Cockroaches

Cockroaches are a common household pest in New Zealand. They are not high health risk pests but according to the Ministry of Health, cockroaches thrive in unhealthy environments and they can transmit a number of diseases.

The biggest household cockroach pests in NZ are the American cockroach (Periplaneta americana) and the German cockroach (Blattella germanica). They are especially common in larger commercial buildings such as restaurants, bakeries, grocery stores, food processing plants, hospitals, etc., where they usually infest food storage and food preparation areas, boiler rooms, steam tunnels and basements. These cockroaches prefer damp, warm, dark places. They are often found inside walls, behind or underneath electric appliances and in cupboards.

The third type of cockroach that we encounter inside houses in NZ sometimes is the Gisborne cockroach (Drymaplaneta semivitta). The Gisborne cockroach was named as such by a Western Australian immigrant when he first found one in Gisborne. It is a usually a bush cockroach and prefers to live outside – however it can come into houses by mistake in the winter or if it’s wet or too hot.

 

Distinctive features

German Cockroach

The German cockroach is the most common cockroach species found worldwide. Adult German cockroaches are a small (13-16mm), elongated, nocturnal, penny sized light brown to tan coloured with two dark parallel stripes on their backs. Female German cockroaches tend to be darker than males. German cockroach nymphs are dark brown to black in colour with the same dark stripes located on their backs. German roaches have wings but they rarely fly. They are fast moving roaches that can quickly escape into cracks and crevices in the wall. Adult females may be seen carrying an egg case. The egg case contains about 30-40 eggs and a female can lay up to 3-4 egg cases during her life span of 100- 200 days.

They prefer to live indoors as they can’t survive hash cold and dry conditions. They can be found outdoors in warm and tropical environments. Out of all cockroach species they live and reproduce near or in human structures the most. The German cockroaches are the truest of scavengers, eating almost anything they can get. This includes things such as soap, booking bindings, glue, toothpaste, and pet foods in addition to all foods and crumbs left by people.

 

German cockroach Blattella germanica

German cockroach¹

American cockroach

American cockroach Periplaneta americanaThe American cockroach is 32- 54mm long, reddish brown in colour with a yellowish margin on the body behind the head. They are long, slender, very thin and can squeeze through very tiny spaces. Both males and females have wings and can fly short distances. Adult females can produce up to 150 young roaches during its lifespan. The female carries an egg case (protruding from the tip of its abdomen) for a couple of days before placing it on a surface in a safe location. The nymphs hatch 6-8 weeks later and have a slower growth than German roaches reaching adult status in 6-12 months.

American cockroaches live primarily outdoors and are often found around sewers and drains, but it’s not uncommon to find them inside a structure. They move indoors when they experience a food shortage or a significant change in the climate. They eat crumbs found under appliances, in drains, behind kitchen cabinets and on the floor. They will also eat pet food that is left uncovered.

American cockroach²

 

Gisborne Cockroach

The Gisborne cockroach was introduced from Australia and was first recorded in New Zealand at Gisborne, hence the name Gisborne cockroach. They are now more widespread in the North Island, and in Nelson and Blenheim. It is about 45mm long and 12-15mm wide, and has glossy dark brown colour with distinctive white stripes along each side of its head. It has no vestigial wings, hind legs are very prominent and its flattened body can squeeze through gaps less than two millimetres high.

Gisborne cockroaches commonly live outdoors in primarily damp, dark areas and decaying forest matter. As omnivores they feed on organic materials including dead wood and have symbiotic gut flora which helps them digest dead wood and similar matter. While they may be considered a household pest, these insects do not naturally live indoors and are most commonly brought into a home via firewood or are attracted by timber and bark chips.

 

Gisborne cockroach Drymaplaneta semivitta

Gisborne cockroach

 

The Native Bush and Golden cockroach can be mistaken for the Gisborne but they have different characteristics and are much smaller than the adult Gisborne.

 

Habitat

Cockroaches are highly adaptable and can live wherever enough food, moisture, and heat exist to support them. These pests regularly enter buildings inhabited by humans to look for warm, damp environments in close proximity to sources of food and water. Basements, bathrooms, greenhouses, kitchens, and rooms containing sewer pipes or plumbing make ideal habitats for cockroaches. With origins in the tropics, these insects prefer to reside in spaces offering high levels of warmth and humidity. Cockroaches also demonstrate nocturnal tendencies by hiding during the day and becoming active at night. The six-legged creatures flee rapidly when exposed and move easily from one room to another.

 

Health Risks associated with cockroaches

Cockroaches are filthy pests. They can eat a range of foods, from faecal matter to fresh food intended for people to eat. American and German cockroaches can transmit diseases like dysentery, salmonella and diarrhoea. Cockroaches in general have been reported to spread at least 33 kinds of bacteria, including E. coli and Salmonella, as well as six kinds of parasitic worms and at least seven other kinds of human pathogens. They pick up germs on the spines of their legs and body as they crawl through decaying matter or sewage, and then transfer the germs onto food or cooking surfaces. The saliva, urine and faecal droppings from American cockroaches contain allergen proteins known to elicit allergic reactions and asthma attacks. As such, cockroaches are a common trigger of year-round allergy and asthma symptoms, especially in children.

The Gisborne cockroach is generally a lot more harmless. Unlike German or American cockroaches, it does not spread disease, nor can it fly. It typically doesn’t invade food supplies, unless they’re decaying.

 

Signs of an Infestation

Beside adults and nymphs, the faecal spots that are deposited around harbourage areas are the other signs of infestation for cockroaches. German roach produce faeces that resemble coffee grounds or specks of pepper. American roach droppings are blunt on the ends and have ridges on the sides. They are often mistaken for mouse droppings. Another sign of infestation is the presence of egg capsules. Cockroach eggs are collected together in an egg case, sac or capsule called an ootheca. These are usually glued to surfaces near food sources, and can be found in basements, laundry rooms and kitchens, as well as behind appliances or underneath cabinets and can contain a significant number of cockroach eggs. There is also a very distinctive odour also described as “musty” smell by some people in American cockroach infested areas.

Prevention and Control

Cockroaches are some of the most resilient pests in the world. They thrive in warm and damp conditions and will dehydrate if the environment is too dry. However, they can survive in extreme conditions for short periods of time with their unique survival tactics. Cockroaches can survive months without food and up to 4 weeks without water. A cockroach can survive without its head for up to a week! This makes them very difficult to get rid of. In case of German roaches, the fast reproduction rate (50-60days) and large number of eggs (18-50) per egg case makes it even harder to wipe them all once they establish.

There are several ways for cockroach control in NZ, and while these traditonal cockroach pest control techniques will successfully eradicate the cockroaches, they will only temporarily clear up the problem. In order to make sure roaches don’t return, you must take preventative measures to support the effectiveness of your selected treatment methods. The most effective and long-lasting method of controlling cockroaches is sanitation.

  • Keep living areas, counters, sinks, tables, and floors free of clutter and food materials
  • Deep clean the microwave and keep spills inside wiped up
  • Wipe up spills quickly, sweep and mop floors, vacuum rugs, and carpets, take additional steps to be sure no food residue is left behind for pests to find.
  • Seal up harbourage areas or entrance points. Fill cracks in walls and foundations, gaps near electric sockets and switch plates, and up through drains in your home or business.
  • Clean out the inside of toasters and toaster ovens and empty and wipe the crumb tray after each use
  • Clean the inside and outside of indoor garbage cans; use can liners and keep lids tightly closed
  • Dispose of rubbish and removing human waste and food waste from the home quickly and efficiently.
  • Store food in airtight containers and avoid leaving pet food out in the open.
  • Any standing water will encourage roaches to hang around. Take steps to dry up any areas with potential to hold water.
  • Dry out sinks every evening and cover the drain hole with a cap or stopper
  • Ventilating crawl spaces to prevent moisture build-up
  • Remove items in your yard that collect standing, stagnant water. Remove debris and piles of leaves.
  • Cut foliage back to a 5cm gap around houses- if possible. This will reduce the chances of the Gisborne cockroach getting into the house.

 

Cockroach Control

Although good housekeeping is helpful, a specialised cockroach bait or cockroach spray is usually necessary to eliminate infestations, especially of the highly prolific German cockroaches. Cockroaches spend little time out in the open; places that are hard to see and reach is where they tend to be. Dark, secluded areas near food, warmth, and moisture are preferred so a bright flashlight helps when performing inspections. German cockroaches move very fast and will scatter quickly when a torch is shone on their harbourage. Emphasis should be on finding and treating preferred harbourage locations, rather than randomly spraying baseboards, countertops and other exposed surfaces. If key harbourage areas are missed problems are likely to continue.

Cockroach Gel Baits

Baiting with baits like Hawkeye Cockroach Bait is the most effective and safest control method to controlling cockroach infestations. This type of bait has been specifically formulated to be both attractive (draws them in) and palatable (they like the taste) to German and American cockroaches. Only a very small amount of cockroach bait is required but multiple bait spots must be set out in appropriate locations. Cockroach baits are best when applied directly to harbourage and foraging sites, corners, ledges, and crevices close to other points of entry and works on all types of roaches. Baits should never be placed in open, exposed, or extremely hot or wet areas.

*Note: The bait placement should be away from the reach of children or pets.

Method– Apply roach bait in cracks and crevices, place several evenly spaced 5mm spots under or behind any furniture, under the sink in the kitchen and bathroom, next to the dishwasher, behind the oven where cockroach infestation is found. Where possible use an applicator dot such as those supplied with Hawkeye Cockroach Bait to ensure the correct amount of bait is placed and to protect the surface the bait is applied to. Periodically check the bait for consumption or attractiveness and reapply if needed or clean the remaining paste if dead cockroaches are spotted and there is no further cockroach movement/infestation.

*Notes: Baits may require a couple of weeks to significantly reduce cockroach population numbers, so be patient.

 

Residual insecticides

Residual insecticide treatment is done to get rid of cockroaches present in large numbers quickly. Usually a combination of residual insecticide and bait is used to knock down the numbers then mop up the remaining cockroaches that are missed with the initial spray. Apply Hawkeye Flea, Ant & Roach Spray into cracks, crevices and any harbourages identified to help keep the cockroaches from hiding in the treated areas. If the infestation is very high, a barrier spray in areas such as washers, behind ovens, fridge/ freezers, cupboards etc and around the perimeter of rooms is recommended. A perimeter spray around buildings will help control outdoor cockroach species such as Gisborne and American cockroach. For areas where sprays are not suitable (for example around electrical equipment and power points), the use of Hawkeye Cockroach Bait is recommended.

 

Photo attributions

¹ German cockroach: Lmbuga / CC BY-SA
² American cockroach: Gary Alpert / CC BY-SA