A reference of the terms used across natural pest control. Defined in plain English so the rest of the site is easier to read.
A
Aphid. Small, soft-bodied sap-sucking insect found on plant stems and the underside of leaves. Reproduces extremely quickly. Common targets of biological control via ladybugs and lacewings. See the aphids page.
Aphidius. A parasitoid wasp that lays eggs inside aphids; the larva eats the aphid from the inside out. Released commercially as a biological control in greenhouses and outdoor gardens.
B
Bacillus thuringiensis (Bt). A naturally-occurring soil bacterium that produces proteins toxic to specific insect groups when ingested. Different Bt strains target different pests — Bt kurstaki for caterpillars (cabbage worms, hornworms), Bt israelensis (Bti) for mosquito larvae and fungus gnats. Considered one of the safest biological insecticides.
Beneficial insect. Any insect that contributes positively to the garden ecosystem — typically pollinators (bees, butterflies, hoverflies) or predators of pest species (ladybugs, lacewings, predatory beetles, parasitoid wasps). The opposite of a pest.
Boric acid. A mineral compound (a salt of boron) used for cockroach and ant control. Acts as a stomach poison when insects ingest it during grooming. Low toxicity to mammals at typical exposure levels but should be kept away from food and out of reach of children and pets.
C
Chemical control. The use of synthetic pesticides to kill or repel pests. The opposite end of the spectrum from cultural and biological control. Most natural pest control reduces or eliminates chemical control in favor of other approaches.
Companion planting. The practice of placing plants near each other so that one repels pests of the other, or attracts beneficial insects. See the companion planting page for what the evidence actually supports.
Cultural control. Pest management that works by changing the environment rather than killing pests. Crop rotation, sanitation, moisture management, mulch placement, and lighting changes are all cultural controls.
D
Deterrent. Anything that discourages pests from approaching but does not physically block them. Distinct from a barrier. Copper tape, light-spectrum changes, and scent-based repellents are all deterrents. See Physical Barriers and Deterrents for the difference.
Diatomaceous Earth (DE). A fine powder made from the fossilized remains of microscopic algae (diatoms). Kills insects mechanically by abrading their waxy outer cuticle, causing dehydration. Food-grade DE is the right type for pest control — pool-grade DE has been heat-treated and is hazardous to inhale. See the diatomaceous earth page.
E
Exclusion. Physically preventing pests from entering a structure or growing space. Door sweeps, window screens, caulked cracks, and hardware cloth on vents are all exclusion tactics. The EPA describes exclusion as a foundational element of Integrated Pest Management.
I
Integrated Pest Management (IPM). A framework promoted by the EPA, university extension services, and most agricultural authorities. Pest control through a hierarchy: cultural controls and exclusion first, biological and physical controls second, targeted chemical controls only as a last resort with monitored thresholds. The standard model for sustainable pest management.
Insect Growth Regulator (IGR). A compound that interferes with insect development — preventing larvae from maturing or eggs from hatching. Methoprene is a common IGR for fleas. Generally low toxicity to mammals because the targets (insect-specific hormones) don’t exist in vertebrates. Used in some natural pest control programs alongside biological controls.
Insecticidal soap. Potassium fatty acid soap diluted in water, sprayed directly on soft-bodied insects (aphids, whiteflies, spider mites, mealybugs). Disrupts the insect’s outer membrane, causing dehydration. Limited effect — needs direct contact and reapplication. Considered low-risk for non-target organisms.
N
Neem oil. Oil pressed from the seeds of the neem tree (Azadirachta indica). Acts as a feeding deterrent, antifeedant, and insect growth regulator on a wide range of pests. Effective on soft-bodied insects, fungal diseases, and some leaf-eating caterpillars. Less harmful to bees and other pollinators than many synthetic alternatives, but still has non-target effects so use targeted, not preventatively.
Nematode (parasitic). Microscopic roundworms applied to soil to control soil-dwelling pest larvae — fungus gnats, root-knot grubs, cutworms, fleas in soil. Entomopathogenic nematode species like Steinernema feltiae and Heterorhabditis bacteriophora enter pest larvae through natural openings and release symbiotic bacteria that kill the host.
N+1 rule. Used in cat care contexts on related sites, not directly relevant here.
O
Oocyst. A protected egg form of certain parasites. In pest control contexts, relevant for Toxoplasma gondii shed in cat feces — covered on the composting cat litter page on a related site, not addressed in pest control here.
P
Parasitoid. An insect (often a wasp) that lays eggs inside or on another insect; the larva develops by feeding on the host, eventually killing it. Different from a parasite (which usually doesn’t kill the host) or a predator (which eats prey directly). Aphidius wasps and braconid wasps are common parasitoids used in biological control.
Pheromone. A chemical signal insects use to communicate. In pest control: ant trail pheromones (which vinegar can disrupt), sex pheromones used in moth traps, and aggregation pheromones in cockroach harborage detection.
Predatory insect. An insect that eats other insects directly — ladybugs eating aphids, lacewings eating thrips and mites, ground beetles eating slugs and snails, dragonflies eating mosquitoes. Encouraging predatory insects through diverse plantings is a cornerstone of biological control.
Pyrethrin. A natural insecticide derived from chrysanthemum flowers. Broad-spectrum (kills many insect species, including beneficial ones). Considered “natural” but still has non-target effects. Use targeted, not as a routine spray. Distinct from “pyrethroids” which are synthetic analogues with longer persistence.
R
Repellent. A substance or device that discourages pests from approaching. Closely related to “deterrent” but typically refers to scent-based or sensory products like DEET, citronella, peppermint oil, or ultrasonic devices. See the essential oils page and ultrasonic repellers page for evidence on common repellents.
Row cover. Lightweight spun-bonded fabric placed over garden beds to physically exclude flying insects while allowing light, air, and water through. Considered one of the most effective non-chemical pest controls for vegetables. Brand names include Reemay and Agribon.
T
Trap crop. A sacrificial planting that attracts pests away from a primary crop. Nasturtiums planted near beans draw aphids; blue Hubbard squash draws squash bugs away from main squash plantings. The trap crop is then either treated, removed, or accepted as a pest reservoir contained away from the protected plants.
U
Ultrasonic pest repeller. A device that emits high-frequency sound, marketed as a deterrent for rodents, insects, or both. Published evidence is largely negative — the FTC has taken enforcement action against manufacturers making unsupported claims. See the ultrasonic repellers page for the full evidence picture.