All Pests, All Hours

Residential, Commercial

Industrial, Remote

Builders, Renovators

Welcome to our section on German cockroaches.

         The most common cockroach species found in Alice Springs and Tenant Creek.

German cockroach

Distribution

The German cockroach is found throughout the world in association with humans.  THIS SPECIES IS VERY COMMON IN ALICE SPRINGS, TENNANT CREEK AND THE WIDER CENTRAL AUSTRALIAN REGION. The major factor limiting German cockroach survival appears to be cold temperatures. Studies have shown that German cockroaches were unable to colonize in active ships during cool temperatures and could not survive in homes without central heating in northern climates. The availability of water, food, and harbourage also govern the ability of German cockroaches to establish massive populations, in short periods of time.

First instar nymphs emerging from the oothecae (egg case) of a German cockroach, Blattella germanica (Linnaeus).

Oothecae of the German cockroach, Blattella germanica.

Larva or Nymph

The nymphal stage begins with egg hatch and ends with the emergence of the adult.  Nymphs are dark brown to black in colour, with distinct dark parallel bands running the length of the pronotum. Nymphs do not possess wings. The number of moults required to reach the adult stage varies, but the most frequently reported number of moults is six. The stage between moults is called an in-star   At room temperature nymphs complete development in about 60 days. All developmental stages actively forage for food and water.

Third instar nymph of German cockroach Blattella germanica (Linnaeus).

Newly moulted adult German cockroach, Blattella germanica (Linnaeus). Within a few hours the cuticle will harden and darken.

Adult

The adult is 10-15 mm long, brown to dark brown in colour with two distinct parallel bands running the length of the pronotum. The sexes can be distinguished by the following characteristics: male body,s are thin and slender, posterior abdomen is tapered, terminal segments of abdomen visible, not covered by tegmina (leathery outer wings); female has a stout  body, posterior or abdomen is rounded, the entire abdomen is covered by tegmina

Adult male German cockroach, Blattella germanica (Linnaeus).

Adult female German cockroach, Blattella germanica (Linnaeus).

Life Cycle

The German cockroach has three life stages typical of insects with incomplete metamorphosis: the egg, nymph, and adult. The entire life cycle is completed in about 100 days. However, factors such as temperature, nutritional status, and strain differences may influence the time required to complete a life cycle. German cockroaches breed continuously with many overlapping generations present at any one time. Under ideal conditions, population growth has been shown to be exponential. Actively growing field populations are comprised of 80 percent nymphs and 20 percent adults. The German cockroach is omnivorous, eating table scraps, pet food, and even book bindings.

Medical and Economic Significance

German cockroaches adulterate food or food products with their faeces and defensive secretions, physically transport and often harbor pathogenic organisms, which may cause severe allergic responses, and in extremely heavy infestations have been reported to bite humans and feed on food residues on the faces of sleeping humans. In addition, some scientists suggest that German cockroach infestations may cause human psychological stress and that the stigma associated with infestations alters human behavior. For example, people with infested houses do less entertaining, and avoid the kitchen at night for fear of encountering a cockroach.

Action Threshold

Since the German cockroach is considered an aesthetic pest, the action threshold for this insect depends upon the tolerance of the people living in the infested dwelling. However, most people associate cockroach infestations with poor sanitary conditions and typically go to excessive lengths to eradicate them from their houses.

Management

Insecticides in the , carbamate, synthetic pyrethroid, amidinohydrazone, insect growth regulator, inorganic, microbial, and botanical classes are still available for controlling German cockroaches. Insecticide treatments are available in a wide variety of formulations including baits, sprays
(emulsifiable concentrates, wettable powders, microencapsulated), dusts, and powders.

Non toxic and low toxic alternatives for German cockroach control are available. Sticky traps can be used to monitor or reduce population size.  Improving sanitation by eliminating food and water sources and clutter can have a significant impact on reducing the chances of infestation population size. Finally, exclusion practices such as sealing cracks and crevices will reduce harbourage space and also negatively impact population size.

A few interesting facts, about German cockroaches.

German cockroaches are about 12-15 mm long.

They are coloured light brown with 2 dark stripes on the thorax.

		The wings are as long as their body, and overlap in both sexes.
		The oothecae is carried by the female until  hatching is imminent.
		This young lady produces 4 - 8 oothecae in her lifetime.
		In this species, the oothecae contain 35 - 40 eggs.
		The hatching time is only one month.
		The nymph achieves adulthood in 5 - 7 moults, remember cockroaches don't pupate.
		The nymphal development can be as quick as 6 weeks, but can take up to 6 months.

So let's do a theoretical calculation based on the facts above:-

Let us assume that the first female lays 1 oothecae, this will give us 40 eggs for arguments sake.

Say that there is plenty of food about and nymphal development is completed in 8 weeks and that 50% of these nymphs turn out to be females, let's say 20 females.

These females then lay 1 oothecae each.

This will give us 20 times 40 eggs which is 800.

Again there is plenty of food about and nymphal development is 8 weeks and again 50% are females.

These females lay 1 oothecae each.

This gives us 400 times 40 which is 16000

So after 9 months we have got sixteen thousand cockroaches, this assumes that none would die in development (mortality rate) but it does not take into account the fact that the original cockroaches would still be laying further oothecae and that these would be hatching and maturing.

There is of course a high mortality rate probably about 90%, and a good job too, but even so, if an infestation is not controlled it can very soon get out of hand