# GTBOP Webinar Archives — Quiz
Getting the Best of Pests — Processed webinar archives for the UGA Center for Urban Agriculture

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# GTBOP Moodle Quiz

## Principles of Insecticide Mode of Action — Dr. Michael Scharf

Webinar Date: October 18, 2017 Series: Structural Pest Control Activity Type: Multiple Choice Quiz Questions: 15 Difficulty Distribution: 6 Recall (40%) / 6 Application (40%) / 3 Analysis (20%)

### CHAIN OF CUSTODY

- Source documents: Corrected SRT (GTBOP_Transcript_2017-10-18_InsecticideMOA.srt) + Archive Package (GTBOP_Archive_Summary_2017-10-18_InsecticideMOA.md)
- All questions and answers derived exclusively from presentation content
- No external knowledge required to answer correctly

### Question 1

Timestamp Reference: 17:51 – 19:30 Difficulty: Recall

According to Dr. Scharf, how many basic modes of action do all insecticides fall into?

a) Two b) Four c) Six d) Nine

Correct Answer: b Explanation: Scharf states there are only four basic modes of action: stimulation, blockage, modulation, and inhibition. He emphasizes that all insecticide effects on target sites can be categorized into one of these four mechanisms. Source in transcript: ~18:07 — "We can really break it down into four modes of action. There are only four kinds that occur."

### Question 2

Timestamp Reference: 32:24 – 34:07 Difficulty: Recall

Which insecticide class targets axonal sodium channels by stimulating them, causing rapid knockdown and excitation in insects?

a) Phenylpyrazoles b) Diamides c) Pyrethroids d) Organophosphates

Correct Answer: c Explanation: Scharf explains that pyrethroids (along with DDT and pyrethrins) stimulate sodium channels on the nerve axon, causing excitation and the rapid knockdown commonly observed when insects are treated with pyrethrins. Source in transcript: ~32:56 — "We have pyrethroids and also DDT and pyrethrins... They stimulate sodium channels and cause excitation."

### Question 3

Timestamp Reference: 34:12 – 36:16 Difficulty: Application

A technician applies fipronil to a cockroach harborage area and observes insects exhibiting hyperexcitation rather than paralysis. Based on Dr. Scharf's explanation of fipronil's mode of action, why does fipronil cause excitation rather than sedation?

a) Fipronil stimulates sodium channels, causing nerves to fire rapidly b) Fipronil blocks chloride channels, removing the calming effect of chloride on neurons c) Fipronil inhibits acetylcholinesterase, causing neurotransmitter buildup d) Fipronil stimulates muscular calcium channels, causing uncontrolled contraction

Correct Answer: b Explanation: Scharf explains that chloride normally has a "mellowing" effect on neurons. Fipronil blocks the chloride channel, removing that calming influence, which leads to excitation. He demonstrated this with nerve recordings showing increased firing rate after fipronil application. Source in transcript: ~34:48 — "Fipronil blocks the chloride channel so you're blocking this mellowing effect which leads to excitation."

### Question 4

Timestamp Reference: 33:22 – 34:10 Difficulty: Application

A pest management professional encounters a situation where rapid knockdown is undesirable and instead needs an insecticide that paralyzes insects by blocking nervous system function. Which sodium channel insecticide would best fit this need, based on the presentation?

a) Bifenthrin b) Indoxacarb c) Fipronil d) Imidacloprid

Correct Answer: b Explanation: Scharf explains that indoxacarb (an oxadiazine) blocks sodium channels rather than stimulating them, causing the "on switch" to be stuck in the off position, which paralyzes the insect. This contrasts with pyrethroids like bifenthrin, which stimulate sodium channels and cause excitation. Source in transcript: ~33:34 — "Indoxacarb affects the sodium channel but it blocks it... the insect is actually paralyzed because its sodium channels don't work."

### Question 5

Timestamp Reference: 40:02 – 41:40 Difficulty: Recall

What is unique about the mammalian safety profile of diamide insecticides such as chlorantraniliprole?

a) They require a "Danger" signal word due to moderate toxicity b) Their mammalian toxicity is so low that the EPA initially did not require a signal word c) They are equally toxic to mammals and insects d) They are safe only when applied as baits, not as sprays

Correct Answer: b Explanation: Scharf states that diamides are so safe for mammals that the EPA initially required no signal word. Manufacturers voluntarily adopted a "caution" label. He still emphasized that safety guidelines should be followed. Source in transcript: ~41:04 — "These products are actually so safe for mammals that no signal words were required by the EPA initially."

### Question 6

Timestamp Reference: 40:02 – 41:03 Difficulty: Recall

According to Dr. Scharf, what happens physiologically when a diamide insecticide like chlorantraniliprole affects an insect?

a) It blocks sodium channels, preventing nerve impulses b) It inhibits chitin synthesis during molting c) It stimulates muscular calcium channels, causing contraction followed by energy depletion and paralysis d) It disrupts the insect's respiratory chain in the mitochondria

Correct Answer: c Explanation: Scharf explains that diamides stimulate neuromuscular calcium channels, causing muscles to contract for hours until the insect's energy is burned up, after which it enters a paralyzed state for days until it dies. Source in transcript: ~40:48 — "What these things do is they stimulate the neuromuscular calcium channel and that causes that muscle to contract for a few hours and then it burns up all its energy."

### Question 7

Timestamp Reference: 36:20 – 38:01 Difficulty: Recall

Which of the following target sites do nicotinoid insecticides affect?

a) Sodium channels on the nerve axon b) Chloride channels on neurons c) Acetylcholine receptors at the synapse d) Muscular calcium channels

Correct Answer: c Explanation: Scharf identifies nicotinoids as affecting the acetylcholine receptor by stimulating it and causing excitation in the insect. He also notes that sulfoximines and spinosyns share this same target site. Source in transcript: ~36:54 — "We have our mainly the nicotinoids... They're affecting the acetylcholine receptor by stimulating it."

### Question 8

Timestamp Reference: 37:28 – 38:01 Difficulty: Analysis

Dr. Scharf notes that organophosphates and carbamates are subject to more regulatory restrictions than many newer insecticide classes. Based on his explanation, what is the underlying reason for these restrictions?

a) They are more expensive to manufacture than newer products b) Their target site (acetylcholinesterase) is not insect-specific, so they are equally effective against mammals c) They cause environmental persistence that exceeds all other insecticide classes d) They are only effective against a narrow range of pest species

Correct Answer: b Explanation: Scharf explicitly states that the acetylcholinesterase target site is "not a really insect specific target site" and that "these things work equally well against humans and mammals," which is the reason for restrictions on these product classes. Source in transcript: ~37:53 — "This is not a really insect specific target site. You know these things work equally well against humans and mammals and so we have a lot of restrictions."

### Question 9

Timestamp Reference: 38:04 – 39:05 Difficulty: Application

A combination product pairs a nicotinoid with a pyrethroid. Based on Dr. Scharf's presentation, what advantage does this combination provide over a single active ingredient?

a) The two ingredients target the same site for a doubled dose effect b) The combination eliminates the need for product rotation c) Hitting two different target sites simultaneously produces a potentiation effect — synergy greater than either alone d) The pyrethroid component makes the product non-repellent

Correct Answer: c Explanation: Scharf explains that combination products produce potentiation by hitting two target sites at once — the nicotinoid targets the acetylcholine receptor while the pyrethroid targets sodium channels — creating a "one plus one equals three" synergistic effect. Source in transcript: ~38:35 — "They cause this effect called potentiation, which is actually hitting two target sites at once. So you get this synergy, this one plus one equals three kind of effect."

### Question 10

Timestamp Reference: 51:02 – 53:01 Difficulty: Application

A pest control operator is treating a heavy German cockroach infestation with gel bait. Based on Dr. Scharf's discussion of pest behavior, why might the actual number of cockroaches killed exceed the number that directly consumed the bait?

a) Gel bait releases a fumigant vapor that kills nearby cockroaches b) Cockroaches that eat bait excrete insecticide in their feces, which other cockroaches consume, producing secondary and even tertiary kill c) The bait becomes more concentrated as it dries, increasing its toxicity over time d) Cockroaches are attracted to the pheromones of dead individuals, bringing them into contact with remaining bait

Correct Answer: b Explanation: Scharf describes secondary and tertiary kill in cockroaches: one cockroach eats bait, excretes insecticide, and other cockroaches consume the feces. He notes research showing the toxin can pass through two digestive tracts and still affect a third cockroach. Source in transcript: ~51:24 — "If we have a cockroach that eats a bait and it either excretes, you know, some of the bait in its excrement... We can have secondary kill and even tertiary kill."

### Question 11

Timestamp Reference: 54:19 – 56:28 Difficulty: Recall

What rotation frequency does Dr. Scharf recommend for switching active ingredients in cockroach management to help manage resistance?

a) Every week b) Every month or every three months c) Every six months d) Annually

Correct Answer: b Explanation: Scharf recommends switching active ingredients every three months, or even every month if possible, as part of a resistance management rotation strategy for cockroach accounts. Source in transcript: ~55:49 — "Every three months switch active ingredients, maybe even every month if you can do it."

### Question 12

Timestamp Reference: 53:04 – 54:11 Difficulty: Application

A technician is having difficulty achieving control with gel bait in a commercial kitchen. The kitchen has grease buildup on surfaces and abundant food debris. Based on Dr. Scharf's discussion, what is the most likely reason for reduced bait performance?

a) The bait has developed resistance to the cockroach population b) Grease and dirt tie up insecticides on surfaces, and excess food competes directly with bait for cockroach feeding c) The kitchen's humidity is degrading the active ingredient d) The bait formulation is incompatible with commercial kitchen environments

Correct Answer: b Explanation: Scharf specifically identifies three sanitation-related factors that reduce insecticide efficacy: excess food competing with bait, clutter creating untreatable harborage, and dirt and grease that physically bind insecticides. He frames sanitation as essential to making insecticides more effective. Source in transcript: ~53:31 — "Excess food in an account will compete with bait" and ~54:02 — "dirt and grease tie up insecticides too."

### Question 13

Timestamp Reference: 41:42 – 44:46 Difficulty: Application

A technician inspects a cockroach account and notices several German cockroaches with twisted, malformed wings. Based on the presentation, what does this observation most likely indicate?

a) The cockroaches are infected with a fungal pathogen b) The population has been exposed to insect growth regulators, specifically juvenile hormone analogs c) The cockroaches have developed pyrethroid resistance d) The cockroaches are immature nymphs that have not yet completed development

Correct Answer: b Explanation: Scharf specifically identifies wing twist as a diagnostic sign that IGRs (particularly juvenile hormone analogs like pyriproxyfen) are active in a cockroach population. He advises that when wing twist is visible, it may be appropriate to rotate to a different product class. Source in transcript: ~44:25 — "If you go into a new account and you see individuals with wing twist... you can put good money down on the fact that IGRs are in that population affecting it."

### Question 14

Timestamp Reference: 19:41 – 22:40 Difficulty: Analysis

Dr. Scharf states that the relationship between LD50 and product toxicity is inverse. A professional is comparing two insecticides: Product A has an LD50 of 5 mg/kg for cockroaches, and Product B has an LD50 of 500 mg/kg for cockroaches. Which product is more toxic to cockroaches, and why?

a) Product B, because a higher LD50 means more insecticide reaches the target site b) Product A, because a smaller LD50 means a smaller dose is needed to kill 50% of the test population c) Both are equally toxic; LD50 only measures speed of action d) Product B, because a higher LD50 indicates greater potency

Correct Answer: b Explanation: Scharf explains that LD50 is the lethal dose required to kill 50% of a test population, and the relationship to toxicity is inverse — the smaller the LD50, the higher the toxicity, because less product is needed to achieve the lethal effect. Source in transcript: ~20:24 — "The smaller the LD50, the higher the toxicity of a product. That means... you only need a small dose to kill half of your test population."

### Question 15

Timestamp Reference: 46:56 – 48:09 and 04:01 – 04:00 (pollinator context) Difficulty: Analysis

Dr. Scharf discusses cuticle dehydrating dusts like diatomaceous earth and silica gel. Considering his earlier discussion of insect physiology, why are these products effective against insects but pose minimal chemical toxicity risk to mammals?

a) They work through a physical mechanism — abrading the waxy cuticle layer and causing water loss — rather than through a biochemical target site interaction b) They contain active ingredients that are specific to insect nervous systems c) They are formulated with attractants that only insects will consume d) They degrade too quickly in the environment to affect mammals

Correct Answer: a Explanation: Scharf explains that silica gel and diatomaceous earth are essentially finely ground glass powder that abrades the protective waxy outer layer of the insect cuticle, leading to water loss and death. This is a physical mechanism rather than a chemical mode of action targeting a specific biochemical pathway, which is why these products do not pose the same chemical toxicity concerns for mammals. Source in transcript: ~47:00 — "We have silica gel and diatomaceous earth which are just basically finely ground glass powder... they abrade the cuticle, they break it down, which leads to water loss."

## Moodle Activity Verification

- [x] All 15 questions traceable to specific presentation segments
- [x] Timestamp references verified against corrected SRT
- [x] No external knowledge required to answer correctly
- [x] Difficulty distribution: 6 Recall / 6 Application / 3 Analysis
- [x] Answer keys unambiguously correct based on presentation content
- [x] Distractors plausible but definitively wrong per speaker's content
- [x] Questions drawn from early (Q1, Q2, Q14), middle (Q3–Q9, Q13), and late (Q10–Q12, Q15) presentation content
- [x] No "all of the above" or "none of the above" options used