Entomology exam 3

entomophagous insects

carnivorous insects who feed on other arthropods

high in nitrogen and water compared to other food sources

energetically expensive to capture

parasite

lives at expense of host, without directly killing host

may be vectors for disease and other things that kill host, but feeding does not kill

predator

kills and consumes more than one prey item to reach maturity

parasitoid

symbiont that feeds on host, eventually resulting in host’s death

host death related to development of parasitoid

slavery

primarily in ants

workers take pupa of another species and make them do most of the work in the colony

some enslaved species will neglect the young of their slavemakers in rebellion

phoresy

transport of individuals by another (hitchhiking)

often done by wingless or small insects with low mobility

may lead to predation or parasitism of eggs

Meloe franciscanus phoresy

Meloid beetles lay masses of larvae that emit pheromones of female bees

attracts male bees that the larvae jump onto

when the male bee mates with an actual female, the larvae jump onto the female

beetle larvae are transported to host nest, where they feed

How common are predatory insect?

about 25% of insect species are predatory

monophagous predators

predators that feed exclusively on a single species of prey

highly specialized

oligophagous predators

feeds on a few number of prey species

polyphagous predators

generalist predators that feed on prey based on abundance (prey switching)

seven orders that are exclusively predatory

1. odonata

2. mantophasmatodea

3. mantodea

4. megaloptera

5. neuroptera

6. raphidioptera

7. mecoptera (adults)

orders with some predatory species

grylloblatodea

thysanoptera

hemiptera

coleoptera

diptera

hymenoptera

etc

general adaptation of predatory insects

1. larger than other entomophagous insects

2. larger eyes with good visual detection

3. raptorial forelegs common

4. mandibulate or stylet mouthparts

5. defensive adaptation, like armor that deters counter attacks from prey

6. well-equipped to travel (decent fliers)

Size as a predatory adaptation

predator size is proportional to prey size (large prey = large predator)

some exceptions, predators that can sting and paralyze prey, or team up against prey, can go after larger things

eyes as a predator adaptation

wider spaced eyes have better binocular perception

good visual detection relative to number of ommatidia and angles

mouthparts as a predator adaptation

neuroptera — mandibles and fused maxillae

hemiptera — stylet-like mandibles and maxillae, all fused

coleoptera — scythe-like mandibles

odonata naiads — hinged and enlarged labium to scoop in prey

extra-oral digestion is common

extra-oral digestion in predators

allows for relatively larger prey items to be consumed

concentrated nutrients can be extracted more quickly

ingested food does not contain any bulky or indigestible items

optimal foraging theory

differences between the costs and benefits associated with strategy are maximized

predators can either maximize energy obtained or minimize time

requires appropriate habitat

benefits of optimal foraging theory

quality and quantity of food

costs of optimal foraging theory

time spent obtaining food (time not spent reproducing)

energy spent obtaining and processing food

exposure to adverse elements

increased risk of being eaten or parasitized

sit and wait/ambush strategy

find suitable habitat and wait for mobile prey to come within striking distance

use camouflage — aggressive mimicry and crypsis

ambushers usually perch on vegetation and make short forays to capture prey (dragonfly adults and robber flies)

aggressive mimicry

mimic another animal in some way to lure prey/host into clsoer proximity

aggressive mimicry of Femme fatale firefly (subfamily Photurinae)

each species of firefly has their own flashing pattern that advertises themselves to mates (mate recognition)

female femme fatale firefly mimics the flashing of another firefly species to lure in males of that species, then eats them

femme fatale firefly sequesters protective chemicals from males because they can’t produce their own

aggressive mimicry of Emesines assassin bugs

Emesines crawl into spiderwebs. movement of web makes spider think there is prey

Emesine can move through silk and eats the spider

aggressive mimicry of flower-mimicking mantis

Mantids that mimic flowers (typically orchids) to lure in predators

crypsis of odonata naiads

aquatic naiads blend into background to avoid detection by prey

trapping

predator foraging strategy

constructing traps to catch prey

trapping of net-spinning caddisflies

spin silken tubes to catch micro arthropods

trapping of antlion

build sand traps that ants fall into

trapping of new Zealand glowworms

glowworms build silken tubes that hang from cave ceilings

glow reflects through silk threads and attracts prey, which gets trapped in silk

Active searching

predator foraging strategy

more energetically expensive than sit & wait/ambush strategies

includes random and directional foraging

random/non-directional foraging

insect moves in a seemingly erratic or exploratory pattern

No directional cues directly leading to food

insect is sampling the environment, often in areas where food might be expected but not immediately detectable.

non-directional foraging of ladybug larvae

ladybug larvae will whip their heads back and forth to locate aphids

directional foraging

a non-random search strategy where an insect moves in a specific direction and follows particular cues to locate prey

stimuli may include chemical, tactile, light, or visual cues

How common are parasitic/parasitoid insects?

15% of insects have some parasitic aspect to life history

exclusively parasitic orders

phthiraptera (lice)

siphonaptera (fleas)

strepsiptera (twisted-wing parasites)

orders with some parasitic species

diptera

hymenoptera

hemiptera

coleoptera

strepsiptera hosts

thysanura

blattodea

mantodea

orthoptera

hemiptera

diptera

mostly aculeate (with stingers) hymenoptera

life cycle of strepsiptera

1. The first instars (triungulins) develop inside the female bee host’s body.

2. When the host bee visits flowers, the triungulins exit the female and cling to the bee.

3. triungulin is deposited in the bee’s nest cell when the bee lays her eggs.

4. it penetrates the bee’s egg and transforms into the second instar, becoming an endoparasite.

5. The second instar larva feeds on non-vital tissues and fluids of the developing bee.

6. The parasite pupates within the bee and the pupa protrudes from host’s abdominal segments

7. Males emerge small (<3 mm), winged, and short-lived. After emerging, they search immediately for females.

8. Females are reduced to sac of reproductive organs and never leave the pupa embedded in the host. Release sex pheromones to attract males.

9. The male punctures the female’s pupa to inseminate her. After mating, the male dies.

10. The female remains inside the host, producing the next generation of triungulins that explode out of her.

ectoparasites

parasites that feed externally

endoparasites

parasites that feed internally

tend to be more specific than ectoparasites

idiobionts

parasites that rapidly consume their host

tend to be ectoparasites

venom keeps host fresh and prevents host from entering metamorphosis

parasite selects fully developed hosts

hosts are either concealed or protected

koinobionts

parasites that interact and feed on host for an extended periods

host typically develops beyond original stage attacked

tend to be endoparasites

venom injection is temporary

younger instars preferred

solitary vs gregarious parasites

Solitary parasites develop as a single individual per host

gregarious parasites allow multiple offspring to develop and share a single host

primary parasitoids

parasitoids attacking phytophagous hosts

hyperparasitoids

parasitoids attacking other parasitoidss

superparasitoidism

if more larvae of the same species than can reach maturity are in one host

general adaptations of ectoparasites

body forms that prevent grooming (flattened body, or claws, hooks, or barbs for attachment)

anesthetizing agents allow for feeding

feeding times are short (idiobionts)

general adaptations of endoparasites

digestion can be typical or nutrients can be directly absorbed

respiration varied

rapid development, hypermetamorphosis, or polyembryony

overcoming host immune response

maternal oviposition

respiratory adaptations for endoparasites

most endoparasites have a closed tracheal system (gas exchange directly through integument)

some perforate host’s tracheal system or integument to access atmospheric air

some use host hemolymph (high O2 concentration)

Encyrtus wasp respiration 

endoparasites

tiny, lay eggs into a single scale

larvae live in hole created by mother puncturing scale to oviposit

larvae move to larger tracheal tubes as they grow

hypermetamorphosis

first instars are morphologically and behaviorally different than subsequent molts

1st instars mobile to find target host tissue

2nd instar for feeding

polyembryony

single egg results in 2+ individuals (sometimes 1000s)

found only in parasitic and parasitoid species

possible by totipotent property of early cleavage embryo

Copidosoma floridanum polymebryony

if one egg is laid, one sex emerges (usually female)

if two eggs are laid, both sexes emerge

1st ones to emerge are defender morphs — well-functioning on their own, attack other parasitoids because it lessens competition, and fail to pupate (allows siblings to feed)

2nd ones to emerge are reproductive — emerge, mate, and disperse

female defender morphs attack male reproductive larvae, skews sex ratio (keeps enough males to breed but conserves food for females)

encapsulation host response to endoparasites

endoparasite is surrounded by hemocytes

hemocytes flatten around invader

phagocytosis begins as hemocyte number increases

capsule eventually forms that kills invader

usually observed in non-typical hosts (no coevolution between species)

molecular mimciry

method of circumventing host response by parasites

invader produces something similar to host proteins or insulates itself in a capsule derived of host membranes or tissues

destruction

method of circumventing host response by parasites

invader destroys host hemocytes or tissue

suppresion

method of circumventing host response by parasites

use of viruses to suppress host immune response

Ichneumonidae/Braconidae and viral (PDV) mutualism

ichneumonid and braconid wasps oviposit into larvae and inject secretions containing viruses

PDV viruses replicate in epithelial lining of female’s reproductive tract

resulting eggs are coated in viral particle

viruses prevent encapsulation and host pupating out of 5th instar

hymenoptera parasite ovipositors

suitable length and strength to penetrate host defenses

short ovipositors for penetrating thin tissues (caterpillars, etc)

long for penetrating thick tissues (wood, etc)

ovipositors with chemoreceptors at tip

many with paralytic venom

dipteran parasite oviposition

dipterans lack ovipositors

stick eggs to host bodies

lay eggs in suitable habitat and 1st instars locate host

sit and wait parasites

many parasites wingless and with reduced mobility and vision

adults locate host

do not emerge until host cues are detected (vibration, rise in temperature, increased CO2)

active searching parasites

more energetically expensive than sit and wait parasite strategies

limited to directional foraging

usually in response to host stimulus (pheromones, sound, etc)

pheromone detection of active searching parasites

detect pheromones in host frass

detect pheromones produced by other species for mate recognition

detect chemicals produced by plants in response to herbivory

sound detection of active searching parasites examples

Corethrella flies find treefrog hosts by following frog calls

Tachinid flies have specialized “Ears” to hear male cricket calls

thanatosis

host counter-adaptation

feigning death in chrysomelid beetles

osmeterium

Y-shaped, forked organ found on swallowtail caterpillars that they can extend from their head when threatened

emits chemicals to deter parasites

Cleptoparasites

lay their eggs in the nests of other species

parasite’s offspring directly or indirectly (via competition) kill the host’s offspring

Common in cuckoo leafcutter bees

social parasites

females enter another’s nest and takes over role as queen (inquilines)

ex) cuckoo bumblebees

integument

basis for exoskeleton

largest organ system

determines form and size of insect (forces ecdysis)

integument functions

barrier to water loss

barrier to disease and chemicals

resists attack by predators, conceals, and aposematically warns

nervous system connected to specialized regions

layers of integument

cuticle

epidermis

basement membrane

cuticle

made of multiple specialized layers

secreted by epidermis

noncellular

epicuticle

outermost layer of cuticle

thin but multilayered (thinness provides flexibility)

has sites for muscle attachment

one of outermost layers is a wax layer (prevents water loss)

procuticle

2nd layer of cuticle

includes exocuticle and endocuticle

composed of protein and chitin

exocuticle has thicker protein structure and is responsible for rigidity of exoskeleton

endocuticle is more flexible and allows for movement

where sclerotization takes place (not all areas are sclerotized)

proteins in procuticle

10-100 different types of proteins in procuticle

harder exoskeletons have more protein diversity

includes arthropodin (predominant protein, provides rigidity) and resilin (flexible)

types of proteins vary with life stages; larvae have less than adults

chitin in procuticle

60% of the dry weight of an insect’s cuticle

chitin chains are bundled together

sclerotization

process of crosslinking the proteins in exocuticle

fixing chitin tubules to each other in an organized way

enzymes transform proteins into stable molecular structure

chitin molecules dehydrate, hydrogen bond with adjacent chains and become linked with other proteins

each layer of chitin is twisted slightly, provides structural integrity

epidermis

single layer of cells beneath cuticle

basement membrane

beneath epidermis, anchors connective tissue

spines

immobile cuticular extensions

multicellular with undifferentiated epidermal cells

spurs

mobile cuticular extensions

multicellular with undifferentiated epidermal cells

setae

multicellular cuticular extensions with specialized cells

hairs, bristles, scales, etc

acanthae

unicellular cuticular extensions

provide ridges

Microtrichia

subcellular cuticular extensions

multiple extensions per cell

production of color

color is typically independent of sclerotization

majority of coloration due to properties of cuticle

structural colors

selective reflection of light by physical structure

interference or scattering of light

interference

structural colors caused by air bubbles or distortions in the cuticle, or helicoidal arrangement of chitin fibrils

how do air bubbles cause interference?

both the upper and lower surface of air bubbles reflect light

light from lower surface travels a longer distance than light from the upper surface

lights waves become out of phase

reflections cancel each other out and the only colors visible are those in phase

colors seen by observer changes with their point of view

interference caused by chitin fibrils

chitin fibers arranged helicoidally

requires a particular spacing and arrangement of layers with respect to one another

act like different films

can also polarize light; may be used in insect communication

scattering of light

not dependent on angle of observer

caused by small particles or waxy secretions

Tyndall blue caused by particles that selectively reflect blue (appears green in most due to presence of yellow pigments as well)

larger granules reflect all wavelengths and produce structural white

pigments

wider range of colors but not metallic or iridescent

frequently excretory products

may be absorbed from food

melanin

excretory pigments

ex) pieridae pigments derived from uric acid (yellow)

ex) reddish-yellow pigments produced from a meamorphosis byproduct

diet-based pigments

ex) carotenoids

deposited into epidermis or fat cells

deposited in different areas = patterns

melanin

results in black, brown, or dark yellow

synthesis poorly understood, but includes oxidation with tyrosine in hemolymph

melanogenesis

production of melanin

influenced by temperature; lower temps increase the process