Parasiter - skrupellösa och fascinerande varelser?

Häckningsparasitism, eller boparasitism, förekommer hos fåglar, insekter och även vissa fiskarter (malar). Det innebär att honan lägger sitt ägg i en annan individs bo och överlåter ruvningen och uppfödningen åt den andra värden.

Här är ett klipp på fungi (svampar) som parasiterar på insekter från BBC Planet Earth, håller tydligen insektskolonierna från att bli för många / sprida sig så enormt. Så blir dom infekterade av en svamp.
http://www.youtube.com/watch?v=vgkL8PulPdE

Visst är det äckligt, fundamentalt för varenda livsform att finna parasiter repellerande för deras eget bästa. Ändå coolt att dom lyckas så bra, fast förjävligt på samma gång skaffa ett eget liv istället!

Olika humlearter har olika lång snabel och väljer därför att besöka olika blommor. Blommor med nektar i spetsen på en lång pip eller sporre besöks av arter med lång snabel. En del humlearter har hittat på ett knep. De biter hål på sporren med sina käkar och tar nektar utifrån. Då behöver de inte krypa in i blomman som då heller inte blir pollinerad. Mörk jordhumla och tjuvhumla är utpräglade "nektartjuvar".

Cuckoo bumblebees are members of the subgenus Psithyrus in the bumblebee genus Bombus. Up until recently, the 29 species of Psithyrus were considered to constitute a separate genus. They are a specialized lineage which has lost social behavior, and lost the ability to collect pollen, and are instead cleptoparasitic [parasitism genom stöld] in the colonies of other bumblebees. Before finding and invading a host colony, a Psithyrus female (there is no caste system in these species) will feed directly from flowers. Once she has infiltrated a host colony, the Psithyrus female will kill or subdue the queen of that colony and forcibly (using pheromones and/or physical attacks) "enslave" the workers of that colony to feed her and her developing young. When the young emerge, they leave the colony to mate, and the females seek out other nests to attack.

Female cuckoo bumblebees will aggressively attack host colony members, and sting the host queen, but will ignore other animals (including humans) unless disturbed.

Snylthumlor, även kallade gökhumlor, lever som boparasiter i humlebon. Ofta är de specialiserade att parasitera en viss, social humleart. Snylthumlorna betraktades länge som det egna släktet Psithyrus men kategoriseras idag som ett undersläkte inom släktet Bombus.

I Sverige finns 39 arter av humlor om man räknar in de nio arterna av snylthumlor.

Although this may sound surprising, fungi are often parasitic on other fungi. In fact, mycoparasitism is common among fungi, with whole groups specialized for this way of life. We can view mycoparasites in much the same way we do plant parasites, that is as necrotrophs and biotrophs. Necrotrophs kill the tissues they will consume while biotrophs obtain nutrition from living tissues.

Necrotrophic mycoparasites, like the species of Trichoderma at right can be extremely destructive to other fungi. They often spread rapidly, completely surrounding and covering their hosts in a few hours or days. The mechanisms used by necrotrophic mycoparasites to kill their hosts are not thoroughly studied but probably involve toxins as happens with necrotrophic plant parasites. Trichoderma, the most frequently studied mycoparasite occurs in soils, rotting wood, old mushrooms and many other environments. When it grows over another fungus it simply dissolves its host's hyphae with extracellular enzymes.

[...]

Biotrophic mycoparasites appear to be less destructive to their hosts and to remain active as long as the host is active. Most biotrophs obtain nutrients from their host via specialized cells, usually either contact cells or haustoria. Contact cells, the most common means of biotrophic mycoparasitism, are small sucker-like cells that are attached to the surface of a host hypha. Connection between the two is by means of a small pore. Haustoria, found in certain mycoparasitic Zygomycota, are a kind of absorptive cell produced inside the hyphae of the host. Biotrophic mycoparasites are very wiespread but their parasitic nature may not be obvious. If two fungi are found growing together there is a great likelihood that one of them is a parasite. However it requires careful experimentation to demonstrate parasitism in fungi and much work has yet to be done before scientists have a clear understanding of its extent.

Insects live among fungi, pushing their way through hyphal masses and brushing against their spores. Many insects even eat fungi. With such close contact between insects and fungi is is not at all surprising that some fungi have developed the ability to live as parasites on insects. Like the fungi that attack nematodes many of those attacking insects are highly specialized and have sophisticated means of locating and infecting their prey. They may also be host-specific and occur on a few or even single species of insect.

The number and diversity of fungi parasitic upon insects is so great that is is impractical to try to deal with it here. Instead we will discuss a few characteristic types and leave it to you to delve more deeply into the subject.


Of the many fungi infecting insects three groups stand out as especially numerous. These are the orders Entomophthorales, Laboulbeniales and Clavicipitaceae. The picture above illustrates these three common groups. At the left is Entomophthora muscae a common parasite of flies in our area. Infected flies often land on an upright plant stem, turn bottom up and die. The parasite, which has been growing inside the insect, grows out of its recently killed prey and produces masses of white spores along each of the abdominal segments. You can easily find this fungus in the garden during late summer. Just look for grasses or other plants with an inverted dead fly clinging to ther tops. If the fungus is not obvious, place the fly on a piece of glass or plastic food wrap and enclose it so it will not dry out. By morning you will have a halo of spores surrounding the fly.

The middle picture is of Laboulbenia philonthi, a member of the Laboulbeniales. Members of this group grow attached to the outside of the insect; the black structure at the bottom is the point at which it is attached. Although external, the fungus does have an absorption cell called a haustorium inside the insect at the point of attachment. Although clearly parasitic the Laboulbeniales probably do little harm to their hosts. They are equivalent to fleas and ticks on mammals

The fungus at right is Cordyceps variabilis. It was infecting the larva of a beetle inside a dead log, which has been cut away to show the relationship between host and parasite. Cordyceps, a member of the Clavicipitaceae, produces its spores inside the swollen head-like structure above the log. The Clavicipitaceae are fairly common in temperate parts of the world but become exceedingly abundant in the tropics.

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Species of several genera of Oomycota are known to attack fish. Home aquarium owners will undoubtedly recognize the genus Saprolegnia, a notorious group of parasites that can wipe out an aquarium in a short period of time. Species of Saprolegnia get into the fish through open wounds and rapidly penetrate its tissues with broad tubular hyphae. Infected but still-living fish may be seen swimming with a tuft of hyphae trailing out behind them. The next time you visit a pet store have a look at the fish medicines; many claim effectiveness against Saprolegnia.