SeleksiTanInangDJ Chap05 Host Finding

8/2/2019 SeleksiTanInangDJ Chap05 Host Finding

1/47

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.


2/47

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.


3/47

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 +


4/47

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.


5/47

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.


6/47

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.


7/47

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.


8/47

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


9/47

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.


10/47

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


11/47

Orientation

AttractantRepellent

Assesment

Landing

Arrestant

StimulantDeterrent


12/47


13/47


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.


14/47


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)


15/47



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


16/47



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.


17/47



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


18/47



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


19/47



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.


20/47



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).


21/47



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.


22/47


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


23/47



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.)


24/47



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


25/47



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 )


26/47



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)


27/47



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)


28/47



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)


29/47



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)


30/47



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)


31/47


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)


32/47



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.

Host Finding (Pages 79 84)


33/47



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



34/47



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.



35/47



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).



36/47



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



37/47



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



38/47



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.



39/47



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.



40/47




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.



41/47




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.



42/47


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.



43/47



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.



44/47



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.



45/47


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.



46/47


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



47/47


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

SeleksiTanInangDJ Chap05 Host Finding

Documents