Myth 1: boric acid powder eliminates cockroach infestations
Boric acid (H3BO3) has genuine insecticidal properties against cockroaches when applied correctly. The mechanism: cockroaches pick up boric acid powder on their legs and body as they walk through treated areas, then ingest it during grooming. The acid disrupts the insect's digestive system and exoskeleton. This is a real mode of action. The problem is application practice, not the chemistry. Most homeowners apply boric acid too thickly — visible white powder layers along baseboards and under appliances. Cockroaches avoid powders they can see and feel. The effective application is a barely-visible dust in the interior of harborage voids: a light coating inside the void under a cabinet kickplate, not a visible ring around the appliance exterior. Consumer application almost never achieves the correct dust density. Additionally, boric acid has no effect on eggs and very limited effect on nymphs in the youngest instars. Professional dust applications in structural voids can contribute to cockroach control as part of a broader protocol, but boric acid alone, applied as consumer advice typically describes, does not eliminate established infestations.
Myth 2: bleach poured down drains kills the cockroach population
Pouring bleach down kitchen or bathroom drains produces a brief chemical burn in the drain pipe that kills cockroaches directly in contact with the solution. This is occasionally useful for Oriental or American cockroaches that have entered via drain lines — it kills a small number of individuals in the immediate drain area. It does not reach cockroaches in wall voids, harborage sites away from drains, or the German cockroach populations in appliance motor housings that constitute the vast majority of Metro Vancouver cockroach infestations. Bleach is also corrosive to drain seals and P-trap gaskets over repeated use. In a multi-unit building, pouring bleach down shared drain lines may affect neighbours' drain seals. Bleach is not a cockroach control tool — it is a surface disinfectant that incidentally kills a tiny fraction of a drain-accessible population.
Myth 3: leaving the lights on deters cockroaches
Cockroaches are negatively phototactic in the short term — they avoid sudden light exposure, which is why they scatter when you turn on the kitchen light at night. However, this light-avoidance response is a reflexive survival response, not a durable deterrent. Cockroaches in an established infestation habituate to consistent light within days. A kitchen kept at high ambient light level continuously does not see population reduction — it sees cockroaches active in illuminated areas once habituation occurs. The practical implication: leaving lights on at night may produce the psychological relief of 'not seeing cockroaches' while the population forages undetected in slightly deeper harborage zones rather than on open surfaces. The infestation continues; you just see less of it.
Myth 4: natural repellents (bay leaves, peppermint, catnip, cedar) work on established infestations
Multiple plant-derived compounds have been studied for cockroach repellent activity. Nepetalactone (active compound in catnip), peppermint oil, and eucalyptus have all shown some repellent effect in laboratory settings at high concentrations. Bay leaves have no documented cockroach repellent activity in peer-reviewed literature. The laboratory results do not translate to field effectiveness for three reasons: the concentrations required for sustained repellency are impractical in a home environment; the repellent effect is short-duration as volatile compounds disperse; and repellent products do not kill cockroaches — they redirect movement without reducing population. An established German cockroach colony of hundreds of individuals in an apartment's service voids will not be deterred from foraging by bay leaves in the cabinet.
What actually works and why
The evidence base for German cockroach control in Metro Vancouver residential and commercial settings converges on gel bait plus IGR as the most effective approach: non-repellent (avoids behavioural avoidance), harborage-targeted (reaches the 75–90% of the population that doesn't forage), horizontal transfer (multiplies the kill beyond direct bait contact), and reproductive disruption via IGR that prevents rebuilding from surviving oothecae. Physical exclusion (sealing plumbing penetrations, drain covers, outlet gaskets) prevents reinfestation. Sticky monitoring detects early recurrence. These three components — targeted baiting, exclusion, and monitoring — are the protocol. Everything else is either supplementary or ineffective.