Predation & Parasitism

DEFINITIONS (Gullen & Cranston, 2000)

Predator. “An organism that eats more than one other organism (animal) during its life.” Usually larger than prey (exception: social predators).

Parasite. “An organism that lives at the expense of another (host), which it does not usually kill.” Usually smaller than host.

Parasitoid. “A parasite that kills its host.” Usually smaller than host.

(DEFINITIONS)

Cleptoparasite. ‘A “thief” parasite, one that consumes the food stored by another insect in a nest. (Evans, 1984) Smaller or similar size as host; often closely related.

Hyperparasite. Parasite of a parasite. Usually smaller than host.

Inquiline. “An organism that lives in the home of another, sharing food; in entomology, used particularly of residents in the nests of social insects or in plant galls induced by another organism.” (Gullen & Cranston 2005)

Social Parasite. “An insect that invades or lays its eggs in the nest of a social insect and eats and develops on food stores or on host immatures.” (Evans, 1984)

Predators

Predation by social insects challenges the usual rule that the predator must be larger than the prey unless one considers the entire colony the predator.

Predation

Paleohistory. 1st hexapods were likely predaceous.

Modern Representatives. All ARACHNIDA, all CHILOPODA, most “Soil Arthropods”, all ODONATA, representatives in most other orders, some predominantly. Exceptions: a few minor insect orders with only saprophagous or parasitic members, ISOPTERA, LEPIDOPTERA (but counter-exceptions even here).

The evolution of plant-feeding by insects was a major adaptive leap, leading to huge increases in species diversity. But many species remained predaceous (or parasitic), eventually diversifying in response to more varied prey. Also, as has happened many times in insect evolution, there have been reversions to previous food habits, so some plant-eaters branched off into secondarily evolved predation, e.g. some stink bugs.

1) Prey Distribution in Space & Time

a) Coarse vs. Fine-grained

b) Patchy vs. Even

c) Continuous vs. Intermittent

>> Terms relative to predator’s “viewpoint”

2) Foraging Strategy: Cost vs. Benefit

Costs: Time (T), energy (e)

Benefit: Nutrition (energy, protein)

>> “Optimal Foraging Theory”: Successful strategies optimize Benefit/Cost ratio by maximizing prey capture while minimizing inputs, either T or e or both.

How to be a Predator (Behavior & Ecology).Some major quantifiable factors in the life of a predator.

Resource Dispersion models influencing adaptations of predators &/or parasites.

Patch or perch departure criteria (thresholds):• Elapsed Overall Time• Elapsed Search time • Prey encounter rate • Prey capture rateMother may play a role in selecting prey patch choice of offspring, e.g. syrphid flies.

Major Types of Prey Searching Behavior

Sit & Wait

Trapping

Active Searching Random Directional

T e Strategy Immature Adult

Sit & Wait dragonfly, mantid, (dragonfly), mantid, tiger beetle,

≈ ≈ Trappingspider, ant lion, tiger beetle, cave midge

spider

Active Foraging

(dragonfly), robber fly, syrphid fly

spider (some non-web species), dragonfly, robber fly

- -Non-feeding or non-predatory -

ant lion, cave midge, syrphid fly (nectar only)

Generalized Predator Foraging Strategies with Examples Time & energy are balanced in any strategy.

Dragonfly nymph switches strategies depending on prey density; adult strategy depends on species. Immature & adult strategies often the same in hemimetabolous species. Some holometabolous adults do not feed at all.

Parasites & Parasitoids

Paleohistory & Evolution

• Small size => poor fossil record of parasites.

• Probable radiation with increased importance of phytophagy.

• ~25% of all insect species are parasitic in one or more stages of development.

• The parasitic life style represents a major adaptive advantage and has arisen many times. Only 3 orders are completely parasitic (probably relatively recent in evolutionary terms; 2 linked to vertebrate hosts). But there are parasitic representatives in 4 hemimetabolous orders and all but two (minor) endopterygote orders.

Various Parasites, Parasitoids, & Cleptoparasites in the Diptera, Hymenoptera, and Acari, orders with a high proportion of parasitic species.

57) Tachinid fly, parasitoid of Pandora moth larvae.58) Parasitized larvae and host pupae of 57.59) Braconid wasp, parasite of bark beetles.60) Jewel wasp, parasitoid of ground-nesting bees.61) Velvet ant, parasitoid of ground nesting wasps.62) Soft tick, parasite of gulls.

Diverse Parasite Relationships to Host

Louse (PHTHIRAPTERA): All stages, permanent on host Flea (SIPHONAPTERA):

adult only, intermittent, usually same host individual

Mosquito (DIPTERA): adult only, intermittent, many host indiv’s

Some Factors:• Host specificity• Duration on Host• Life cycle dependency on Host• Alternate hosts• Number of host individuals

For most parasites, the environment is patchy (very “coarse grain”) in terms of host-finding.> Much time & energy are expended to find a new host and there is serious exposure to predation and physical harm.> Once a host is found, however, the parasite and possibly is offspring can live on their unlimited food source, depending on their relationship to the host.

Host Relationships

1) Long-term host (many generations; host as “island”)

a) Continuous host residence, e.g. lice (PHTHIRAPTERA)b) Intermittant host residence (usually “rest” near same

host), e.g. bed bugs (HEMIPTERA)

both: Advantage: limited or no host-finding Disadvantage: host may die!

Environment & Host Relations in Parasites

2) New Host with Each Generation

a) Larva searches

• Frequently the adult selects a likely host-encounter area.

• Active early instar larvae, often with hypermetamorphosis. E.g. “triungulins” or “planidia” of some DIPTERA, COLEOPTERA, STREPSIPTERA, HYMENOPTERA

• Phoresy, “hitchhiking”

• Adult can broadcast eggs; no host-search required (eggs usually small)

• High egg mortality if broadcast; often time-expensive for larva, hazards in hitchhiking, host defenses

b) Adult searches

• Highly developed sensory abilities: Substrate vibrations, e.g. fruit fly parasite Visual/olfactory: syphid flies/lady beetles laying eggs near aphid colonies Chemical cues, pheromones => kairomones; sources incl. frass, host CO2, bark beetle and cavity-nesting bee parasitoids

• Host Acceptance, Manipulation

• Faster development: larva can specialize in feeding

• All offspring dependent on search success of adult

Two Different Parasitoid Host-Finding Strategies

Bee Fly: Larval host-searching; eggs laid near host burrow, active larvae find host.

Parasitoid wasps: Adult search, larvae deposited inside host

Host Specificity & Evolution

Farenholz’s Rule: phylogeny of parasite mirrors phylogeny of host. Implications, one parasite per host, one host per parasite, with corresponding evolution. This is now considered more theoretical than real.

Reality: dynamic evolution of hosts & parasites influenced by:• Irregularities in host distribution,• Sudden host declines or extinctions• Differential vagility of parasites vs. hosts• Differential host defenses.• Length of association

GeneralizationsMonoxenous (single host species) Usually full-time parasites (permanent host-residence)Oligoxenous (narrow host range, e.g. within one genus) Many parasitoids, cleptoparasites

Hymenopterous parasitoids of potential importance in biocontrol.A. Habrocytus (Pteromalidae); B. H. feeding from oviposition puncture; C. Zarhopalus inquisitor (Encyrtidae); D. Aphelinus jucundus (Eulophidae); E. Euplectrus (Eulophidae).

from Borror, DeLong, & Triplehorn 1981

Variations in Parasitism

Hyperparasitism, parasite of a parasite (of a….up to 7 levels!)

Superparasitism, mulitple eggs from one or more individuals of the same parasitoid species in a single host.

Multiparasitism, eggs from more than one species. Many parasites have been shown to protect themselves from competition with larvae of other parasitic species. It is relatively rare to find more than one species of parasitoid in a single host individual.

Hyperparasitism Complex, part of a dynamic food web

from Evans, 1984

Inquilines & Social Parasites

• Taking advantage of social insect colonies as a special concentrated resource.

• Requires highly specialized means of overcoming colony defenses.

• Most are non-lethal to the colony.

from Holdobler & Wilson

COLEOPTERA THYSANURA

ACARI

Complex behavioral/physiological ruse of an inquiline staphylinid beetle.

3 glands:adoption glanddefensive glandapeasement gland

Ant-simulating behavior(as perceived by attending ant)

from Holdobler & Wilson

Adoption strategy of a predaceous, socially parasitic predatory caterpillar.

2 glands are used to:pacify an ant andencourage “adoption”.

Worker ant bringing home a Lycaenid caterpillar.

Once in the ant nest, the caterpillar commences to feed on the ant larvae.

from Holldobler & Wilson 1986

Cleptoparasitic bumbe bee, Bombus (Psithyrus) vestalis.Females are all queens that aggressively take over mature colonies of host bumble bees. The host queen is killed and the worker bees raise the (all-queen) larvae of the parasite.

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