Reproduction, Insect Evolution, Ground and Aquatic Insects, predation & parasitism, insect defenses

Reproduction Steps

Mate finding, Courtship, Copulation, Fertilization, Ovipositing

synchronized emergence

extreme synchronicity if emergence and sexual readiness, males and females emerge at the same time and near each other, insect adult life may end as soon as they mate

calling

using sounds communication to find a mate through stridulation, forced air, etc.

long range call

initial call to come closer

short range call

used to convince an individual to mate

visual signaling

involves bright colors and unusual structures on body, most are useful during courtship behavior after mate is already found (except light is used for mate finding)

swarming

aerial aggregation of males near resource likely to be visited by females, when female visits males all swarm to initiate copulation or perform a ritual

example of swarming

male midges swarm over rivers for mates, male mosquitos swarm animals and other food that females may feed from

sex pheromones

used for long and short range mate finding and recognition

leks

occurs when mate defends territory that has no resources but females are likely to be present, male will fight anyone who enters lek

example of leks

Darwin’s stag beetle and Madagascar hissing cockroaches

Mate finding behaviors

synchronized emergence, calling, visual signaling, swarming, sex pheromones, leks

courtship

close range intersexual behaviors that induce sexual receptiveness prior to or during mating where one or both sexes seek to facilitate fertilization by influencing the behavior of the other

courtship can involve…

leks, dancing, visual displays, stridulation, close range calls, nuptial gifts

copulation

ensures sperm is exchanged but not necessarily directly from male to female

primitive copulation

male lays a spermatophore in the environment for female to accept and insert into vaginal opening

Origin of spermatophore

In primitive insects like Collembola, evolved from aquatic environments and must still be moist or will dry up, why Collembola are limited to wetter environments

Internal copulation

Males aedeagus and penis insert into bursa copulatrix to eject sperm, sperm then transfers to spermatheca to be stored. Reason insects dominated terrestrial environments

Traumatic insemination

males insert aedeagus directly through body wall into burse copulatrix

spermalege

In bed bug females, on abdomen and guides aedeagus into specific place on abdominal wall to avoid damage

Steps to fertilization

Egg ready→ released from ovary→ passes spermatheca→ sperm swims to micropyle→ micropyle is capped→ most eggs laid outside of body through ovipositor

ovipositing

act of placing eggs in the environment, ovipositor is formed from sclerotized plates at the apical end of abdomen, length and shape depend on where eggs are laid

Common places to oviposit

On a plant (lacewings, katydids), in the plant (cicadas, katydids), on in or near water (mosquitos), carrying them on the body (giant water bugs), inside a host

sex determination

determined by genes, environment, whether egg is fertilized or not

Male vs female chromosomes

Females are XX, males are XO. Female offspring have one X from mom and one X from dad, male offspring only have one X from mom

parthenogenesis

Animals produce egg but offspring may develop from unfertilized egg

haplo-diploidy

Some generations of offspring are haploid, some are diploid. Haploid offspring undergo meiosis, diploid offspring don’t undergo meiosis

hermaphroditism

male and female organs in one individual or when males and females can swap, can be reciprocal or one acts as male/female, very rare in bugs and may be parthenogenic

polyembryony

insects can increase offspring number by laying only a few eggs, allows females who cannot readily find multiple hosts to get in and get out fast

adenotropic viviparity

Occurs in certain true flies, eggs hatch within females and are nourished by special milk glands, When mature they are laid and immediately pupate

Where do we find ground-dwelling insects?

leaf litter (decaying vegetative material), humus (upper A horizon), A to B horizons, caves

Why do insects live in the ground?

foraging, living there (foraging and mating), laying eggs, pupating, escaping the elements and overwintering

Most abundant insects in leaf litter

Collembola, ground beetles, rove beetles, earwigs

Most abundant insects in soil (mostly larvae)

Adults: ants, termites, mole crickets, ground wasps, ground crickets Juveniles: crane and robber flies, weevils, dung beetle, scarab beetle

xylophagous

wood eating (wood boring beetles, carpenter bees)

pyrophilous

attracted to burnt wood (fire wasps)

coprophagous

dung-eating (ding beetle larvae)

troglobiants

living in caves to escape cold, heat, aestivation, or hibernation

troglobites

insects restricted to caves (blind cave beetle with very reduced eyes)

soil living adaptation for Collembola

soft bodied

soil living adaptation for adult insects

fossorial limbs, harder exoskeleton, elytra in beetles, mycangium, antifungal and antimicrobial agents

mycangium

structure on insects to transport symbiotic fungi

What roles do insects play in below ground living?

primary decomposers, parasites and predators, fungus propagation

example of ground dwelling parasitism

red velvet ants parasitize ground nesting wasp larvae by laying eggs on them, so hatched babies can eat larvae

example of ground dwelling fungal propagation

- mountain pine beetles spread blue stain fungus among conifers resulting in accidental disease vectoring

- leaf cutter ant cultivate leaves and fecal matter in fungus garden for food

insect groups prevalent in aquatic environments

Ephemeroptera, Odonata, Trichoptera, Diptera, Hemiptera (adults too), Coleoptera (adults too), Neuroptera

Explain how O2 transfers from air to water

Enters by diffusion or as a byproduct, highest at water surface and depends on wind, ~30% of air is made of O2

How does water density effect O2 transfer?

Higher water density makes O2 extraction much more difficult, requires higher expenditure of energy

How does water temp affect chemical rxn rates in insects?

Affects foraging, digestion, mating, reproduction, growth (when temp is highest insects have fast chemical reactions)

How does water temp effect O2 concentration in insects?

When water temp is high oxygen concentration goes down (when O2 is high in cold waters, insects have slow chemical reactions)

turnover

In spring and fall surface water becomes dense at 39degrees, so it sinks. Brings oxygenated and nutrient dense water to the bottom layers

thermoclines

In summer and winter upper and lower water temps are very different, leading to different water densities and O2 unable to circulate into other water densities

Effect of water depth on O2 availability

Upper layers have more sunlight penetration for photosynthesis and wind cycling, at certain depths water is so dense its not effected by wind cycling, decaying organisms at the bottom are decomposed by O2 consuming bacteria

lentic water body

standing water (ponds, marshes, tree holes), O2 saturation low, very little water circulation, organic matter not washed away and accumulates. O2 drops significantly with each layer

lotic water body

running water with high O2 saturation, movement of water over irregular surface folds gas into water layers, organism matter is washed away and doesn’t accumulate, high turnover

Aquatic juvenile adaptations

Have respiratory system even if no spiracles, spiracle adaptations, hold on to things in moving water, obtaining food

arthrodial membrane

oxygen diffuses across porous membrane, serves as respiratory organ

oligopneusic

juveniles with one or two spiracles

apneustic

juveniles with only direct diffusion across exoskeleton, no spiracles

polypneustic

adults with multiple spiracles on thorax and abdomen

example of arthrodial membrane in aquatic insects

bloodworms lack tracheal systems, O2 diffuses directly into hemolymph and gets circulated, have heme protein to maximize

example of aquatic insect adaptation in moving water

Diptera larvae attach to rocks with silk and filter feed on food passing by

Example of aquatic insect adaptation for obtaining food

Mosquito larvae hang down from water surface and filter feed on organic matter using feathery mouthparts

Adult aquatic insect adaptations

respiratory systems and ability to obtain air, getting around, laying eggs

example of adult aquatic insect adaptation to obtain air

Hydrophilidae beetles have hydro fugal hairs called a plastron, it traps air between hairs of plastron and surrounding spiracle

Example of adult aquatic insect in getting around

Anteapical claws in Gerridae and Veliidae, paddle like metathoracic legs in Corixidae

1st (minor) adaptive radiation

300 mya of herbivory by hexapods, first lineage of insects and lots of decaying food

1st adaptive radiation of gymnosperms

lower Paleozoic and Mesozoic, led to an increase in Orders

2nd adaptive radiation of angiosperms

lower Mesozoic and Cenozoic, high diversity, plant feeders, and pollinators

Proof of plant insect coevolution

plant feeders, pollinators, seed dispersers, living commensally with plants

Groups most likely to interact with plants

Diptera, Orthoptera, Lepidoptera, Coleoptera, Hymenoptera (bees, wasps, ants)

Structures allowing adhesion to plant surface

claws and pre-tarsal spines helped insects evolve off of forest floor, and empodia, arolia, pulvilli on heavier insects

How did insects evolve to drier environments

Thick layer of scales (1st to arise) trap moist air around body and lower water loss, heavier sclerotization for fully terrestrial adults

Evolution of specialized mouthparts for plant diet

early hexapods mandibulate for detritus feeding, then scratching piercing, lastly piercing sucking

Evolution of digestive system for plant diet

gut microorganisms assist in plant cell-wall breakdown, filter chamber concentrates plant nutrients and eliminates sugar and water

allelochemicals

either metabolic byproducts or used for something else but now for defense

Insects counter allelochemicals by…

Breaking down toxins in fat bodies or sequestering it in blood and fat bodies for defense

ways secondary metabolites effect insects

recruit predators and parasitoids of insects, reduce nutrient absorption, feeding deterrent, stop development or kill

Plant mechanical defenses

Oftentimes the primary defense preventing feeding in the first place since insects usually avoid, trichomes, gaseous chemicals to attract then impale, spines prevent large bugs, extra floral nectaries attract predators of pests

phytophagy

plant feeding

monophagous insects

specialists that only feed on one species of plant or maybe a few closely related species, most insects due since they had to adapt to every single plant defense

oligophagous insects

Feed on several species within a plant genera, only occasionally cross into different genera. Small number of insects

polyphagous insects

Generalists that feed on many genera and sometimes different families

leaf chewing 

entire sections of leaf or entire leaves consumed by mandibulate insects (Lepidoptera, Coleoptera, Orthoptera, Sawfly larvae)

leaf skeletonization (type of leaf chewing)

shot hole (type of leaf chewing)

girdling (type of leaf chewing)

window panning (type of leaf chewing)

leaf mining

between upper and lower epidermis of leaf, just under epidermis of stems and other organs (larvae of Diptera, Lepidoptera, Coleoptera, Hymenoptera)

leaf boring

penetrate deeper into plant tissue, occurs in stems, roots, fruits, bugs, etc (Coleoptera and Lepidoptera)

girdling

significant feeding around a stem, adult lays eggs in terminal end of stem and juveniles may overwinter in fallen dead stem

seed feeding & boring

consuming whole seed, part of a seed, or bore into seed to feed on the inside

root feeding

chewing roots or sucking fluids (beetle larvae, aphid and scale insects)

fluid feeding in plant tissues

Piercing/sucking of phloem, xylem, and cellular fluid. Lapping fluids of ripe fruits (Hemiptera, beetles, mosquitoes, Hymenoptera adults)

galling

Provides extra food for juveniles, structural defense and moist microclimate. Induced by insects, bacteria, nematodes, fungi, mites, viruses by chemical secretions from mouth or fecal matter

galls

Pathologically developed cells, tissues, or organs of plants that arise by hypertrophy or hyperplasia as a result of stimulation from foreign organisms (Aphids, Coccoids, Diptera, Hymenoptera, Thysanoptera)

hypertrophy

increase cell size

hyperplasia

increase cell number

covering gall

nipple gall