How to Speed up Cockroach Baiting

Using an IGR such as Sumilarv can greatly increase the success rate of a cockroach treatment.

 

There are some excellent cockroach baits on the market, capable of killing individual German cockroaches within 24 hours. However, all cockroach baits struggle to gain rapid population control of German cockroach infestations in real-life situations, due to the unique biology of the female cockroach, with females ceasing to feed when carrying their ootheca. Perversely, the solution to speeding up the performance of baits is to use insect growth regulators (IGRs), which are not normally known for their fast action. More specifically it’s necessary to use IGRs in the class of juvenile hormone mimics, such as Sumilarv.

Female German cockroaches eat large amounts of food during ootheca formation. However, once formed, the female cockroach eats very little or nothing. With German cockroaches carrying their ootheca for up to three weeks before hatching, female cockroaches will eat little food (including baits) for an extended period. This means pregnant female cockroaches are unlikely to be affected by baits and furthermore, will be able to hatch a new generation of nymphs. This can cause the population to rebound quickly, especially if the initial bait placements have been eaten out.

The level of juvenile hormone in the female German cockroach varies greatly depending on the stage of the reproductive cycle. Interestingly, it is kept at very low levels during pregnancy (whilst carrying the ootheca). Researchers have demonstrated that the exposure of pregnant female German cockroaches to high levels of juvenile hormone mimic causes the female to abort the pregnancy, dropping the ootheca before the nymphs have developed.1 Not only does this generally result in the death of the nymphs, but it also means the female cockroach starts feeding again.

The consequence of this observation means that to achieve fast German cockroach population control, it is important to combine a bait application with a spray treatment of a juvenile hormone mimic IGR such as Sumilarv. With female German cockroaches aborting soon after contact with Sumilarv, it means the whole population has the opportunity to ingest the cockroach bait shortly after placement. The bait/Sumilarv combination then has the potential to deliver fast and complete German cockroach control. With Sumilarv being non-repellent, pest managers can be confident it won’t impact the palatability of their chosen bait.

However, this cessation of feeding behaviour is not exhibited by all cockroach species. Females of species that deposit their ootheca as soon as they have developed, such as the brown banded and American cockroaches, generally keep feeding throughout their reproductive cycle. That is not to say that the inclusion of IGRs doesn’t have value in treatment programs with these cockroaches; IGRs such as Sumilarv also impact the development of the nymphal stages and can effectively make the females sterile. So even if bait is not available, a residual treatment of Sumilarv, which is very long lasting and active at very low concentrations, will keep cockroach populations in check.

1 Schal, C. et al. (1997). Reproductive Biology of the German Cockroach, Blattella germanica: Juvenile Hormone as a Pleiotropic Master Regulator. Archives of Insect Biochemistry and Physiology 35:405–426.

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