As Sydney heads into warmer weather, it is a familiar pattern. You see a cockroach in the kitchen, spray it and watch it die. For a few days everything seems quiet, then another appears. Sometimes several.
It can feel as though the cockroaches have come back, but if there is an established infestation, they may never have gone away. The cockroach running across the kitchen was simply the part of the problem you could see.
You may be killing the cockroach, not the infestation
Cockroaches do not build a nest in the same way ants do, but they congregate in hidden harbourage areas. In a kitchen, that can mean narrow spaces around cabinetry, behind the refrigerator or dishwasher, around plumbing and inside cracks and voids.
They also reproduce through egg cases called oothecae. German cockroach females carry their egg cases until close to hatching, while other species may deposit them somewhere protected. Even after visible adults have been killed, egg cases already present can result in small nymphs appearing later.
That is one reason a DIY spray can appear successful for several days before the problem becomes visible again.
Some sprays can make control harder
Aerosol and residual sprays can provide a quick knockdown, but that is not the same as long-term control of an established cockroach population.
The University of California Statewide Integrated Pest Management Program advises that foggers and aerosol sprays can repel and disperse cockroaches into other areas rather than providing effective long-term control. It also notes that baits generally provide better control than sprays for indoor cockroach problems.
German cockroaches add another complication. Populations can develop resistance to commonly used insecticides, which can help explain why a spray that appeared effective in the past may perform poorly against an established infestation.
This becomes particularly important if professional treatment involves gel baits. Baits depend on cockroaches finding and feeding on them. Spraying insecticide or cleaning products around bait placements can discourage feeding, meaning the DIY treatment can interfere with the professional treatment that follows.
Treat what is happening behind the sighting
Professional cockroach control is less about finding a stronger version of the same spray and more about understanding what is happening.
Depending on the species and infestation, treatment may involve gels or bait stations, dusts and targeted treatment of the areas where cockroaches are harbouring. Food, moisture and access also need to be considered because pesticides alone do not remove the conditions supporting them.
One large cockroach wandering inside from outdoors can represent a very different problem from small cockroaches repeatedly appearing around the dishwasher or kitchen cupboards. The size, location and frequency of sightings all help tell that story.
If cockroach activity is becoming more noticeable as summer approaches, Getting Your Home Pest-Ready for Summer Entertaining and Holidays also looks at the food, water and access points worth dealing with before the busy season.
If cockroaches seem to return a few days after you spray, it may not mean the spray did nothing. It may mean it only killed the ones you could see.
