Tiphane’ N. Randall

ynaffitr@hotmail.com

2 May 2001

All species of cockroaches exhibit very distinct mating behaviors to ensure that they have sufficient access to mates. Elaborate mating displays have been carefully observed in laboratory studies. Wing flapping, waving of the abdomen, exposing abdominal sexual glands (tergites), nibbling, aggressive fighting, and hissing are involved during male courtship of the female. Tactics of sexual mimicry have also been observed in various species of cockroaches while they attempt to acquire partners. When normal mating rituals prove to be unsuccessful, the male will use alternative methods that involve deception in order to copulate. One of the benefits of this intraspecific (i.e., mating within its own species) mimicry for the males is that it provides easier access to the population of sexually receptive females. When the females observe this mimicry, they welcome the female mimic and become more receptive to it for they think it is an individual belonging to their own sex. This in turn gives the female mimic a chance to approach the female, which allows successful reproduction to occur between the two sexes. These mating habits are utilized more when the males are at a certain disadvantage. One particular example is the competition over food resources. Females have the ability to access specific territories. Once the male mimics the females’ behavior, he will also have that same access to the food resources, perhaps to nuptial gifts, and later on to the females themselves. Studies have shown that these deceptions can lead to the males having priority over some of the larger territories belonging to other males. This also allows the smaller cockroaches to steal nuptial gifts from the larger territorial males. Once these are obtained, they can use them to present as gifts to the females in order to initiate copulation. There are studies looking at this in even more detail to determine if these tactics have any other biological significance.

According to fossil records, cockroaches belong to a very ancient group of organisms dating back to about 400 million years ago during the Carboniferous period. Their appearance has not changed much over this extensive time period (Luft 1996). They are classified within the order Blattodea which includes five families: Blattidae (the Oriental cockroach-Blatta orientalis and the American cockroach-Periplaneta americana), Blattellidae (the Asian cockroach-Blatella asahinai, the German cockroach-Blatella germanica, and the brown-banded cockroach-Supella longipalpa), Blaberidae (the Madagascar hissing cockroach-Gromphadorina portentosa, the Madeira cockroach-Leucophaea madera, and the Brazilian cockroach-Blaberus giganteus), Cryptocercidae, and Polyphagidae. The fact that these organisms have remained extant for this long is due in large part to their non-reliance on a single mode of sexual reproduction, i.e. various sexual behaviors that will ensure procreation are triggered by hormonal interactions.

These agile organisms typically have flat and oval body plans with downward pointing heads. A hard, yet oily, exoskeleton called the cuticle protects their fragile viscera. This oily skin helps them escape predators and keeps them from dehydrating. Cockroaches can survive for a week without water and at least a month without food. This exoskeletal covering is shed several times throughout the year as their body continues to develop. They are mostly known for the foul and putrid odor they leave lurking in their surroundings. Cockroaches have also gained the reputation of being household nuisances because they often infest their human habitats by feeding on food storages and garbage and are very difficult to decimate (Encarta 2001). Even though they are considered to be annoying vermin, they play a very important ecological role. They help decompose forest litter and the fecal matter of animals. Because they possess cellulytic symbiotic protozoa and other bacteria in their digestive tracts, they are able to digest a wide range of animal matter although they prefer starchy foods and meats (Luft 1996). They are thought to share a common ancestry with termites because some can even digest wood. Only one percent of this order is the pest that has given the whole order an appalling name (Encarta 2001). Cockroaches are not as filthy as thought to be. They actually clean themselves many times throughout the day and spend up to seventy-five percent of their time hiding and resting in protected areas such as cracks and crevices (New Jersey Online 2000). Empirical evidence in laboratory experiments has demonstrated that household cockroaches have not been involved in outbreaks of illness but can indeed contaminate food and other objects with human disease. Many people have shown allergic skin reactions to these insects due to airborne allergens in their feces (Luft 1996). Cockroaches have been found all over the world even in the coldest climates (the North and South Poles) but survive by cohabitating with humans when the temperature falls below 32 degrees Fahrenheit (New Jersey Online 200).

Their closest relatives are grasshoppers, mantids, stick insects, crickets, and katydids because they exhibit some of the same entomological morphology. The size of this organism can vary widely (some are so small they inhabit ant, wasp, and termite nests) and can be brightly colored, especially those dwelling in South America (the world’s largest lives there, is six inches long, and possesses a one foot wingspan). Some species have diaphanous (somewhat transparent) wings while others do not. Winged species do not always fly, however (New Jersey Online 2000). Cockroaches have highly sensitive antennae and sensory bristles (cerci) that can detect the slightest hint of moisture and food in their surroundings. They are also equipped with cerci that extend from the posterior of the abdomen that can perceive any air movement so they are able to scurry out of the way of any potential danger. These armored insects are extremely photosensitive, and thus are nocturnal (Encarta 2001). Therefore, one can safely assume that if these creatures are sighted during a diurnal period, this is an indication that there is a heavy environmental infestation.

Courtship patterns differ depending on the species of cockroach. The life cycle of the American cockroach (Periplaneta americana) is initiated when a mature female emits a pheromone that attracts a male or many males to the mating grounds. When the male receives this enticing signal, he approaches and flaps his wings to show his interest towards her. He will then probe for females with his abdomen as a way of searching for the origin of the emitted pheromone. Eventually mating commences by the male backing into the female and exchanging his sperm. In other species, nibbling, waving of the abdomen, and hissing are also displays of mating behavior (Encarta 2001). Some males will even emit a sexual pheromone of their own to initiate courtship and assume a calling posture by exposing sexual glands on their abdomens called tergites (Blatta orientalis). Once the female is near the male, she will open her genital atrium widely thus exposing her atrial glands, the site of female sex pheromone production. (Abed D., Brossut R., and Farine J.P. 1993). The presentation of a nuptial gift from the male to the female has also been observed as a courtship gesture. The male will transfer his sperm into a protein-rich package know as a spermatophore. He gives this to her to show his interest. If she accepts it, she will begin to consume the protein coat that may have some nutritional value as he commences to copulate with her (New Jersey Online 1997-200).

After the female has been fertilized, she will produce an ootheca (egg case). This is a small sausage shaped capsule. Each ootheca can contain hundreds of eggs that hatch into nymphs, smaller versions of the adults, and undergo gradual metamorphosis by several moltings of their exoskeletons (Encarta 2001). They can carry an egg case for an extensive period and then and drop it wherever it happens to fall. Some females mate just once and are pregnant for the rest of their lives. Other species lay the ootheca in a protected area or keep it attached to their egg-laying organ (ovipositor). Some pregnant females will even display maternal care at the right time. The nymphs of the American cockroach that emerge from the oothecas linger around the mother for a number of days (Encarta 2001). In the Diploptera punctata cockroach, a protein-rich milk is produced to support its young during the gestation period (Evans, Stay 1995). Various experimental treatments were performed to determine precisely when this behavior is exhibited. Researchers used a topical application of a juvenile hormone analog (7S-hydroprene) to the postoviposition females of this species. Higher doses of this analog prevented the ability to produce milk while smaller doses allowed competence. Allatectomy (removal of the corpora allata (CA)-part of the brain that regulates reproductive bodily processes) in mated females of Diploptera punctata showed that there is a dependence on the corpora allata in order to produce milk. Unmated females, however, became capable of milk production even if their corpora allata remained intact. In addition, they became incapable once the spermatophore (structure containing sperm covered by a protein casing) was removed. Once this structure was detached, there was no longer a need for the female to produce milk. Ovaries were also removed to observe what effect this may have had on competence. Researches found that ovarian removal in the allatectomized, mated females did allow milk production to occur. The results showed that a male mating with an allatectomized female induced a change in the ovary that inhibits competence. In order for competence to manifest itself at a suitable time, additional changes must subsequently occur (Evans, Stay 1995).

Sexual selection has been observed in Nauphoeta cinerea cockroaches by examining the effects of male competition and the female’s mate choice. The dominant males mated more frequently but not entirely within their newly established hierarchy. Studies have revealed that the concentration and composition of the males’ sexual pheromone had an effect on the attraction of females, either at close- or long-range distances. Researchers hypothesized that the most attractive composition would be the most potent out of rival males. Females, however, favored a blend of this attractive pheromone that proves to be the most effective in male-male competition rather than the most potent one (Moore and Moore 1999). They were then able to determine which male was overly aggressive thus avoiding mating with him in order to prevent overly aggressive progeny. These creatures are also very selective regarding from what environment the male originates. The environments they were reared in resulted in an affect on behavior and in the quantities of the sex pheromone emitted by the male. Males in low-quality surroundings took longer to commence courtship and spent more time copulating with females from all environments. This caused the female to react slower to their tactics and required more attention. Thus, low-quality environments increase the females’ choosiness of a mate (Clark, DeBano, and Moore 1997).

Many cockroaches demonstrate defensive tactics when they are capable of sexual reproduction. In the species Nauphoeta cinerea, males establish dominance-subordinate relationships by using aggressive behaviors towards one another. Researchers suspect that these cockroaches are able to distinguish the rank of another individual by chemical signals emitted when another male trying to appropriate its territory approaches the dominant male (Everaerts C., 1996).

Other defense mechanisms are exhibited in this organism in order for them to ward off predators while mating. This allows the males to remain at the feeding sites longer and even lures the females back. Some species are capable of producing hissing sounds when disturbed (Madeira and Madagascar hissing cockroaches). Males often use more aggressive tactics to drive off their inferiors during copulation. When a male and female of Diploptera punctatae are disturbed during reproduction, the male will eject his bitter, defensive spray (quinone) onto the offender only when he is the victim. The female does not have this chemical, however, without the assistance of the male. After her last molting, she is ready to mate but is vulnerable to predators without her hard exoskeleton. In addition, her quinone-producing glands are empty (Wyttenbach R., Eisner T. 2001) leaving her without any means of protection. Mating with a male whose defense glands are fully operational causes her to indirectly benefit by gaining his glandular discharges in order to protect herself during her susceptible stage.

Further research has suggested that male-male competition during courtship towards the female may have an effect on mating success. Placing pairs of male Madagascar hissing cockroaches (Gromphadorhina portentosa) with a group association in an arena with a single virgin female revealed this behavior. The smaller, inferior males mated less frequently than their larger, dominant counterparts. The dominant mated males exhibited aggression by restricting access of their inferiors to the females and showed a longer duration of interaction with her. In cases where both males remained unmated, the inferior males acquired increased access to the female as interactions progressed (Clark 1998).

As normal mating rituals may often fail at times, some species of these cockroaches have other methods of approaching sexually receptive females. Three genera of tropical cockroaches (Archimandria, Blaberus, and Brysotria) participate in pseudofemale behavior (Corcoran 1995) in order to acquire contact with females. When courtship is initiated, the male will open his wings as a display of his interest while exposing his tergites. The female feeds on these when she mounts him. If another male is observing this mating ritual, he will then impersonate the female’s behavior and mount his competitor. This pseudofemale then feeds on the competitor’s tergites making him believe he has another female to mate with. Ultimately the pseudofemale’s behavior turns aggressive as "she" bites off the competitor’s vulnerable raised wings causing the once dominant male to retreat to safer grounds (Corcoran 1995). This mimicry can also be used as a mate-guarding tactic. This gives an advantage to the mimics so they may be able to mate with as many females as possible and dominate over that territory. This allows the males to remain at the feeding sites longer and even lures the females back.

 Pheromonal Interactions During Sexual Reproduction

Scientists have conducted various experiments with the purpose of determining the exact role in which the organism’s brain plays in the release of sex pheromones. The mechanisms affecting the regulation of these chemicals are still unclear due to the lack of sufficient physiological data. Male Nauphoeta cinerea cockroaches have been the subjects of determining the role of the brain, corpora allata, and juvenile hormone III (JHIII) in sexual pheromone production (Sreng, Leoncini, and Clement 1999). To observe the effects of these components, allatectomy or complete decapitation of the male was preformed. Their attractive sex pheromone levels were seen to decrease as a result. Researchers then injected JHIII into these altered males. This in turn induced the production of the sexual pheromone (Sreng, Leoncini, and Clement 1999) denoting that JHIII has an effect on creating this sex pheromone.

Olfactometers (devices that estimate the keenness of the sense of smell) have revealed that males of Eurycotis floridana emit a potent sex pheromone that attracts females to them. The male at eight days old is mature enough to mate while the female becomes an adult at eighteen days. He begins by exposing his anterior glands from his abdomen to produce his attractive pheromone. This is known as male calling behavior. His pheromone is only attractive to the females at a certain distance, however. When she receives his signal, she approaches and opens her genital atrium, climbs onto the male’s back, and feeds on the glandular secretions from his backside. As she licks the sensitive setae containing this secretion, this informs the male that she is in the exact position to begin copulation (Farine et al 1996). A similar type of male calling is also seen in the German cockroach. They usually assemble around food or shelter so no long distance searching is obligatory. Studies have shown that sexually receptive males can distinguish the presence of heterosexual odor and prefer virgin females to mated females. Females can also perceive heterosexual odors also but have no partiality towards either sex’s odors, nor do they demonstrate a different reaction. When these virgin females are attracted, the rate of their locomotion to find males increases. They also display a calling behavior to discharge a sex pheromone to communicate back to them. She will persist in releasing her pheromone more frequently if she does not sense a male nearby (Tsai, Lee 1997).

 Hormonal Control and Sexual Receptivity

Certain behaviors are expressed only when cockroaches are reproductively competent. Hormones are any internally secreted chemicals that specifically trigger target organs or tissues. These are not to be confused with pheromones which are chemicals emitted by means of hormonal triggers to attract members of the same species. Gonadal maturation of the male invariably occurs simultaneously with ovarian maturation in the female (Schal 1995). One species that exhibits this particular behavior is Blatella germanica; commonly know as the German cockroach. Juvenile hormone (JH) is produced within this organism’s corpora alatta (CA). This is part of the brain that regulates reproductive bodily processes. JH is fundamental in determining when an organism will begin copulation and when an egg will begin to mature. While performing various experimental manipulations, JH has been discovered to control the female’s receptiveness of the male. This in turn accelerates the eagerness of the male to the female.

JH has also been seen to regulate calling behavior and sexual signals (pheromone release) in this species. Allatectomy proved to reduce the speed and frequency of the females’ locomotion and sexual receptivity towards the males (Lin and Lee 1998). This is due to the fact that the CA is the production site of JH, which triggers the release of their sex pheromone. The removal of it causes reverse affects. The ovaries of these cockroaches also affect the synthesis of this hormone. Ovariectomy of adult virgin females caused the CA to increase then decrease in activity just as it occurs in females in which their ovaries were left intact. It was also observed that when ovariectomized females mated, it caused an increase of activity in the CA. Therefore, both mating and the ovaries stimulate the production of JH in the reproductive cycle but neither is needed to view a complete JH synthesis cycle.

 Conclusion

All of the discussed mating behaviors have contributed to the evolutionary success of this organism. Cockroaches have shown their adeptness to thrive in many diverse environments over a period of millions of years. Their use of their many modes of sexual reproduction ensures procreation, and the proliferation of their progeny. They exhibit several mating tactics in order to reproduce successfully. The secretion of special hormones have been observed to trigger the release of enticing pheromones to further lure the organism’s object of desire in closer. The female may choose to stay and observe her persistent male caller. Depending on the environment he was reared in and the potency of his sex pheromone, she will then decide if he is worthy to mate with her. Once the couple is face to face, the male performs an elaborate display of bobbing, weaving, and wing flapping just long enough so he can commence copulation. Competition will often arise between two or more males. They will then use aggressive methods to drive off the smaller individuals. This will allow the dominant male to have access to the sexually receptive females and the breeding grounds. Some males will even mimic other females so they can get closer to them, bettering their chances of mating with them. Scientific manipulations of various species of cockroaches have shown that the corpora allata (CA) in the brain has an effect on the levels of juvenile hormone (JH) produced. This in turn determines what age they will begin mating, the amount of female receptiveness towards the male, and how long their calling behavior will last. With these diverse sexual behavior methods combined with its unique body characteristics, the cockroach just may thrive for several more millions of years enduring any environmental condition.

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