Effective management of German cockroaches requires an understanding of their physiology and behaviours.
The German cockroach (Blattella germanica) is a species that has evolved within the genus Blattella to uniquely exist only in close habitation with humans. B. germanica is also the only species in the genus that is flightless. This adaptation to life indoors greatly impacts upon its behavioural ecology, seen in its preference for living in dark environments in aggregates (groups). Consequently, chemical cues for smell and taste play vital roles in aggregation, foraging and mating behaviour. Effectively managing cockroach populations with insecticides requires an understanding of these distinctive behaviours.
Living in aggregates
German cockroaches thrive as solitary individuals but prefer to form social aggregations near food and water sources. As these aggregates develop, the harbourages become ‘marked’ with attractant and arrestant semiochemicals emitted through their faeces and vomitus. In fact, more than 150 chemicals have been identified in cockroach faeces alone! German cockroaches at all life stages show a strong preference for aggregating in shelters that have been marked with these semiochemicals. The cockroaches remain committed to their harbourages and will generally only break up the aggregate due to overcrowding.
The aggregations allow nutrients and beneficial gut microbes to be shared amongst the group. Foraging adults and older instar nymphs leave the harbourage at night-time, while early instar nymphs and females carrying oothecae will rarely leave the harbourage. Through coprophagy (faecal feeding) and proctodeal feeding, especially from the anus of the females, the older cockroaches feed the younger cockroaches, transferring beneficial microbes and bacteria that kickstart their gut biome. A healthy gut biome is essential for amino acid production, nitrogen cycling and the production of some pheromones.
German cockroaches are referred to as ‘extreme generalist omnivores’ meaning they will consume just about anything, including most human and pet foods as well as hard soaps, paper, glues, leather, clothing, and furnishings. They have also developed a range of mechanisms to protect themselves from foreign chemicals and pathogens. They will seek out and memorise food sources to develop a nutritionally balanced diet. Physiologically they are driven by phagostimulants (food attractants).
Monitoring and control
Professional pest managers can exploit the biology and behaviour of German cockroaches by using a targeted approach. Steve Broadbent, regional director for Ensystex, advises that there are two cornerstones of a successful strategy.
“The first is using monitor traps so we know what the population density is, whether cockroach numbers are on the increase, and where they are located,” explained Mr Broadbent. “The Blattathor Insect Monitor consists of a plastic station that holds a glueboard impregnated with a highly attractive, aromatic, food-based lure. “In addition to providing improved catch rates, the monitor is designed to be left in place, with just the glueboard changed on a routine basis. This enhances the effectiveness of the monitor as it will retain the natural cockroach aggregation pheromones, improving its attractiveness.
“After identifying the cockroaches’ location and population density, the second task is to implement a targeted control program using Attrathor Targeted Insecticide, a liquid bait solution. Since Attrathor is target sprayed into harbourages, it allows professional pest managers to more thoroughly and more quickly treat a site, when compared to using cockroach gels.”
Attrathor contains tiny, solid-core microcapsules that contain a liquid form of Ensystex’s own low-repellent fipronil, protected by ten different patents. The microcapsules are pressurised with carbon dioxide; cockroaches simply need to come into contact with the microcapsules, which will burst and dose them with the deadly fipronil. Due to the microcapsule design, cockroaches are not required to eat the liquid bait, so there is no concern with cockroaches identifying the presence of a toxin or developing bait aversion.
To ensure uptake of the bait, Attrathor contains an aromatic natural plant extract that draws the cockroaches in. “Even during the day, we have observed cockroaches coming out of their harbourages within minutes of its application,” commented Mr Broadbent.
Formulated to achieve transfer
The Attrathor microcapsules also contain a slow-acting emetic, so the cockroaches will vomit on their return to their harbourage. This vomitus is highly attractive to the early instar nymphs and, combined with the fipronil passing through into the faeces, this allows for viral transfer of the active through the entire aggregate, leading to improved control.
Mr Broadbent said, “Death occurs in one of three ways: through contact, as the Attrathor passes into the cockroach through the cuticle; through the stomach, as the cockroach either consumes the microcapsules or grooms itself and bursts the microcapsules laced with fipronil; or through the above viral transfer effect.
“Passive control is also possible with the liquid film forming a residual kill zone when applied into cracks and crevices, which cockroaches can simply walk over. Attrathor ensures that German cockroaches have nowhere to hide.”