⚡ CHEAT SHEET

Ch.8: Mosquito Insecticides & Safety

What the exam tests on larvicide and adulticide active ingredients, signal words, toxicity categories, and pesticide registration requirements.

🎯 Top 5 Traps

Pesticide RISK = TOXICITY x EXPOSURE. Both factors matter. The EPA evaluates both before approval. Reduced exposure (rapid breakdown, application to non-drinking water, small AI quantities) is a key reason microbial larvicides are low-risk — not because the product is non-toxic in isolation. Short residual time also reduces risk by limiting exposure duration.

All Michigan pesticides must be registered by BOTH the EPA AND the state of Michigan — not just one." Repellents follow a slightly different rule: registered with state of MI; registered or exempt at EPA.

Signal words map: DANGER = Category I; WARNING = Category II; CAUTION = Categories III AND IV. Caution covers TWO categories. Common slip: assuming Category III gets its own signal word."

Bti and Bs work by binding to receptor cells in INSECT gut — receptors that mammals do NOT have. This is why microbial larvicides are essentially non-toxic to humans. Both must be INGESTED by larvae (no contact action). Same MOA, different bacteria, different optimal habitats.

Temephos is the ONLY organophosphate approved as a larvicide. All other OPs covered in this chapter (malathion, chlorpyrifos, naled) are adulticides. Temephos is also a key resistance management tool — its use prevents mosquitoes from developing resistance to bacterial larvicides like Bti/Bs.

🔢 Numbers You Must Know

Number

What It Represents

4 toxicity categories

EPA classifies pesticides into Categories I (most toxic), II, III, and IV (least toxic) based on oral, inhalation, dermal, and eye effects

3 signal words

DANGER (Cat I), WARNING (Cat II), CAUTION (Cat III AND IV) — only three signal words for four categories

Temephos: less than 1 oz / 8 oz per acre

Less than 1 oz active ingredient per acre for liquid; 8 oz/acre for granular formulations

Malathion: 0.23 lb (~2.5 fl oz) AI/acre

Maximum mosquito-control application rate of malathion active ingredient

Naled: 0.1 lb AI/acre

Maximum rate for ground AND aerial application of naled active ingredient

1956 — Malathion

EPA registration year — oldest mosquito-control insecticide in this chapter

1959 — Naled

EPA registration year — Trumpet brand

1965 — Temephos

EPA registration year — only OP approved as a larvicide

1975 — Methoprene

EPA registration year — IGR / juvenile hormone analog (Altosid)

1983 — Bti

EPA registration year — first microbial mosquito larvicide

1991 — Bs

EPA registration year — second microbial larvicide; works well in organic systems

🔀 Easily Confused

Pair / Group

Distinguishing Feature

Specific vs Broad-spectrum

Specific: effective against certain insects or stages — usually less toxic to humans/non-targets. Broad-spectrum: toxic to the target pest AND a wide range of similar organisms — greater non-target effects.

Toxicity vs Risk

Toxicity: inherent capacity to cause harm. Risk: function of toxicity AND exposure. Reducing exposure (rapid breakdown, low rates, application to non-drinking water) reduces risk even with toxic compounds.

Bti vs Bs

Both microbial bacteria, both registered larvicides, both bind to insect-gut receptor cells (not in mammals), both must be INGESTED. Bti: registered 1983; broadly used. Bs: registered 1991; especially good in richly organic systems (Culex).

Bti vs Spinosad

Both produced by bacteria. Bti: requires ingestion of bacterial cells; gut-disruption MOA. Spinosad (Natular): does NOT require ingestion of bacterial cells; affects nervous system. Spinosad has wider habitat applicability including stormwater catch basins.

Temephos vs other organophosphates

Temephos: the ONLY OP approved as a LARVICIDE; resistance management tool; WHO-approved for potable water; more toxic to aquatic invertebrates than alternatives. Malathion / Chlorpyrifos / Naled: OP ADULTICIDES.

Monomolecular films vs Larviciding oils

Both form a surface barrier on water; both affect larvae/pupae. Films: surfactants reduce surface tension — larvae/pupae/emerging adults can't attach and drown. Oils: petroleum distillates physically clog breathing tubes. Oils may be toxic to fish if misapplied.

Pyrethrins vs Pyrethroids vs PBO

Pyrethrins: natural compounds from chrysanthemum flowers. Pyrethroids (permethrin, resmethrin, sumithrin): synthetic chemicals modeled on pyrethrins. PBO (piperonyl butoxide): synergist mixed with pyrethroids — enhances effectiveness; not an insecticide itself.

🧪 Mosquito Control Insecticides Quick Reference

LARVICIDES (target aquatic stages)

Active Ingredient

Class

Key Facts & Risks

Bti

Microbial bacterium (1983)

Must be ingested. Gut-disruption MOA via insect-only receptor cells. Essentially non-toxic to humans, wildlife, non-targets.

Microbial bacterium (1991)

Same MOA as Bti. Works especially well in richly organic water (Culex habitats).

Methoprene

IGR / JH analog (1975)

Mimics juvenile hormone — prevents emergence to adult. Non-toxic to bees; low toxicity to fish/birds. Won't leach groundwater.

Temephos

Organophosphate (1965) — ONLY OP larvicide

Less than 1 oz/acre liquid; 8 oz/acre granular. Resistance management tool. WHO-approved for potable water. More toxic to aquatic invertebrates than alternatives — EPA limiting use.

Spinosad (Natular)

Bacterial-derived; nervous system MOA

Does NOT require ingestion of bacterial cells. Wide habitat range — floodwater, stormwater catch basins, artificial containers. Low risk to vertebrates; affects non-target insects.

Monomolecular films

Surfactant — reduces surface tension

Larvae/pupae/emerging adults can't attach to water surface and drown. Minimal environmental risk; short persistence.

Larviciding oils

Petroleum distillate — physical barrier

Coats water surface; clogs larval/pupal breathing tubes. Toxic to fish if misapplied — EPA label precautions required.

ADULTICIDES (target flying adults via ULV / thermal fog / barrier sprays)

Active Ingredient

Class

Key Facts & Risks

Permethrin, Resmethrin, Sumithrin

Pyrethroid (since 1970s)

Synthetic; models on pyrethrins from chrysanthemum. Nervous system MOA. Often mixed with PBO synergist. Toxic to fish and bees; degraded by sunlight and high temperatures.

Malathion

Organophosphate (1956)

Max 0.23 lb (~2.5 fl oz) AI/acre. Degrades in moist soil. Low toxicity to birds/mammals. Highly toxic to bees.

Chlorpyrifos (MosquitoMist)

Organophosphate

Highly toxic to non-target insects and fish. Slightly toxic to humans and other mammals.

Naled (Trumpet)

Organophosphate (1959)

Max 0.1 lb AI/acre — ground OR aerial. Degrades rapidly. Low toxicity to birds/mammals; highly toxic to bees and to invertebrates from repeated use.

⚠️ Toxicity Categories & Signal Words

💡 Memory Hooks

Risk equation: "Risk = Toxicity x Exposure." Both factors. Reduce either, reduce risk.

Signal words: "Danger I, Warning II, Caution covers III AND IV." Three words for four categories — Caution does double duty.

Microbial MOA: "Insect guts only — mammals lack the receptor." Why Bti and Bs are safe for humans. Larvae must INGEST.

OP placement: "Temephos is the one OP that's a larvicide." Malathion, chlorpyrifos, and naled are all OP adulticides. Memorize this exception.

Pyrethroids + PBO: "PBO boosts the dose, doesn't deliver it." Piperonyl butoxide is a synergist that enhances pyrethroid effectiveness — not an insecticide itself.

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