Blattella germanica
(German cockroach)

B. germanica is one of the most widespread cockroaches in the genus Blattella. It is native to North Africa (Ethiopia and Sudan) and has since spread rapidly around the world facilitated by international trade. This species is not tolerant of cold conditions and lives in close association with humans and/or human activities. B. germanica can be a major pest species which is both a nuisance and can cause health problems (allergies and infections). This species can also vector a number of potentially harmful pathogens and is linked with the spread of pathogens in hospitals and can lead to food borne illnesses. The ability of this species to spread rapidly is exacerbated by a resistance to chemicals for control.

B. germanica is probably the most widespread species to occur in the genus Blattella (Roth, 1985). Early documentation considered B. germanica to be native to Europe (Cory and McConnell, 1917) however it is now thought to be a native of Ethiopia and Sudan (Hill, 2002) or elsewhere in North Africa (Eaton and Kaufmann, 2007). This species has since been widely introduced around the world into parts of Australia, Africa, North America and the Oceanic Islands. The distribution presented in the Distribution Table, is likely an underestimate of the actual distribution of B. germanica.

It is likely that the distribution of B. germanica will increase and be introduced into new countries. This is a result of urbanisation and commerce providing the opportunity and favourable conditions encouraging an increase in the range of B. germanica (Sommer, 1974; Hill, 2002). For example, the structural features of a building can assist in the dispersal of cockroaches. In addition to this globalisation and increased trade between countries increases the likelihood of it spreading between countries.

B. germanica is unable to survive in locations away from humans or human activity (Valles, 1996). This pest is therefore found in hotels, residential areas, farm produce markets, catering establishments (Jia et al., 2011), swimming baths (Rivault, 1989), hospitals, shops, stores, restaurants, food manufactures’, nurseries, crèches (Engelbrecht and Buske, 1983) and grain stores (Stejskal et al., 2006). They are gregarious during their resting period and research by Ame et al. (2004) suggested that different strains are able to aggregate at the same site.

The major limiting factor for survival of B. germanica appears to be cold temperatures. They are unable to colonise inactive ships during cool temperatures and survival in northern climates is dependent on the presence of central heating installations (Valles, 1996). In contrast to this, Vater (1979) studied B. germanica found in a refrigerator in Germany where the temperature ranged from 7-12°C. The first to sixth larval instars were found to be mobile in this environment.

Genetics

Xiao et al. (2012) reported that the complete mtDNA nucleotide sequence of B. germanica is 15,584 bp.

Reproductive Biology

B. germanica has panoistic ovaries (Irles et al., 2013), meaning that the ovarian follicle is formed exclusively by one germinal cell (the oocyte) surrounded by a monolayer of follicular cells (the most basal ovarian type in insects) (Piulachs, 2013). B. germanica breeds continuously (Valles, 1996) and during a study under laboratory conditions females were shown to oviposit up to five oothecae during their lifetime (Aguilera et al., 1996). The egg case is approximately 8 mm long, 3 mm high and 2 mm wide, brown and purse-shaped and thirty to forty eggs are usually held in a typical egg case (Valles, 1996). The eggs are carried by the female in egg cases (ootheca) until just before egg hatch. The egg case protrudes from the posterior of the adult female and the nymphs often hatch from the case while the female is carrying it.

Typical field populations consist of 80% nymphs and 20% adults (Valles, 1996). B. germanica has a short lifecycle and under optimum conditions one female could, in theory, produce over 10 million females within one year and over 10 billion females in 11/12 years (Hill, 2002).

Longevity

On average, male B. germanica live for up to 130 days and females for 150 days (Hill, 2002). However, a study by Aguilera et al. (1996) found that under laboratory conditions mean development time of the six nymphal stages was 114.71 days at 29+/-1°C and 80.9% RH. The average longevity of the males (77.23 days) was lower than that of the females (98.40 days). Dambach and Goehlen (1999) showed that humidity affects survival times of nymphs when deprived of food and drinking water. The longevity was found to be inversely proportional to saturation deficiency.

Activity Patterns

B. germanica demonstrates aggregation behaviour, where individuals accumulate due to a mutual attraction (Sommer, 1974; Jeanson et al., 2005). The aggregation pheromone is both emitted and perceived using antennae. Various physiological and ecological factors determine the spatial-temporal patterns of aggregation (Sommer, 1974). At lower relative humidity grouping is denser than under higher humidity (Dambach and Goehlen, 1999).

In a survey of B. germanica in Yichun city, Jiangxi, China, a peak in activity was recorded from June to August (Wu et al., 2009). In South Korea, the peak densities of B. germanica occurred between May and September in hospitals (Lee, 1995).

When Stein and Haschemi (1994) studied dispersal and emigration of B. germanica in a rubbish tip in Germany, they reported that movement was influenced by the sun which resulted in a southward dispersal. Rivault (1989) studying the spatial distribution of B. germanica in a swimming bath in France, found it to be contiguous. Insects move from the centre to the periphery in a circular motion within an aggregate and vice versa, which is dependent on lifecycle stage. New larvae explore further afield to the border of the aggregate; considered as the spreading phase when they need to forage or find new shelters. Older larvae tend to gather in the middle of the aggregate and newly-moulted adults search for a sexual partner. The females remain in the shelters during maturation of the oothecae.

Durier and Rivault (2003) reported when familiar with their environment B. germanica does not follow edges, rather it exploits different parts of accessible surfaces within their range. When placed into a new environment they showed a tendency to follow edges.

Heating and food supply are said to be factors that influence the distribution and population of B. germanica in buildings (Tanaka et al., 1993) and male adults tend to seek new space more actively than female adults (Takahashi et al., 1998). Starvation increases the distance travelled, velocity and the proportion of time in motion of adult males and final instars, but not adult females (Barclay and Bennett, 1991).

Nutrition

B. germanica are omnivorous and eat items such as table scraps, pet food and book bindings (Valles, 1996). When three different diets of poultry feed, sugar and wheat flour and rusk were investigated for their effect on biological parameters of B. germanica, it was found that individuals which fed on poultry feed showed maximum hatching and male and female longevity (Khuhro et al., 2007). The minimum mean incubation period and minimum mean nymphal development period was also recorded on a poultry diet.

Associations

Blattabacterium are mutualistic endosymbiont bacteria which inhabit specialised cells in the body fat of B. germanica and all species of cockroach except those in the genus Nocticola (Bandi et al., 1994).

Environmental Requirements

B. germanica is unable to survive in locations away from humans or human activity, but the major limiting factor for survival appears to be cold temperatures (Valles, 1996). It is reported that this species is unable to colonise inactive ships during cool temperatures. In northern climates survival of B. germanica is dependent on the presence of central heating installations (Valles, 1996). Therefore this species is often found in temperate and tropical environments. Due to cold temperatures, B. germanica is found at elevations of 1,200 m and rarely found above 2000 m (Encyclopedia of Life, 2015).

The natural enemies of B. germanica include nematodes (Blatticola blattae and Cephalobellus ovumglutinosus) (Waerebeke, 1978; Rizvi and Jairajpuri, 2002), parasitoids (Ripidius pectinicornis) (Falinm 2001), predators (Ampulex compressa) (Menke and Yustiz, 1983) and parasitic fungi (Herpomyces ectobiae) (Kesel, 2001).

The parasitic wasp Aprostocetus hagenowii lays its eggs in the egg cases of B. germanica and have been used as a biocontrol agent (Cook Islands Biodiversity Database, 2016). The fungus Metarhizium anisopliae has been studied under laboratory conditions as a potential biocontrol agent (Quesada-Moraga et al., 2004). Other reports suggest that entomophilic nematodes such as Neoaplectana carpocapsae and Steinernema carpocapsae could provide control of B. germanica (Zukowski, 1984; Manweiler et al., 1993).

The presence of B. germanica in food stuffs can be detected by visual inspection for filth and extraneous material using microscopy; however, this can be time-consuming and inaccurate. Jones et al. (2013) sequenced DNA from common pests, including B. germanica and generated DNA barcodes for each one. The authors suggested that this could be a powerful tool to aid the mission of the U.S. Food, Drug and Cosmetic Act, which is to prohibit the distribution of adulterated food.

B. germanica, B. asahinai and B. vaga are morphologically similar species of cockroach, therefore there has been much research carried out into different ways of reliably identifying them. The tenth tergite (T10) of male B. asahinai is narrower than that of B. germanica; a trait that is intermediate in F1 hybrids (Ross, 1992). The oothecae of B. asahinai are also smaller than those of B. germanica; first instars of B. asahinai are smaller and the number of the antennal annuli is less in B. asahinai. In addition, the abdominal margins of late-instar nymphs and the spots on each side of the mid-dorsal line are colourless in B. asahinai, as opposed to lightly pigmented in B. germanica (Ross and Mullins, 1988).

Carlson (1988) reported on the use of hydrocarbons for identifying these species and reported that the hydrocarbon components of the three species were consistently different, independent of geography, sex or age.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Prevention and Control

Public Awareness

Infestations of B. germanica are exacerbated by poor hygiene, therefore it is important to create public awareness on how to prevent and control the spread of this public health pest. Shahraki et al. (2010) studied the efficacy of sanitation and sanitary factors against B. germanica infestations and the effectiveness of educational programmes on sanitation in Iran. Pamphlets, posters and lectures were used to describe the importance of sanitation and the comprehensive education programme led to a reduction in infestations.

Control

Cultural Control and Sanitary Measures

B. germanica live where humans and human activity is, feeding on scraps of food (Valles, 1996) and their presence is associated with poor hygiene. However they can also occur in the cleanest and most hygiene-conscious dairies and cheese factories (Rockman, 1992). By eliminating food and water sources and clutter, the risk of encouraging new infestations and population increase is decreased (Valles, 1996). Sealing cracks and crevices can be effective in reducing harbourage space and population size (Valles, 1996) because B. germanica are smaller than most other cockroaches, with the ability to conceal themselves in many places inaccessible to larger species (Jacobs, 2013).

Beccaloni (1991) reported that freshly cut plants of Tagetes minuta placed into the wooden walls and thatched roofs of dwellings in Papua New Guinea repelled B. germanica.Tabaru and Mochizuki (2005) reported that B. germanica was repelled by ethanol extracts of some herbs under laboratory conditions. Herbs showing the most repellent effect were Anethum graveolens (dill), Apium graveolens (celery), Carum carvi (caraway), Cuminum cymimum (cumin), Coriandrum sativum (coriander), Cinamomum zeylanicum (cinnamon), Myristica fragrans (mace) and Capsicum annuum (chili pepper).

Physical/Mechanical Control

Sticky traps can be used to monitor and/or reduce population size of B. germanica (Valles, 1996); however, Ballard and Gold (1983) reported that sticky traps did not reduce populations in Nebraska, USA. Ballard and Gold (1983) evaluated two different types of traps for the control of B. germanica: tent-shaped sticky traps and electrified traps, in Macy, Nebraska, USA. It was found that the sticky traps did not reduce populations, but the electrified traps caused a 76% reduction in catch after two months of trapping.

Biological Control

Pathogens and in particular fungi, appear to be the most promising group for the biological control of B. germanica, according to a review of different methods published by Suiter (1997). Ren et al. (2005) reported successful infection rates of B. germanica using Metarhizium anisopliae under laboratory conditions. Infected B. germanica were erratic in their movements and hyphae of the fungi were found in most parts of the body 4-5 days post-infection. Other reported symptoms of infection by M. anisopliae are a reduction in the mean number of oothecae laid by females, oothecal production, hatchability and nymphal production (Quesada-Moraga et al., 2004).

Other reports suggest that entomophilic nematodes such as Neoaplectana carpocapsae and Steinernema carpocapsae could provide acceptable control of B. germanica (Zukowski, 1984; Manweiler et al., 1993). The parasitic wasp Aprostocetus hagenowii lays its eggs in the egg cases of B. germanica and other species of cockroach and have been used as a biocontrol agent (Cook Islands Biodiversity Database, 2016).

Chemical Control

Due to the speed at which B. germanica reproduces and thus the rapidity of developing resistance to chemicals, much of the early work on chemical control is out of date.

Resistance of B. germanica to insecticides poses a serious concern; they have been shown to be resistant to organophosphorous insecticides (Ge at al., 2009) and tetramethrin (Deng et al., 2013). The extent to which they are resistant has been studied in the Chaoyang District, Beijing, China and it was found that the highest resistance was observed for organophosphorous insecticides. Resistance differed between the eight sites sampled, indicating that control methods should be modified accordingly (Ge et al., 2009).

In a review of B. germanica, Jacobs (2013) indicated that the use of baits containing hydramethylnon, fipronil, sulfluramid, boric acid or abamectin is a successful method of chemical control. Also insecticidal dusts such as boric acid, silica aerogel and diatomaceous earth can provide additional control. Populations of B. germanica were observed to rapidly evolve to become repelled by the glucose present in bait traps rather than attracted to it, a process known as bait aversion (Silverman and Bieman, 1993). This highlights the ability of B. germanica to rapidly change in response to environmental pressures.

Jacobs (2013) indicated that residual insecticidal sprays or aerosol foggers are of little value and may actually disperse B. germanica, hampering control. Bacterial insecticides based on Bacillus thuringiensis were evaluated against B. germanica (Zukowski, 1994). Thuridan (based on B. thuringiensis subsp. thuringiensis) was reported as the most effective and males were more sensitive than females.

IPM

Alternative methods for controlling cockroaches have been the focus of numerous studies (Miller and Meek, 2004; Shahraki et al., 2011), particularly with the advent of resistance to chemicals used in conventional control methods (Nasirian et al., 2006) and the fact that cockroaches live in close proximity to humans. Methods used in IPM include the provision of education using pamphlets and lectures and hydramethylnon gel baits (Shahraki et al., 2011), vacuuming and insect growth regulator devices (Miller and Meek, 2004).

Monitoring and Surveillance

It is important to survey populations by setting traps before applying control measures to ascertain the level of infestation (Jacobs, 2013). Sticky traps can be used to both monitor population sizes (Valles, 1996). Jacobs (2013) suggested that one week of trapping at approximately ten or more trapping sites usually provides sufficient information for effective control.

Passenger ships provide a suitable environment for populations of B. germanica and a Hazard Analysis Critical Control Point (HACCP) system is employed on vessels to ensure food safety is adhered to. Mouchtouri et al. (2008) reported a negative association between infestations and the application of HACCP on board ferries.

29/05/2014 Original text by:

Claire Beverley, CABI, UK