SeleksiTanInangDJ Chap05 Host Finding
Transcript of SeleksiTanInangDJ Chap05 Host Finding
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Host Finding and Semiochemicals (Pages 73-84)
Read Chapter 15 in your text, see Chapter 6 in Debach
The world is a big place.
Now envision yourself as a wasp that is 0.1 mm long
How do you find your host?
Totally random searching is a quick route to extinction(except in rare cases)
Insects use many types of cues in a multi-step process tolocate hosts or prey.
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Semiochemicals (Pages 73-78)
Semiochemicals are chemical messengers.
They operate in one, two or three species systems.
They function between individuals of the same or or different
species, or between a non-living source and a living receiver.
Semiochemicals can function as air-borne or contact stimuli.
They can be used directly for pest management (see thehandout), but they are commonly important in the host findingprocess, thus their immediate relevance here.
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Semiochemicals (Page 73)
Thus, some definitions of classes of semiochemicals.
Category of Semiochemical Impact of SemiochemicalEmitter Receiver Other
Intraspecific : Pheromones +/0 +
Interspecific: Allomones + 0/-Kairomones - +
Synomones + + -
Non-living source: Apneumones 0 +
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Semiochemicals
Examples of Pheromones (Pages 74-76)
Sex pheromonecommonly used to detect pests or in mating disruption
Aggregation pheromone
mass-attacking bark beetles, can be a used as a baitAnti-aggregation pheromone
spruce beetleAlarm pheromone
many species of gregarious insects, could be repellentsEpidietic pheromone
marks exploited resource, could be repellents
Pheromones may be used as kairomones by natural enemies.
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Semiochemicals
Examples of Allomones (Page 76)
Defensive secretions to deter would be predatorscommon, e. g. skatole of Chrysopaspp.
Chemical mimicrysome myrmecophiles chemically mimic their ant hosts
to avoid attackbola spider mimics sex pheromone of female noctuids
to lure males within range for capture
Aggressive or Prey Subduction Allomonerare, used to subdue prey, Lomamyia
Allomones may be used as kairomones by natural enemies.
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Semiochemicals
Examples of Kairomones (Pages 76-77)
Chemical secretion that is used to thebenefit of a heterospecific receiver ina two-species interaction.
Host plant odors attract many herbivores.
Females of the green lacewing Chrysoperla plorabundaareattracted to indole acetaldehyde a breakdown product of the
amino acid tryptophan which occurs in aphid honeydew. Thus,the females can locate aphid infestations and deposit theireggs near a larval food source.
Pheromones can be subverted by a predaceous species and
used as kairomones.
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Semiochemicals
Examples of Synomones (Page 77)
A secretion that is used to the benefit of the emitter and aheterospecific receiver, and to the detriment of a third species.
Plant odors can be used by entomophages to locate prey.
Sinigrin a constituitive component in crucifers attracts thecabbage aphid, Brevicorynebrassicae(Kairomone), and itsparasite Diaeretiella rapae(Synomone).
Similarly, caryophyllene is attractive to Chrysoperlaplorabunda, indicating a possible source of aphids.This attraction interacts positively with the attraction to indole
acetaldehyde.
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Semiochemicals
Examples of Synomones (Page 77)
A more sophisticated system is seen with the beet armyworm,Spodoptera exigua, and its braconid parasite Cotesiamarginiventris.
C. marginiventrisresponds to chemicals produced whencaterpillar saliva interacts with plant chemicals.
This is more efficient for host location.
Cotesia marginiventrison
Spodopteralarva
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Semiochemicals
Examples of Apneumones (Page 78)
Apneumones arise from non-living sources, so this is a one-way interaction that benefits the receiver.
Venturia canescens(Ichnemonidae) is attracted to oatmeal,whether or not its host, the Mediterranean flour moth, Ephestiakuhniella(Pyralidae), is present.
The chemical must not be due to the presence of the host, or it
would be a kairomone.
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Host Finding (Pages 79-84)
Host finding is a highly variable, often complex process.
Some extreme generalists do not search for hosts, e. g. sometropical walkingsticks simply drop eggs wherever they are.
This is a rare situation.
Most insects go through some or all of the following steps:
1. Host habitat finding
2. Host finding3. Host acceptance4. Host suitability5. Host regulation
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Orientation
AttractantRepellent
Assesment
Landing
Arrestant
StimulantDeterrent
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Host Finding (Pages 79-84)
1. Host habitat finding (Page 79)
This process can involve intrinsic preferences for a cue thatindicates a general area that may support the host or morespecific cues that indicate a specific potential host habitat.
Intrinsic habitat preferences are not well-known and ofteninvolve color cues.
Many aphids are attracted to yellow, indicating the possible
presence of plants. (Hence the utility of yellow pan traps.)
Similarly, some green lacewings are attracted to green.
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Host Finding (Pages 79-84)
1. Host habitat finding
An unusual example involves Brachymeria intermedia, achalcidid parasites of the gypsy moth.
B. intermediais attracted to dappled light, as occurs at the
edge of a forest or in defoliated areas.
Brachymeria intermediaand gypsy moth pupa
Enlarged hind femur
Exit holeVenation
(Page 79)
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Host Finding (Pages 79-84)
1. Host habitat finding (Page 79)
More commonly an insect is attracted to cues more directlyrelated to the presence of a host or prey. The host plant odoris a common cue
Recall the cabbage aphid and its parasite Diaeretiella rapae,both are attracted to cruciferous plants by sinigrin.
Host finding for the aphid, but host habitat finding for the wasp.
Brevicorynebrassicaeoncanola
Diaeretiellarapaeovipositing ina cabbageaphid
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Host Finding (Pages 79-84)
1. Host habitat finding (Page 79)
Host pheromones are often taken over as kairomones byentomophages.
Aphid alarm pheromones are released from the cornicles in a
viscous liquid and can be quite effective against small,parasitic wasps, e. g. D. rapae.
Some large coccinellid beetles use the alarm pheromone as akairomone to locate their prey.
Anovipositing wasp elicits alarmpheromone release from an aphid.
A coccinellid is attracted to the odorof the alarm pheromone.
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Host Finding (Pages 79-84)
1. Host habitat finding (Page 79)
Host/prey pheromones are also used by numerous predatorsand parasites of mass-attacking bark beetles.
This is well-known in clerid beetles, e. g. Enoclerusand
Thanasimusspp.
Thanasimus formicariuson conifer bark
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Host Finding (Pages 79-84)
1. Host habitat finding (Page 79)
A final enhancement of this system is seen when the chemicalcue is dependent upon the density of the host/prey.
A good example is seen with Chrysoperla plorabunda.
The gravid female lacewing flies downwind, landing in theindole acetaldehyde odor plume from an aphid colony, thenmoves upwind to deposit eggs near the aphid colony.
Lacewing flight Wind
Aphid colony
Oviposition siteField
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Host Finding (Pages 79-84)
1. Host habitat finding (Page 79)
Some insect stop at this point in the sequence.
They rely on mobile, sometime starvation tolerant larvae tocomplete the host finding process.
Examples include taxa where the first-instar larva is atriungulin or planidium.
Mantispidae deposit eggs in masses, the triungulins then mustdisperse and locate their spider hosts.
Eucharitidae deposit eggs in areas where ants are likely tooccur. The planidium waits for an ant to come by then rides
back to the ant colony to attack an ant larva.
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Host Finding (Pages 79-84)
1. Host habitat finding (Page 79)
Some insect stop at this point in the sequence.
They rely on mobile or starvation tolerant larvae to complete
the host finding process.
Examples include taxa where the first-instar larva is atriungulin (active searcher) or planidium (sit-and-wait).
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Host Finding (Pages 79-84)
1. Host habitat finding (Page 79)
Mantispidae deposit eggs in masses on foliage, the triungulinsthen seek their hunting spider hosts and practice phoresy untilthe host oviposits, then attacking the spider eggs.
Mantispasp., Mantispidae Kapalasp., Eucharitidae
Eucharitidae deposit eggs in areas that ants are likely to occur,then the planidia wait until they can attach to an ant to ride
back to the colony and attack an ant larva.
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Host Finding (Pages 79-84)
2. Host finding (Pages 79-80)
Host finding can be a continuation of host habitat finding, e. g.the clerids mentioned earlier or it may involve different cues.
Host food plant damage is used by many parasitoids.
Recall the case of Cotesia marginiventrisbeing attracted to thebeet armyworm by chemicals produced when caterpillar salivainteracts with plant compounds.
Cotesia marginiventrisonSpodopteralarva
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Host Finding (Pages 79-84)
2. Host finding (Pages 79-80)
Chemical cues need not arise directly from the host.
Ibaliaspp (Hymenoptera: Ibaliidae) are attracted to horntail(Hymenoptera: Siricidae) oviposition sites by the odor of the
horntails symbiotic fungus.(Ibaliaspp. oviposit into the host egg and develop in hostlarvae.)
Rhyssa persuasoria(Hymenoptera: Ichnemonidae) is attractedto the odor of horntail (Hymenotpera: Siricidae) frass due thepresence of fragments of symbiotic fungus in the frass.(Rhyssa spp. oviposit into nearly mature host larvae.)
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Host Finding (Pages 79-84)
2. Host finding (Pages 79-80)
Host finding can involve contact pheromones, less volatilechemical compounds that are perceived on contact.
Cardiochiles nigriceps(Hymenoptera: Braconidae) responds to
13-methylhentriacontane on plant surfaces in the mandibulargland secretion of its hosts, Heliothis virescenslarvae.
Trichogrammaspp. (Hymenoptera: Trichogrammatidae)respond to trichosane rubbed on the plant surface from thewing scales of adult moths as they oviposit.
Trichogrammasp.antennating moth eggs
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Host Finding (Pages 79-84)
2. Host finding (Pages 79-80)
Non-chemical cues are also used, but are less well known.
Physical cues:
Lypha dubia(Diptera: Tachinidae) detects then searches alongthe silk trails of the winter moth, Operophtera brumata, tolocate host larvae for oviposition.
H Fi di (P 9 8 )
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Host Finding (Pages 79-84)
2. Host finding (Pages 79-80)
Sound and Vibration:
Euphasiopteryx(Diptera: Tachindae) locates its field crickethosts at night by the sound of the male crickerts song.
Vibrations are used by several parasites that attackendophytophagous hosts, e. g.
Opius(now Biosteres) spp. that attack fruit fly (Tephritidae)larvae in fruit.
Coeloides vancouverensisfemales use the vibration of wood-boring beetle larvae chewing to guide their oviposition.
H Fi di (P 79 84)
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Host Finding (Pages 79-84)
2. Host finding (Pages 79-80)
Coeloides vancouverensis
Temperature:
Coeloidessupplements the use of vibration by detecting the
temperature difference between the host and its surroundings.
Temperature has also been exploited by nematodes.Neoaplectana carpocapsaelocates hosts in the soil bytemperature differential.
H t Fi di (P 79 84)
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Host Finding (Pages 79-84)
2. Host finding (Pages 79-80)
Sight and Movement:
Perilitussp.
Perilitus spp. (Hymenoptera: Braconidae) locate their adultbeetle hosts by color and movement.
Following the host:
An extrapolation of this is seen in Stomorhina lunata(Diptera:Calliphoridae) which follows flying locusts swarms to their
oviposition site to attack locust eggs.
H t Fi di (P 79 84)
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Host Finding (Pages 79-84)
2. Host finding (Pages 79-80)
Phoresy:
Hitchhiking (usually by a larva) on the (usually adult) host is aneffective means of locating the life stage of the host to be
attacked.
We already mentioned the cases of the Mantispidae andEucharitidae.
H t Fi di (P 79 84)
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Host Finding (Pages 79-84)
2. Host finding (Pages 79-80)
Phoresy:
Adult phoresy is rarer, but occurs.
Adult female Rieliaspp. (Hymenoptera: Scelionidae) that rideon adult female Mantidae to be present when the hostoviposits so the short-ovipositored wasps can parasitizemantis eggs before the ootheca is formed.
Adult female Pteromalus puparium(Hymenoptera:Pteromalidae) ride on cabbage butterfly, Pieris rapae,caterpillars to be present immediately after the host pupates sothe wasp can attack the young, teneral (soft) pupa.
H t Fi di (P 79 84)
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Host Finding (Pages 79-84)
3. Host acceptance (Pages 80-81)
Having located a potential host some insects, especiallyparasitic Hymenoptera, assess the host for probable suitabilitybefore ovipositing.
This preliminary check reduces the risk of wasting eggs on/inan unsuitable host. Many types of cues are used.
Thus, it is logical that this behavior is more common in morehost-specific natural enemies and those that need to avoidintrinsic competition.
Greater host specificity is one of the main reasons that hostassessment is more common in Hymenoptera.
H t Fi di (P 79 84)
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Host Finding (Pages 79-84)
3. Host acceptance (Pages 80-81)
Contact kairomones are very important in host acceptance.
Epicuticular waxes of gypsy moth larvae and pupae contain
compounds that stimulate oviposition by parasitic wasps.These are detected and assessed using the antennae.
This has been demonstrated in Apanteles melanoscutus(Braconidae) and Brachymeria intermedia(Chalcididae)
responding to hexane extracts of gypsy moth larval and pupalcuticle, respectively.
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Host Finding (Pages 79-84)
3. Host acceptance (Pages 80-81)
Texture:
Nasoniaspp. (Hymenoptera: Pteromalidae) parasitize muscoid
fly pupae. The host range of a specific species is limited, e. g.some species prefer muscid hosts other attack calliphorids.
One of the ways they discriminate between more and lesssuitable hosts is the surface texture of the puparium.
Nasoniasp. antennatingthe surface of a fly puparium
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Host Finding (Pages 79-84)
3. Host acceptance (Pages 80-81)
Size:
Size is a minor factor with predators, they can eat fewer or
more prey to compensate.
It is a critical factor in determining the acceptability of a host.
A large host is a greater resource, but if the entire host cannotbe consumed the body contents will decay, killing anyendoparasite pupa present.
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Host Finding (Pages 79-84)
3. Host acceptance (Pages 80-81)
Size: Aphelinidae parasitizinga scale insect
Chalcidoid parasites of scales (Encyrtidae and Aphelinidae)reject scales that are too small to permit larval development.(This is a common phenomenon among parasites.)
Species that can control fertilization of the egg will deposit 1N(male) eggs in small scales (sperm is small and cheap).
They will deposit 2N (female) eggs in larger scales to optimize
fecundity of female offspring (eggs large and costly).
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Host Finding (Pages 79-84)
3. Host acceptance (Pages 80-81)
Size:
Gregarious parasites can also use host size to determine thenumber of eggs to deposit in any given host.
Trichogrammaspp. are known to deposit from 1 to 50 eggs in ahost egg, depending of the size of the host egg.
This is a very efficient way to optimize host utilization.
Trichogrammaassessingmoth eggs
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Host Finding (Pages 79-84)
3. Host acceptance (Pages 80-81)
Stage of development:
This is obviously an important characteristic of the host,
thus we define egg parasites, larval parasites, etc.
Consider a holometabolous host:eggs, larvae, pupae and adults may not co-occur in
space or time
the four life stages are anatomically and physiologicallydifferent
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Host Finding (Pages 79-84)
3. Host acceptance (Pages 80-81)
Stage of development:
However, finer constraints are known for some parasites.
Recall Pteromalus puparium (Pteromalidae) attacking only veryyoung cabbage butterfly pupae, before the cuticle hardens soits ovipositor can penetrate the host.
Similarly, but for physiological reasons, Trichogrammaspp.attack only recently deposited eggs in the early stages ofembryogenesis to avoid the developing hosts immune system.
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Host Finding (Pages 79-84)
3. Host acceptance (Pages 80-81)
Parasitized/Not Parasitized:
This question is critical to obligatory primary parasites and
many obligatory secondary parasites.
Progeny could die due to intrinsic competition (1 parasite) orlack of intermediate host (2 parasite).
Hymenoptera have the best systems for assessment, usuallyusing sensors on their ovipositor to refine the assessment.
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Host Finding (Pages 79-84)
3. Host acceptance (Pages 80-81)
Parasitized/Not Parasitized:
Snowberry maggot marking fruit
Some insects leave external markers (epidietic pheromones) todeter later attack.
Rhagoletisspp. (Diptera: Tephritidae) mark their oviposition site
in the fruit with such a pheromone.
Trissolcus basalis(Hymenoptera: Scelionidae) makes a figure-8with its ovipositor on the pentatomid eggs it has parasitized toleave its epidietic pheromone.
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Host Finding (Pages 79-84)
3. Host acceptance (Pages 80-81)
Parasitized/Not Parasitized:
Internal markers have been hypothesized for manyHymenoptera.
However, venoms and substances that disable the hosts
immune system may also induce detectable changes in thehost, thus serving two purposes. (More on these later)
Changes in hemolymph composition due to parasitism havebeen reported: amino acids, salts and sugars have all beenseen to change. These can be detected with chemosensors onthe wasps ovipositor.
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Host Finding (Pages 79-84)
4. Host suitability (Page 81)
Host suitability can only be evaluated as the successfulemergence of viable progeny from the parasitized host.
Despite the previous steps, not all parasite attacks are
successful.
Nutrient deficiency in the host is rarely a problem, e. g. allinsects contain all of the essential amino acids.
Host toxicity can occur due to the plant the phytophage isconsuming. Habrolepis rouxi(Hymenoptera: Encyrtidae) canparasitize California red scale on citrus, but not on sago palm.
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Host Finding (Pages 79-84)
4. Host suitability (Page 81)
The dominant factor in determining host suitability is usually thehosts immune system.
Hemocytes respond to non-self tissue and surround it to protectthe insect from infection, etc.
This is also the primary defense against parasitism. It is termedencapsulation. Thehemocytes cover the parasite, melanize
and deprive the parasite egg or larva of oxygen.
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Host Finding (Pages 79-84)
4. Host suitability (Page 81)
Parasitic Diptera larvae overcome the hosts defenses by
feeding continually to keep an opening in the capsule.(Effective, but not highly specific.)
Parasitic Hymenoptera may inject immuno-suppressants withthe egg and/or have the larvae secrete them.
The immuno-suppressants are usually chemicals (venoms) in
the accessory gland fluid that accompanies the egg.
In the Ichneumonoidea, polydna viruses in the accessory glandfluid serve this role.
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Host Finding (Pages 79-84)
5. Host regulation (Page 81)
Some parasites take control of their hosts development to
optimize benefit to the parasite.
The parasite may delay or hasten host maturity, or even alter
the number of instars host passes through to mature.
Aphidius platensis(Hymenoptera: Braconidae: Aphidiinae)slows development of its aphid host with secretions from its
teratocytes (cells from embryonic membrane).
Syrphoctonusspp. (Hymenoptera: Ichneumonidae) accelleratedevelopment of their syrphid hosts. Yielding smaller hosts thatthe wasp larva can completely consume.
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Host Finding (Pages 79-84)
5. Host regulation (Page 81)
Mantispaspp. (Neuroptera: Mantispidae) larvae shortenmaturation of female spider nymphs by one instar, reducing therisk of host death before she lays eggs.
Copidosomaspp. (Hymenoptera: Encyrtidae) are gregariousparasites and are polyembryonic. They induce supernumerarymolts in their Lepidoptera larvae hosts, producing larger hosts,increasing the number of wasps that will emerge from that host.
Copidosoma adult, 1 mm Copidosoma, host with pupae Copidosoma emerging
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Host Finding (Pages 79-84)
Diagrammatic summary of host finding activities (Page 82)
Inactivity
Scanning
Intense Searching
Post-oviposition Orientation to/search pattern examination of
host
Oviposition
See examples on pages 83 and 84.
Appetetive drive
Host cues (longrange)
Host cues (shortrange)
Absence of host cues
Satiation/egg depletion
Absence of host cues
Host cuescontact or internal
Absence of host cuesFixed behaviors, e. g.cleaning ovipositor
Fixed behaviors