Urban pest control mostly uses insecticides from diverse chemical groups, including inorganics, botanicals, organochlorines, organophosphates, carbamates, synthetic pyrethroids, IGRs, miscellaneous insecticides, and fumigants.
Inorganic insecticides
Inorganic insecticides, mineral-based and carbon-free, were likely the first chemical used against insects, boasting a long history of use. Predominantly in crystalline form, they were commonly applied as baits or dusts. However, their use has declined in recent decades, likely due to increased mammalian toxicity, compound accumulation from stability, and the emergence of safer synthetic alternatives.
Few organic insecticides are currently in use. Arsenic trioxide serves as a stomach poison in termite control, while boric acid, with low mammalian toxicity, acts as a dust for cockroach and silverfish control and is used in baits for ants and cockroaches, disrupting insect cell energy conversion. Silica aerogels, finely ground silica formulations, function as a physical abrasive in cockroaches and stored product pest control, causing death through dehydration.
Botanical insecticides
Botanical insecticides, also known as natural or plant-derived insecticides, are extracted from specific plant parts with a rich history of use. Nicotine from tobacco was an early example, dating back to the late 1660s. Pyrethrins, the most widely used botanical insecticide, are obtained from Chrysanthemum flowers. Kenya and Tasmania are major suppliers. Pyrethrins find application in controlling household, industrial, stored product, and garden pests due to their diverse characteristics such as:
- Broad range of activity;
- Low toxicity to mammals;
- Fast breakdown after application; and
- Fast knockdown, flushing, and repellent properties.
Pyrethrins, as expensive insecticide, is often paired with piperonyl butoxide for increased potency. Acting as a contact insecticide with nerve-poisoning effects, it has low mammalian toxicity but it is relatively harmful to fish and reptiles.
Rotenone, a botanical insecticide extracted from South American plant roots, is primarily used to manage plant pests and external parasites on animals. It is typically formulated as a dust for controlling plant pests and animal ectoparasites.
Organochlorine insecticides
Organochlorine insecticides, composed of carbon, chlorine, and hydrogen, vary widely in structure, activity, and mammalian toxicity. Cyclodiene organochlorines, including aldrin, dieldrin, chlordane, and heptachlor, are particularly stable in soil, making them prevalent in preventing and controlling subterranean termites.
Due to concerns about their persistence and potential environmental health effects, organochlorines (OCs) have been banned for urban pest control in Australia. They primarily act as contact and oral poisons, targeting the nervous system.
Organophosphorus insecticides
Organophosphorus insecticides are derived from phosphoric acid. They were a product of wartime research on ‘nerve gases’. Some OPs have low mammalian toxicity, but others are highly toxic to higher animals.
OPs are chemically less stable than organochlorine compounds. While some OPs have a brief insecticidal life span of a few hours, others can remain effective for weeks or even months. Their greater stability has led to the replacement of organochlorines in many applications. OPs are also effective against organochlorine-resistant strains of insects.
Numerous organophosphates developed for agricultural pest control are also widely used in urban settings, primarily for managing “household pests”. This utilization Stems from their relative instability. Examples of OPs used in urban pest control include: azamethiphos, chlorpyrifos, diazinon, dichlorvos, fenthion, promiphiphos-methyl, and temephos. With the decrease in the use of organochlorine insecticides for subterranean termite control, the OP chlorpyrifos has taken its place in chemical barrier treatments against termites.
The majority of OPs Act as contact and oral poisons, with some volatile ones causing inhalation toxicity. Certain OPs possessing specific solubility and toxicity characteristics are used as systemic insecticides for plant and animal pest control. Categorized as nerve poisons OPs disrupt the cholinesterase enzyme at nerve synapses, leading to the accumulation of transmitter substances and resulting in convulsions, paralysis, and death.
Carbamate insecticides
Research into chemicals with anti-cholinesterase effects on the nervous system in the 1950s ultimately resulted in the creation of carbamate insecticides. These compounds, which are derived from carbamic acid, exhibit differences in their range of effectiveness, toxicity in mammals and duration of persistence.
Carbamates like bendiocarb, propoxur, and methomyl, commonly used in urban pest control break down quickly in the environment. They are applier as surface sprays, dust, or baits for household pests, acting as nerve toxins with anti-cholinesterase effects.
Synthetic pyrethroids
After World War II, there was a necessity to increase the gap between insecticide toxicity to target insects and higher animals, including humans. Synthetic pyrethroids were developed since the 1950s through mimicking natural pyrethrins. They have shown advancements like faster knockdown, higher insect toxicity, improved human safety, and extended residual action., many of these insecticides are now considered among the safety options available.
Pyrethroids, such as allethrin, alpha-cypermethrin, beta-cyfluthrin, bifenthrin, bioresmethrin, cyfluthrin, cypermethrin, d-phenothrin, lambda-cyhalothrin, deltamethrin, permethrin, and tetramethrin, find extensive use in the supermarket household aerosol sprays and urban pest control. Their broad spectrum of activity against household pests, and in most cases, safety for humans make them popular choices.
Synthetic pyrethroids disrupt nerve fibres, causing intense electrical activity and blocking nerve impulses. This technology is likely to be pivotal in future pest control applications