When tackling German cockroach control in apartments, a whole of building approach is required. A recent study showed that an IPM approach gets good results, but that understanding the patterns of cockroach movement is key to success.
In any commercial or apartment block cockroach management program, understanding the building structure and how apartments and rooms are interconnected is important to success. Even if contracted to treat a single apartment, understanding the building structure is important to predict what level of success you are likely to achieve in treating a single apartment, which also feeds into the length of any service free period you may want to offer.
It is generally understood that cockroach movement within and between apartments is common, but movement between buildings in a complex is rare. One study estimated that when construction features allow, up to 30% of the population may move between apartments each week. Furthermore, incomplete control measures, especially when using pyrethroid sprays may increase the level of movement.
With significant cockroach dispersal known to occur between apartments, a whole of building approach is likely to deliver the best results in any cockroach management program. In a recent study, researchers in the US mapped the level of cockroach infestation in an entire apartment block and carried out an IPM (integrated pest management) cockroach program over a 12 month period, to assess both the effectiveness of the treatment and its impact on the spatial distribution of cockroaches within the building.
Researchers assessed the cockroach population in a 188 apartment high rise in New Jersey, by placing a number of sticky traps in every apartment. Within infested apartments, cockroach populations were concentrated in ‘food areas’ – numbers being higher under the cooker and refrigerator than in kitchen cabinets or the bathroom.
Once the monitoring was completed, a basic whole of building IPM program was implemented – residents were trained and given an instruction sheet to clean floors, reduce clutter, not leave pet food out overnight and stop using consumer pest control products.
Apartments with significant cockroach infestations were then treated with a combination of cockroach gel and insecticide dust. Over the next six months, these apartments were monitored bi-weekly and additional bait was applied if the cockroach catch in sticky traps remained above a certain level. Researchers rotated through three different cockroach baits to avoid any resistance / avoidance issues. During the 6-12 month period, apartment visits and any required treatments were carried out on a monthly basis.
Whole of building monitoring was carried out at the six and twelve month visits. The study compared infestations in neighbouring apartments – sharing common walls, above and below, as a well as across the hallway. The infested apartments were mapped and analysed to see if the pattern of infestation in neighbouring apartments was correlated or the level of occurrence was no different to that expected by chance.
Initially, apartments sharing a common wall or ceiling/floor, were correlated in their infestation status – the chances of the apartments either being all infested or all uninfested being higher than expected. In this particular building, shared plumbing both vertically and horizontally between apartments provided the likely route of population movement. Interestingly, there seemed to be significant movement across hallways, with the chances of apartments across from each other being more likely to be either both infested or both uninfested.
At the six month inspection, there was no correlation in cockroach infestations between apartments with shared walls. However, the observed frequencies of infestations between apartments across the hallway and sharing ceilings/ floors was still significantly higher than expected.
At the 12 month inspection, there was no correlation in cockroach infestations in apartments across the hallways as well as with shared walls. However, the correlation in cockroach infestations vertically was still evident.
Initially, out of the 188 apartments, 49% were classified as having a cockroach infestation, with 25% or 23 apartments having a heavy infestation. By the end of the 12 month trial, 23 apartments were still classified as having cockroach infestations with 13% or three apartments classified as a heavy infestation.
Whilst complete eradication of German cockroaches from the building was not achieved, the researchers concluded that an IPM program applied to all apartments can not only successfully eliminate cockroach infestations within apartments, but can reduce dispersal between units.
For this particular building, the ongoing lower level of infestation was largely attributed to the utility pipework that was conducive to vertical movement of cockroaches. They recommended that the ongoing cockroach management plan would benefit from control measures targeted at wall void and pipework conduit treatments.
The researchers also noted that cockroaches were recorded in apartments that did not have cockroaches initially or at the six month assessment. Although the levels of infestation were low, attributed to good hygiene practice, they acknowledged that in a commercial cockroach management plan, all apartments would benefit from a monitoring and treatment program. This would also cover the potential threat of new introductions from outside the building.
More information on cockroaches.
Zha, C. et al (2019). Spatial Distribution of German Cockroaches in a High-Rise Apartment Building During Building-Wide Integrated Pest Management. Journal of Economic Entomology, 112(5), pages 2302–2310.