Cockroaches are among the most common house pests. There are several species of cockroaches, and they include Blattela, Periplaneta, and the Nauphoeta, among others. However, the Blatella germanica, also known as the German cockroach, is popular among researchers since it possesses several characteristics that differ from other species. This is primarily because it is regarded as the most troublesome species, as it is difficult to control using insecticidal baits (Schal, 1997). Second, unlike other insects that have shorter adult lives, the adult females of the B. germanica can produce up to nine broods and have a longer lifespan of up to 250 days (Breed, Hinkle & Bell, 1975).
Therefore, they breed continuously, with many overlapping generations present at any given time. Relative to its social and economic impact, the B. germanica is associated with several adversarial outcomes. This is because the cockroaches contaminate food with their insect excreta and indigestible cast skins that could lead to digestive upsets in consumers. Furthermore, they sometimes carry food-borne pathogens that cause severe illnesses.
Different invasive species interact differently with each other in their respective environments. With regard to cockroaches, several studies have examined the patterns of aggression and reproduction behavior among the organisms (Bell & Gorton, 1978; Bell & Sams, 1973; Breed et al., 1975). The results of these studies were mainly based on observing the agonistic action patterns, in which it was seen that they use body-jerking and stilt-walking as a threat or intention movements (Bell & Gorton, 1978).
Other agonistic action patterns comprise kicking, biting, and butting with the head. On the other hand, non-aggressive agonistic actions consist of retreat, truce, and antennation (when a cockroach touches the other with the flagellum of its antennae) (Bell & Gorton, 1978). These agonistic action patterns are a resultant of six categories of aggression behavior, which include fear-induced, territorial, inter-male, instrumental, irritable, and maternal aggressive behavior. Out of all these categories, only the maternal, territorial, and inter-male aggression behaviors can be easily differentiated among cockroaches.
Fear triggers a flea response, while irritable and instrumental aggression behaviors are dependent on a complex of factors exceeding the capabilities of a cockroach (Breed et al., 1975). Maternal aggression is the most prevalent form of aggressive behavior exhibited by the B. germanica species. This is usually portrayed by mothers or females carrying oothecal as they elicit this behavior to increase the likelihood of the survival of their young. However, maternal aggression is rarely observed in insects as they a reproductively programmed to lay a large number of eggs within a short period.
When it comes to territoriality, aggressive encounters present among the B. germanica species is often caused by population factors, for instance, population density rather than their spatial relationships with food, water, mating sites and resting places (Breed et al., 1975). However, although the population-initiated aggressive encounters may still be regarded as territorial, they cannot be fully considered as such as they are incapable of establishing a fixed spatial relationship between them and their immediate environment. One primary reason for their lack of territoriality is that they are a highly gregarious species; that is, they secrete an aggregation hormone when subjected to light, and hence they aggregate in a dense cluster (Breed et al., 1975). Lastly, inter-male aggression behavior usually occurs to increase the chances of mating for the winner.
This because the fight may lead to the loser leaving the area; thus, reducing the male to female ratio, or dismemberment. However, for the B. germanica species, aggressive behavior is independent of sex and inter-male aggression (Breed et al., 1975). Overall, aggression behavior in the B. germanica species has a lower intensity as compared to other cockroaches. These aggressive behaviors can result in the reduction in population either through death or dispersion, enhanced recruitment to a population, or spacing of organisms within the population.
The ideal habitat for the B. germanica species is that which is dark, has relatively warm temperatures, and contains adequate food and water. Therefore, any alteration from the optimal level may lead to aggressive behavior and dominance, with specific triggers in the environment being the release of the sex pheromone, light perturbations, and population size (Bell & Sams, 1973). Although there is an abundance of research that has examined aggressive behavior between different cockroach species, there is limited research exists on how the presence of reproductive competition and particular environmental factors affect the level of aggressive behavior. As a result, this study will be guided by the following research question:
Are aggressive interactions between male B. germanica instigated more by the presence of females or unfavorable living conditions?
From the research question, the following hypothesis is derived:
H1– B. germanica is most aggressive in favorable living conditions (moist soil) and with the presence of females because of its reproductive desire and an ideal environment.
Consequentially, it is predicted that B. germanica will exhibit the most aggressive behavior in the habitat with females present and with the most favorable living conditions.
References
Bell, W.J., & Gorton, R.E. (1978). Informational analysis of agonistic behaviour and dominance hierarchy formation in a cockroach, Nauphoeta cinerea. Behaviour, 67(3/4), 217-235.
Bell, W.J., & Sams, G.R. (1973). Aggressiveness in the cockroach Periplaneta Americana (Orthoptera, Blattidae). Behavioural Biology, 9, 581-593.
Breed, M.D., Hinkle, C.M., & Bell, J.W. (1975). Agonistic behaviour in the German cockroach, Blattella germanica. Zetitschrift fur Tierpsychologie, 39, 24-32.
Schal, C. (1997). Reproductive biology of the German cockroach, Blattella germanica: Juvenile hormone as a pleiotropic master regulator. Archives of Insect Biochemistry and Physiology, 35(4), 405-426.