Download Handout – Insect predators

Handout – Insect predators
I. Predators
1. Diversity (taxonomic distribution)
Predatory insects are a major portion of the following orders (see cladogram): Odonata,
Mantodea, Neuroptera, Mecoptera (100% predatory), and Dermaptera, Hemiptera, Hymenoptera,
Coleoptera (partially predatory).
2. morphological adaptations to predation
a. eyes -- eyes generally large, with excellent visual acuity (e.g., dragonflies and
mantids). Visual acuity increased by having large number of ommatidia with very small interommatidial angles between them. Often regions of the eye are specialized for focussing on prey.
Binocular depth perception enhanced by widely spaced eyes.
b. legs -- raptorial forelegs common
c. mouthparts
i. Hemiptera -- stylet-like mandibles, maxillae
ii. Neuroptera -- fused maxillae, mandibles
iii. Coleoptera -- scythe-like mandibles.
d. defensive adaptations -- often predatory insects are heavily armored to defend against
the counter attacks of their prey.
3. Extra-oral digestion -- approximately 80% of all predatory insects practice this form of
digestion. Involves injecting either salivary secretions or digestive enzymes into host and
liquifying the innards. Remains are withdrawn through piercing mouthparts.
4. mechanisms of prey location (search strategies)
a. Sit-and-wait predators (larval tiger beetles, ant-lions)
b. Active hunting (lady bugs, lace wings) -- active hunters use visual and olfactory cues
to locate their prey. Learning may be involved.
c. Lures -- Bolitophila (New Zealand) & Arachnocampa Australia -- cave dwelling
fungus-gnats; also known as glow-worms.
5. Ecological roles of predatory insects -- limit prey populations; may also limit predatory
populations when predators prey on predators.
"indirect" effects -- predatory insects may cause changes in prey behavior that decrease
herbivory. Such indirect effects have been demonstrated in aquatic and terrestrial ecosystems.
Commonly, the introduction of a predator (or in some cases the odor of a predator) causes prey
to become more secretive, nocturnal, or sedentary. All these effects cause decreased herbivory.
6. Predatory insects in biological control -- important in controlling herbivorous pests in
agricultural ecosystems. Lady bugs are the most commonly sold biological control agents
available. See some of the following web sites for more information:
http://www.gardens-alive.com/
http://www.nysaes.cornell.edu/ent/biocontrol/
http://ipmwww.ncsu.edu/biocontrol/biocontrol.html
We will cover more general aspects of biological control later in the course.
II. The Red Queen hypothesis -- insect predators and their prey are in an ongoing race. To stay in
one place they have to keep running.
Predators rare
Predators common
All species are predators
Phylogeny of the insect orders
From: Gullan & Cranston, The Insects,
Third Ed., 2005