Introduction

Cockroaches are among the most common insects. They are found in nearly all parts of the world. The massive movement of people and supplies throughout the world has increased the possibility of introducing more pest cockroach species from other countries. Most of the major species are now found throughout the world wherever humans live. They are considered by some of the biologists to be one of the most adaptable and successful group of animals (Bennett et al. 1997).

Cockroaches are capable of transmitting many pathogens including bacteria, viruses, fungi, protozoa, and pathogenic helminthes that threaten human health. They act as potential transmitters of agents of bacterial diarrhea and nosocomial infection in hospitals (Agbodaze and Owusu 1989, Fotedar et al.1991, Vythilingam et al.1997). In addition, cockroaches not only spoil food but cause allergic reactions and psychological distress (Brenner1995).

Sanitation and good hygiene practices in homes and properties are essential for restricting cockroach populations, but when infestations become a problem there are no realistic alternatives to the use of insecticides. (Bennett et al 1997)

Low levels of sanitation and clutter provide more food, water, and harborages to cockroaches. These conditions favor the growth and survival of cockroach populations. Sanitation condition is correlated with cockroach populations (Wright 1979, Schal 1988).

Sanitation also is closely correlated to the control result because cockroaches can avoid contacting insecticide dust or spray or feeding on insecticide bait (Gupta et al. 1973, Schal 1988, Lee and Lee 2000).

Control of German cockroach by use of chemical insecticides has a long history going back to at least the early of this century (Mallis 1969).

The main insecticide groups that are currently being used for cockroach control are the organophosphates, carbamates and pyrethroids (Koehler and Patterson 1988, Reierson et al. 1988, Rust and Reierson 1978. Schal 1988). Chemicals in several other classes are also being used to a lesser extent (Fisher 1990).

In recent years, chemists have become increasingly aware of the fascinating versatility of boron compounds, some of them remarkably complex for inorganic compounds, and the wide range of their application in industry (Borax review 1988).

Boric acid is often recommended because of its low mammalian toxicity (Ebeling1975, Piper and Frankie 1978a, Slater et al. 1979).

Baits are starting to gain wide acceptance in the management of cockroaches (Reierson 1995). Gel bait formulation may be more effective than dry baits (Denzer et al. 1988).

Gel baits can be selectively used in sensitive areas, such as premises used for the preparation of food, hospitals and kindergartens (Benson and Zungoli, 1997).

Application of insecticidal baits is one of the most common and effective strategies for controlling the B. germanica (Reierson 1995, Bennett et al.1997). Toxic baits are commonly used in urban pest and management programs and provide several advantages over other insecticide application methods.

Since basic studies on the role of sanitation and other control measures in controlling cockroaches in Saudi Arabia are still lacking, and to date, no any study as such have been published. This study was conducted to evaluate the role of sanitation in the German cockroach program.

Materials and Methods

Study area and Duration

The study was carried out in a residential compound in an urban area at Al-Ajwad district in east of Jeddah city from September 2007 to January 2008.

Houses selected were similar in area (50 m² each). Each house had kitchen, hall, two rooms (bed and dinning), and bathroom.

Cockroach density was estimated in all houses of the compound. Of the 76 similar houses included initially, 48 had high cockroach infestation. Of these 28 houses were selected for sanitation and chemical  treatments by simple random sampling method. Seven treatments were applied and each treatment was replicated in four randomly selected houses.

Treatments applied were: sanitation, lambda-cyhalothrin 2.5% CS, boric acid dust, imidacloprid 2.15% gel bait, combination of sanitation and lambda-cyhalothrin 2.5% CS, combination of sanitation and boric acid dust, and combination of sanitation and imidacloprid 2.15% gel bait.

Residents cooperation

The individuals whose houses were selected for the seven control treatments were briefed about the study to get their full cooperation and participation. The precaution to be followed post-treatment in the treated houses were explained to the concerned residents and it was ensured that the same were complied with during the entire trial period.

Pre-treatment assessment in field

In every house included in the study, 5 sticky traps were placed around each of the usual harborages of cockroaches (stove, fridge, under the sink, bathroom, and dinning room). Traps were removed next morning to estimate the average cockroach density for every house.

Post-treatment density

Post-treatment density was assessed for every house by placing the sticky traps in the same cockroach harborages of pre-treatment. The assessment was done at two, four, eight and twelve weeks after application of control measures. The percentages reduction of cockroach infestation in the respective houses were calculated using the following formula:

Sanitation

Residents whose houses were selected for sanitation treatment were taught to thoroughly clean areas beneath cabinets, sinks, stoves, refrigerators, etc. as well as, cupboards, pantry shelves and food storage bins. Clean up spilled foods and liquids. They were asked to avoid leaving scraps of food on unwashed dishes and countertops overnight. In addition, they have been instructed to keep food in tightly sealed containers, rinse cans and bottles before putting in the trash, and transfer garbage outdoors every night into roach-proof receptacles away from the house.

Residents were briefed how to inspect for cockroaches and their egg cases in sacks, cartons, boxes, used appliances and furniture, etc., brought into the home, because infestations are usually initiated through the introduction of infested materials.

Some structural modifications such as caulking holes in walls where pipes pass through are necessary in the kitchen, bathroom, and other areas of the house were requested from the residents in houses selected for sanitation treatment in order to control German cockroaches.

Lambda-cyhalothrin 2.5% CS

The chemical used was Lambda-cyhalothrin 2.5% CS (Demand) in a form of Capsulated Suspension (CS), Syngenta, Switzerland.

Lambda-cyhalothrin 2.5% CS was applied at a rate of 50ml per 5 litre water.

The residents were required to empty all cabinets and closets. Once the residents had left the houses, a through insecticide treatment with Lambda-cyhalothrin 2.5% CS was applied with a  B&G sprayer system operated at 1.4 kg/cm2 (20psi) with a fan spray nozzle .

The spray was applied to areas around kitchen cabinets, closets, appliances, and toilet facilities and on all baseboards, door and window frames and moldings. In addition, insecticide was directed into cracks and crevices in the kitchen, dinning room, and bathroom, as well as, any additional areas of the house specified by the residents.

Boric acid dust

Chemical used was orthoboric acid dust 99.90% (H3BO3) min., produced by Inkobar Company, Peru.

Boric acid dust was applied lightly (thin layer), by using a hand duster in: cracks and crevices  of clothes closet shelves , hollow legs of chairs and tables, and wall or floor cracks and crevices throughout the house. Boric acid dust was lightly spread under the sink, in the dead space between the sink and wall, and around utility pipes. Also along the back edges and in corners of shelves in cabinets, cupboards, under/behind the refrigerator, stove, into the opening where plumbing pipes enter walls (such as behind the shower and washing machine), into openings around drainpipes and electrical conduits.

Imidacloprid 2.15% gel bait

Chemical used was Imidacloprid 2.15% gel bait, Bayer AG Leverkusen, Germany.

Imidacloprid 2.15% gel bait (single application at 0.1 gel spots of 2-3 per linear meter) was used in the selected houses at the primary harborages such as the cabinet, under the kitchen sink, and around the stove and refrigerator (Appel and Reid 1992, Lund and Bennett 1978).  In addition, gel spots were placed at floor–wall junctions, in corners, next to cracks and crevices (Ebeling et al.1966, Ebeling and Reierson 1974a, Ebeling 1991). Other treated sites included lower kitchen cupboards, upper kitchen cupboards, the infested sites and potential harborages in the bathrooms and dinning rooms.

Combination of sanitation and Lambda-cyhalothrin 2.5% CS, sanitation and boric acid dust and sanitation Imidacloprid gel

In the houses selected for the combination of sanitation and the three formulations, the residents were briefed about sanitation requirements daily needed in their houses as mentioned before. In addition, the three formulations were applied in the same manner as described previously.

Statistical analysis

Data was statistically analyzed by using SAS (2001) software program.

Results

The effect of sanitation on the population of Blattella  germanica:

The effect of sanitation on the population of B. germanica is presented in table (1) and Fig.(1). The statistical analysis indicated that there were no significant differences between all the post treatment cockroach counts when compared to the 24 hours pretreatment counts (P < 0.05). Similarly, when the post-treatments counts of the cockroaches were compared with each other they showed no significant differences among them (P < 0.05).

However, the percentages reduction of B. germanica over time when compared to the pretreatment counts (mean = 32.75) revealed that there was a gradual reduction in the population of B. germanica at week two, week four, and week eight, after treatment (32.8%, 69.5%, and 72.5% respectively), whereas the percentage reduction at week twelve after treatment declined to only 17.6% indicating an increase in the population of B. germanica at this period.

The best performance of sanitation was obtained at week eight after treatment.

Table 1: The effect of sanitation on Cockroach population.

*Number of cockroaches per house.

Means with the same letters are not significantly different

LSD = Least Significant Difference

Figure 1: The effect of sanitation on cockroach population.   Click here to View figure

The effect of sanitation when combined with lambda- cyhalothrin 2.5% CS on the population of Blattella  germanica 

Table (2) and fig (2). summarize the comparison between the efficacy of the liquid spray used alone and when combined with sanitation. At all the post-treatment counts the introduction of sanitation has increased the percentage reduction in the of the German cockroach population. The percentage reduction has increased in two weeks after application from 73% to 83.2%, in four weeks from 69.7% to 92% in eight weeks from 30.3 to 88.4% in twelve weeks from (-31.1) to 82.5% .

Counts of B. germanica when using sanitation with the liquid spray indicated a significant difference among the post treatments counts at the 4 intervals compared to the 24-hour pretreatment counts (P > 0.05).

The results indicated that sanitation has improved the performance of the spray formulation throughout the twelve weeks control period and the level of reduction in the cockroach population was always above 80% and no recovery of the suppressed cockroach population has occurred.

Table 2: The effect of sanitation on the performance of lambda-cyhalothrin.

*Number of cockroaches per house.

Means with the same letters are not significantly different

LSD = Least Significant Difference

Figure 2: The effect of sanitation on performance of Lambda-cyhalothrin.   Click here to View figure

The effect of sanitation on the performance of boric acid dust:

The results in table (3) and fig. (3) revealed no apparent difference between applying the boric acid alone or together with sanitation.

The trap catch of B. germanica showed a significant difference between    all the post-treatment counts when compared to the 24h pretreatment trap catch (P>  0.05).

However, when the post treatment counts were compared with each other, no significant difference was found (P < 0.05).

The higher percentage reduction in the post-treatment cockroach counts when compared with the pretreatment counts was 96.3 % reduction obtained at week four after treatment followed by week twelve (93.4%,), then week eight (92.6 %5), and finally week two with a 91.2%, reduction.

It also worth mentioning that the percentage reduction post-treatment remained almost stable above 90% level throughout the twelve weeks.

Table 3: The effect of sanitation on the performance of boric acid dust .  

 *Number of cockroaches per house.

Means with the same letters are not significantly different

LSD = Least Significant Difference

Figure 3: The effect of sanitation on the performance of boric acid.   Click here to View figure

The effect of sanitation on performance of Imidacloprid gel bait

The results in table (4) and fig. (4) indicated that throughout the experiment, the combination of sanitation and the gel gave better reduction percentages than when using the gel alone.

A significant reduction in B. germanica population was obtained at all the post-treatment counts at the different intervals when compared to the 24h pretreatment counts (P > 0.05). Nonetheless, the four post-treatment counts of cockroaches when compared to each other reflected no significant difference (P < 0.05).

The best performance of (sanitation + Imidacloprid 2.15% gel bait) when compared to pretreatment counts was obtained at week four with (99.3. %) reduction in population counts, then week eight (97.8%), followed by week two (95.6%), and finally week twelve when the reduction fell to only (77%).

Sanitation enhanced the efficacy of the gel and reduced the population recovery observed when applying the gel alone.

Table 4: The effect of Sanitation on performance of Imidacloprid gel.

 *Number of cockroaches per house.

Means with the same letters are not significantly different

LSD = Least Significant Difference

Figure 4: The effect of Sanitation on performance of Imidacloprid gel.   Click here to View figure

Discussion

When conducting control measures against German cockroaches, the houses having high infestation were found to be poor in environmental sanitation. The common hiding places in the study areas were stoves, refrigerators, under the sinks, under cabinets, washing machines, and water pipes.

The infestation in the houses was primarily of German cockroach Blattella germanica.

The results of the effect of sanitation singly on the population of German cockroach indicated no significant effect throughout the experiment period. (table 1 and Fig.1).

This could be due to the fact that sanitation has more effect on preventing establishment of infestations than in reducing existing populations. When the cleanliness is improved, there it may not be drastic effect on the existing cockroaches because they will continue to live for a considerable period of time. It may therefore be more appropriate to say that the role of sanitation is to limit rather than control infestations (Milligan 1984).

Lee and Lee (2000) also found that sanitation has been shown not to have a direct relationship with the level of domiciliary cockroach infestation in Malaysia.

An obstacle in the utilization of sanitation is the difficulty in establishing acceptable sanitary standards. Residents cannot be asked to keep their premises “clean” since this word is interpreted differently by each person. Which areas to clean and how often must be clearly laid out. Bennett (1978) reported criteria for rating sanitation of residences; however, the values of his categories are greatly diminished by their subjectivity (Milligan 1984).

The results of sanitation seen in treated houses in Jeddah province are similar to those of Owens (1980) who used commercial services to increase the sanitary level of apartments, but was unable to reduce the population levels significantly. Results are also similar to those obtained by Milligan (1984).

The reason for that can be explained by the fact that virtually no situation exists indoor where cockroaches food in some form is not available (Marsh and Bertholf 1986). Therefore, proper storage of food and sanitation in kitchens and bathrooms will not starve cockroaches.

Once German cockroach populations are established, it can be impossible to reduce the population by sanitation alone (Owens 1980; Bertholf 1983). Other control methods must be integrated into the control program for significant population reduction.

The use of Lambda- cyhalothrin 2.5% CS singly to control German cockroach in this study did not result in a significant reduction of the insect populations. The best performance of the chemical was noticed at week two which may be due to the fast knockdown effect of the liquid formulation (table 2). At week twelve, the cockroach population witnessed more than 30% increase indicating a recovery of the suppressed population even more than the respective pretreatment levels.

The relatively low percent reduction in German cockroach populations through the 12 weeks of this study is similar to other control failures in some field population that have been reported by Cochran1989, Scott et al. 1990, Atkinson et al.1991, Valles and Yu 1996, Dong et al. 1998, Valles 1999, Valles et al. 2000, Wei et al. 2001.

Vythilingam et al. (1997) carried out Control measures using lambda cyhalothrin against American cockroach (Periplaneta americana) and Smoky brown cockroach (Periplaneta brunnea) found that there was no significant difference between treated and control sites.

In this study, boric acid significantly reduced the population of  the German cockroach throughout the twelve weeks, and the higher percentage reduction was obtained at week two post-treatment (96.5 %,), (table 3). This may be explained by the fact that there were more cockroaches that encountered the dust in the treated areas (the mean of the pretreatment cockroach counts were 43.75) resulted in more cockroaches being affected and died by the insecticide at this period. While the percentages reduction achieved at week four were (88.1%), week eight (92.3%), and week twelve (94.4%) indicating a gradual suppression in the cockroach population towards the end of the experiment (Fig.3). In addition, it suggests the long residual effects of boric acid over time.

The results of the combination between sanitation and lambda- cyhalothrin 2.5% CS in table (2), and Fig.(2) indicated that sanitation has improved the performance of the spray formulation throughout the twelve weeks control period and the level of reduction in the cockroach population was always above 80% .

Similarly, sanitation enhanced the efficacy of the imidacloprid gel and reduced the population recovery observed when applying the gel alone (table 4 and Fig 4).

When applying boric acid dust singly or in combination with sanitation, it was observed that the percentage reduction post-treatment remained almost stable above 90% level throughout the twelve weeks (Fig.3and table 3).

When sanitation is integrated with other control strategies, such as residual treatments and baits, cockroaches are more likely to contact insecticide residues since they have to spend more time foraging for food and water (Schal and Hamilton 1990). In addition, Schal (1988) found greater efficacy of the pyrethroid cypermethrin in clean rather than cluttered, greasy apartments.

An important factor that has been reported to affect bait performance against German cockroaches in the field is sanitation (Christensen 1991).

Lee and Lee (2000) reported that chlorpyriphos bait stations placed in houses with moderate and poor sanitary conditions generally took longer to achieve the level of effectiveness that was observed in houses with good sanitary conditions.

This may indicate that cockroaches in houses with these conditions took a longer time to locate the baits due to availability of competitive food. These data suggest that sanitation affected the effectiveness of baits in the field.

As the cockroach forages for food materials solely by chance (Reierson 1995), the presence of food debris and other clutter in houses with moderate and poor sanitary conditions is a competing factor to the attractiveness of bait material. In addition, under good sanitary conditions, cockroaches may be stressed with starvation and dehydration due to lack of food and water sources. This might encourage cockroach foraging and dispersal (Bertholf 1983) and thus the chance of cockroaches coming into contact with the bait will increase. Furthermore, under starved conditions, cockroaches become more susceptible to insecticide action (Lee et al. 1996b, Lee and Heng 2000).

Good sanitation practice is essential for better control of cockroaches using baiting and other application methods (Lee and Lee 2000).

Gupta et al. (1973, 1975) reported that insecticide applications (spraying and dusting) were more effective against German cockroaches in apartments with better sanitation. Lee (1998) also emphasized the importance of good sanitation when baiting against insecticide-resistant German cockroaches in food-outlets.

Conclusion

This study has successfully demonstrated that sanitation influenced the performance of other control strategies, such as residual treatments and baits, by significantly enhance the performance of those control measures. Therefore, it is highly recommended when applying the different control measures against German cockroach to include sanitation practices in order to obtain best results.

Boric acid proved to have an excellent efficacy on the cockroaches, and all treatments including this chemical gave a highly significant suppression of the cockroaches over a longer period of time. It is therefore, recommended to be used in any control programs against cockroaches.

This study demonstrated clearly that combinations of more than one control method against German cockroach are more effective and better than using a single one.

References

1.  Agbodaze, D., and Owusu, S.B. (1989). Cockroaches (Periplaneta americana ) as carriers of agents of bacterial diarrhoea in Accra , Ghana. Cent. Afr. J. Med. 35: 484 – 486.
2. Appel, A.G., and Reid B.L. (1992). Sampling German cockroach field populations: theory, reliability, and analysis, pp. 51-65. In Proc. Nat. Conf. Urban Entomol. University of Maryland, College Park, MD.
3. Atkinson,T.H., WadleighR.W., Koehler P.G., and Patterson, R.S. (1991). Pyerthroid resistance and synergism in a field strain of the German cockroach (Dictyoptera: Blattellidae). J Econ Entomol. 84: 1247-1250.
4. Bennett, G.W. (1978). Evaluating pesticides in urban environment. Chem. Times and Trends 2:55-61.
5. Bennett, G.W., Owens, J.M., and Corrigan, R.M. (1997). Truman’s Scientific Guide to Pest Control Operations. 5^th Edition, p.119 -143.
6. Benson, E. P., Zungoli, P.A. (1997). In Mallis A, Handbook of pest control ,8^th ed. Mallis Handbook & Technical Training Company; 1997 p. 123-202.
7. Bertholf, J.K. (1983). The influence of sanitation on German cockroach populations. PhD. Dissertation. Purdue University, Indiana, U.S.A. 71 pp.
8. Borax  Review ( 1988). Current status and likely future developments of boron compounds . Borax Holdings Ltd.., London: U.S. Borax, Los Angelos, No. 4, 20pp.
9. Brenner, R. (1995). Economics and medical importance of German cockroaches. In: Rust MK, Owens JM, Reierson DA. { edt.}, Understanding and controlling of the German cockroach. Oxford University Press, New York. Pp. 77-92.
10. Christensen, C. ( 1991).Cockroach baits. Pest Cont. Technol. 19: 45-47, 50-51.
11. Cochran, D.G. (1989). Monitoring for insecticide resistance in field-collected strains of the German cockroach (Dictyoptera: Blattellidae). J Econ Entomol. 1989; 81: 536-44.
12. Denzer, D.J., Fuchs, M.E.A., and Stein, G. (1988). Zum verhalten von Blattella germanica L. aktionstradius  and refugientreue. (Behaviour study on : radius of action and loyalty to the refuge). J. Appl. Ent. 105: 330-343. (German with English summary).
13. Dong, K.,Valles, S.M., Scharf, M.E, Zeichner B., and Bennett, G.W.(1998). The knockdown resistance (nkr) mutation in pyrethroid-resistant German cockroaches. Pest Biochem. Physio. 60: 195-204.
14. Ebeling, W. (1975). Urban Entomology. Univ. Calif., Div. Agr. Sci. Berkeley, CA.
15. Ebeling, W.(1991). Ecological and behavioral aspects of cockroach management. In Ecology and Management of food-industry Pests , (J.R. Gorham, Ed.), pp. 85-119. Assoc. Official Analt. Chemists, Arlington, VA.
16. Ebeling, W. and Reierson, D.A. (1974a). Bait trapping silverfish, cockroaches, and earwigs. Pest Contr. 42(4): 24, 36-39.
17. Ebeling, W., Wagner, R.E., and Reierson, D. A. (1966). Influence of repellency on the efficacy of Blatticides 1. Learned modification of behavior of the German cockroach. J. Econ. Ent. 59, 1374-1388.
18. Fisher, T. (1990). Survey of pesticide use and efficacy of cockroach control. Pest Manage. 9(6), 22.
19. Fotedar, R., Shriniwas, U.B., and Verma,A. (1991). Cockroaches (Blattella germanica ) as carriers of microorganisms of medical importance in hospitals. Epidemiol.Infect. 107: 181-187.
20. Gupta,A.P., Das, Y.T., Trout, J.R., Gusciora, W.R., Adam, D.S., and Bordash, G.J., (1973). Effectiveness of spray-dust-bait combination and the importance of sanitation in the control of German cockroaches in an inner-city area. Pest Contr. 41(9), 20-26, 58-62.
21. Gupta, A.P., Das, Y.T., Gusciora, W.R., Adam, D.S., and Jangowsky, L. (1975). Effectiveness of 3 spray-dust combinations and the significance of “correction treatment” and community education in the control of German cockroaches in an inner-city area. Pest Contr. 43(7), 28-33.
22. Koehler, P.G., and Patterson, R.S. (1988). Suppression of German cockroach( Orthoptera: Blattellidae) populations with cypermethrin and two chlorpyrifos formulations. J. Econ, Ent. 81, 845-849.
23. Lee, C.Y. (1998). Control of insecticide-resistant German cockroach Blattella germanica L. (Dictyoptera: Blattellidae) in food-outlets with hydramethylnon-based bait stations.  Trop. Biomed. 15: 45-51.
24. Lee, C.Y., and Heng, C.Y. (2000). Effects of food and water deprivation on nymphal development , fecundityand insecticide susceptibility of German cockroach Blattella germanica (Dictyoptera: Blattellidae). Trop. Biomed. : In press.
25. Lee, C.Y., and Lee, L.C. (2000). Influence of sanitary conditions on the field performance of chlorpyrifos-based baits against American cockroaches, Periplaneta americana (L.) (Dictyoptera: Blattidae). J Vector Ecol. 2000 Dec; 25(2):218-21.
26. Lee, C.Y., Yap, H.H., and Chong N.L. (1996b). Insecticide toxicity on the adult German cockroach Blattella germanica L. (Dictyoptera: Blattellidae). Malay. J. Sci. 17A: 1-7.
27. Lund, R.D. and  Bennett, G.W. (1978). Evaluation of Blot roach bait, 1977. Insectic. Acar. Test3, 176-177.
28. Mallis, A. (1969). Handbook of pest control, 5^th Ed. MacNair-Dorland Co., NY.
29. Marsh,B.T., and Bertholf, J.K. (1986). Importance of sanitation. In advances in Urban Pest Management, (G.W. Bennett and Owens, J.M. Eds.). pp. 51- 68. Van Nostrand Reinhold , NY.
30. Milligan, B.(1984).  Integrated management of German cockroaches in rental housing. Msc. Thesis.  Department of biological sciences, Simon Fraser University. April 1984.
31. Owens, J.M. (1980). Some aspects of German cockroach population ecology in urban apartment . PhD. Thesis, Purdue University.
32. Piper, G. L., and Frankie G. w. (1978a). Integrated management of urban cockroach population. Final report . U. S, Environmental Protection Agency. Washington, D. C.
33. Reierson, D.A. (1995). Baits for German cockroach control. In: Rust, M.K., Owens, J.M., and Reierson, D.A., Understanding and controlling the German cockroach. Oxford: Oxford University Press, 1995; 231-265 pp.
34. Reierson, D.A., Rust, M.K., Slater, A.J, and Slater, T.A.M.(1988). Insecticide resistance affects cockroach control. Calif. Agric. 42(5), 18-20.
35. Rust, M.K., and Reierson, D.A. (1978). Comparison of the laboratory and field efficacy of insecticides used for German cockroach control.  J Econ Ent. 71, 704-708.
36. SAS (2001). Sas System for windows. Sas Institute, Inc., Cary.NC., USA.
37. Schal, C. (1988). Relation among efficacy of insecticides, resistance levels, and sanitation in the control of the German cockroach (Dictyoptera: Blattellidae). J Econ Entomol. 1988 ;81:536-44.
38. Schal, C. and Hamilton, R.L. (1990). Integrated suppression of synanthropic cockroaches. Ann. R. Entom. 35, 521-551.
39. Scott, J.G., Cochran, D.G., and Siegfried B.D. (1990). Insecticide toxicity, synergism and resistance to in the German cockroaches (Dictyoptera: Blattellidae). J Econ Entomol. 83, 1698-1703.
40. Slater, A.J., Mclntosh, L., Coleman, R.B., and Hulbert, L..(1979). German cockroach management in student housing.  J.Envir. Hea.42, 21-24.
41. Valles, S.M. (1999). K-cyhalothrin-resistance detection in the German cockroach (Blattodea: Blattellidae). J Econ Entomol.92: 293-297.
42. Valles, S.M., and Yu, S.J. (1996). Detection and biochemical characterization of insecticide resistance in the German cockroach (Dictyoptera: Blatellidae). J Econ Entomol. 89, 21-26.
43. Valles, S.M. Dong, K., and Brenner, R.J. (2000). Mechanisms responsible for cypermethrin resistance in a strain of German cockroach Blattella germanica. Pestic Biochem Physiol. 66: 195-205.
44. Vythilingam, I., Jeffery, j., Oothuman, P., Abdulrazak, A. R and Suilman, A. (1997). Cockroaches  from human dwellings: isolation of bacterial pathogens and control . Southeast Asian J. Trop. Med. Pub. Hlth. 1997 Mar 28: (1) 218- 222.
45. Wei, Y., Appel , A.G., Moar, W.J.,Liu, N. ( 2001).Pyrethroid resistance and cross-resistance in the German cockroach Blattella germanica L. Pest Manage. Sci. 2001; 57(11): 1055-9.
46. Wright C. G. (1979). Survey confirms correlation between sanitation and cockroach populations. Pest Contr. 47(9), 28.