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Bad Bugs: Cockroaches

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As Halloween approaches, our thoughts turn to creepy-crawly, bats-and-spiders, fallen-leaves-in-cemeteries musings. One of humankind’s least favorite creepy-crawly critters is the household cockroach, Blattella germanica.

According to the University of California Integrated Pest Management Program (, the German cockroach is the most common indoor cockroach, especially in multi-unit housing environments. They love kitchens and bathrooms, preferring warm, moist environments that provide food, water and dark places to hide. An adult German cockroach can hide in a crack 1/16 of an inch wide!

Even though cockroaches do not bite humans, they are implicated in a number of health problems. Shuttling between garbage, food and human waste, they are believed to be capable of transmitting staph, strep, Hepatitis A and E. coli. In her Halloween-worthy book, “Wicked Bugs,” author Amy Stewart adds salmonella, leprosy, plague, typhoid, dysentery and hookworm to that list.

However, in his book, “Never Home Alone,” ecologist and North Carolina State University Professor Rob Dunn says the most serious cockroach problem is that of allergens, created from regurgitated food, droppings, bits of cast-off skin and egg casings, stains and odors. Half of all people with asthma are allergic to cockroaches. Ten percent of non-allergic people have a sensitivity to cockroaches, ranging from mild to anaphylactic shock. A roach allergy can also cause cross-allergic reactions to shrimp, lobster, crab, crawfish, dust mites and other bugs.

But, unfortunately, our human tendency to resort to chemical warfare to destroy pests we fear and hate has had a rebound effect. Each time we create a new pesticide, cockroaches (and many other pest insects) develop resistance and immunity to it. According to Dunn, the pesticide chlordane, thought to be invincible, was developed in 1948. By 1951, Texas cockroaches were resistant to it. By 1966, roaches were found that were resistant to malathion, diazinon, fenthion, and then DDT. It was discovered that sugar baits laced with insecticide killed most cockroaches, except for those that had an errant gene that caused their “taste buds” to experience sugar as bitter. They avoided sucrose baits and survived. Since one female cockroach can conceivably create ten thousand descendants in a year, many generations of sugar-bait-resistant cockroaches came to be.

If you need to control an indoor infestation of German cockroaches, a many-faceted approach is best. Detect and monitor: use sticky traps and glue boards. Store food in insect-proof glass or plastic containers. Keep garbage in containers with tight-fitting lids. Remove piles of trash, newspapers, magazines, paper bags, boxes, and lumber that provide hiding places. Treat cracks and crevices with gel baits. Insect dust containing boric acid or silica can be very effective but take some time to achieve control.

The best long-term solution may be to return to a better-balanced environment. As Rob Dunn says, “The problem with cockroaches is us.” He recommends de-escalating our chemical warfare and opening our windows and doors to allow tiny, unseen predator wasps that exist everywhere to come in and find their cockroach prey. This is Integrated Pest Management (IPM) at its best.

Rebecca Miller-Cripps is a University of California Cooperative Extension Master Gardener of Tuolumne County.

UCCE Master Gardeners can answer gardening questions.  In Tuolumne County call (209) 533-2912 and in Calaveras County call (209) 754-2880. You can fill out our easy-to-use problem questionnaire here. Check out our website here. You can also find us on Facebook.

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