only feed and breed in dung.Throughout the world, muscidcoprophages such as Musca domestica ,Musca vetustissima and Haematobia irritans are pests of cattle. But somemuscids are facultative predators (e.g.,Muscina spp.) and obligate predatorylarvae (e.g., Mydaeae spp.). The best-known species of Scatophagidae is

probably Scatophaga stercoraria , aspecies frequently found visiting dunganywhere in the Northern Hemisphere,and also in northern and southernAfrica. Scatophaga stercoraria has

coprophagous larvae, but adults areprimarily predators or nectar feeding,only occasionally feeding on liquefieddung.

Females of flies may lay eggs inbatches of about 150, which hatch infrom 8 to10 hours, to three days,depending on the environmentalconditions and the species involved.Muscid larvae may complete theirdevelopment within two days in

favorable environmental periods, ordelay several weeks in the coldertemperatures.

Among beetles that use dungresources, the dung beetles belongingto the Scarabaeidae (Scarabaeinae,Geotrupinae and Aphodiinae) are themost important and numerous. Not allscarab larvae are strictly coprophagous,and some ingest soil organic matter orfeed on roots of plants. However, manyare coprophages, and often exceedinglyabundant. Thousands of individualsfrom many species may be foundcolonizing single dung pats in temperateand tropical grazing ecosystems. MostAphodiinae are saprophagous andwithin the Geotrupinae coprophagy isthe rule for the Geotrupini. OnlyScarabaeinae has coprophagy as acharacteristic of most of its species. Inthis case, most of the nutrients eaten bythe adults are derived from eatingmicrobes or colloids suspended in dung.The larvae feed on the dung supplied bytheir parents in a nest chamber.

Various other groups of beetlesvisit dung but they are primarilypredators. Coleoptera of the familiesHydrophilidae, Staphylinidae, and


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Histeridae are associated with carrionas predators of larvae of flies and dung-beetles. However, the two formerfamilies also include coprophagousspecies. In the temperate region, the

hydrophilids Cercyon and Sphaeridium (Coleoptera Hydrophilidae) arecoprophagous, arriving within the earlyhours after deposition of dung.

The behavior of dung beetles(Coleoptera: Scarabaeidae) isspecialized and diversified in responseto exploitation of excrement by adultsand larvae (Fig. 4). The Scarabaeidaeconsist of approximately 7,000 species(5,000 Scarabaeinae, 1,900 Aphodiinae

and 150 Geotrupinae). Many species ofScarabaeinae and Geotrupinae havedeveloped special feeding and breedingstrategies that allow them to removedung rapidly the soil surfaces by diggingburrows below the dung pad to storefragments of dung in tunnels. The alsomay form dung into balls and roll themaway from the pad for burial far from thefood source. The importance of thesehabits is the protection of food for adultor larvae, avoiding competitors,predators and unfavorable climaticconditions. Only Aphodiidae do notmake a nest. Aphodiidae eat directlyinto the dung and many species deposittheirs eggs directly in dung pads withoutnest chamber or in the surrounding soil.Geotrupinae and many tribes ofScarabaeinae are tunnelers. Thesespecies dig a tunnel below the dung patand accumulate dung in the bottom ofthe burrow; this food can be used eitherfor adult or for larval feeding. Finally,some species of Scarabaeinae arerollers, making a ball of dung that isrolled away from the pat for a variabledistance before burying.

One of the most importantaspects of the biology of Scarabaeinae

and Geotrupini is their nesting behavior.Geotrupini nests are the most primitiveand consist of simple burrows filled withsausages of dung, usually containingone egg each.

The reproductive biology ofScarabaeinae has several distinctpatterns, which have been reviewed andcompiled in comprehensive andwonderful books by Halffter andMatthews (1966) and Halffter andEdmonds (1982). The process ofnesting involves the creation of a placein the soil where a supply of dung isaccumulated for development of larvae.

Scarabaeinae nesting frequently

involves bisexual cooperation of a pairof beetles, for either short or longperiods of time, and parental caresometimes exists. The adults makebrood balls in the protected nest, eachof which contains the amount of foodrequired for larvae to enable them tocomplete larval development. Nestingbehavior is considered as an adaptationto isolate immature larvae from eachother and from adults, increasing thesurvival of offspring. Obviously this is aprocess that requires the investment ofconsiderable time and energy on thepart of the parents. Nesting derives fromfeeding behavior and basicallycorresponds to food relocation:tunneling and ball rolling.

The tunneling scarabs take foodfrom the dung pat and bring it into apreviously excavated gallery. Varioustypes of nesting have been describedfor tunnelers, and it is sometimesdifficult to ascribe a particular type ofnesting to a species.

The most primitive and simplestnest behavior is observed in somegenera of Dichotomini, Oniticellini,Onitini, and also Onthophagini. A femaledigs a simple burrow, fills it with food,


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forms a brood mass and provides asingle egg. In this case, there is nobisexual cooperation or maternal care,and the species involved show relativelyhigh fecundity.

Other groups of dung beetlesmake nests containing several or manybrood masses such as those observedin some species of Dichotomini, Onitini,Onthophagini and Oniticellini. The broodmasses are constructed in series, in thesame tunnel or separated in individualside branches. In this type of nesting,bisexual cooperation may exist, but therole of the male is restricted tointroducing food into the tunnel. These

species have relatively high fecundity,and there is no maternal care.Coprini and several Dichotomini,

Onitini and Oniticellini species constructnests that contain several sphericalbrood masses arranged in a single orbranched tunnel with or withoutseparation.

Some scarabs produce a nestcontaining only a few brood balls in achamber, and physically separated fromother chambers. This nesting behavioris present in species with low fecundity:Phanaeni (without maternal care),several Dichotomini (with or withoutmaternal care), and several Coprini(with maternal care).

Finally, the species of Oniticellus (Oniticellini) show endocoprid nestingbehavior: digging burrows and makingbrood chambers in the dung pat, wherenesting takes place. The species of thisgenus present moderate to extensivematernal care.

The roller habit of food relocationis only present in some tribes ofScarabaeinae: Scarabaeini, Chantonini,Gymnopleurini and Sisyphini. Species ofthese groups make a brood ball that isrolled away from the pat. The weight of

the ball can be up to more than fiftytimes the weight of the beetle. Theprocess is initiated by one partner andthe ball acts as a sexual display to theother sex. The brood ball also may be

rolled by two partners, but sometimesthe female is transported on the ball.Combat is common between membersof the same species when rolling balls.Generally, sexual cooperation finisheswhen copulation takes place in theburrow, after which the male leaves thefemale. Females prepare 4 to 5 pyriformbrood balls and lay eggs in a narrowcavity at the upper end of each pair. Thefemale may abandon the nest after

oviposition, such as in Scarabaeini,Canthonini, Gymnopleurini andSisyphini, or they can remain in the nestuntil the offspring emerge, as has beendescribed for the African genus Kheper .

Finally, there are some species ofdung beetles that demonstrate specialfeeding and nesting biology. They arespecies using part of the food resourcesaccumulated by other dung beetlespecies in burrows or a breedingchamber. These species are calledkleptoparasites, and examples arefound in Aphodiidae and Scarabaeidae.These species live as parasites in thenest prepared by either roller or tunnelerdung beetles.

Beneficial actions of decomposerinsects in ecosystems

The viability of every ecosystemis based on the normal functioning of itsnutrient cycle. This is a very complexecological process with a great numberof components, including decomposerorganisms. The activity of decomposersbenefits humus formation in the soil, andthe availability of nutrients for plants.This feature is especially evident inpasture ecosystems, where an


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indispensable condition for correctfunctioning is that the cattle dung israpidly used and transformed. If thisdoes not occur, dung deposited on thesoil may eventually cause serious

damage because it deteriorates thepastureland by preventing plant growth.When pats are not removed, they

cover the pasture, inhibiting the growthof grass. The effect is a loss of availablesurface for cattle. Several authors havereported several estimates of the loss ofpasture. In the U.S.A., for example,Fincher (1981) reported that cattlecontinuously covered more than 300hectares of pasture with dung each

year. Dung pats remaining on pasturehave a noxious effect because cattle donot graze on the rank growth aroundthese cowpats. Refusal by cattle tograze on pasture grass growing neardung is a response to the offensiveproperties of the dung itself.Furthermore, most of the valuablenutrients of the unburied pats are lost.For example, 80% of the nitrogencontent in a pat may be lost, but whenadequate numbers of dung beetles arepresent and efficient burial by dungbeetles exist, the nitrogen loss isreduced by 15%, with the nitrogen heldby soil colloids. Another potential benefitof dung beetle activity is the increase inpasture by the incorporation of organicmatter into the soil and increases in soilaeration and water content.

Several authors have mentionedthe possible role of dung beetles inreducing infestation of livestock by wormparasites. Feces remaining on the soilcould be an incubator for parasite wormlarvae. If dung beetles bury these fecesbefore parasites reach the infectiousstage, the parasitism of cattle can beminimized. Dung beetles are also useful

agents in the control of flies breeding indung. The scarabs compete with flylarvae for food, reducing the amount ofbreeding by depriving the flies of food.

Some authors have calculated

the economic value of the rolerecovered by dung beetles in pastures.Fincher (1981) estimated that theagricultural sector in the U.S.A. wouldhave potential benefits of more than2000 million dollars a year if suitablefauna were present for rapid burial ofcattle dung. The value of dung beetlesin pasture ecosystems was firstobserved in Australia, where dungbeetles were introduced to help solve

the problems of loss of pasture surfaceand increase of flies breeding in dung.The Australian pasture was profoundlydisturbed by domestic animals broughtby the first European settlers whoarrived 200 years ago. The native dungbeetles were adapted to the dungpellets of kangaroos and othermarsupials, not to the large grazing andbrowsing herbivores. The large,voluminous accumulated dung ofhorses, cattle, and sheep generated apollution problem as a result of itsunattractiveness for the native beetlefauna. In Australia, a program of dungbeetle species introduction wasproposed by Bornemissza about 1960and several species of scarabs fromSouth Africa, France and Spain,adapted to use the dung of domesticcattle in open pastures, wereestablished successfully. These beetleswere introduced to help solve theproblems of pasture degeneration andincrease of populations of fly pestsbreeding in dung.

See also, FORENSICENTOMOLOGY.


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References Bornemissza, G.F. 1979. The Australian Dung Beetle Research Unit of Pretoria. South

African Journal of Sciences 75: 257-260.Byrd, J.H., and J.L. Castner. 2001. Forensic entomology. The utility of arthropods in

legal investigations. CRC Press, New York, New York.Fincher, G.T. 1981. The potential value of dung beetles in pasture ecosystems. Journalof the Georgia Entomological Society 16 ( suppl.): 316-333.

Halffter, G., and W.D. Edmonds. 1982 . The nesting behaviour of dung beetles(Coleoptera: Scarabaeidae). An ecological and evolutive approach. Publication ofthe Institute of Ecology, Mexico.

Halffter, G., and E.G. Matthews. 1966. The natural history of dung beetles of thesubfamily Scarabaeinae. Folia Entomologica Mexicana. Mxico 12-14. Reprintfor Medical Books di C. Cafaro (1999). Palermo. Italy.

Hanski, I., and Y. Cambefort (eds.). 1991. Dung beetle ecology. Princeton UniversityPress, Princeton, New Jersey.

Putman, R.J. 1983. Carrion and dung. The decomposition of animal wastes. EdwardArnold, London, United Kingdom.


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Figure 1. The arthropods involved in the process of decomposition of animal and plantremains belong to such taxa as Diplopoda (1 and 2), Isopoda (3), Collembola (4),Diptera larvae (5), Coleoptera (6), Acari (7).

Figure 2. Adult and larva of a blow fly (Diptera: Calliphoridae) on a lizard cadaver. Blowflies constitute the first wave of insects colonizing corpses.


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Figure 3. Male and female Nicrophorus (Coleoptera: Silphidae) burying a mouse corpseunderground. These insects are specifically adapted for living in carrion.

Figure 4. Behavior of dung beetles (Coleoptera: Scarabaeidae) is both specialized anddiversified to allow exploitation of excrement. Aphodiinae do not make nests, and dwellwithin the dung (1). Geotrupinae and many tribes of Scarabaeinae are tunnelers (2).Some tribes of Scarabaeinae are rollers (3), making a ball of dung that they roll awayfrom the dung pat.

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DECOMPOSER INSECTS Eduardo Galante and Mª Angeles Marcos-Garcia Centro Iberoamericano