Insecticide use and organophosphate resistance in the coffee leaf miner Leucoptera coffeella (Lepidoptera: Lyonetiidae)

Increasing rates of insecticide use against the coffee leaf minerLeucoptera coffeella(Guérin-Méneville) and field reports on insecticide resistance led to an investigation of the possible occurrence of resistance of this species to some of the oldest insecticides used against it in Brazil: chlorpyrifos, disulfoton, ethion and methyl parathion. Insect populations were collected from ten sites in the state of Minas Gerais, Brazil and these populations were subjected to discriminating concentrations established from insecticide LC99s estimated for a susceptible standard population. Eight of the field-collected populations showed resistance to disulfoton, five showed resistance to ethion, four showed resistance to methyl parathion, and one showed resistance to chlorpyrifos. The frequency of resistant individuals in each population ranged from 10 to 93% for disulfoton, 53 to 75% for ethion, 23 to 76% for methyl parathion, and the frequency of resistant individuals in the chlorpyrifos resistant population was 35%. A higher frequency of individuals resistant to chlorpyrifos, disulfoton and ethion was associated with greater use of insecticides, especially other organophosphates. This finding suggests that cross-selection, mainly between organophosphates, played a major role in the evolution of insecticide resistance in Brazilian populations of L. coffeella. Results from insecticide bioassays with synergists (diethyl maleate, piperonyl butoxide and triphenyl phosphate) suggested that cytochrome P450-dependent monooxygenases may play a major role in resistance with minor involvement of esterases and glutathione S-transferases.     

Asymmetry – where evolutionary and developmental genetics meet

The mechanisms responsible for the fine tuning of development, where the wildtype phenotype is reproduced with high fidelity, are not well understood. The difficulty in approaching this problem is the identification of mutant phenotypes indicative of a defect in these fine-tuning control mechanisms. Evolutionary biologists have used asymmetry as a measure of developmental homeostasis. The rationale for this was that, since the same genome controls the development of the left and right sides of a bilaterally symmetrical organism, departures from symmetry can be used to measure genetic or environmental perturbations. This paper examines the relationship between asymmtry and resistance to organophosphorous insecticides in the Australian sheep blowfly, Lucilia cuprina. A resistance gene, Rop-1, which encodes a carboxylesterase enzyme, also confers a significant increase in asymmetry. Continued exposure of resistant populations to insecticide has selected a dominant suppressor of the asymmetry phenotype. Genetic evidence indicates that the modifier is the L. cuprina Notch homologue.     

High levels of insecticide resistance in introduced horn fly (Diptera: Muscidae) populations and implications for management

The horn fly, Haematobia irritans (L.) (Diptera: Muscidae), was introduced to Chile in the beginning of the 1990s. Since its introduction, farmers have controlled this pest almost exclusively with insecticides. To understand the consequences of different control strategies on the development of insecticide resistance and their persistence, a field survey was conducted at eight farms in the south of Chile to characterize insecticide resistance in field populations and resistance mechanisms. Horn fly samples were assayed to determine levels of resistance to pyrethroids and diazinon, genotyped for kdr and HialphaE7 mutations, and tested for general esterase activity. All field populations, including ones that were not treated with insecticides for the past 5 yr, showed high levels of cypermethrin resistance and high frequencies of the kdr mutation. None of the fly populations demonstrated resistance to diazinon and the HialphaE7 mutation was not detected in any of the fly samples. Esterase activities in all populations were comparable to those found in the susceptible reference strain. The findings of high frequencies of homozygous resistant and heterozygous individuals both in insecticide treated horn fly populations and in the untreated fly populations suggests complex interactions among field populations of the horn fly in Chile.     

Using Drosophila melanogaster to validate metabolism-based insecticide resistance from insect pests

Identifying molecular mechanisms of insecticide resistance is important for preserving insecticide efficacy, developing new insecticides and implementing insect control. The metabolic detoxification of insecticides is a widespread resistance mechanism. Enzymes with the potential to detoxify insecticides are commonly encoded by members of the large cytochrome P450, glutathione S-transferase and carboxylesterase gene families, all rapidly evolving in insects. Here, we demonstrate that the model insect Drosophila melanogaster is useful for functionally validating the role of metabolic enzymes in conferring metabolism-based insecticide resistance. Alleles of three well-characterized genes from different pest insects were expressed in transgenic D. melanogaster : a carboxylesterase gene (αE7) from the Australian sheep blowfly Lucilia cuprina, a glutathione S-transferase gene (GstE2) from the mosquito Anopheles gambiae and a cytochrome P450 gene (Cyp6cm1) from the whitefly Bemisia tabaci. For all genes, expression in D. melanogaster resulted in insecticide resistance phenotypes mirroring those observed in resistant populations of the pest species. Using D. melanogaster to assess the potential for novel metabolic resistance mechanisms to evolve in pest species is discussed.     

Selection of dieldrin-resistant strains of Lucilia cuprina (Diptera: Calliphoridae) after ethyl methanesulfonate mutagenesis of a susceptible strain.

After ethyl methanesulfonate (EMS) mutagenesis of a susceptible strain (SWT), selective screening of Lucilia cuprina (Wiedemann) resulted in four strains that were resistant to the insecticide dieldrin. Concentrations used for selection were greater than LC99 of susceptible phenotypes. No resistant variants were screened from the standard laboratory strain (SWT) not treated with EMS. The resistance phenotypes of the four resistant strains were similar to each other and to that of a field-selected resistant strain. The genetic basis of resistance is monogenic in all strains and the data are consistent with the same locus, Rdl, determining resistance status in each strain. The Rdl locus maps to chromosome V, approximately 3.5 map units distal to the Sut locus. Dieldrin resistance may be caused by less effective blocking of insect neuronal GABA receptors by the chemical in resistant strains. The data indicate that the evolution of resistance to an insecticide in the field may be constrained by a limited number of genetical and biochemical options if a monogenic response is selected for and that the spontaneous mutation rate to the Rdl allele is less than 1 in 10(6) in the laboratory.     

Plasma IP-10, apoptotic and angiogenic factors associated with fatal cerebral malaria in India

Background

Knowledge on insecticide resistance in target species is a basic requirement to guide insecticide use in malaria control programmes. Malaria transmission in the Mekong region is mainly concentrated in forested areas along the country borders, so that decisions on insecticide use should ideally be made at regional level. Consequently, cross-country monitoring of insecticide resistance is indispensable to acquire comparable baseline data on insecticide resistance.

Methods

A network for the monitoring of insecticide resistance, MALVECASIA, was set up in the Mekong region in order to assess the insecticide resistance status of the major malaria vectors in Cambodia, Laos, Thailand, and Vietnam. From 2003 till 2005, bioassays were performed on adult mosquitoes using the standard WHO susceptibility test with diagnostic concentrations of permethrin 0.75% and DDT 4%. Additional tests were done with pyrethroid insecticides applied by the different national malaria control programmes.

Results

Anopheles dirus s.s., the main vector in forested malaria foci, was susceptible to permethrin. However, in central Vietnam, it showed possible resistance to type II pyrethroids. In the Mekong delta, Anopheles epiroticus was highly resistant to all pyrethroid insecticides tested. It was susceptible to DDT, except near Ho Chi Minh City where it showed possible DDT resistance. In Vietnam, pyrethroid susceptible and tolerant Anopheles minimus s.l. populations were found, whereas An. minimus s.l. from Cambodia, Laos and Thailand were susceptible. Only two An. minimus s.l. populations showed DDT tolerance. Anopheles vagus was found resistant to DDT and to several pyrethroids in Vietnam and Cambodia.

Conclusion

This is the first large scale, cross-country survey of insecticide resistance in Anopheles species in the Mekong Region. A unique baseline data on insecticide resistance for the Mekong region is now available, which enables the follow-up of trends in susceptibility status in the region and which will serve as the basis for further resistance management. Large differences in insecticide resistance status were observed among species and countries. In Vietnam, insecticide resistance was mainly observed in low or transmission-free areas, hence an immediate change of malaria vector control strategy is not required. Though, resistance management is important because the risk of migration of mosquitoes carrying resistance genes from non-endemic to endemic areas. Moreover, trends in resistance status should be carefully monitored and the impact of existing vector control tools on resistant populations should be assessed.     

Insecticide resistance in populations of Tuta absoluta (Lepidoptera: Gelechiidae)

1 Control failures of insecticides used against the tomato leafminer Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in Brazil led to the investigation of the possible occurrence of resistance of this insect pest to abamectin, cartap, methamidophos and permethrin. 2 The insect populations were collected from seven sites in the states of Minas Gerais, Rio de Janeiro, and São Paulo. These populations were subjected to concentration–mortality bioassays using insecticide‐impregnated filter papers. 3 We were unable to obtain a single population which provided a susceptibility standard for all insecticides tested. Therefore, the resistance levels were estimated in relation to the most susceptible population to each insecticide. Resistance to abamectin and cartap were observed in all populations when compared with the susceptible standard population, with resistance ratios ranging from 5.2‐ to 9.4‐fold and from 2.2‐ to 21.9‐fold for abamectin and cartap, respectively. Resistance to permethrin was observed in five populations with resistance ratios ranging from 1.9‐ to 6.6‐fold, whereas resistance to methamidophos was observed in four populations with resistance ratios ranging from 2.6‐ to 4.2‐fold. 4 The long period and high frequency of use of these insecticides against this insect pest suggest that the evolution of insecticide resistance on them has been relatively slow. Alternatively, the phenomenon might be widespread among Brazilian populations of T. absoluta making the finding of suitable standard susceptible populations difficult and leading to an underestimation of the insecticide resistance levels in this pest. 5 Higher levels of resistance to abamectin, cartap and permethrin are correlated with greater use of these compounds by growers. This finding suggests that local variation in insecticide use was an important cause of variation in susceptibility.     

Enhanced activity of carbohydrate- and lipid-metabolizing enzymes in insecticide-resistant populations of the maize weevil, Sitophilus zeamais

Insecticide resistance is frequently associated with fitness disadvantages in the absence of insecticides. However, intense past selection with insecticides may allow the evolution of fitness modifier alleles that mitigate the cost of insecticide resistance and their consequent fitness disadvantages. Populations of Sitophilus zeamais with different levels of susceptibility to insecticides show differences in the accumulation and mobilization of energy reserves. These differences may allow S. zeamais to better withstand toxic compounds without reducing the beetles' reproductive fitness. Enzymatic assays with carbohydrate- and lipid-metabolizing enzymes were, therefore, carried out to test this hypothesis. Activity levels of trehalase, glycogen phosphorylase, lipase, glycosidase and amylase were determined in two insecticide-resistant populations showing (resistant cost) or not showing (resistant no-cost) associated fitness cost, and in an insecticide-susceptible population. Respirometry bioassays were also carried out with these weevil populations. The resistant no-cost population showed significantly higher body mass and respiration rate than the other two populations, which were similar. No significant differences in glycogen phosphorylase and glycosidase were observed among the populations. Among the enzymes studied, trehalase and lipase showed higher activity in the resistant cost population. The results obtained in the assays with amylase also indicate significant differences in activity among the populations, but with higher activity in the resistant no-cost population. The inverse activity trends of lipases and amylases in both resistant populations, one showing fitness disadvantage without insecticide exposure and the other not showing it, may underlay the mitigation of insecticide resistance physiological costs observed in the resistant no-cost population. The higher amylase activity observed in the resistant no-cost population may favor energy storage, preventing potential trade-offs between insecticide resistance mechanisms and basic physiological processes in this population, unlike what seems to take place in the resistant cost population.     

High levels of resistance to chlorantraniliprole evolved in field populations of Plutella xylostella

Chlorantraniliprole is the first commercial insecticide from a new class of chemistry, the anthranilic diamides. Chlorantraniliprole provides an effective alternative insecticide for control of Plutella xylostella (L.) populations resistant to other insecticides. Baseline susceptibility to chlorantraniliprole for P. xylostella was surveyed previously from 16 geographical populations sampled from China during 2008-2009, and the median lethal concentrations (LC50s) varied among populations from 1.8- to 8.9-fold higher than the LC50 of a susceptible strain (Roth). In the present work, 20 field populations of P. xylostella sampled in 2010-2011 from China were tested with laboratory bioassays to determine if resistance to chlorantraniliprole had evolved in the field. The LC50s of the 14 populations from northern China ranged from 1.7- to 5.4-fold compared with the LC50 of Roth, which indicates these populations remain reasonably susceptible to chlorantraniliprole. However, the LC50s of the six populations from southern China (Guangdong Province) were 2.6-, 12-, 18-, 81-, 140-, and 2,000-fold higher than the LC50 of Roth. The results showed that high levels of resistance to chlorantraniliprole had evolved in field populations from Guangdong Province of southern China. Intensive use and misuse of chlorantraniliprole may be responsible for the rapid evolution of high-level resistance in P. xylostella in this region. The implementation of resistance monitoring plans and resistance management strategies is urgently needed in China to preserve susceptibility to chlorantraniliprole in P. xylostella.     

湖北四个地区草地贪夜蛾田间种群的杀虫剂敏感性及靶标突变检测

【目的】测定湖北草地贪夜蛾田间种群对4种杀虫剂的敏感性,并对杀虫剂靶标Ace-1,VGSC和RyR的基因型和突变频率进行检测,以明确湖北草地贪夜蛾田间种群药剂敏感性现状,进而指导田间科学用药。【方法】采集湖北黄冈、武穴、咸宁和荆州4个地区玉米田中的草地贪夜蛾幼虫,采用浸叶法测定其对氯虫苯甲酰胺、乙基多杀菌素、茚虫威和甲维盐4种杀虫剂的敏感性;提取4个种群80头个体的单头总RNA合成cDNA,利用特异性引物进行PCR扩增,获得目的基因片段,根据序列比对和测序峰图分析,确定Ace-1,VGSC和RyR的基因型和靶标突变位点的突变频率。【结果】生测结果表明,湖北这4个田间种群的草地贪夜蛾幼虫对氯虫苯甲酰胺、乙基多杀菌素、茚虫威和甲维盐均比较敏感,敏感性从高到低依次为:甲维盐>乙基多杀菌素>氯虫苯甲酰胺>茚虫威。分子检测结果表明,湖北草地贪夜蛾这4个田间种群Ace-1基因在A201S, G227A和F290V位点均存在抗性杂合突变,且在F290V位点检测到抗性纯合突变,而VGSC和RyR两个基因均没有检测到靶标位点突变。【结论】湖北草地贪夜蛾4个田间种群对氯虫苯甲酰胺、乙基多...     

Interactions between Pesticide Genes: Model and Experiment

In response to years of intense selection pressure by organophosphate insecticides, several different insecticide resistance mechanisms have evolved in natural populations of the mosquito Culex pipiens. We examined interactions between two of the most important mechanisms using a four-compartment model of insecticide pharmacokinetics. The joint effect of different mechanisms of resistance can be expressed in terms of epistasis at the physiological level in this model. The type of epistasis predicted by the model depends on the particular physiological mechanisms of resistance involved. Resistance due to a reduced penetration of the insecticide combines multiplicatively with other resistance factors, but resistance due to detoxicative processes and to insensitivity of the target site combines additively. How the pattern of epistasis at the physiological level is translated into fitness epistasis in natural populations of this mosquito depends on the intensity and pattern of insecticide selection in the field.     

Cost and mitigation of insecticide resistance in the maize weevil, Sitophilus zeamais

Abstract.  A common assumption in models of insecticide resistance evolution is the association between resistance and fitness costs in the absence of insecticides. There is empirical evidence of such associations, but their physiological basis (and mitigation) is little investigated. Pyrethroid-resistant populations of the maize weevil Sitophilus zeamais (Coleoptera: Curculionidae) offer this opportunity. Pyrethroid resistance in this species was initially observed in five Brazilian states by 1995, but the phenomenon apparently decreased and did not spread to other regions, probably due to the occurrence of a fitness disadvantage in resistant individuals in the absence of insecticides. The present investigation aims to verify whether differences in respiration rate and fat body morphology are related to differences in rate of development in Brazilian populations of S. zeamais resistant to insecticides, and thereby provide evidence for the existence (or not) of a physiological fitness cost acting against insecticide resistance in maize weevils. This may occur due to a possible energy trade-off between insecticide resistance and other physiological processes associated with development and reproduction. To achieve this, studies of the rate of development, respiration and fat body cytomorphology are carried out in one insecticide-susceptible (from Sete Lagoas) and two resistant populations (from Jacarezinho and Juiz de Fora) of S. zeamais . The resistant population from Jacarezinho shows that higher body mass is associated with higher energy reserves (larger trophocyte area) for development and reproduction, as well as for insecticide resistance. However, the resistant population from Juiz de Fora does not appear to have large enough energy allocation for insecticide-resistance expression and development and/or reproductive performance, suggesting a trade-off between resistance and other life history traits.     

Insect growth regulator cross-resistance studies in field- and laboratory-selected strains of the Australian sheep blowfly, Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae)

Abstract Resistance to diflubenzuron in the Australian sheep blowfly, Lucilia cuprina , has rendered this insecticide incapable of preventing flystrike in sheep from a few districts in eastern Australia. Wool producers affected by this situation must find suitable alternatives to protect their flocks. Results of laboratory bioassays against one population demonstrated that, despite extremely high diflubenzuron resistance (Resistance Factor >791), it had only very low (2x) tolerance of cyromazine and dicyclanil. It is unlikely that this level of tolerance would have any practical impact on field control with either insecticide. Consequently, wool producers in districts where diflubenzuron-resistant flies are common can rotate insecticide treatment to either of these compounds to prevent flystrike in their flocks. However, unlike the highly diflubenzuron-resistant field strain, a laboratory strain selected for resistance to diflubenzuron (Resistance Factor = 617) was 10 times more resistant to dicyclanil than a susceptible strain but, like the field strain, was only two times more tolerant of cyromazine. Conversely, a field-derived strain selected in the laboratory for cyromazine resistance was 20 times more resistant to dicyclanil and 362 times more resistant to diflubenzuron than the reference susceptible strain.     

An aphid-dip bioassay to evaluate susceptibility of soybean aphid (Hemiptera: Aphididae) to pyrethroid, organophosphate, and neonicotinoid insecticides

Since the discovery of the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), in North America in 2000, chemical control has been the most effective method to manage aphid outbreaks. Increased insecticide use in soybean raises the possibility of developing insecticide resistance in soybean aphid, and monitoring insecticide susceptibility is essential to maintain pesticide tools. We developed a simple and reliable aphid-dip bioassay by using a tea strainer that resulted in -90% survival in controls. Using this technique, we tested susceptibility of a greenhouse strain of soybean aphid that has never been exposed to insecticides, and field-collected aphid strains from two counties in Michigan. Aphid susceptibility was tested for five insecticides by dipping groups of five aphids in each insecticide dose for 10 s. After 48 h, aphids were classified as dead or alive, and counted. Aphids from all strains were highly susceptible to chlorpyrifos, lambda-cyhalothrin, esfenvalerate, and dimethoate, with LC50 and LC90 values well below the recommended application rates. However, aphids showed less susceptibility after 48 h to neonicotinoid imidacloprid, with higher LC90s and wider fiducial limits. This illustrated the potential limitation of using a 48-h assay to evaluate insecticides with longer-term, sublethal impacts. Nevertheless, this study made use of a simple aphid-dip method to test and compare insecticide susceptibility of soybean aphid. In the event of a field failure, the aphid populations involved can be tested in comparison to a susceptible greenhouse strain to determine the extent of resistance development.     

Genetic basis of cross-resistance to three organophosphate insecticides in Drosophila melanogaster (Diptera: Drosophilidae)

To investigate the genetic basis of cross-resistance to insecticides, we conducted genetic analyses of resistance to three organophosphate insecticides, malathion, prothiophos, and fenitrothion. After isofemale lines resistant and susceptible to all of the three organophosphates had been screened from natural populations of Drosophila melanogaster (Meigen), chromosomal analyses were performed by using chromosome-substituted lines between the resistant and the susceptible lines. The chromosomal analyses revealed that both the second and the third chromosomes contributed to resistance to the organophosphates, suggesting that this resistant line possessed at least two factors for organophosphate resistance. However, the relative contribution of each chromosome was different in resistance to different organophosphates. We further carried out genetic mapping of a resistance factor for each organophosphate on each of the two chromosomes. Each resistance factor was mapped to the position of each chromosome, about II-62 and III-50. Results of the chromosomal analyses and the genetic mapping revealed that at least two resistance factors exhibiting different patterns of cross-resistance to the organophosphates existed within a natural population of D. melanogaster. Based on this research, genetic variation in insecticide resistance within natural populations and complex as well as simple aspects of the mechanism of cross-resistance are discussed.     

Phosphine resistance in Tribolium castaneum and Rhyzopertha dominica from stored wheat in Oklahoma

Phosphine gas, or hydrogen phosphide (PH3), is the most common insecticide applied to durable stored products worldwide and is routinely used in the United States for treatment of bulk-stored cereal grains and other durable stored products. Research from the late 1980s revealed low frequencies of resistance to various residual grain protectant insecticides and to phosphine in grain insect species collected in Oklahoma. The present work, which used the same previously established discriminating dose bioassays for phosphine toxicity as in the earlier study, evaluated adults of nine different populations of red flour beetle, Tribolium castaneum (Herbst), and five populations of lesser grain borer, Rhyzopertha dominica (F.) collected from different geographic locations in Oklahoma. One additional population for each species was a laboratory susceptible strain. Discriminating dose assays determined eight out of the nine T. castaneum populations, and all five populations of R. dominica, contained phosphine-resistant individuals, and highest resistance frequencies were 94 and 98%, respectively. Dose-response bioassays and logit analyses determined that LC99 values were approximately 3 ppm for susceptible and 377 ppm for resistant T. castaneum, and approximately 2 ppm for susceptible and 3,430 ppm for resistant R. dominica. The most resistant T. castaneum population was 119-fold more resistant than the susceptible strain and the most resistant R. dominica population was over 1,500-fold more resistant. Results suggest a substantial increase in phosphine resistance in these major stored-wheat pests in the past 21 yr, and these levels of resistance to phosphine approach those reported for other stored-grain pest species in other countries.     

Survey of susceptibilities to monosultap, triazophos, fipronil, and abamectin in Chilo suppressalis (Lepidoptera: Crambidae)

To provide a foundation for national resistance management of the Asiatic rice borer, Chilo suppressalis (Walker) (Lepidoptera: Crambidae), a study was carried out to determine dose-response and susceptibility changes over a 5-yr period in the insect from representative rice, Oryza sativa L., production regions. In total, 11 populations were collected from 2002 to 2006 in seven rice-growing provinces in China, and they were used to examine their susceptibility levels to monosultap, triazophos, fipronil, and abamectin. Results indicated that most populations had increased tolerance to monosultap. Several field populations, especially those in the southeastern Zhejiang Province, were highly or extremely highly resistant to triazophos (resistance ratio [RR] = 52.57-899.93-fold), and some populations in Anhui, Jiangsu, Shanghai, and the northern rice regions were susceptible or had a low level of resistance to triazophos (RR = 1.00-10.69). Results also showed that most field populations were susceptible to fipronil (RR < 3), but the populations from Ruian and Cangnan, Zhejiang, in 2006 showed moderate levels of resistance to fipronil (RR = 20.99-25.35). All 11 field populations collected in 2002-2006 were susceptible to abamectin (RR < 5). The tolerance levels in the rice stem borer exhibited an increasing trend (or with fluctuation) over a 5-yr period for different insecticides, and they reached a maximal level in 2006 for all four insecticides. Analysis of regional resistance ratios indicated that the history and intensity of insecticide application are the major driving forces for the resistance evolution in C. suppressalis. Strategic development of insecticide resistance management also is proposed.     

Patterns of insecticide resistance in larval Culex pipiens populations in Israel: dynamics and trends.

Resistance to insecticides of larval Culex pipiens populations in Israel has been monitored for ten years and the results were used for control planning. The insecticides tested were the organophosphates chlorpyrifos, fenthion, and temephos and the pyrethroids permethrin and cypermethrin. Over the years the relative resistance (R/R) values to chlorpyrifos in most populations tested were between 200-400, with records of up to 700 R/R. Practically no susceptible populations were found and the compound has been withdrawn from use, resulting in a decrease in the relative resistance values. In 1996 when fenthion was reintroduced, no resistant populations were found, but in the following years significant resistance appeared in an increasing number of populations with values lower than recorded for chlorpyrifos but still high (up to 100 R/R). All populations tested were found to be susceptible to temephos and accordingly the compound was reintroduced in 2002. Over the ten years, no significant resistance to cypermethrin was found in the majority of the populations tested, while a trend of increased resistance to permethrin was noted with a few records of >1000 R/R. The results demonstrate the importance of continuous monitoring of insecticide resistance for efficient mosquito control. Alternative insecticides and methods of control are discussed.