VL 9 Flashcards
Predator
Animal that kills and consumes other animals (prey) and requires multiple prey items to reach maturity
Parasite
An organism living on or in another living organism, obtaining its nutrition from that organism and causing some kind of measurable damage to the host. Will spend most of its life on a single host, but rarely kills it. Close long term interaction
Insect herbivores as parasites
Many insect herbivores fit this broad definition
Insect herbivores can be called plant parasites, seed predators or seed parasitoids
Parasitoids
free living insects as adults, but lay their eggs within or on another host. The immature parasitoid will develop parasitically on the host and eventually kill it
Are blood feeding insects parasites?
Most disease vectoring insects are not parasites by definition
However, some insects, such as bed bugs, are considered parasitic due to their obligate, close association with hosts
How can parasites affect the host?
can moderate trophic dynamics and competition - ‘ecosystem engineers’
can affect behaviour of host or decrease its reproduction ot development in order to benefit themselves and their own growth / survival / reproduction - divert resources
Ectoparasite
Live on the body surface
Feed on blood or epidermis
Usually have specialized structures to cling to the body of the host
Eg. lice, bat bugs, bed bugs, varroa mites
Endoparasites
Undergo most of life cycle inside the host, except for moving to new hosts
Feed on host internal tissues or live inside host cavities or spaces
Need to combat immune system or avoid too much damage to host
eg. Strepsiptera, Bot flies
Endoparasites - Strepsiptera
endoparasites of ants, bees, wasps, leafhoppers, cockroaches
Most larval stages and the adult females are parasitic, males are free living
Endoparasites - Bot flies
The larvae are endoparasites of many different mammal species
- myiasis: the parasitic infestation of the body of a mammal by a fly larvae
Feed on tissue under the host’s skin or within the host’s gut
Often have complex behaviour involving using other insects to vector their eggs
How many insects are parasitoids?
10% of all known insect species are parasitoids
Most parasitoids (75%) are wasps (Hymenoptera) belonging to the superfamilies Chalcidoidea or Ichneumonoidea. The other important parasitoid group is the Family Tachinidae in the Diptera
Specialized, making them useful for biocontrol programs. They inject venom and eggs directly into hosts
Parasitoid classification
Where they lay eggs - endoparasitoids / ectoparaitoids
How they attack their host - Idiobionts (immobile host stages or cause permanent immobilization) / Koinobionts (mobile hosts)
Number of offspring per host - solitary / gregarious
Idiobiont ectoparasitoids
paralyze host with venom, offspring develops outside host
do not have to overcome immune response - feed externally on paralyzed organism, but vulnerable to predators
Idiobiont endoparasitoids
attack sessile life stages (eggs, pupae), offspring develop in host
have to overwhelm host immune system
some inject a venom or virus alongside the eggs to aid this
Koinobiont ectoparasitoids
offspring feeds on growing host exterior
Have to avoid being brushed off by the host’s molting, as well as desiccation and being exposed to hyperparasitoids
Koinobiont endoparasitoids
very diverse; offspring develop inside the host and cause a variety of physiological changes
Tightl linked to the biology of their hosts. Tend to be very specialized. Must evade / overwhelm continuously functioning immune system
Example of both endo or ecto parasite
The jewel wasp, Ampulex compressa, immobilises its cockroach host and lays an egg on the abdomen
The larvae feeds for 4 days on the outside of the cockroach, then chews its way into the abdomen and feeds internally
It carefully consumes the organs in an order which keeps the host alive for as long as possible
What are adaptations of parasites and prarsitoids?
Small body size
Specificity
Adaptation - specifity
Parasitoid: 90% of all parasitoid wasps attack only one or two host species
Bird lice: 87% recorded only a single host species
Parasites / parasitoids tend to have very intimate interactions with their hosts, specializing to bypass host defenses / behavior or fit within host body regions
Specificity - co-speciation
Parasites speciate alongside their hosts - dependent on its host and must adapt with it
This is most expected when parasites cannot move long distances or are transmitted from parents to offspring (vertical transmission)
Lice are prime examples of this type of parasite
Host immune response to parasitoids
Foreign objects are attacked by immune system
Parasitoid egg / larvae ‘encapsulated’ by caterpillar hemocytes, then broken down
Parasitoid adaptation to host immune response
Venom secreted with eggs kill host immune cells
PolyDNA-virus replicates in parasitic wasp ovaries - >Virus particles secreted with wasp eggs
Immune response - parasitoids: PolyDNA virus
PolyDNA virus enters host tissue with egs and triggers release of proteins that disrupt encapsulation reaction
Host immune response delayed
Wasp larvae can develop inside host without interference
Host immune response - malaria
If there is damage consistent with parasite presence in a mosquito gut cell -> apoptosis and cell death
Encapsulation of parasites with melanin to help sequester and kill them (melanization)
Parasite adaptation to host response (Malaria)
Can switch to neighbouring, naïve gut cells to avoid cell death
Co-evolved Plasmodium strains evade recognition by incorporationg host proteins
Do parasites influence their hist’s behaviour?
Parasites may alter the behaviour of the host to enhance their own transmission
example:
Crickets with parasitic horsehair worms suicidally leap into water, where the worm’s next life cycle stage occurs, due to neurotransmitters produced by the parasite
Ophiocordyceps fungus affects the nervous system of ants, causing them to climb before they die so that the spores can spread further
Does malaria manipulate mosquitoes?
Plasmodium parasites have separate life cycles in mosquitoes and humans
In order to be transmitted, a mosquito must bite an infected host, survive until the parasite migrates to the salivary glands, and then bite another potential host
These are the three stages at which transmission potential could be influenced by the parasite
How does malaria manipulate mosquitoes?
Mice which had the transmissible stage of Plasmodium parasite were more attractive to mosquitoes
These mice emitted different amounts of volatile compounds than uninfected mice. The same happens in humans
How does malaria manipulate the vector?
Mosquitoes carrying the transmissible stage of malaria are more attracted to human odour than uninfected mosquitoes and will bite more often
Mosquitoes carrying the non-transmissible stage may be less attracted to humans, reducing the risk of mortality and therefore more likely to survive until able to transmit
What types of plant viruses are transmitted by aphids?
non-persistent (mechanical)
persistent (propagative and circulative)
Each plant virus species is only on eof these types
each type has different transmission dynamics which take advantage of insect feeding behaviour / ecology
How are plant viruses aquired? (Non persistent)
Acquired during short-term probing phase
Virions located in epidermal cells of plant become “stuck” to the inside of the aphid’s mouthparts - mechanical transmission$$WHen the aphid next probes, the virion detach and enter the new cell the aphid is probing
Therefore requires that the aphid does not stay and feed
How are viruses aquired? (Persistent)
Acquired during long-term feeding stage
Virions in the phloem cells are taken up when the aphid begins consuming phloem sap
Replicate in aphid gut and also infect the aphid
Requires that aphids reach the “ingestion” phase of their feeding behavior on both first and second host
Why don’t all parasites / pathogens manipulate their hosts?
Selection only when high transmission pressure
Scarcity of hosts / vectors
Length of transmission period
