Module 9 - Sustainable Human-Insect Interactions I

Question 1

Pests

Answer 1

Insects and other animals that interfere with human activities or the resources that we care about

Question 2

In order to manage pests in an effective, sustainable, and environmentally friendly way what do managers employ?

Answer 2

Integrated Pest Management (IPM)

Question 3

How does IPM differ from traditional pest control?

Answer 3

Traditional: used calendar-based chemical insecticide treatments to reduce insect pest populations

IPM: integrates multiple control methods to manage pest populations; therefore, can provide economical management with the same or better results than traditional chemical applications alone

Question 4

IPM not only allows effective pest management, but the integration of multiple control tactics reduces pesticide applications which provides what?

Answer 4

Health and environmental benefits
- reduced pesticide use lowers the impact on non-target and beneficial insect species
- less pesticide = slow the development of pesticide resistance by lowering the selective pressure on pests

Question 5

What is the Four-Tiered IPM Implementation Approach?

Answer 5

If controls need to be applied, several IPM tactics are used to control pests in an economically and environmentally sustainable way. These management strategies employed together are referred to as the FOUR-TIERED IPM IMPLEMENTATION APPROACH:
1. Economic/Action Thresholds
2. Identification and Monitoring
3. Prevention
4. Control

Question 6

First IPM Tier: Economic/Action Thresholds

Answer 6

Economic/Action Thresholds = the level of a pest population that will require managers to implement control measures to prevent losses due to pest activity.
- can be measured directly by estimating the number of pests, but is often measured using other factors easier to notice
- as pest populations increase, they may reach the economic threshold and at this point the POTENTIAL economic loss from the pest outweighs the cost of management so a control or management strategy should be applied
- if controls are not implemented, pests may increase to the ECONOMIC INJURY LEVEL, which is set slightly higher than the economic threshold; levels of pets will begin to cause economic losses; controls should be implemented at economic threshold
- thresholds differ between regions, pests, and managed ecosystems
- development of thresholds is difficult but they are useful

Question 7

Second IPM Tier: Identification and Monitoring

Answer 7

• Once economic thresholds have been established, the next step in IPM requires the identification and monitoring of pest populations
• Monitoring occurs before control measure implementation but then continue after and during implementation
• Direct surveillance of pest pops or measuring pest activity or damage
• Requires identification of the species
• Successful monitoring programs detect a pest’s presence at low densities before they reach critical levels that can harm the resource
• Allows implementation of control measures in timely manner and assessment of the effectiveness of their prevention and control methods
• In-situ sampling = a more labour-intensive form of sampling, involves manual inspection of the affected resource for the insect or its associated damage; used for inactive species easy to spot of cause obvious damage
• Sweep netting = another method of sampling conducted by sweeping an insect net through vegetation to collect arthropods
• Knockdown method = a sampling method for larger vegetation, a plant or branch is struck to dislodge any insects, with a tray or sheet placed below to catch the falling arthropods so they can be collected and/or counted
• Passive sampling techniques = such as insect traps; provide a sample of natural insect movement and distribution in the managed area; baited with visual and chemical cues
• Data collected from insect monitoring activities can be used to predict the timing of insect activities using degree day models, as well as the potential growth of pest populations under different environmental or climatic conditions

Question 8

Third IPM Tier: Prevention

Answer 8

• Prevention of pest establishment or the prevention of pest population growth from reaching injurious levels
• Prevention = first line of defense in pest management; regulatory practices, quarantine regulations, and other preventative tactics that stop pest pops from entering or expanding in a managed area
• QUARANTINE = a legal tool used by agencies and managers that involves the restraint of the movement of goods to prevent the spread of pests and disease
• Inspection of quarantined goods for pests can be done visually or with the use of a range of techniques and technologies to find a specific pests
• At a local level, regulatory practices (ex. sanitation or removal of infested plant parts or physical barriers) can reduce pest population level
• Other preventative practices can include the selection of crop varieties resistant to the target pest, or manipulation of the enviro to reduce attraction and establishment of the pest
• Education and outreach are also preventative practices

Question 9

Fourth IPM Tier: Control

Answer 9

• Pest control; chemical, biological, and cultural
• Effective IPM programs integrate multiple control methods together
• Controls are implemented when monitoring programs indicate that pest populations have breached the action threshold
• Control measures evaluated based on their: economics, efficiency, effectiveness, human health risks, and environmental risks

Question 10

What are pesticides?

Answer 10

Chemicals lethal to organism considered to be pests, which include a variety of organisms other than insects such as fungi, plants, and even some vertebrates, like rates

Question 11

What are insecticides?

Answer 11

Pesticides that are used to kill insect pests, and form an important component of most IPM systems
- must be applied carefully to prevent harm to users, non-target organisms, and the enviro, as well as to avoid the development of resistance in the target pest

Question 12

What criteria is used by managers to evaluate pesticides?

Answer 12

• Safety for the user
• Species specificity
• Effectiveness/efficiency
• Persistence of the chemicals in the enviro
• Speed of action
• Cost of use

Question 13

What is the mode by which an insecticide is applied dependent on?

Answer 13

The way the poison is intended to affect the pest in question

Question 14

What are the 3 basic categories of modes of insecticide application?

Answer 14

1. Stomach poisons
2. Contact poisons
3. Fumigants

Question 15

Stomach Poisons

Answer 15

• Chemicals that impact an insect by entering through the digestive system
• Must be ingested = applied to resource insect uses as food
• Some applied as SYSTEMIC INSECTICIDES so they are absorbed by the plants and become present in all tissue
• NEONICOTINOIDS (neurotoxic insecticides) are often applied through seed coats and root baths to act as systemic insecticides

Question 16

Contact Poisons

Answer 16

• Penetrate the insect cuticle to enter through the body wall; insect needs only to crawl over a treated surface
• Ineffective for insects that feed within a plant
• Ex. synthetic chemicals such as the synaptic poison Malathion

Question 17

Fumigation

Answer 17

• Fumigants are insecticides that are gaseous above 5 degrees celsius, applied as a sort of vapour or smoke to the area
• Poison enters the body of an insect through the spiracles and invade the tracheal system from which it can be absorbed into the body tissues
• Can impact all life stages, including the often difficult to kill eggs and they can penetrate areas difficult to reach with sprays
• Primarily applied in enclosed enviros such as greenhouses or for treatment of stored products

Question 18

What 3 categories can chemical insecticides be grouped into?

Answer 18

1. Natural insecticides
2. Synthetic insecticides
3. Hormone analogs

Question 19

Natural Insecticides

Answer 19

Chemicals used to kill insect pests that are derived from natural sources
- Longest history of usage in pest management (ex. sulphur)
- Sulphur is attractive to pest managers due to its low cost, high availability, ability to mix with other pesticides, and species specificity
- Negligible effects on many beneficial insects such as bees and is safe for applicators and consumers
- Most natural insecticides used today are natural botanical insecticides derived directly from plants (ex. neem oil, pyrethrins, nicotine)
- Drawbacks: collection process may be costly and tend to break down quickly in the environment

Question 20

Synthetic Insecticides

Answer 20

• Molecular structures of many natural insecticides have been used as templates to develop synthetic versions of the chemicals
• Mode of action of most synthetic chemicals is similar to the natural compounds they were based on
• Ex. neonicotinoids were derived from the natural insecticide nicotine
• Use of synthetic insecticides took off during WWII (ex. DDT)
• Grouped based on their modes of action aka the way they impact the insect’s physiology
• Most affect the nervous system and are categorized as either axonic or synaptic poisons
• Can be used to disrupt cycles of growth and metamorphosis

Question 21

Axonic Poisons

Answer 21

Neurotoxins that impact the transmission of APs along the axons of nerve cells
- Fxn by disrupting the balance of sodium and potassium influxes along the axon’s membrane
- DDT is an axonic poison that falls into the category known as chlorinated hydrocarbons. DDT is a broad-spectrum insecticide that can also impact other, larger organisms. Problem is it has a high chemical stability in the enviro and is fat soluble.

• Another group are the pyrethroids, which mimic pyrethrins, the naturally occurring compounds in chrysanthemum flowers.
• Highly toxic to insects but not vertebrates
• Fast-acting = they are effective in pest outbreaks
• keep sodium channels in the axons open, preventing a sodium gradient from establishing = interrupts transmission of nervous impulses
• Widely used bc they are effective at low doses, economical to manufacture, relatively non-toxic to mammals, and do not accumulate in the environment

Question 22

Biomagnification

Answer 22

The increasing concentration of a chemical at higher trophic levels
- DDT; accumulates in fatty tissues
- Stability of DDT and its ability to accumulate at higher trophic levels contributed to the banning of DDT in many regions; still used for disease vector control in some areas

Question 23

Synaptic Poisons

Answer 23

Disrupt signal transmission through the synapse btw neurons or btw a neuron and a muscle cell
- Organophosphates = class of synthetic synaptic insecticide that inactivate specific enzymes that act at the synapse by adding a phosphate group to the active site of the enzymes. Inhibit acetylcholinesterases, which break down the excitatory neurotransmitter, acetylcholine. As the neurotransmitters are not
broken down by enzymatic activity, they stay in the synapse and cause constant stimulation of
acetylcholine receptors in the dendrites of the
receiving neuron. This in turn causes rapid nerve. Organophosphates are highly effective, and break down in UV light which prevents them from accumulating in the environment. Some are toxic to vertebrates and dangerous if inhaled, ingested, or contact is made with skin = no longer commonly availble for home gardening.

• Neonicotinoids = another class of synaptic poison, analogs of the natural insecticide nicotine. Acts as a mimic for the neurotransmitter acetylecholine. However, unlike the molecules they mimic, neonicotinoids cannot be broken down and cleared by the enzyme acetylocholinesterase. This results in the post-synaptic acetylcholine receptors being continuously activated and resulting in similar symptoms as organophosphate poisoning. Unlike organophosphates, neonicotinoids have low mammalian toxicity, but they may be linked to the decline of bees and other pollinators, which has caused the use of neonicotinoids to be banned in some parts of the world. However, the unique mode of action of neonicotinoids means that they
  can mitigate the development of resistance to
  other poisons when alternated with other
  insecticides.

Question 24

Synthetic Insecticides: Muscle Poisons

Answer 24

• Valuable in integrated pest management bc they act on an entirely different biological system than neurotoxins; useful for mitigation of resistance to other poisons by alternating their usage with muscle poisons
• Anthranilic diamides (class) ex. chlorantraniliprole. Act by

Question 25

How does chlorantraniliprole (a muscle poison) work?

Answer 25

These poisons act by depleting calcium stored in muscle cells through activation of the receptors
that stimulate calcium release. Without calcium, muscle cells no longer function properly,
which can lead to paralysis in the affected insects, and eventually death.
Chlorantraniliprole quickly kills insects after contact or ingestion, and can impact any life
stage in most pest species. This insecticide has low toxicity for vertebrates because the
receptor activated is only present in insect muscle cells. Relatively specific and has minimal impacts on beneficial organisms. Lack of non-target impacts, safety for the user, quick activity and the fact that it targets the muscular system are all factors that allow this insecticide to fit very well within IPM programs

Question 26

Hormone Analog Insecticides

Answer 26

• Can be used as insecticides; mimics naturally occurring hormones = can disrupt regular processes such as growth and metamorphosis
• Most common mimics the activity of JH and ecdysteroids
• Analogs of JH interfere w/ metamorphosis; cycle is disrupted and a larval insect may produce extra, larger larval instars which can be lethal if it is unable to moult into a reproductively capable adult
• JH analogs useful against insects that are pests as adults such as mosquitoes
• Ecdysteroid analogs mimic ecdysone by binding to moulting hormone receptors to stimulate the initiation of the moulting process
• cannot be cleared from receptors, disrupting the moulting process and dying
• Both JH and ecdysteroid analogs bind to receptors only found in insects so they have little effect on vertebrates and other non-target organisms.
• Lack of non-target effects, safety for the user, effectiveness, and different mode of action make them a safe alternative to integrate into IPM programs

Question 27

What are the 3 issues, known as the three R’s, of IPM?

Answer 27

1. Pest resurgence
2. Replacement
3. Resistance

Question 28

Non-Target Effects of Insecticides

Answer 28

• Health risks to applicators and consumers
• Detrimental impacts on non-target species
• Non-target effects especially true for insecticides considers “broad-spectrum”
• Dramatic effects on ecological health and disrupt the balance of manage ecosystems
• Can leach into water systems and kill aquatic arthropods and larger animals
• Broad-spectrum insecticides and neurotoxins can be dangerous for larger animals because the neurons of vertebrates fxn in much the same way as they do in insects
• Insecticides today are rigorously tested and researched to assess toxicity; label provides a warming of the toxicity to the user, other organisms, potential health effects, and the preventative measures that should be taken
• Consumers have a relatively low risk of insecticide poisoning as strict standards are put in place by governing officials to reduce pesticide residues on consumable foods
• Specific guidelines in place to minimize enviro contamination: nozzle size, specific dose, time of day, crop stage
• Another factor that must be considered when using pesticides is how to properly dispose of crop residue and other pesticide contaminated material; one technique to break down and eliminate pesticide waste is using biobeds; pesticide-contaminated wastes are dumped into designated biobed area, which is filled with a mixture of plant material and soil that provides an excellent habitat for microbes which break down pesticide residues; very effective

Question 29

What are biobeds?

Answer 29

• technique to break down and eliminate pesticide waste
• pesticide-contaminated wastes are dumped into biobed area, which is filled with a mix of plant material and soil that provides habitat for microbes with break down pesticide residues
• biobed must be lined w/ impermeable material to prevent leaching
• very effective
• afterwards, the broken down mix of plant material and soil is relatively free from pesticides, and can be spread onto an ag field as fertilizer

Question 30

Resurgence

Answer 30

The rebound of pest populations due to the absence of natural enemies caused by insecticide poisoning is known as pest resurgence, the first of the 3 R’s of IPM
- common when broad-spectrum pesticides are used w/o understanding of the biological system

Question 31

Replacement

Answer 31

Pest replacement occurs under similar conditions as pest resurgence, whereby application of a broad spectrum insecticide kills off predators and parasitoids in the management area.
- natural enemies help control pops of the target pests and control pops of other herbivorous species not considered pests in the system since they are normally under natural control
- as species are released from predation pressures, pops increase until they become an economic problem; insects that were not initially problematic in the manage system can become serious pests
- Ex. spider mites; historically insignificant but became a problem when synthetic pesticides wiped out predators

Question 32

Resistance

Answer 32

The most significant problem with insecticide use today is the development of insecticide resistance in pest pops
- reduction in the sensitivity of a pest population to a particular method of pest control; insects can develop resistance to chemical insecticides
- ex. diamondback moth, colorado potato beetle, green peach aphid
- resistance occurs through genetic means and arises due to natural section
- can occur anytime a selective pressure is applied to a pop, which occurs with the application of insecticides and other pest management
- subset of pop may have mutations that enable them to resist poisoning; survive and reproduce
- insecticide resistance is the most common type of resistance to pest control methods
- biological qualities of the pest species and operational factors in pest management can impact the speed at which resistance can develop in a given population; pests w/ limited rance of resources and short dispersal distance fact greater exposure and thus greater selective pressure
- shorter generation times = higher likelihood that individuals resistant will appear
- OPERATIONAL FACTORS: the type of chemical and the method in which it is applied can impact the development of resistance in a pest population
- Factors that increase insecticide application can increase rate of resistance (ex. quantity, type, and time)

Question 33

Mechanisms of Resistance

Answer 33

Pest species can develop resistance to insecticides in a variety of ways
1. Behavioural Resistance
- occurs when a pest modifies its behaviour in a way that decreases its exposure to a toxin; achieved by recognition of toxins and learning to avoid the toxins by arrestment of feeding, moving, or feeding on a different part of the plant

2. Metabolic resistance
   - the poison is detoxified or destroyed by enzymes in the insect before it can reach its target site of activity
   - common bc most herbivorous insects already have some ability to detoxify poisons which are naturally found in their plant hosts
   - other forms = ability to excrete toxins with other waste before they reach target or shifting the toxins into the exocuticle so they are shed
3. Altered Target Site resistance
   - changes to the site of activity of the insecticide that can render the poison ineffective to the targeted system
   - may occur with changes to the receptors to which the insecticides normally bind
   - occurs in response to treatment with hormone analog insecticides
4. Penetration resistance
   - adaptations to the exoskeleton that decrease penetration of the cuticle by insecticides
   - occurs with other forms of resistance, and can make the other forms such as metabolic resistance more effective
5. Cross resistance
   - occurs when an organism develops a resistance to an insecticide, which in turn allows it to tolerate other insecticides as well
   - especially likely to occur if the insecticides share a similar mode of action

Question 34

Slowing Resistance

Answer 34

• Crucial that we manage the development of resistance in pests today to prevent serious problems in the future
• limited in the ways we manage biological factors that promote chemical resistance but managers are able to implement IPM systems
• one effective strategy in preventing the development of resistance is to alternate the application of insecticides with different modes of action
• another way to slow down resistance is by providing a refuge for the pest species, or an area of the crop kept insecticide-free; susceptible individuals mate with resistant individuals to produce offspring still susceptible
• passive approaches that don’t place selective pressure can also be used; resources can be supplemented that support populations of natural enemies