#ento lecture

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Plant Insect Herbivory

Primary Herbivorous Insects

Non-complex foods

Orthoptera, Phasmotodea, Thysanoptera.

Complex foods

Hymenoptera, Coleoptera, Lepidoptera, Diptera, Hemiptera.

Amount of Insect Herbivores

40-50% of all insects are herbivores

Types of Herbivores

1. Chewing

ancestral form

2. Leaf Mining

3. Plant-Boring

economic damage

fruits/vegetables

4. Sap-Sucking

Inserts stylet into stems/leaves

Insects with this style of feeding pass pathogens/diseases.

5. Gall-Forming

Highly plant-specific

Larval hosts

The World is Green Hypothesis

Herbivores are limited by predators

Hypothesis Error: Not everything that is green is edible.

Why More Plant Matter Isn't Consumed

Morphological Barriers

Spines

Waxy Leaves

Nutritional Barriers

Insects that lack certain gut microbes can't digest cellulose.

Plants with low nitrogen or proteins require the insect to overeat to get dietary needs.

Plants with micronutrient/salt deficit result in insect not getting dietary needs.

Toxins in plants harm predators.

Plants with low water content.

Hidden Costs To Herbivory

Leaf consumption leaves holes in leaves

reduces photosynthesis

reduces seed production

long term reduces food source

Meristem consumption prevents leaf production

Fruit damage

specialized insects for fruits

Insect vector disease

damages host plant through disease

reduces food source

Induces plants chemical defense

plant diverts energy away from reproduction

Honeydew

sugar excrement induces fungal growth

Ecological Impact of Insects on Plants

Limits the geographical range of plants

Reduces growth rate of plants

Impacts plant communities

insect feeds heavily on plant A which allows dominance of plant B

Affects Seed Production

seed feeding insects can remove the possibility of a plant successfully reproducing

Some plants only reproduce once

Plant Response to Herbivory

Escape Time and Space

Temporal Displacement: Plant shifts date of buds opening to starve out their predator.

Insect Response: Insect synchronizes to host plant.

Habitat Location: plant shifts habitat location to avoid an expected predator.

Morphology: Modify leaf shape to an unexpected shape.

Insect Response: Learns to look for different leaf formations.

Olfaction: evolves out of producing certain compounds to avoid predators that are attracted to its scent.

Plant Resistance

Physical

plant produces hooks/spines/hairs

Chemical

Acute Toxins

immediate toxicity

high potency = death

Chronic toxins

overtime toxicity

low potency = illness

Toxin Presence

Constitutive

allelochemicals/toxins

always present with or without attack

Inducible

allelochemicals/toxins produced as needed

constant production is costly

Insect Adaptations To Chemical Plant Defense

Behavioral adaptations

selective feeding to avoid toxicity

leaf rolling/web-spinning leaves of phototoxic

trenching, eating around leaf veins

Biochemical adaptation

enzymes in gut to detoxify

Physiological adjusts gut pH, lessens toxicity

sequesters toxin

Herbivores + Microbes

orally secretes bacteria to suppress plant defenses

Plant Defense: Tolerance

focus energy into regrowth.

bares through the attack.

may overstimulate growth with the expectation of more attacks.

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Insect Behavior: Innate and Learned Behavior

Innate

Innate

instinctive behaviors such as mating, to consume plants or others, and avoidance of being preyed upon.

Fixed Action Patterns

A complex innate behavior that is species specific. The behavior is triggered by an external stimulus, once the behavior is start it has to be followed through until completion. Even if the behavior is disrupted the species will continue until it can complete its task.

Fixed Action Pattern Without Disruption

Triggering Event -> Goose's egg rolls out of nest ->

Behavior Triggered -> Goose rolls egg back into nest ->

Completed Behavior

Fixed Action Pattern With Disruption

Triggering Event -> Goose's egg rolls out of nest ->

Behavior Triggered -> Goose begins to roll egg back into nest ->

Disruption Event -> Asshat scientist switches egg with beer can ->

Continuing Behavior -> Goose rolls beer can back into nest

Completed Behavior

Learning

Associative Learning

Situation-dependent learning, choosing an action based on the situation you're in.

Ex. choosing host quality, learning odors to choose hosts, learning actions to locate food.

Transitive Inference

The inference of a relationship is based on previous knowledge.

bees/waps seek out sugar ->

soda cans have lots of sugar ->

also gets caffeine from the soda ->

memory becomes stronger every time they get sugar from soda -> seeks out soda for caffeine.

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Semiochemicals: Pheromones, Allelochemicals, and Infochemicals.

Semiochemicals

Chemical signal between organisms that alters behavior.

Pheromones: chemical signals within a species.

Allelochemical: chemical signals between different species.

Pheromones

Alarm Pheromone

The release of a certain pheromone that signals to a colony to do a defensive action. Occurs with social insects.

Ex. Aphids wiggle, bees swarm and sting.

Aggregation Pheromones

Common in aposematic species (species that exhibit warning colors). Gathering together exhibits strong warning signs.

Epideitic Pheromones

A marker placed by a female to indicate a host has been used. Keeps others away from using things.

Allelochemicals

Allomones

An chemical set off by prey that is an irritant to the predator. It's positive for the prey but neutral or slightly negative to the predator.

Ex. Predator goes to eat a caterpillar -> the caterpillar sprays its stink gland -> the predator decides to not eat the prey.

The only thing wasted is the energy of the predator.

Kairomones

A chemical that is released that attracts a predator. Negative for the prey but positive for the predator.

Ex. male releases pheromone to signal other males away from a female -> wasp picks up on pheromone -> wasp parasitizes eggs.

Synomone

A call for defense that benefits both predator and prey.

Plant releases alarm pheromone -> Parasitoid wasp picks up on this as an allelochemical -> Parasitoid wasp lays eggs in the attacker.

Infochemical

Infochemical

sex pheromone traps used in agriculture

used to monitor emergence times, pest density, invasive species detection, aids control programs, disrupts mating behaviors, and can act as bait for insecticides.

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Reviewing Assigned Paper

Goal of the research:

To differentiate between the two hypothetical causes of inbreeding depression. Partial dominance hypothesis and Overdominance.

Partial Dominance Hypothesis

an increased expression of deleterious recessive alleles.

Overdominance Hypothesis

loss of favourable heterozygote combinations. predicts a decline in fitness but not necessarily increased extinction.

What questions are being asked

Is inbreeding depression greater in life-history than morphological traits? Which of the two hypotheses is the major underlying cause of inbreeding depression? Does inbreeding elevate population extinction risk?

Why is this important?

Inbreeding depression thus has potential significance for the management and conservation of endangered species (Hedrick and Kalinowski 2000), and it is important that the causes, costs and patterns of inbreeding depression are well understood. Understanding which one is right, partial dominance or overdominance, can help with this.

Hypothesis

The primary aim of this experiment was to distinguish between the two mechanisms that might cause inbreeding depression by comparing traits in lines with different histories of inbreeding and different heterozygosity levels.

If overdominance is responsible then the crossed lines should be similar to the outbred lines

If partial dominance was responsible then we should have seen a small increase in trait values of the cross-bred lines.

Results

Outbred lines were far higher than either the inbred or crossed-inbred lines.

we think the evidence weakly supportive of the partial dominance idea.

Our study also reveals significantly higher extinction risk of inbred lines compared to outbred lines, supporting the notion that inbreeding increases the extinction risk of small, inbred populations.

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Pest Management: Pesticides, Resistance, and Biocontrol

The Problem With Pesticides

1. Extremely Toxic To Helpful Insects

Insect predators, parasitoids, pollinators, and soil arthropods.

Herbivore insect pests naturally process toxins from plants which makes them more resistant to pesticides.

2. Pest Resurgence

After removing predators for pests a population resurgence occurs.

3. Secondary Pest Outbreaks

Chemical control removes the primary pest but then a secondary pest takes over.

4. Adverse Environmental Effects

Biomagnification: the movement of toxins from lower trophic levels to higher trophic levels.

+ shows the accumulation of toxin

pesticide on grass + < mouse ++ < snake +++ < hawk ++++

Bioaccumulation: the process where chemicals accumulate in an organism over its lifespan because of exposure to it in the soil, water, or air.

5. Human Health Concerns

The handling and application of pesticides can be extremely harmful to humans. Causes death and permanent injuries. (cancer, blindness)

6. Insecticide Resistance

The increase in insecticide use has resulted in over 700 insect species that are resistant to insecticides. Agricultural losses have worsened.

Cross-Resistance

The resistance built from one pesticide resulted in resistance to other pesticides with similar chemical structures.

Multiple Resistance

When an insect has more than one detoxification mechanism in its body that makes them resistant to multiple pesticides.

Mechanisms of Resistance

1. Behavioral Avoidance

Insects learn to avoid places on the plant where insecticide has been applied.

2. Physiological Changes

Sequestration: The insect population begins building up the insecticide in their body to help deter predators.

Reduced Penetration: The insect population begins producing thicker cuticles which decrease the penetration of pesticides.

Accelerated Excretion: The insect body processes the pesticide faster to expel it and minimize its effects.

3. Biochemical Detoxification

The insect body becomes capable of detoxifying pesticides.

4. Target-Site Resistance

The site in the insect body that produces the desired effect from pesticides becomes less sensitive.

How Does Resistance Spread in a Population?

An insect that has genetically resistant to pesticides survives to reproduce. This results in the passing of the resistant trait. An insect that does not have this resistance trait dies due to the pesticides. Over time a population is built having pesticide resistance.

Types of Biocontrol

Classical Biocontrol

Introduction of a predator to consume a pest. Purpose to maintain control of a pest population naturally.

Augmentative Biocontrol

Also called Inundative Biocontrol. The temporary introduction of a predator to an unnatural environment to control a pest population. Predators and pests cannot survive outside of this environment. (Greenhouses)

Conservation Biocontrol

Habitat gets modified for the favorability of natural predators.

Other Pest Control Approaches

1. Plant Resistance

Selective plant breeding to create resistance to insect consumption. Results in evolutionary pressure on pests that are resistant to the modification building over time.

2. Physical Control

The physical removal of an insect pest. Only works in small greenhouses or households.

3. Cultural Control

Altering the time of planting or intercropping other species of plants.

4. Pheromones/Attractants

Pheromone traps.

5. Sterile Male Technique

Introduction of sterile males into the population where female pests can only mate once. Results in a decrease in pest populations.

6. RNA Interference

Gene editing pest populations

What Are Genetically Modified Crops?

A gene from a plant that is resistant to a certain disease or insect population is incorporated into a different plant.

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Pest Management: What Makes an Insect a Pest?

How Insects Become Pests

1. Accidental Introduction

An insect is introduced into a population where they have no natural enemies. This results in them creating a lot of damage without natural population control measures.

Ex. Invasive species such as lanternflies that damage forests

2. Vector Diseases

An insect causes minor physical damage through feeding (human or plant) but is a vector for disease. Resulting in the passage of disease to humans or plants.

Ex. Mosquitoes for humans. Leafhoppers for vineyards.

3. Native Insects Attack Introduced Crops

A insect finds a new preferred food source from an introduced crop.

Ex. A species of beetle that is native to the US preferred feeding on the introduced crop of potatoes. Beetle was then able to spread throughout the US because of more food availability.

4. Monocropping

The growth of a single agricultural product attracts large aggregations of an insect to its preferred food source.

5. Improper Use of Insecticides

Overuse: Insects become genetically resistant over time. Resulting in the resurgence of a pest.

Misuse: Kills natural enemies of a pest insect causing secondary outbreaks of the pest.

Historical Overview of Pest Management

Biocontrol Natural

A pest of grains is parasitized by a species of wasp. Resulting in higher yields of grain.

Intentional Biocontrol

In China (324 BCE) it was recorded that a certain species of weaver ants could control caterpillars on citrus trees. In the late 1800s the citrus industry was failing in California due to cottony-cushion scales. A species of beetle and parasitic fly was introduced and able to help successfully grow citrus.

Chemical Control

Sulfur was used by Sumerians in Mesopotamia to control mites and other pests.

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Pest Management: Equation for Economic Injury Level and Other Terms

Terminology

Economic Injury Level (EIL): The lowest population density that causes economic damage.

Cost (C): The cost of control measures put into each unit of agricultural crop produced.

Value (V): The market value of a crop.

Damage (D): The crop yield loss per number of insects

Injury Reduction (K): The effectiveness of the control method used. How much of the insect population is reduced from using this method.

EIL = C/(VDK)

Economic Threshold (ET): The pest density when control methods need to be applied to prevent pest populations from reaching economic injury level (EIL).

General Equilibrium Population of Pest (GEP): The average pest population in absence of control methods.

The Different Economic Categories That Pests Can Fall In

Non-Economic Pest:

Graph A. The populations never each the Economic Threshold (ET) where insect control methods need to start being applied.

Occasional Pests:

Graph B. The populations occasionally reach Economic Threshold (ET) where insect control methods need to start being applied.

Perennial Pests:

Graph C. The populations frequently reach Economic Threshold (ET). This can occur once a year or more frequently depending on the insect species. Insect control methods need to be frequently applied to ensure Economic Injury Level (EIL) doesn't occur.

Severe Pests:

Graph D.

Also called Key Pests. The populations will always reach Economic Injury Level(EIL). Insect control methods must be continuous to maintain crops.

Limitations of EIL

1. Designed for agriculture. Sensible use of pesticides is required.

2. This doesn't account for external factors like natural enemies or pesticide resistance.

3. Some pests have an Economic Threshold near 0. These pests are vectors for plant pathogens. Meaning they pass on diseases to plants despite causing minimal physical damage to the plant themselves.

4. Economic Injury Level equation isn't suited for multiple pests impacting crops.

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Medical and Veterinary Entomology Lecture

Terminology

Disease: An abnormal condition that impairs bodily function associated with certain symptoms and signs. Does not always involve a pathogen.

Pathogen: disease-causing organism

Host: an organism that harbors another organism.

Vector: an organism that transmits a pathogen from a reservoir to a host. To be a vector (mosquito) the one carrying the pathogen (malaria) must be a different species to the one carrying the pathogen (human).

Insects that cause diseases

The insect causes disease but there is NO pathogen involved.

Pediculosis

The infestation of lice in the head, body, or pubic hair. The lice are specialized to human hosts. The saliva of the louse causes an allergic reaction that results in itching. The itching results in sores on the skin.

Scabies

A disease caused by a mite, Sarcoptes scabiel, that is specialized to human hosts. Mites are not an insect but a type of arachnid. These microscopic mites burrow under the skin. Their droppings are what results in itchy rashes of the skin. Itching can worsen at night due to the increase in body temperature. It is most commonly spread between adults through sexual contact. However, it can spread between family members through normal physical contact.

Myiasis

(Diptera: Calliphoridae, Sacrophagidae, Muscidae)

An infection of blowfly larvae that feed on the living tissue of humans and livestock. Blowfly larvae that infects livestock is an economical problem. A method of control in certain species of blowfly is called the sterile-male technique (SIT). Where sterile males are introduced to a population to lower the success in mating with females.

Insects as Vectors of Disease-Causing Pathogens

Modes of Pathogen Transfer

Mechanical Transfer

Pathogens do not replicate in the vector. The vector picks it up and then transfers it over to a host. Within the host, replication begins.

Biological Transfer

Propagative: pathogens replicate within the vector.

Cyclodevelopmental: Pathogen undergoes development but doesn't reproduce within the vector.

Cyclopropagative: Pathogen undergoes development and replication within the vector.

Biological Transfer: Single Cycle

human-to-vector-to-human.

Insect picks up the pathogen from human A. Pathogen undergoes some sort of development or replication within the insect vector. Insect vector then goes on to pass pathogen to human B.

Possible to eliminate in humans since it moves from human to vector to human.

Biological Transfer: Secondary Cycle/Zoonotic

human to vector to human OR animal.

animal to vector to human.

Animal hosts are called reservoirs.

Harder to eliminate in humans because of more variability for implantation. Can be moved through multiple species of vectors. Then it is able to be implanted in both humans and animals.