Introduction

Cockroaches are primarily tropical and subtropical insects, but they occur in nearly all of the climatic regions of the world. Most of the approximately 4000 described species live in small populations in forest habitats, some little-known species are semi-aquatic, some are cave-dwelling, and a small number of species are associated with the nests of other insects. They are predominantly nocturnal and vegetarian, but many adjust their habits and food preferences to fit environmental conditions and available food resources. Cockroaches as a group are one of the most primitive winged insects, and seem to have remained in primitive habitats and undergone little morphological change since the Carboniferous geological period, about 250 million years ago. It is their association with decaying organic matter and humid conditions that maintains some species in the urban environment. Some have adapted to living indoors, but in this habitat they generally select sites that provide the temperature and humidity features oftheir natural habitat.

Adults are 10-50 mm long, brown to blackish brown or black, generally oval, and dorsoventrally flattened. Eyes are large and there are two ocelli, antennae are filiform and usually as long as or longer than the body. The head is usually concealed from above by a large pronotum, and chewing mouthparts are directed downwards. Legs have strong spines and setae, and the tarsi are five-segmented. Wings are presentin mostadults; the front wings are usually thickened and they overlap when closed over the abdomen. The hind wings may be large and fan-like when extended. Winged species are usually capable ofdirected and sustained flight or gliding. Some cockroaches are brachypterous, and females of many species have shorter wings than males. Nymphs are similar to adults except for their size and the absence of wings. Eggs of all cockroaches are enclosed within a covering, the eggcase or ootheca. This is a hard and protective shell, or it is reduced in thickness and unseen because itis within the female, or it encloses only partof the eggs. The number of eggs per ootheca ranges from 12 to 40, but not all the eggs will hatch to produce live nymphs. When incubation is complete the nymphs swallow air to increase their body size, and the collective expansion of their bodies splits the ootheca along a dorsal seam or ridge. Nymphs emerge enclosed in an embryonic cuticle, but this is shed immediately. There are 5-12 nymph stages, depending on species and sex. Adults are usually long-lived, some for up to 2.5 years.

A relatively small number, considering the large number of species, of cockroaches have adapted to peridomestic and domestic habitats. Their synanthropic association and success may be due to egg-laying and feeding habits, and some physiological features. The habitat preferences ofspecies in tropical Africa and Asia probably brought them into close contact with human dwellings. Some Periplaneta and Blattella species occur in caves and feed on animal waste or other organic matter. They may have become associated with humans using caves as temporary living or storage space. Periplaneta eggcases or gravid B. germanica females could have easily moved with household materials from cave dwellings to outdoor shelters.

The behavioral responses of cockroaches to disturbances influence their ability to tolerate transportation. Those species with evasive behavior patterns in response to slight disturbance would be less likely to be transported by commerce. Physiological preadaptations to household conditions would have included temperature and humidity tolerances, and viability on diets that were limited to human food and food scraps. However, cockroach pestspecies are not tolerant of all the variations in the living space. P. americana and P.fUliginosa are restricted to warm and humid habitats because of their temperature-dependent development, and their relatively high cuticular permeability, which makes them susceptible to water loss. The permeability of their cuticle severely limits their tolerance to dry conditions. B. germanica is relatively restricted to humid locations indoors, such as kitchens and bathrooms, and is generally not known to breed outdoors where it occurs as a domiciliary pest.

Food includes a variety of plant and animal materials in the immediate habitat. Although they are considered omnivorous, a balance of carbohydrates, proteins, and fats is ingested. Food location and selection involve chemoreceptors that are located on the antennae and the mouthparts. In general, cockroaches prefer food in which the carbohydrate contentis higher than fat and protein. For German and oriental cockroaches, rapid development and low nymph mortality occur on a diet of 22-24% protein, and for the American cockroach, 49-79% protein provided favorable development. Female B. germanica compensate for low dietary nitrogen (5% protein) by increasing consumption rates, but elevated dietary nitrogen (65% protein) results in delayed mating and smaller than normal oothecae. In this species, the relatively small size of the female in proportion to the ootheca produced requires that about 90% of her food reserves be incorporated into the ootheca. Food availability often controls the reproductive cycle, and in B. germanica females, peaks in feeding and drinking occur during egg maturation, and reduced food and water foraging when they carry the ootheca. Food availability influences the growth and molting ofnymphs. Bacterial symbionts in specialized cells or bacteriocytes within the fat body increase the metabolic capabilities of cockroaches. Without these microorganisms cockroach development and reproduction are prolonged or disrupted, and mortality is increased. The symbionts have a role in uric acid metabolism and the formation ofamino acid precursors for hemolymph proteins essential for egg development. The hindgut contains various symbiotic and parasitic microorganisms.

Pest status

Pest status is primarily limited to the domiciliary and a few of the peridomestic species. Those cockroaches that primarily live outdoors may sometimes occur indoors. Some of the indoors species rarely move outdoors, except in their original habitat. These characteristics may indirectly indicate the adaptability of some species, and their original environment. Species of Periplaneta and Blatta typically occur in outdoor populations, but they may become established indoors, or include indoor habitats when foraging from outdoors. The survival of these species is not linked to human activity. They are members of reservoir populations away from buildings that are sustained habitats with adequate food and harborage. These and other peridomestic species are characterized by their relatively large size, lengthy development period, low reproductive potential, and mobility. Blattella and Supella species in the urban environment are domestic and only find suitable habitats indoors. They are closely associated with food, harborage, and conditions provided by humans. These species are typically small, have a relatively short development time from egg to adult, a high reproductive potential, and only limited natural mobility.

Pathogenic organisms thatnaturallyinfectdomiciliary cockroaches include viruses and species of protozoa, bacteria, fungi, and helminths. Feeding and movement habits ofcock-roaches in the urban environment bring them into contact with a wide range of decaying organic matter, and provide the potential of spreading organisms that are encountered. Mechanical carrying and transferring organisms are facilitated by the spines and setae on legs and tarsi of adult and nymph cockroaches. Grooming their legs is an important behavior, and potentially transfers pathogenic organisms from the tarsi to the mouthparts and from there to the foregut. While feeding, cockroaches often regurgitate digestive fluid that contains organisms ingested in a previous meal. The habit of defecating as they rest, move about the habitat, and while feeding spreads pathogens to surfaces in the living space, including areas of food preparation and storage. Domiciliary cockroaches may not be the prime means of spread and cause of specific disease outbreaks, but they have habits that give them the potential of being chronic carriers ofvarious pathogenic organisms.

A large number of microbes that are pathogenic to humans have been isolated from field-collected cockroaches. B. germanica, P. americana,and other species thatfeed on decaying organic matter, feces, or inhabit sewers have the potential of acquiring and carrying organisms pathogenic to humans. In some cases, cockroaches may be involved as a vector of disease pathogens. Bacteria associated with cockroaches include:

Alcaligensfaecalis Bacillus subtilis Bacillus cereus Campylobacter jejuni Clostridium novii Clostridium perfringens Enterobacter aerogenes Escherichia coli Klebsiella pneumoniae

Mycobacterium leprae Proteus morgani Proteus mirabilis Proteus rettgeri Proteus vulgaris Salmonella bareilly Salmonella bovis-morbificans Salmonella bredeny Salmonella newport Salmonella oranienburg Salmonella panama

Salmonella paratyphi-B Salmonella typhi Salmonella typhimurium Serratia marcescens Shigella dysenteriae Staphylococcus aureus Streptococcus faecalis Streptococcus pyogenes Vibrio spp. Yersinia pestis

Fungi and molds isolated from field-collected cockroaches include:

Alternaria spp. Aspergillus niger Aspergillusflavus Aspergillus fumigatis Candida krusei Candida paraspilosis

Candida tropicalis Cladosporium spp. Fusarium spp. Geotrichum candidum Mucor spp. Penicillum spp.

Rhizopus spp. Rhodotorula rubra Trichoderma viride Trichosporon cutaneum

Helminth species isolated from field-collected cockroaches include Ancylostomo duodenale, Ascaris lumbricoides,Enterobium ver-micularis, Hymenolopsis spp., Necator americanus, and Trichuris trichiura; protozoans include Entamoeba histolytica and Giardia spp.; and viruses include hepatitus and poliomyelitis.

Atleast 11 proteins from German and American cockroaches can cause allergic reactions and contribute to respiratory asthma in humans. Allergenic proteins from cockroaches are contained in cast skins of nymphs, fragments ofantennae, legs and wings, excrement, pieces of partially consumed food, and living cockroaches. These allergens are heat-stable and persistent in the living space. Hypersensitization to these proteins occurs by inhalation of airborne allergens, suchas dryfeces, or through dermal contact with allergen-contaminated surfaces, or possibly by ingesting food contaminated with cockroach body fragments or feces. If cockroaches are present in the living or workspace, allergens are almost certainly present, and these proteins are produced throughout the life of the insect. Some will persist in infested harborages after the death of the insect, and long after the cockroach infestation has been controlled or eliminated.

Human encounters with cockroaches include incidences of biting. There are reports of cockroaches that gnawed the cal-lused portions of skin, fingernails and toenails, and eyelashes of people, sometimes children, while they were sleeping. Peri-planeta species are often implicated in gnawing on calluses, and causing small wounds on soft skin on the face of children. The bites and wounds were probably accidental and inflicted while feeding on small amounts of food that remained around the mouth and chin of these individuals. Cockroach behavior does not include aggressive biting ofhumans or other animals. The cockroach mite Pimeliaphilus cunliffei (Pterogosomatidae) is an obligatory parasite of cockroaches. It feeds on live individuals, and cannot survive on cast skins or dead cockroaches. This mite has been linked to bites ofhumans living in households with cockroach infestations.

Development and distribution

Growth is relatively slow. Small-sized species usually mature more rapidly and have shorter lives than large species. The first few molts tend to occur at regular intervals, whereas later ones are often irregular and dependent on habitat and food. Duration of early instars is usually shorter than late instars, and depending on conditions the late stages can be extended manymonths. Under adverse conditions, suchas lowtempera-tures or limited food and water, nymphs nearly stop development. For most species, the molts, especially the last, occur in a secluded harborage, and the tanning and hardening of the cuticle are completed in a few hours. Adults and large nymphs often cannibalize other individuals in the harborage during tanning.

Egg-laying habits of cockroaches can be considered in an evolutionary series. It begins with the species that deposit thick-walled oothecae, whichare unattended by thefemale, and extends to thin-walled and slightly sclerotized oothecaretained within the female's body until the developing nymphs are prepared to hatch. Females ofmany species deposit the ootheca soonafteritis formed, while others carry ituntil the eggs complete development, and the females of other species retract the formed ootheca into a brood sac and eggs complete development there. Oviparous species deposit the recently formed ootheca, or turn the ootheca on its side and retain it in the female's genital chamber prior to deposition. Oothecae that are deposited soon after formation, such as those of the American and oriental cockroach, are tanned and hardened capsules that protect the developing eggs. Oothecae that are turned on their side and retained by the female are permeable to water provided by the female's body. In oviparous species, the dorsal edge of the ootheca is formed into a series of respiratory chambers, usually one per egg, which admit air to the developing embryo (Fig. 4.1). Nymphs hatch from the eggcase by increasing their body size with a small amount of air; this spreads apart the dorsal edge of the eggcase for the nymphs to exit.

Ovoviviparous species, such as the Madeira and lobster cockroach, retract the developed ootheca into a specialized brood sac in the female's abdomen. Hatching occurs within the brood sac, either while the ootheca is being extruded, or shortly after itis deposited by the female. Oothecae of ovoviviparous species are thin-walled to allow for the transfer ofwater to the developing embryos. Viviparous development occurs in Diploptera species, the most common ofwhich is D. punctata. The ootheca of this species protrudes from the female's abdomen for a short time before it is turned on its side and then withdrawn into the

Figure 4.1 Blattaria oothecae. (a) Blatta lateralis; (b) B. oriental's; (c) Periplaneta americana; (d) P.brunnea; (e) P. fuliginosa; (f) B.germanica; (g) Parcoblatta spp.; (h) Supella longipalpa.

brood sac and absorbed. The developing embryos are provided water and nutrients, and the nymphs hatch from the female's abdomen.

Early-stage nymphs resemble adult males in having abdominal sterna 8 and 9 visible, and 9 with styles. In females, these sterna gradually disappear from view and they are incorporated into the genital atrium. The number of segments of the antenna and cerci usually increase from stage to stage. First- and last-stage nymphs of some domiciliary cockroaches are distinctly colored or banded, and these characteristics are useful for species identification. In winged species, the wing buds appear late in development; usually this condition distinguishes late-stage nymphs, and wings appear on adults. Adults of brachypterous species, and short-winged females of some winged species are sometimes difficult to distinguish from large nymphs.

Aggregation is an important behavior of most cockroaches. First-stage nymphs remain close to the ootheca or the ovipositing female, as in ovoviviparous species Rhyparobia maderae and Nauphoeta cinera. Adult Blattella germanica and Periplaneta americana secrete an aggregation pheromone in the feces. Aggregation pheromone in P. americana attracts at low concentrations, and acts to inhibit movement at high concentrations. Pheromones probably function to mark suitable harborages or successful foraging routes, oviposition sites, or act to reduce crowding in favorable harborage sites. The odor of cockroach feces detected by humans is not a necessary component of the aggregation pheromone. Purified extracts that are perceived as odorless by humans are as attractive to cockroaches as the odorous material.

Mating in cockroaches is usually preceded by a simple courtship behavior, and typically itinvolves volatile and contact pheromones. These chemicals stimulate males to sexual excitement, which is usually characterized by wing fluttering and attempts at copulation, with males as well as females. P. americana males begin searching for a female within 20 min of being exposed to a sexpheromone. The adultmale oriental cockroach responds to the American cockroach sex pheromone, and the male American cockroach responds to high concentrations of the oriental cockroach pheromone. In B. gemanica there seem to be several short-range and contact pheromones involved in mating. Chemically, these pheromones are some ofthe largest among all known sex pheromones. During cockroach mating, the male and female are linked end to end, and copulation lasts from several minutes to several hours.

Males form a spermatophore and it is transferred during copulation to the female genital atrium. The empty sper-matophore is discarded after a few hours or days, and before the female mates again. Subsequent ingestion of the sper-matophore, into which the male has incorporated urates, by female B. gemanica provides required nitrogen-based nutrients important for oothecae production. Parthenogenesis occurs regularly in some cockroach species or strains, such as in Pyc-noscelussurinamensis strains in temperate regions. Parthenogenesis is known for some Periplaneta species, but the resulting adult cockroaches are abnormal and unable to reproduce.

Distribution of the principal domiciliary cockroaches is not indicative of their origin. Most pest species are native to northern tropical regions of Africa and southern Asia, and their present geographic range is indicative of their association with humans and their ability to adapt to alternative environments. Scientific and common names of species such as Periplaneta americana, P. australasiae, Blattella germanica, and Blatta orientalis are misleading, and not linked to their origin or predominant distribution. Commercial shipping of people, possessions, and food material was probably the major dispersal mechanism for these and the other domestic and peri-domestic cockroach species. Spice, dye, aromatics, and fabric traders moved their material by ship from ports in southern Asia. These goods moved to the Mediterranean and into central Europe through a network of food warehouses that provided conditions suitable for survival of cockroaches and other six-and four-legged pests. Seaport storage in Asia and the eastern Mediterranean often combined warehouse and lodging.

Under this arrangement, cockroaches that flourished in ships that came from tropical regions might find indoor habitats with temperatures and humidity suitable for survival, and the opportunity to spread further with household goods. Domiciliary cockroaches moved then and now from warehouses to markets and from markets to households, following a network ofhabitats and reservoir populations.

Predators and parasites

Natural enemies ofcockroaches include a variety ofpredators and parasites. Vertebrate predators include frogs, fish, reptiles, birds, and mammals. Among arthropods, the predators include dragonflies, mantids, reduviid bugs, carabid beetles, wasps, ants, scorpions, house centipedes, and spiders. Spiders found associated with cockroaches include the theridiid, Steatodagrossa,and the sparassid, Heteropoda venatoria in Hawaii. German cockroach populations often sustain the protozoan parasite, Nephridiophaga blattellae and the parasitic nematode, Blattacola blattae. The mite, Pimeliaphilus cunliffei (Pterygo-somatidae) is an obligatory parasite of several species of cockroaches.

Hymenoptera egg parasites attack several cockroach species. Encyritidae: Comperia merceti is apparently limited to parasitizing the brownbanded cockroach, Supella longipalpa. It has been successful in management programs for this cockroach. Eupelmidae: Anastatus blattidarium is a parasite of the brownbanded cockroach. Eulophidae: Aprostocetus hagenowii attacks eggs of Blattella germanica, Blatta orientalis, Periplaneta americana, P. fuliginosa, and P. australasiae. Evaniidae: ensign wasps Evania appendigaster and E. punctata parasitize Periplaneta spp. and oriental cockroach. Hymenoptera predators ofcock-roaches are not limited to species occurring indoors, but attack inside and outside structures. Ampulicidae: Ampulexcompressa is a cockroach-hunting wasp that is endemic in India and south Asia and extends into Africa and China. These wasps attack Periplaneta americana and P. australasiae, and often enter houses in search of their prey. They do not form nests but, after the female has stung the prey, it is dragged away to a hole or crevice. Ampulex and a related genus, Dolichurus,occurincentral Europe. In Australia, species ofAphelotoma are predators of cockroaches in outdoor habitats. Sphecidae: Tachyspex lativalvis and others in this widespread genus attack cockroaches.

Cannibalism is known to occur in several cockroach species. Adult Periplaneta feed on eggcases in their habitat, and adults and nymphs of Blattella and Blatta feed on injured or weak individuals in crowded harborages, presumably where these individuals have little room to escape. Adult German cockroaches, and to a lesser degree nymphs, feed on molting individuals, but usually only nymphs older than the third-instar nymph. Late-stage nymphs are the subjects of attack, and molting adults usually suffer the greatest attack and mortality. There is apparently no correlation between population density and cannibalism in Blattella gemanica.

Classification

Current classification of cockroaches is based on adult morphology and egg-laying characteristics. The features used to establish the relationships are female genitalia and its musculature, the external male genitalia, structural aspects of the proventriculus (gizzard), and female egg-laying behavior. The order Blatteria is subdivided into two superfamilies, Blattoidea and Blaberoidea, which are further subdivided into five families and 20 superfamilies. Cockroach evolution seems to have followed two divergent lines, which are represented by the two superfamilies. The small superfamily, Blattoidea, includes many pest species: Blatta orientalis, Eurycotis floridana, Neosty-lopyga rhombifolia, Periplaneta americana, P. australasiae, P. brun-nea, P. fuliginosa, and P. japonica. Females of these and other Blattoidea species do not turn the ootheca in the female genital chamber after it is formed. One of the most primitive living cockroaches is Cryptocercus punctulatus. It is a wood-eating species in the Blattoidea family Cryptocercidae. Blaberoidea is a large superfamily with many genera and species distributed worldwide. Females in the majority ofBlattellidae families turn the ootheca after it is formed (Plectopterinae, represented by Supella longipalpa, are the exception), and female Blaberidae turn and retract the ootheca into a genital chamber, and eggs are incubated internally.

Common names for cockroaches often indicate their habits, location of their natural habitat, or the suspected location of their origin. Because they are common household pests around the world, common names are often regional and difficult to chronicle. The common names used here are considered the most frequently used.

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