Cockroaches are
common and familiar insect. They are characterized by their oval shape, foul
odor, and their status as household pests. About 4000 species are known
worldwide and about 25 species have attained worldwide distribution due to
accidental transport in commerce and their affinity for human habitation
(Microsoft Encarta, 2009). Most of them inhabit the warm tropical regions of
the globe.
Cockroaches are known to live around cracks and crevices
in cupboards, sewers, sinks, etc which make it easy for them to contaminate
vast quantities of materials at homes. They are also potential mechanical
vectors of diseases. Since cockroaches feed from sewers, drains and garbage
areas which bring them in contact with disease organisms including salmonella
and other organisms associated with typhoid, hepatitis, dysentery and
tuberculosis. Their presence poses threat to any
unprotected foodstuffs thereby leading infestation and contamination. AEPMA (2015) also noted that a generally
accepted notion exist, that for every cockroach seen there are at least a
further ten that are hidden away out of sight in areas such as cracks and
crevices, dishwashers, electrical motors and switches, ovens and almost any warm,
moist areas where food is available.
Fossil records
have equally indicated that cockroaches are predominant insects during the
Carboniferous period 360 to 290 million years ago (Microsoft Encarta, 2009).
Common cockroaches include the American, German,
Oriental, Madeira, and brownbanded cockroaches.
TAXONOMY
Taxonomically, cockroaches make up the order Blattodea,
which contains five families. The American cockroach is Periplaneta
americana, and the Oriental cockroach is Blatta orientalis, both in the
family Blattidae. The German cockroach, Blatella germanica, the Asian
cockroach, Blatella asahinai, and the brownbanded cockroach, Supella
longipalpa, are in the family Blatellidae. The Madeira cockroach is Leucophaea
maderae, the Brazilian cockroach is Blaberus giganteus, and the
Madagascar hissing cockroach is Gromphadorina portentosa, all in the
family Blaberidae. The remaining families are the Cryptocercidae and the
Polyphagidae.
IDENTIFICATION AND MORPHOLOGY
Cockroaches are flat and oval in outline. They emit foul
odor. The head of a cockroach points
downward and is protected by the enlarged flanges of the thorax. Cockroaches
may or may not have wings. but even winged species do not always fly. Adults
range from 1 mm (0.04 in) to more than 9 cm (3.6 in) in length. Antennae are
long and slender. Their long, hairlike,
highly sensitive antennae and sensory bristles enable them to detect tiny
amounts of food and moisture. The cerci, sensory structures extending
from the rear of the abdomen, can sense minute air movements, enabling the
cockroach to rapidly detect and flee from potential danger.
Figure: Diagram showing a Cockroach
 |
| Adult Cockroach |
Most cockroaches can run very fast and are difficult to
catch due to their soft, slippery outer skin, called the cuticle. They can hide
in very narrow crevices. The oily cuticle also protects them from dehydration.
Cockroaches prefer to
live in kitchens and other food preparation areas, so they can feed off food
spills and have access to water. Hiding spots for the household cockroaches
include: Cracks in walls, confined spaces such as behind the refrigerator, in a
pantry or underneath a stack of magazines, newspapers or cardboard boxes, kitchen
cupboards, below sinks, around water heaters and in drains and grease traps.
They feed at night on a wide variety of food. They hide in cracks, under
floors, and other dark places during the day. Cockroaches feed
on various kinds of foods or materials; thus capable of digesting a wide range
of substances due to the variety of bacteria and protozoa in their digestive
systems.
Individual species may be restricted
to very specific habitats such as leaf litter, bromeliads, the splash zone of
waterfalls, or bat caves. Some species are brightly colored, defying the
stereotype of the drab, brown or black household roach. Some species, including
the Madeira cockroach, can produce sound. Most cockroaches are sensitive to
light; most species prefer darkness, being largely nocturnal.
LIFE
CYCLE AND REPRODUCTION
Courtship patterns vary
with the species. When the American cockroach is ready to mate, the female
produces a chemical odor, or pheromone,
that attracts males. The males flap their wings and probe for females with
their abdomens when they sense the pheromone; eventually, they back into a
female and mating ensue. Other species have more elaborate mating displays,
including hissing noises, bobbing and waving of the abdomen, or nibbling. The
males of one African species form dominance hierarchies, and the females
preferentially mate with the dominant male.
Egg
The fertilized eggs that
result from mating are cemented together by the female in a sausage-shaped egg
case known as the ootheca.
The American cockroach simply deposits the ootheca in a protected place and
abandons it. German cockroaches keep the ootheca extended from their egg-laying
organ, known as the ovipositor, depositing it only when the eggs are ready to
hatch. An ootheca contains from 16 to 32 eggs, depending on the species. Female
ootheca-tending cockroaches sometimes display maternal care.
Nymph
The nymphs emerge
from the eggs. They often remain around their mother for several days. Nymphs
undergo gradual metamorphosis—that is, they grow and mature in stages, each
separated by a molt of the exoskeleton. Each successive stage, or instar, comes
to resemble the adult insect more and more.
Under good
conditions and optimal temperatures, immature cockroaches, also known as
nymphs, will emerge within 24 to 38 days. As they grow, nymphs undergo
metamorphosis. They do this by shedding their exoskeleton. By the time they are
adult roaches, this will happen 10 to 13 times (Orkin, 2016). At each molt,
they appear more and more like adults. After undergoing their final molt, they
are equipped with wings and reproductive capabilities. This process spans
between six months to over a year. American cockroaches live for approximately
one year. ( Orkin, 2016).
Adult
The final molt
gives rise to a winged, sexually mature individual.
The
length of the American cockroach’s life is dependent upon environment, diet and
other conditions. Favorable conditions lead to rapid population growth, while
unfavorable conditions cause adult cockroaches to develop more slowly or to die
prematurely. ( Orkin, 2016).
Figure: Diagram showing The Life
Cycle of a Cockroach
Source: ( Orkin,
2016).
BEHAVIOUR AND DEVELOPMENT CONDITIONS
Only about 1 percent of
cockroach species are considered pests to humans and these are basically
nuisance pests. Cockroaches have earned a bad reputation not only because they
feed on human food stores and garbage but because they foul their surroundings,
leave behind a repugnant odor, and are extremely difficult to eradicate.
However, cockroaches may not be as dirty as they seem. In laboratory
experiments, household species are capable of contaminating food and other
objects with human disease organisms, but they have not been implicated in
actual disease outbreaks. Findings have equally shown that cockroaches spend a
great deal of time cleaning themselves. Cockroaches prefer warm, humid conditions.
Major hiding spots
for the household cockroach are:
- Furniture items that are
generally left undisturbed.
- Around water heaters.
- Below sinks.
- Confined spaces, such as behind
the refrigerator, in a pantry or underneath a stack of magazines,
newspapers or cardboard boxes.
- Cracks in walls.
- Gardens.
- In drains and grease traps.
- Kitchen cupboards.
The success of
their survival strategies is proven by the longevity of the group and their
amazing diversity.
PUBLIC HEALTH
IMPORTANCE
Cockroaches also constitute an important public health
problem by contaminating food and eating utensils. Cockroaches are known to
carry human pathogens, such as Salmonella and E. coli,
which can result in human diseases, such as food poisoning or diarrhea. Products
of cockroach infestations, including saliva, feces and cast skins, are a source
of allergens and can irritate allergies and asthma in people, especially
children. In addition they carry the eggs of parasitic worms and may
cause allergic reactions, including dermatitis, itching, swelling of the
eyelids and more serious respiratory conditions (Stankus, et al, 1990).
Occasionally, cockroaches are also destroy fabric and paper products.
In large numbers, they secrete a substance which can result in stains on
surfaces they contact and produce disagreeable odors (Hahn and Ascerno, 2016)
Cockroaches are
important pests because they spread filth and ruin food, fabrics and
book-bindings. They disgorge portions of their partially digested food at intervals
and drop faeces. Thus, cockroaches may play a supplementary role in the spread
of some diseases. WHO (n.d) noted that they are proven or suspected carriers of
the organisms causing the following diseases:
·
diarrhoea
·
dysentery
·
cholera
·
leprosy
·
plague
·
typhoid fever
·
viral diseases such as poliomyelitis.
PREVENTION AND CONTROL
Cockroaches have been
the target of many insecticides over the years but they have developed
resistance to several of them. Attempts to use pheromones as sex lures or to
sterilize male cockroaches have thus far not proved practical on a large scale.
The following methods have proved
effectives:
1.
Exclusion. Keep them out of your house. Most roaches like it outside until
they get hungry, can't find anything tasty there, and walk in through a house's
holes or cracks to feast on the water and food crumbs left from dinner. To stop
them, use caulking, steel wool, and copper mesh to fill the cracks in concrete
works, spaces between trim and brick, and holes of all kinds, including spaces
around pipes. Put wire screens in air vents and stop up any other entryways.
2. Elimination
of cracks. Fill cracks and crevices inside the house. One of the best
weapons against cockroaches is the caulk gun. Every time you fill in a crack
with caulk, you reduce the number of cockroaches that your home can support. Cockroaches
will not mate unless they are nested in the security of a very small space. A
1/8-inch-wide crack is too wide for roach comfort.
3. Redesigning
of cardboard boxes. Cardboard offers miles of tunnels that are perfect
hiding and mating spaces; the glue on cardboard boxes and on paper sacks is
attractive food for these critters. Ensure your cardboard boxes are designed
such that it leaves no crevice for roaches.
4. Use physical traps, such as greased
margarine tubs containing a smear of honey as the lure – cockroaches will climb
in for the food, but be unable to get out because of the grease (or oil) on the
tub.
5. Home Hygiene. The best way to prevent cockroaches
from multiplying is to keep a clean house and block their access to water,
which they need to survive. Eliminating
food and water sources such as dripping faucets, leaks, pet water and food, and
dirty kitchens makes your home much less attractive to cockroaches.
6. Use appropriate
insecticide and follow the manufacturer's instructions. The application of boric acid has proven effective in
killing cockroaches.
Boric acid powder is effective both as abrasive and poisonous to insecticide. Hahn and Ascerno
(2016) noted that insecticides having permethrin,
deltamethrin, cyfluthrin, and cypermethrin as active ingredients are
effective against cockroach control. Spraying should be in precise or specific
sites in cracks and crevices behind sinks, cabinets, around drains and
plumbing, and other sites allowed by the label.
7. Baits. Some
cockroaches baits contain poison that they carry back to their nests, which may
help kill the rest of the nest. Sprinkling of abrasives such as
diatomaceous earth to penetrate their protective cuticles may work in
individual households as a nonpoisonous alternative. Once the cuticle is
abraded, the cockroaches die of dehydration.
Bait should
also be positioned behind the sink splashback, around the junctions of the
pipework or on the underside of surfaces (BASF Plc, 2014).
8. Use of Repellants: Several essential
oils are known to repel cockroaches. These include mint oil, spearmint oil and
eucalyptus oil are . But the best results are obtained with synthetic products
that are easier to standardize. For example, packing materials or interior surfaces
of storerooms can be treated with appropriate dilutions of deet (N,Ndiethyl-3-toluamide)
or DMP (dimethyl phthalate). WHO(n.d) observed that a deposit of 0.5mg of deet
per cm2 repels more than 90% of Blattella germanica and more than 80% of
Periplaneta americana from cardboard boxes for about a week, depending
on temperature and humidity.
REFERENCES
- Australian
Environmental Pest Managers Association Ltd [AEPMA] (2015): Pest Management
Handbook for Food Service Business Operators. www.aepma.com.au, Retrieved
04/06/2016
- BASF
Plc, (2014): Best Practice Cockroach Control. DS229 - Cockroach Control Smart
guide layout. United Kingdom. pages 228,229
- Hahn,
J., Ascerno, Mark E. (2016):
Cockroaches. University of Minnesota.http://www.extension.umn.edu/garden/insects/find/cockroaches/.
Retrieved 04/06/2016
- Microsoft Encarta (2009): Cockroach.
[DVD]. Redmond, WA: Microsoft Corporation
- Orkin
International, (2016). American
Cockroach Life Cycle.http://www.orkin.com/cockroaches/american-cockroach/american-cockroach-life-cycle/, Retrieved 04/06/2016
- Stankus
R. P, Horner E., Lehrer S.B. (1990): Identification and characterization of
important cockroach allergens. Journal of allergy and clinical immunology,
86: 781–787.
- WHO (n.d): Cockroaches, Unhygienic scavengers in human settlements, http://www.who.int/water_sanitation_health/resources/vector288to301.pdf. pages 228,229. Retrieved 04/06/2016
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