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Survey of insect growth regulator (IGR) resistance in house flies (Musca domestica L.) from southwestern Turkey

2009; Wiley; Volume: 34; Issue: 2 Linguagem: Inglês

10.1111/j.1948-7134.2009.00042.x

1948-7134

Hüseyin Çetin, Fedai Erler, Atila Yanıkoğlu,

Insect behavior and control techniques

Insect growth regulators (IGRs) are currently the fastest-growing class of insecticides, and in Turkey these products represent a new approach to pest control. In recent years, several IGRs were also registered for the control of the house fly, Musca domestica L. (Diptera: Muscidae), in Turkey. A field survey was conducted in the summers of 2006 and 2007 to evaluate resistance to some agriculturally and medically used IGRs on house flies from livestock farms and garbage dumps in the greenhouse production areas (Merkez, Kumluca, Manavgat, and Serik) of Antalya province (Southwestern Turkey). The results of larval feeding assay with technical diflubenzuron, methoprene, novaluron, pyripoxyfen, and triflumuron indicate that low levels (RF<10-fold) of resistance to the IGRs exist in the house fly populations from Antalya province. Exceptions, however, were two populations, Guzoren and Toptas, from the Kumluca area which showed moderate resistance to diflubenzuron with 11.8-fold in 2006 and 13.2-fold in 2007, respectively. We found substantial variation in susceptibility of field-collected house fly populations from year to year and from product to product. We generally observed an increase in resistance at many localities sampled from 2006 to 2007. The implications of these results to the future use of IGRs for house fly control are discussed. It will be critically important to continue monitoring efforts so that appropriate steps can be taken if resistance levels start to increase. The house fly, Musca domestica L. (Diptera: Muscidae), is one of the most common flies where people gather for work and livelihood. It is a potential vector of more than 100 different disease organisms harmful to both humans and animals, including protozoans, bacteria, virus, and fungi (Greenberg 1973, Pandian and Asumtha 2001, Clavel et al. 2002, Rajendran and Pandian 2003). The diseases transmitted by Musca species, including M. domestica, can include enteric infections (such as dysentery, diarrhea, typhoid, cholera, and certain helminth infections), eye infections (such as trachoma and epidemic conjunctivitis), poliomyelitis, and certain skin infections (such as yaws, cutaneous diphtheria, some mycoses, and leprosy) (Greenberg 1973, Oliveira et al. 2006). Transmission takes place when the fly makes contact with people or their food (Pandian and Asumtha 2001). The control of house flies in Turkey generally depends on larvicide treatments of breeding places combined with strategic use of neurotoxic insecticides against adult house flies. Organophosphate and carbamate baits and non-persistent pyrethroid aerosol sprays are registered in Turkey for the latter use and are still effective against house flies. Over the last decade, there has been a growing realization that alternate methods to synthetic chemical control need to be considered. More recently, several insect growth regulators (IGRs) have been registered for use in house fly management programs and IGR-based larvicides are becoming more popular than the others. These include compounds that affect molting and metamorphosis by mimicking juvenile hormone (JH agonists) or usually antagonizing JH activity (ecdysteroid agonists), or with chitin synthesis inhibitors by interfering with cuticle formation (Smet et al. 1990, Oberlander et al. 1991, Oberlander et al. 1997). None of them is expected to have harmful effects on wildlife, humans, or the environment when used as specified on the product labels (Oberlander et al. 1997). In the last decade, the use of IGRs has also been one of the best alternatives to the conventional chemical insecticides used against many agricultural pests, especially greenhouse pests, in Turkey. Antalya (in southwestern Turkey) is the leading greenhouse production province with 53% of total greenhouse area in Turkey (Anonymous 2009). Its dominant position is explained by climatic factors and by technological and infrastructure advantages. Insecticide resistance is a major problem in control programs for medically and agriculturally important insects. The presence of widespread resistance results in the spread and increase of pesticide usage causing environmental and health problems. This also causes major problems for agricultural production and for the control of vector-borne diseases. Therefore, resistance management strategies should be developed in order to set a limitation on the usage of the same group of pesticides. Early detection of resistance is considered critical for the implementation of successful resistance management strategies (Leeper et al. 1986, Kristensen et al. 2001). Throughout the world, house flies have developed resistance to virtually every insecticide used against them and insecticide resistance in the house fly is a global problem (Harris et al. 1982, Georghiou and Mellon 1983, Scott et al. 1989, Kaufman et al. 2006, Deacutis et al. 2007, Acevedo et al. 2009). The evolution of resistance to IGR insecticides was not considered to be likely (Williams 1967). However, various studies have shown that resistance can evolve in response to this chemical group, especially if the selection pressure is sufficiently strong (Cerf and Georghiou 1972, Dyte 1972, Keiding et al. 1991, Keiding 1999). Regional assessment of susceptibility of local populations of M. domestica to different insecticides can yield information about house fly control programs that use suitable insecticides and can minimize insecticide resistance. Therefore, the aim of the present study was to survey the IGR resistance level of house fly populations from different localities in the greenhouse production areas of Merkez, Kumluca, Manavgat, and Serik located in Antalya province against some commonly used IGRs. The larvicides used in the bioassay were 20% diflubenzuron (Delphin SC; Belga Chem. Corp., Ankara, Turkey), 5% methoprene (Altosid SC; Biosav Chem. Corp., Ankara, Turkey), 10% novaluron (Oscar EC; Bayer, İstanbul, Turkey), 10% pyripoxyfen (Admiral EC; Sumitomo, Antalya, Turkey), and 48% triflumuron (Starcide SC; Bayer, İstanbul, Turkey). The concentrations used for bioassays were 0.001, 0.01, 0.1, 0.5, 1, 5, 10, 25, and 50 ppm, respectively. First, a stock solution at 100 ppm was prepared in distilled water for each larvicide, and then the lower concentrations were prepared by serial dilution of each stock solution. Field populations of house flies were collected by using sweep nets from livestock farms and garbage dumps in the greenhouse production areas of Merkez, Kumluca, Manavgat, and Serik in the summers of 2006 and 2007. In these areas, the IGR insecticides such as diflubenzuron, novaluron, pyripoxyfen, and triflumuron have been widely used for six to eight years against greenhouse pests and for two years against M. domestica. House fly adult samples were collected from five randomly selected localities in each of the areas: Topcular, Varsak, Yurtpinar, Kepez, and Ciglik in the center area of Antalya city (Merkez); Guzoren, Toptas, Kasapcayi, Haciveliler, and Kavak in the Kumluca area; Celtikci, Asagi isiklar, Merkez, Tasagil, and Colakli in the Manavgat area; and Cumali, Merkez, Gedik, Urundu, and Candir in the Serik area. The localities in each area were more than five km apart from each other and dispersal of house flies between the populations was not expected to occur. The collected flies were transported in fine muslin cages (24 × 24 × 36 cm) including cube sugar and wetted cotton pads to the Toxicology Laboratory within four to six h. One sample consisted of 200–400 house flies. The collected house flies were incubated for two h at 40° C to avoid possible entomopathogenic infections. The World Health Organization strain (WHOss) developed and maintained at the WHO Collaborating Laboratory at the Department of Biology, Akdeniz University, was used as the susceptible standard reference strain for bioassays. The females of field-collected house flies and the susceptible standard reference strain were allowed to lay eggs on cotton pads wetted with milk in the laboratory. Larvicide bioassays were performed with 24 to 36-h-old larvae. The bioassay test for the larvae involved feeding of larvicides carried out according to the method described by Kristensen and Jespersen (2003) and Cetin et al. (2006) with some modifications. To test the toxicity of larvicides, portions of artificial larval rearing medium (one portion: 400 g wheat bran, 10 g baker-yeast, 15 ml malt extract, 500 ml whole milk, and 500 ml water) were treated with different concentrations of each test larvicide. Twenty-five grams of medium were put in a container (100 ml polystyrene cups) and treated with 2.5 ml of water containing larvicide or water alone and then mixed into the medium with a glass spatula. Twenty-five 24 to 36-h-old larvae were placed in rearing containers. Four replicates of twenty-five larvae were used for each concentration level of each larvicide. The number of emerging flies was recorded during the three-week test period and observations continued until no live larvae were found. The larvicidal effect was determined as the percentage of emerging house flies on the basis of the number of introduced larvae. All larvicidal assays were made in triplicate for both field-collected strains and the susceptible standard reference strain. All tests were run at 12:12 (L:D) photoperiod, 60 ± 10% RH, and 26 ± 2° C. The full larvicidal bioassay was performed in triplicate at eight different concentrations (three times 25 larvae at each concentration of larvicide) and a control without larvicide to monitor background mortality. Resistance factor, RF, was calculated by division of the determined LC50 by the standard reference LC50 (Table 1). Percentage mortality observed in the control was subtracted from that observed in the treatments (Abbott 1925). The data are presented as an analysis of variance using the Duncan's Multiple Range Test (DMRT) (SPSS 10.0) at the P≤0.05 level of significance (SPSS 1999). The LC50 values were calculated using a probit analysis program (US EPA, 1999). The resistance factor values were categorized according to Rupes et al. (1976) into four groups: low (RF 160). Low levels (RF 0.05). The same capital letters on the bars showing the larvicides are not significantly different in 2007 (p>0.05). When the areas were compared in terms of mean RF values for each of the larvicides, the highest mean RF value for diflubenzuron was found in the Kumluca area followed by Serik, Manavgat, and Antalya-Merkez areas (Figure 2). In both years, there were no significant differences among the mean RF values for diflubenzuron in all the areas sampled. For novaluron, the highest mean RF value was observed in the Manavgat area in 2006 and in the Kumluca area in 2007. Except for the Kumluca area, no significant differences were found between the RF values for novaluron in both years. For triflumuron, the highest mean RF values were observed in the Kumluca area in both years. Except for this area, there were no significant differences between the RF values for triflumuron in all other areas. For methoprene and pyriproxyfen, the highest mean RF values were observed in the Kumluca area; however, there were no significant differences in all the areas sampled in terms of mean RF values in both years. Resistance ratios (RF) of house fly populations from the sampling areas of Antalya province to the insect growth regulating insecticides in 2006 and 2007. To improve the use of existing insecticides and delay the onset of resistance resulting in treatment failures, it is important to use regular surveys to establish the extent of insecticide resistance, even for species with an extensive resistance history. Regular surveys of resistance to insecticides of interest in relation to house fly control in Turkey have been carried out for many years by collecting urban larval house flies in various parts of the country and testing the resistance in the offspring. The insecticidal effect has usually been bioassayed by topical application with field strains of M. domestica and with a susceptible reference strain. House fly resistance has been previously reported in Turkey for organochlorine, organophosphate, carbamate, and pyrethroid insecticides, but so far there has been no report on IGR resistance in Turkish house fly populations (Taylor 1982, Sisli et al. 1983, Caglar 1991, Yamanel and Cakır 2004, Akiner and Caglar 2006). This study was the first to examine the IGR resistance of Turkish house fly populations. The IGR insecticides have been used for house fly control since 2004 and for greenhouse pest control since the late 1990s in Antalya province, and their usage today is more common than the other groups of insecticides. In this survey we found low levels (RF<10-fold) of resistance in field populations of M. domestica from southwestern Turkey (Antalya province) toward IGR insecticides, except for two populations, Guzoren and Toptas, from the Kumluca area which exhibited moderate resistance to diflubenzuron with 11.8-fold in 2006 and 13.2-fold in 2007, respectively. House flies collected in the second year of the study (2007) showed similar susceptibility to the IGRs tested, compared with the first year (2006). One exception was the Kumluca populations, which had a significantly higher RF value for novaluron in 2007 (3.84), relative to 2006 (0.61). This is consistent with the intensive use of IGR insecticides, especially those included in the present study, at this greenhouse production area starting in 1998 and may be an indication that IGR resistance is evolving at this area. Monitoring IGR resistance at this area should be given a priority. Unfortunately, because of financial limitations, the number of populations from this area that we were able to monitor was limited to five. Unlike our findings, Keiding (1999) reports that two IGRs, diflubenzuron and cyromazine, have been widely used since 1979 and 1988, respectively, for fly control on livestock farms in Denmark, either by direct application to breeding sites, manure, garbage, etc., or as an admixture in feed for poultry or pigs, and regularly monitoring of susceptibility to these IGRs has not shown indication of resistance development. However, there are reports showing that the use of the IGR insecticides, diflubenzuron and cyromazine, mixed into feed has resulted in the development of moderate to high resistance to these compounds, and subsequent complaints of control failure(s) in the U.S.A. and Japan (Iseki and Georghiou 1986, Bloomcamp et al. 1987, Shen and Plapp 1990). Resistance to diflubenzuron and cyromazine was also observed by Kristensen and Jespersen (2003) in a survey of resistance in Danish field populations of M. domestica. There is control failure for all other insecticides used for house fly control in Turkey, and many compounds are still being used by local authorities. Resistance is high and seems to be stable for these compounds (Sisli et al. 1983, Caglar 1991, Akiner and Caglar 2006). Although high resistance in adult flies to organophosphates and pyrethroids does not usually confer cross-resistance to the various IGRs (Keiding et al. 1991, Kristensen and Jespersen 2003), several studies report that there has been cross-resistance between organophosphorus compounds and some juvenile hormone mimics, e.g., methoprene (Cerf and Georghiou 1972, 1974). In that case, the use of conventional insecticides must be restricted before more serious problems occur. However, there is an urgent need for further monitoring and the establishment of more effective programs that cover all aspects of the resistance problem. The authors are thankful to the Scientific and Technological Research Council of Turkey (TÜBİTAK) and the Scientific Projects Administration Unit of Akdeniz University (Antalya, Turkey) for their financial support.