German cockroach resistance: Propoxur selection induces the same resistance spectrum as diazinon selection

A resistant laboratory strain of the German cockroach, Blattella germanica, was developed from a normal laboratory strain by selection with propoxur. Resistance to all insecticides except chlordane began increasing after 15 generations of selection and reached a plateau for most insecticides by generation 27. The resistant colony, designated B-strain, developed significant resistance to carbamates, organophosphorus compounds, pyrethrins and DDT, developed low resistance to gamma-BHC and no resistance to chlordane. The resistance spectrum, effect of synergists and inheritance of resistance of this propoxur resistant strain are similar to a diazinon resistant strain. Therefore, diazinon and propoxur may select for the same resistance mechanism(s) in this species. The practical implications of this research are discussed.     

Pyrethroid resistance and cross‐resistance in the German cockroach,Blattella germanica (L)

A German cockroach (Blatella germanica (L)) strain, Apyr‐R, was collected from Opelika, Alabama after control failures with pyrethroid insecticides. Levels of resistance to permethrin and deltamethrin in Apyr‐R (97‐ and 480‐fold, respectively, compared with a susceptible strain, ACY) were partially or mostly suppressed by piperonyl butoxide (PBO) and S,S,S,‐tributylphosphorotrithioate (DEF), suggesting that P450 monooxygenases and hydrolases are involved in resistance to these two pyrethroids in Apyr‐R. However, incomplete suppression of pyrethroid resistance with PBO and DEF implies that one or more additional mechanisms are involved in resistance. Injection, compared with topical application, resulted in 43‐ and 48‐fold increases in toxicity of permethrin in ACY and Apyr‐R, respectively. Similarly, injection increased the toxicity of deltamethrin 27‐fold in ACY and 28‐fold in Apyr‐R. These data indicate that cuticular penetration is one of the obstacles for the effectiveness of pyrethroids against German cockroaches. However, injection did not change the levels of resistance to either permethrin or deltamethrin, suggesting that a decrease in the rate of cuticular penetration may not play an important role in pyrethroid resistance in Apyr‐R. Apyr‐R showed cross‐resistance to imidacloprid, with a resistance ratio of 10. PBO treatment resulted in no significant change in the toxicity of imidacloprid, implying that P450 monooxygenase‐mediated detoxication is not the mechanism responsible for cross‐resistance. Apyr‐R showed no cross‐resistance to spinosad, although spinosad had relatively low toxicity to German cockroaches compared with other insecticides tested in this study. This result further confirmed that the mode of action of spinosad to insects is unique. Fipronil, a relatively new insecticide, was highly toxic to German cockroaches, and the multi‐resistance mechanisms in Apyr‐R did not confer significant cross‐resistance to this compound. Thus, we propose that fipronil could be a valuable tool in integrated resistance management of German cockroaches. © 2001 Society of Chemical Industry     

DDT-lipoprotein complex in the American cockroach hemolymph: A possible way of insecticide transport

The binding in vitro of ¹⁴C-DDT to proteins from the hemolymph of the American cockroach was shown by means of electrophoresis and isoelectric focusing on polyacrylamide gels. The study of ¹⁴C-DDT penetration into the insect implies the hemolymph as one of the possible manners by which this insecticide could penetrate the central nervous system, and other target organs. The possibility of DDT being transported by the hemolymph bound to lipoproteins is discussed.     

A patch—clamp study of the action of a nitromethylene heterocycle insecticide on cockroach neurones growing in vitro

The mode of action of a nitromethylene heterocycle (NMH) insecticide was studied by patch–clamp techniques using cockroach embryonic cultures as an experimental model. Under whole-cell recordings, this compound elicited inward currents resembling those induced by O-acetylcholine (ACh). The reversal potentials for both ACh and the NMH were similar, suggesting that the inward currents induced by both were carried by the same species of ion. Pharmacological investigations of NMH-induced responses revealed that the insecticidal action of this compound is exerted through agonistic action at the nicotinic acetylcholine receptor. Single-channel studies were also performed to study the interaction of NMH with the nicotinic-receptor-coupled ion channel.     

Fitness costs associated with insecticide resistance

Insects are exposed to a variety of stress factors in their environment, and, in many cases for insect pests to agriculture, those factors include toxic chemical insecticides. Coping with the toxicity of insecticides can be costly and requires energy and resource allocation for adaptation and survival. Several behavioural, physiological and genetic mechanisms are used by insects to handle toxic insecticides, sometimes leading to resistance by constitutive overexpression of detoxification enzymes or inducing mutations in the target sites. Such actions are costly and may affect reproduction, impair dispersal ability and have several other effects on the insect's fitness. Fitness costs resulting from resistance to insecticides has been reported in many insects from different orders, and several examples are given in this mini‐review. Copyright © 2012 Society of Chemical Industry     

Biochemistry of insecticide resistance

After briefly summarizing various resistance mechanisms and their effects on certain types of insecticides, attention is focused on gaps in the understanding of resistance. Most resistance mechanisms consist either of a change in sensitivity of the site of action or an increased capacity for detoxication. In both cases such changes could theoretically be due to quantitative changes of an enzyme (more sites of action or more detoxication enzyme) or to qualitative changes (less-sensitive site of action or more efficient detoxication enzyme). Examples have now been found for each of these possible causes of resistance to insecticides, except for an increased amount of sites of action. Whereas examples of the latter mechanism are known for cell lines resistant to anti-cancer chemicals, so far they have not been found in resistance to insecticides. The impact of the different mechanisms on development and stability of resistance is discussed.     

A review of the interactions between multiple insecticide resistance loci

Insecticide resistance is an ever escalating problem worldwide in many pest populations and numerous cases of insecticide resistance are polygenic. Therefore, it is important to investigate the types of interactions that occur between insecticide resistance loci as this will dictate the level of resistance (and effectiveness of a chemical control strategy). Interactions also play a role in the evolution and/or maintenance of multigenic resistance in the field. Given that a limited number of mechanisms confer resistance, it might be possible to establish general rules for interactions between mechanisms. Several variables might dictate the type of interaction, such as the nature of the resistance mechanisms, genotype, etc. Interactions can be synergistic, antagonistic or additive. Based on this literature review, the most common interaction of multiple homozygous resistance loci is synergistic and additive when loci are heterozygous. When one locus is homozygous and the other locus is heterozygous the most common interaction was synergistic, although very few studies have examined this type of interaction. Possible factors that drive these interactions, exceptions to the trends, and future research needs are discussed.     

Dynamics of insecticide resistance in Bemisia tabaci: a case study with the insect growth regulator pyriproxyfen

The dynamics of pyriproxyfen resistance in Bemisia tabaci (Gennadius) have been studied intensively in cotton fields and greenhouses in Israel. High resistance to pyriproxyfen evolved one year after its introduction for use on flowers in greenhouses, after three successive applications. After ten years of pyriproxyfen use in cotton fields, with only one application per season, a high level of resistance was observed, but its rate of development differed among localities. It is hypothesized that these differences reflect temporal and spatial variations in the availability of alternative host plants for B tabaci, and that pyriproxyfen resistance evolved most readily in geographically isolated areas. It is also likely that the occurrence and development of resistance is partially biotype-related. Pyriproxyfen use has ceased in high-resistance localities, but in areas with low frequencies of resistance, cotton growers have continued to achieve acceptable control of B tabaci with pyriproxyfen. Due to the absence of applications of pyriproxyfen in some cotton fields, resistance levels tended to decline between 1998 and 2001. Laboratory experiments support the hypothesis that this decline reflects, in part, fitness costs associated with pyriproxyfen resistance.     

A simple bioassay for detecting and characterising insecticide resistance

A simple and rapid paralysis assay was developed to detect and characterise knockdown resistance in larvae of the house fly and pink bollworm. Pyrethroidtreated larvae unable to perform a stereotypic curling movement when probed with a warm needle, 10 min (house fly) or 60 min (pink bollworm) after treatment, were considered to be paralysed. Responses in a susceptible strain of house fly were compared with those of the pyrethroid-resistant strains kdr and super-kdr. In this assay, the kdr strain displayed over 28 fold resistance to deltamethrin, and super-kdr larvae were unaffected by doses up to 100μg. These results are in good qualitative agreement with previous studies. The assay detected no significant fenvalerate resistance in pink bollworm larvae collected from the field; this was consistent with mortality bioassays performed on wild adult males. The limitations and potential utility of the paralysis bioassay in resistance screening are discussed.     

Climate change and the genetics of insecticide resistance

Changes in global temperature and humidity as a result of climate change are producing rapid evolutionary changes in many animal species, including agricultural pests and disease vectors, leading to changes in allele frequencies of genes involved in thermotolerance and desiccation resistance. As some of these genes have pleiotropic effects on insecticide resistance, climate change is likely to affect insecticide resistance in the field. In this review, we discuss how the interactions between adaptation to climate change and resistance to insecticides can affect insecticide resistance in the field using examples in phytophagous and hematophagous pest insects, focusing on the effects of increased temperature and increased aridity. We then use detailed genetic and mechanistic studies in the model insect, Drosophila melanogaster, to explain the mechanisms underlying this phenomenon. We suggest that tradeoffs or facilitation between adaptation to climate change and resistance to insecticides can alter insecticide resistance allele frequencies in the field. The dynamics of these interactions will need to be considered when managing agricultural pests and disease vectors in a changing climate. © 2019 Society of Chemical Industry     

不同抗旱性油菜种子萌发期抗旱指标比较研究

采用不同浓度(8%~25%)的PEG-6000高渗溶液,对田间表现为不同抗旱等级的5份油菜品种进行种子萌发期渗透胁迫试验,统计分析相对发芽率、相对根长和相对芽长3个指标的变化规律及其与材料萌发期抗旱性的关联度,筛选油菜萌发期的抗旱性鉴定指标。PEG-6000浓度为19%时,不同抗旱性材料的相对发芽率平均为60.6%,变异系数为51%,强抗旱材料达到90%以上。相对根长平均为57.3%,变异系数为17.9%,强抗旱材料达到70%以上。各材料间差异显著。相对发芽率、相对根长与材料萌发期抗旱性的相关度>0.9。相对发芽率、相对根长可作为油菜萌发期抗旱性鉴定的可靠指标。PEG-6000浓度为19%时,相对发芽率>90%、相对根长>70%的材料,可初步认定具有较强的抗旱性。     

Correlation of a resistance-associated Rdl mutation in the German cockroach, Blattella germanica (L), with persistent dieldrin resistance in two Danish field populations

Danish Blattella germanica (L) populations carry the resistance-associated mutation A302S within the Resistance to dieldrin (Rdl) gene. The mutation has remained in field populations long after the discontinuation of dieldrin for cockroach control. The mutation has also persisted in our laboratory strains with high and intermediate frequencies for more than 8 years without selection. The toxicity of dieldrin was tested by topical application to male cockroaches in the susceptible strain DPIL-SUS and two field strains, Zo960302 and Su960304, which were 1270- and 15-fold resistant to dieldrin at LD50. We report the sequencing of exon 7 of the B. germanica Rdl gene and the finding of the putative resistance-associated A302S mutation. We have developed and implemented a PCR-based diagnostic method with the detection of a restriction endonuclease polymorphism, which allows for easy discrimination of susceptible, resistant and heterozygote genotypes. The frequency of the resistance-associate allele A302S was 0.97 and 0.38 in the Zo960302 and Su960304 populations, respectively. The cockroach Rdl A302S allele confers high dieldrin resistance in homozygotes and intermediate resistance in heterozygotes, and its presence is responsible for the persisting dieldrin resistance in Danish populations of B. germanica.     

The role of behavior in insecticide resistance

Although behavioral resistance remains enigmatic, an examination of the literature firmly supports the existence of behavioral resistance in both the presence and absence of the better understood and accepted physiological and biochemical mechanisms. Studies of pyrethroid resistance in the horn fly and the tobacco budworm have identified several resistance mechanisms, including behavioral adaptations, in addition to target-site insensitivity and enhanced detoxification. The coexistence of physiological and behavioral responses neither precludes a common mechanism nor requires one. Even if a common mechanism such as knockdown resistance or enhanced detoxification is involved, this does not negate the survival benefit of either avoiding the toxicant or reducing movement to avoid exposure. Thus, behavioral resistance may be much more ubiquitous and important than previous interpretation of the literature suggests.     

二化螟对杀虫剂抗药性的研究进展

综述了国内外关于二化螟抗药性的研究成果,包括:二化螟的分布、危害、防治,抗药性产生和发展,抗药性机理,抗药性测定方法以及抗药性治理措施。     

Monitoring of insecticide resistance in damson hop aphid,Phorodon humuli Schrank (Hemiptera: Aphididae) from German hop gardens

The damson hop aphid, Phorodon humuli (Schrank) (Hemiptera: Aphididae), is one of the most important sucking pests of many hop-growing areas world-wide. In this study we determined the efficacy of several insecticides against strains collected throughout the year 2001. All strains were collected in different hop gardens in the Hallertau (Bavaria), Germany, the largest hop-growing area of the world. First of all we established a leaf dip bioassay, carried out using six-well tissue culture plates and appropriate for monitoring susceptibility against imidacloprid, oxydemeton-methyl, cyfluthrin, amitraz, pymetrozine and pirimicarb. Four of these compounds, imidacloprid, cyfluthrin, pymetrozine and amitraz, are currently registered for the control of sucking pests in German hop gardens and are useful against P. humuli. The leaf-dip bioassay system turned out to be very reliable and robust. Ten P. humuli strains were collected in May 2001 and maintained in the laboratory to assess their resistance to the different insecticides in comparison with two laboratory reference strains (H2 and H5). Using diagnostic concentrations, resistance monitoring for imidacloprid and cyfluthrin was investigated during July and August 2001 on 53 populations from 30 sites around the Hallertau, an area of ca 2500 km2. Resistance to diagnostic concentrations (LC95 for reference strains) of imidacloprid, amitraz and pymetrozine was not detected in any strain received in 2001, but late-season (August) populations seemed to respond more heterogeneously than those collected mid-season (July). Overall composite mean mortalities to diagnostic concentrations of imidacloprid (13 mg litre(-1)) in collections from May, July and August were 95 (+/-2.5), 98 (+/-2.3) and 87 (+/-5.9)%, respectively. Moderate resistance to pyrethroids was observed in all strains collected in May and August using a diagnostic concentrations of 10 mg litre(-1) cyfluthrin (LC95 of the susceptible reference strain H5). Slight to moderate resistance to diagnostic concentrations of oxydemeton-methyl and pirimicarb was observed in some, but not all, strains collected early season. The results are discussed in terms of the implemention of hop aphid resistance management strategies in German hop-cultivation areas.     

Homology modelling of Drosophila cytochrome P450 enzymes associated with insecticide resistance

BACKGROUND: Overexpression of the cytochrome P450 gene Cyp6g1 confers resistance against DDT and a broad range of other insecticides in Drosophila melanogaster Meig. In the absence of crystal structures of CYP6G1 or complexes with its substrates, structural studies rely on homology modelling and ligand docking to understand P450–substrate interactions. RESULTS: Homology models are presented for CYP6G1, a P450 associated with resistance to DDT and neonicotinoids, and two other enzymes associated with insecticide resistance in D. melanogaster, CYP12D1 and CYP6A2. The models are based on a template of the X‐ray structure of the phylogenetically related human CYP3A4, which is known for its broad substrate specificity. The model of CYP6G1 has a much smaller active site cavity than the template. The cavity is also ‘V’‐shaped and is lined with hydrophobic residues, showing high shape and chemical complementarity with the molecular characteristics of DDT. Comparison of the DDT–CYP6G1 complex and a non‐resistant CYP6A2 homology model implies that tight‐fit recognition of this insecticide is important in CYP6G1. The active site can accommodate differently shaped substrates ranging from imidacloprid to malathion but not the pyrethroids permethrin and cyfluthrin. CONCLUSION: The CYP6G1, CYP12D1 and CYP6A2 homology models can provide a structural insight into insecticide resistance in flies overexpressing P450 enzymes with broad substrate specificities. Copyright © 2010 Society of Chemical Industry     

A PCR diagnostic for cyclodiene insecticide resistance in the red flour beetle Tribolium castaneum

A molecular diagnostic was used to examine the conservation of cyclodiene resistance associated mutations between different strains of Tribolium castaneum (Herbst.). An improved insecticide bioassay for discrimination between resistant genotypes was developed and seven resistant strains were established from five different continents. In order to develop a molecular diagnostic a partial cDNA of the cyclodiene insecticide resistance gene Rdl, a γ-aminobutyric-acid-gated chloride-ion channel, was cloned and sequenced. This cDNA spans exon 7, the region containing the resistance-associated mutation, and part of exon 8. An ‘allele-specific’ oligonucleotide primer, carrying the resistance-associated mutation at its 3′ end, was used in combination with a flanking ‘allele-independent’ primer in the polymerase chain reaction to selectively amplify a single resistance-associated mutation from all seven strains collected worldwide. The implications of these findings for the population genetics of insecticide resistance and its management in pest insects via quarantine are discussed.     

A comparative study of the metabolic effects of hypertrehalosemic hormone and 1,2,3,4,5,6-hexachlorocyclohexane (γ-HCH) in the American cockroach, Periplaneta americana

Several effects of hypertrehalosemic hormone (Peram-HTH) have been compared with the action of 1,2,3,4,5,6-hexachlorocyclohexane (γ-HCH) in the cockroach, Periplaneta americana. The data show that both agents stimulate respiration while maintaining an R.Q. of approximately 1. The action of γ-HCH differs from that of Peram-HTH-I in that it promotes oxidation of large amounts of soluble carbohydrate. Recent studies show that Peram-HTH-I has an equally potent stimulatory effect on lipid deposition in the fat body and on the release of trehalose from the same tissue. It is of interest that γ-HCH not only increases triacylglycerol accumulation in the fatγ body but that this effect is more pronounced if the γ-HCH is applied to the ventral surface of the mesothorax. γ-HCH also depleted whole body glycoprotein and glycolipid whereas Peram-HTH-I had no effect on glycoprotein but increased that of glycolipid. It is clear that γ-HCH causes complex disruptions to the metabolism of the insect, many of which are related to the release of hormones. The study supports the idea that certain actions of γ-HCH are mediated through the release of Peram-HTH-I.