Cockroach Infestation and Factors Affecting the Estimation of Cockroach Population in Urban Communities

Cockroach Infestation and Factors Affecting the Estimation of Cockroach Population in Urban Communities

1 Faculty of Health Science, Yasuj University of Medical Sciences, Yasuj, Iran


Cockroach is one of the most important pests in urban communities. This study was conducted to determine the situation of cockroach infestation and effective factors on cockroach trap count in urban communities of Yasuj City in southwestern Iran. In this study cockroach population in 573 sampling units (residential units, official places, and hospitals) was monitored using sticky traps over a five-week trapping period. Occupants of 348 residential units were also questioned (by means of questionnaire) for cockroach infestation in their respective residence. The study shows almost 39% of sampling units were infested by cockroach. Five species from two families had been identified: Blattidae (comprising Blatta orientalis, B. lateralis, and Periplaneta americana) and Blattellidae (comprising Blattella germanica and Supella longipalpa). German cockroach, B. germanica, with widespreaddistribution (80% of infested sampling units) showed the highest frequency (96.7%) of trap counts. The expression of the distribution of German cockroach populations and some factors could affect trapping, and population monitoring in an urban community was surveyed. Additionally, affecting some exclusion factors on cockroach infestation was pointed. Rates and source of cockroach infestation were discussed from the viewpoints of the residents.

1. Introduction

Cockroaches have been in existence for about 360 million years [1], and they are one of the important groups of insect pests in urban environments. Cockroaches not only spoil food but also transfer pathogens and cause allergic reactions and psychological distress [2]. As a potential mechanical vector of human diseases, many pathogenic organisms have been associated with cockroaches. These include poliomyelitis viruses, bacteria, fungi, protozoa, and helminthes [3–6]. Pai et al. [7] reported cockroaches as potential vectors of nosocomial infections. Moreover, bacteria with antibiotic resistance have been isolated from household cockroaches [8, 9]. The most common important species is associated to surveyed locations. In the southeastern United States, smokybrown cockroach [10], in New Zealand, German cockroach [11], and in Southeast Asia, American cockroach [12–16] were found to be the most dominant species, respectively. While the German cockroaches, Blattella germanica (L.), are not present in households in Southeast Asia, they are prevalent insect pests in hotels and food outlets [17, 18]. There are over 3,500 species of cockroaches worldwide. Of these only several species are commonly associated with humans. Three domiciliary species of importance are the German cockroach, the American cockroach (Periplaneta americana), and the Oriental cockroach (Blatta orientalis) [19]. German cockroach has a worldwide distribution, although it originated in north or tropical Africa despite the misleading common name [20]. However, German cockroach has created substantial pest problems in many developing countries [21–24]. This species reported a common indoor pest in low-income housing [2].

According to the report by Hanafi-Bojd and Sadaghiani [25], there are 24 species of cockroaches from 4 families: Polyphagidae (12 species), Blattidae (5 species), Blattellidae (5 species), and Ectobiidae (2 species), that have been identified throughout the cities of Iran so far. Three species, the German cockroach, the American cockroach, and the Oriental cockroach, are the most common species that have caused health problems in urban communities (e.g., residential buildings, hotels, hospitals, restaurants, and shopping) of Iran. Additionally, Polyphaga indica, P. aegyptiaca, Periplaneta australasiae, and Blatta lateralis are the other important cockroaches in Iran.

Yasuj, which is situated in southwestern Iran and the capital of Kohgiluyeh va Boyer Ahmad, was chosen for this study. The province covers an area of 15,563 square kilometers and in 2006 had a population of 634,000 [26]. The weather varies with seasons: cold and snowy in the winter, cold or moderate and rainy in the spring and fall, and hot (not more than 35°C) and dry in the summer [27]. Mean annual temperature, rainfall, and humidity are 15°C, 866 mm, and 45% RH, respectively. Although ancient structures of housings are predominant throughout the city, new structures of buildings have sprung up in the last few years [27].

2. Materials and Methods

After a preliminary survey on private and public places in the southwestern of Iran, Yasuj City, 573 sampling units were selected for the study (using sticky trap), and a sampling unit comprised an ‘‘apartment unit’’ for residential building and a ‘‘room’’ for hospital, dormitory, hotel, and government office (Table 1). At the inspection stage, monitoring was performed weekly using sticky traps for sampling units. Moreover 97 private houses had been surveyed by questionnaire. The sticky traps were manufactured by Ridsect (produced by Sara Lee Sch. Bhd. Malaysia) in baited tent form, and the size of the sticky surface of the trap was 16 × 9 cm 2 . Depending on the surveyed locations, traps were placed in cabinets, under the sink, beside the refrigerator, beside the stove, in closets, and on shelves, with one side of the trap resting against a vertical surface. Average one trap per eight square meters was installed in sampling units. Totally the number of cockroaches per trap for each sampling unit was estimated. Infestation rate is defined as cockroach trap count per trap during seven-day trapping period. Numbers of cockroaches trapped were recorded weekly after each 7-day trapping period. The trapping process continued for a 5-week period.

Type of location Number of locations Sampling units Size of units (limitation) Infested sampling units Number of infested units with
B. germanica
Number of identified cockroaches (%)
Dormitories from four universities* 11 dormitories 386 12–18 m 2 × 2.5 m 141 (37%) 116 5758 B. germanica (97.59%)
91 B. lateralis (1.54%)
46 P. americana (0.78%)
4 S. longipalpa (0.07%)
1 B. orientalis (0.02%)
Hospital 2 hospitals 121 12–18 m 2 × 3 m 71 (59%) 60 1125 B. germanica (93.28%)
62 B. lateralis (5.14%)
19 P. americana (1.58%)
Housing complex 7 buildings 27 70 m 2 × 2.5 m 7 (26%) 5 131 B. germanica (94.93%)
6 P. americana (4.35%)
1 Supella longipalpa (0.72%)
Official place 1 building 22 12–14 m 2 × 3 m 4 (18%) 5 B. lateralis (100%)
Hotel 1 building 17 12–18 m 2 × 2.5 m 2 (12%) 2 B. lateralis (100%)

YUMS, YU, AU, and TU.

A set of questionnaires were distributed for occupants of the 348 residential units (from 10 dormitories, 97 private houses, and 7 house building complexes) to obtain information about cockroach infestation in their houses (e.g., size of cockroach, time, and entrance-source of cockroach infestation). Some details of the structural design (conjugated to survival of cockroach) for 69 units of hospital were collected by the other set of questionnaire.

Data was analyzed by Kruskal-Wallis Test and Spearman correlation coefficient besides descriptive statistics using the SPSS software.

3. Results and Discussion

From a total of 573 sampling units inspected using trapping (i.e., apartments, units, or housings), 39.3% (225 units) were infested with cockroaches. The results show that 37, 59, 26, 18, and 12% of the sampling units in the surveyed dormitories, hospitals, housing building complexes, official places, and hotel, respectively, were infested with cockroaches (Table 1). Therefore, the hospitals showed the highest frequency of infested units via trap monitoring. Plumbing facilities (i.e., wash basin), heating source, and openings in the roof for 84, 43.5, and 21% of units (

units) at the hospitals, respectively, obtained from the questionnaire, could be detected as effective factors for survival of cockroach [28] which explained the high rate of infestation for the hospitals. A survey on 97 private houses throughout the city by means of questionnaires showed that 80% of residences complained of cockroach infestation. Therefore, survey by cockroach trap monitoring showed that all surveyed locations (22 areas) in this city were infested with cockroaches, although infestation rates varied throughout the urban communities.

From a total of 7251 cockroaches collected from 22 different locations of the city, five species of cockroaches had been identified. The German cockroach was the most abundant comprising 96.73% of all cockroaches trapped. The other identified species in order of abundance were the Turkestan cockroach (Blatta lateralis) (2.21%), the American cockroach (0.98%), the Brown-banded cockroach (Supella longipalpa) (0.07%), and the Oriental cockroach (0.01%). The recognized species are from two families: Blattidae (comprising B. orientalis, B. lateralis, and P. americana) and Blattellidae (comprising B. germanica and S. longipalpa). Hanafi-Bojd and Sadaghiani [25] previously reported four families from indoor and outdoor survey (Polyphagidae, Blattidae, Blattellidae, and Ectobiidae). However three species, the German, American, and Oriental cockroaches were reported as the most common species in Iran [25]. These species were detected in this study, although the Turkestan cockroach instead of the Oriental cockroach showed the third common species (for frequency of distribution and dispersion). Percentage frequency of the German cockroach in the five types of study locations (Table 1) shows the German cockroach was the most abundant in the dormitories (98%), housing (95%), and hospital (93%), respectively, compared to the other species. However, it was not seen in official places and hotels. Moreover, more than 80% of infested units (181 from 225 units; Table 1) were infested by the German cockroach (i.e., the highest frequency of dispersion among infested units). Therefore, surveyed dormitories showed the most diverse composition with all five species present and the most abundant for the German cockroach compared to the other study locations. Official places and hotels with the lowest infested units (18 and 12%, resp.) revealed the least varied for cockroach species and least abundant for the German cockroaches. However, more official buildings and hotel units need to be surveyed to substantiate the findings.

Sizeable German cockroach trap count was detected for four study locations (Table 2). The expression of the distribution of German cockroach populations in space at four locations based on the formula of the variance to mean ratio ([

] for uniform [ ] for random, and [

] for clumped) [29] was clumped, although for the hospitals this ratio was near to random (Table 2). This index is important because it is consistent from year to year for each species [29]. The German cockroach is known as domestic cockroach and lives in groups (semisocial insect), and they are rarely dispersed throughout a building [30, 31]. Thus clumped distribution for these species is expected. Cockroach infestation rates for hospital and residential building show lower mean than girls’ and boys’ dormitories, although there was no significant difference (

) between mean of cockroach infestation rates for four surveyed locations (Kruskal-Wallis Test; chi-square = 1.352, d.f = 3, and ).

Study locations Number of
surveyed units
Frequency of infested units Mean of infestation rate (per trap/unit)* Variance
/mean ratio
Girls’ dormitory 53 72% 15.90 18.75
Boys’ dormitory 72 72% 16.96 34.87
Residential building 25 60% 7.73 7.39
Hospital 101 61% 4.02 1.36

For infested units.

Some factors affecting the estimating of cockroach population in an urban community were surveyed. Survey on infestation rates (German cockroach infestation) for the units (72 units at four locations) which were located on different floors showed the number of floors (i.e., distance of apartment from ground) did not significantly affect cockroach trap counts (

). Moreover, there was no significant difference in cockroach infestation rates between floors of these buildings (Kruskal-Wallis Test; chi-square = 7.636, d.f = 4, and ) (Table 3). Additionally the variance of the population was positively correlated with elevation of the floors (the highest floor with the biggest variance; Table 3), and this correlation was significant (

). Paige [32] reported strong population fluctuation of German cockroach was negatively correlated with barometric pressure. It can be deduced that the higher the floors of a building, the greater the cockroach population fluctuations. These observations will be useful when conducting survey of cockroach infestations in buildings with more than five floors high or in skyline structures.

Floor Mean N Std. deviation Variance
G 3.4450 4 1.07438 1.154
1 11.8731 25 13.11264 171.941
2 11.4316 29 15.25659 232.763
3 10.1000 10 9.08811 82.594
4 51.5000 4 46.56616 2168.407
Total 13.1823 72 18.52862 343.310

Eighty one percent of residents for three dormitories (comprising 116 units) said that their units were infested by cockroaches, although 53% of those units were detected as infested via cockroach trap monitoring. Actually residents reported 28% higher infestations of units than that determined from trap monitoring. This is probably due to the low tolerance of a considerable number of respondents towards cockroach, prompting to a questionably high incidence of infestation. Moreover, sensitivity of trapping method for clean level of infestation could be influenced by frequency of infestation, and those units with less than one cockroach per trap (nominated as clean level unit) reported as infested instead. Brenner et al. [33] reported different rates of cockroach prevalence for residential apartments from questionnaire and trapping. Agrawal and Tilak [34] reported more cockroach counts based on visual counts method compared to sticky trap method. However, the traps (baited with mouse pellets) were reported as a best way to determine cockroach infestation [35–37]. Only 4% of the occupants at the infested units did not notice any infestation. This could be attributed to these occupants being away from home. Moreover, survey on 348 study units of private houses, dormitories, and housing complex via questionnaires showed that residents for 72% of surveyed residential units admitted to cockroach infestation in their houses (Table 4). Comparison of this rate and total infestation report via trapping (39%) shows 33% reduction for clean level units (in agreement with previous report: 28% for the dormitories). Therefore, the determination of cockroach infested units is highly associated to the type of cockroach monitoring. Survey on 19 house kitchens of the dormitories via two approaches (visual and trap counts) showed that cockroach had been seen immediately once upon entry for 20% of infested kitchens. From 80% remaining kitchens, the cockroach had been seen visually in 8% of these places when the trash container was moved. Survey via sticky trap resulted in 21% high levels of infestation (≥26 cockroach per trap per kitchen) for the kitchens. This is close to the rate of visual survey (20%) even after moving the trash container (28%) in the kitchens. However, the greatest difference between methods is observed for the determination of very low levels of infestation. It shows a limitation for exact determination of infested sampling units.

Type of location Sampling units* Frequency of old ancient Pointed out to infestation of their units Encountered German cockroach size (≤1.5 cm) Pointed out to infestation initiated from more than 6 months ago
Dormitories 228 (153/228) 67% (107/149) 72% (80/150) 53%
Private houses 97 55 (57%) (78/97) 80% (45/77) 58% (52/75) 69%
Housing complex 23 (20/23) 87% (10/18) 56% (11/18) 61%
Total 348 55 (16%) (251/348) 72% (162/245) 66% (143/243) 59%

Unit or houses.

The other factor pointed as an effective factor on infestation is age of building. Only 16% of surveyed places were considered old (≥10 years old). All of these places were in the categories of private houses (Table 4). Surveys on the houses showed 85% of old houses versus 73% of new houses (46 versus 30 houses) were infested by cockroaches. Therefore, age of building could have an impact on infestation, although the correlation between the two factors was not significant based on 95% CI ( , ). Survey also showed 59% of infested units were infested more than six months prior to the survey (Table 2), suggesting infestation did not occur spontaneously and transient in nature.

The other factors that could affect trapping (and/or population monitoring) are attacks by other pests and damage to traps. Out of the 2113 inspection of cockroach traps in the surveyed dormitories throughout the programme, 7.8% of traps were found damaged. The most frequent cause of these damages (4.8%) was that the traps had been thrown out by residents. Although a briefing for occupants to accept and contribute to this programme led to reduction in trap disposition, a number of respondents were not comfortable with the image that their living or working place is infested with cockroaches. The incidences of damage by lizard (0.28%), ant (0.28%), and mice (0.24%) were low in this study, although for other countries, such as Malaysia, lizard (and also ant) could be the greatest cause of trap damages. Therefore incidence of trap damage can be associated with existing factors in the surveyed location.

The other effective factors on cockroach infestations are exclusion factors related to urban buildings. In this survey 35% of units (from 319 units) had opening in the wall or roof without screen. The frequency of this factor for infested units in three surveyed dormitories was 43% versus 33% for clean level units. However, there was no significant ( ) correlation between infestation and opening in the wall or roof.

Crack and crevices had been detected for 39% of units (from 306 units). Frequency of crack and crevices for infested units of three dormitories was 15% versus 27.5% for clean level units. However, there was no significant ( ) correlation between infestation levels and crack and crevices.

Survey on 19 kitchens of dormitories showed electric air fans (air conditioner fans) had been screened for 60% infested kitchens versus 25% clean level kitchens. There was a significant correlation ( , Spearman) between screened fans and infestation (

Cockroach infestation No. of units (%) Total
Fan without screen Screened fan
Clean level of infestation 1 (25.0%) 3 (75.0%) 4
Infested with cockroach 9 (60.0%) 6 (40.0%) 15
Total 10 (52.6%) 9 (47.4%) 19

Kitchen drains were not screened in 53% of infested kitchens versus 25% clean level kitchens in these dormitories. However, there was no significant correlation ( ) between infestation and unscreened drains.

Based on the residence opinions (survey on 283 residential units), the sources of cockroach infestation are the toilet (65.7%), kitchen (40.3%), rubbish containers (22.3%), and neighbors’ residence (21.6%) (Table 6). German cockroaches prefer dry habitats with a nearby water source such as kitchen and bathroom [38]. Stephan [39] reported 65% of the emigrants German cockroach came from adjoining kitchen areas. However, the American cockroach (with 0.6% frequency in the surveyed dormitories) prefers wet and moist locations such as sewers and toilet. Toilet and kitchen with high frequency of choice by respondents could be the main entrance-source of these species. However, the local name of cockroach in the research country is bath beetle which came first from the American cockroach and their harborage. This name may have misled some people to choose toilet as the highest incidence rate for the entrance-source. Therefore, the study shows that the viewpoints of the residents about the entrance-source and predominant species concur with the result from the cockroach trap counts. Seventy percent of occupants in the surveyed dormitories and housing complex (from 167 units; Table 4) encountered cockroaches with sizes less than 1.5 cm (the German cockroach size) close to the rate of the German cockroach-infested units of the same buildings detected via trapping (82% from 148 infested units; Table 1). However, incidence of infested units encountered by residents was 28% higher than that estimated from the cockroach traps counts exercise.

The entrance-source of cockroaches Toilet House kitchen Neighbours Rubbish containers N and T N and R T and R T and K N, T, and R N, T, and K T, K, and R N and K N, T, K, and R Others (yard or drainage) Did not know Total
Frequency 97 39 16 11 6 7 8 44 10 3 9 1 18 7 8 283*
Percentage 34.3 13.8 5.7 3.9 2.12 2.8 2.8 15.6 3.5 1.1 3.2 0.4 6.4 1.2 2.8 100

348 residents were questioned, although 81% of them had answer. T: toilet, K: kitchen, R: rubbish container, and N: neighbours.

In conclusion, more attention needs to be given to viewpoints of residents and factors affecting population (monitoring methods, damages, and exclusion) when conducting a survey on cockroach in urban communities.


The authors are grateful to Professor Dr. Dzolkhifli B. Omar, Prof. Dr. Yusof B. Ibrahim, Dr. Mohd Khadri Shahar, and Dr. Faizah Abood for technical help and their guidance for the duration of this project. They thank the Vice-Chancellor of Yasuj University of Medical Sciences, Yasuj University, Azad University, and Tarbiat Moallem University for their invaluable assistance for access to the study sampling units.


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Copyright © 2013 Gholam Hossein Shahraki et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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