Know Your Enemy: German vs. American Cockroach Control

Chris Keefer

Editor’s note: July is PCT’s annual Cockroach Control Issue. In addition to numerous cockroach control features in the pages of PCT, the following online only feature from Chris Keefer, technical services manager, Professional Pest Management, Syngenta, explores how understanding the differences between German and American cockroaches is key to their control.

More than 4,500 species of cockroaches have been identified to date, however, less than 100 are considered synanthropic — meaning they live near humans to benefit from our lifestyles. Cockroaches date back to the Carboniferous age in Paleozoic era, which was 350 million years ago. They are so abundant in the fossil record that this era is sometimes referred to as the “Age of the Cockroach.” 

Cockroach life cycles progress through hemimetabolous — or gradual — metamorphosis, consisting of the egg, nymph and adult life stages. Cockroach species that are common in urban environments include the following, with the two most common being the German and American cockroaches:

• German
• American
• Oriental
• Smoky brown
• Brown-banded
• Asian
• Australian
• Turkestan and more 

German cockroaches

The No. 1 urban cockroach pest in the U.S. is the German cockroach. German cockroaches are omnivorous, don’t fly, tend to live indoors and are closely associated with humans. 

The German cockroach can progress from egg to adult in about 90 days, but this can be affected by temperature, relative humidity and available resources. When identifying a German cockroach, it is important to note that: 

• Adults are approximately 5/8” long
• They are light brown with two dark stripes on the pronotum 
• Females may be a darker color than the males with a broader, rounded posterior
• Adults generally live four to six months 

A German cockroach population is typically 20-30% adults, with the rest being nymphs. They are gregarious and harbor together because of aggregation pheromones. Foraging cockroaches don’t venture very far from their harborage, especially early-instar nymphs and gravid females. So, if you are seeing a lot of early-instar nymphs, this means you are close to the primary harborage area. 

Some of the top harborage areas for German cockroaches include:

• Corrugated cardboard boxes
• Under sinks
• Near kitchen appliances
• Pantries
• Behind moldings and wall coverings 

Use the behavior of German cockroaches in your favor. When using gel baits, remember that they will help control other individuals within the population by transferring the active ingredients through live cockroaches feeding off the feces, secretions and remains of dead cockroaches in the harborage. 

If you encounter a large, widespread population, using a vacuum with a HEPA filter can save time. Be sure to dispose of the cockroaches appropriately. Vacuuming alone will not control the cockroaches, so implement other control methods as well. 

It’s also important to remember that German cockroaches live in zones. If you discover cockroaches living in a partitioned cabinet where each shelf contains food, water and harborage, the cockroaches are unlikely to venture out of that zone. This means you should treat each zone of the cabinet area. Sticky traps or zone monitors can be useful to help you determine the depth of a cockroach population, especially if you encounter a small or sparse population. 

Other key points for German cockroach control include: 

• Use inspection results to dictate treatment
• Wear gloves when baiting to avoid contaminating the bait with foreign substances
• Focus treatment on areas where moisture is present 
• Make numerous small bait placements as opposed to fewer large bait placements to improve efficacy
• Seal your bait tubes at the end of the day to avoid cross contamination and keep the bait fresh and moist 
• To prevent aversion and resistance, follow all label instructions and rotate cockroach baits based on active ingredient chemical classes 

American cockroaches

The American cockroach is the largest of the urban house-infesting cockroaches in the U.S. American cockroaches are omnivorous, can fly and prefer moist, warm areas to harbor.  

They progress from egg to adult in about 600 days, but this can vary depending on temperature, relative humidity and resources. When identifying an American cockroach, it is important to note that: 

• Each American cockroach egg case can contain between 10-20 eggs 
o A female American cockroach can produce around 160 offspring in her lifetime 
o Egg cases are usually abandoned by the female and glued with her saliva in moist, warm areas
o Once a hatch occurs, nymphs are left to fend for themselves
• Adults are about 2” long
• They are generally dark brown to black with a red-brown pale edge on the pronotum 
• Adults generally live six to 18 months

Although American cockroaches are considered peridomestic, meaning they live inside and outside, they will often invade homes, restaurants, supermarkets and other commercial buildings. In households, they prefer to harbor in moist areas and in clutter such as cardboard boxes and stored paper goods. 

Controlling American cockroaches requires a thorough inspection to locate harborage areas on, near and away from the structure. Maximize efficacy using a multi-pronged control approach with several formulations and active ingredients in the form of:

o Dry flowable baits
o Granular baits
o Gel baits 
o Residual liquid applications

Treat all utility penetrations, window frames, door frames, eaves and overhangs. If applying a synthetic pyrethroid, follow all regulations. Don’t overspray bait applications with a liquid residual, as this will reduce the efficacy of baits. 

With so many cockroach species living so close to humans, proper identification can mean the difference between a successful treatment and costly callbacks. Tailor treatments to American or German cockroaches as needed to help ensure successful control on your tough cockroach jobs.