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Effect of decline of insecticide residues on selection for insecticide resistance in Myzus persicae (Sulzer) (Hemiptera: Aphididae)
Abstract
Residues of pirimicarb or deltamethrin plus heptenophos on potatoes in field cages in southern England reduced artificial infestations of susceptible and insecticide-resistant strains of Myzus persicae (Sulzer) introduced up to 14 days after treatment. Deltamethrin plus heptenophos gave better control than pirimicarb, particularly of nymphs, but also selected more strongly for very resistant (R2) aphids. Susceptible (S) aphids survived the treatment with deltamethrin plus heptenophos better than moderately resistant (R1) aphids, probably due to a different or more pronounced behavioural response to the pyrethroid. However, the combination of the greater persistence of deltamethrin plus heptenophos and the high resistance of M. persicae to the pyrethroid led to more prolonged selection for R2 aphids, which is sometimes associated with a resurgence in aphid numbers.
... It might seem unlikely that biological control agents could be effective given the intensive use of pesticides in seed potato production. However, the tremendous outbreaks that can be induced by insecticides when the aphids have developed resistance are indirect evidence of the importance of natural enemies (ffrench-Constant et al., 1988;Lagnaoui and Radcliffe, 1998). ...
... Volunteer potatoes, which emerge as weeds in rotation crops in the Columbia Basin, are important PLRV reservoirs (Thomas, 1983), as are potatoes sprouting in cull piles in Canada (Frazer, 1987). In regions where winter frost extends below the root zone of potatoes, volunteer potatoes are rare and appear to be inconsequential sources of potato viruses (DiFonzo et al., 1997). Because ware producers often plant tubers with 1-5% virus (375 to 1800 infected plants/ha), potato generally overshadows perennial weeds as a source of potato viruses. ...
This book contains 31 chapters covering aphids as crop pests, from recent advances in molecular science and chemical ecology to forecasting and insect pest management decision support systems. It is a comprehensive reference volume on all aspects of the biology of aphids that are relevant to their pest status (including aphid taxonomy, population genetics, life cycle, host plant selection and feeding, nutrition and symbiosis, growth and development, movement, predators, parasitoids, entomopathogens, insecticide resistance and population dynamics) and management strategies to control these pests. Intended for students, researchers and practitioners in the field of entomology and crop production, this book includes several case study chapters on integrated pest management in specific crops, such as cotton, sorghum and cucurbits.
... FE4 gene amplification, on the other hand, is not linked to a chromosomal rearrangement and can be found throughout the genome at multiple locations [91,93]. Revertant clones can lose esterase gene expression as well as pesticide resistance in the same generation, which is a fascinating component of resistance occurring after increased E4 genes [94]. The deletion of 5-methylcytosine (5 mC) within E4 genes in CpG doublets causes gene silence through demethylation in reverted individuals [95,96]. ...
With the passage of time and indiscreet usage of insecticides on crops, aphids are becoming resistant to their effect. The different classes of insecticides, including organophosphates, carba-mates, pyrethroids and neonicotinoids, have varied effects on insects. Furthermore, the molecular effects of these insecticides in aphids, including effects on the enzymatic machinery and gene mutation , are resulting in aphid resistance to the insecticides. In this review, we will discuss how aphids are affected by the overuse of pesticides, how resistance appears, and which mechanisms participate in the resistance mechanisms in various aphid species as significant crop pests. Gene expression studies were analyzed using the RNA-Seq technique. The stress-responsive genes were analyzed, and their expression in response to insecticide administration was determined. Putative insecticide resistance-related genes, cytochrome P450, glutathione S-transferase, carboxylesterase CarEs, ABC transporters, cuticle protein genes, and trypsin-related genes were studied. The review concluded that if insecticide-susceptible aphids interact with ample dosages of insecticides with sublethal effects , this will result in the upregulation of genes whose primary role is to detoxify insecticides. In the past decade, certain advancements have been observed regarding insecticide resistance on a molecular basis. Even so, not much is known about how aphids detoxify the insecticides at molecular level. Thus, to attain equilibrium, it is important to observe the manipulation of pest and insect species with the aim of restoring susceptibility to insecticides. For this purpose, this review has included critical insights into insecticide resistance in aphids.
... Results demonstrated that Confidor toxicity as a systemic and contact insecticide was much more when applied directly to aphids on infested plants in comparison to the procedures commonly used in the laboratory. On the contrary to the results of Confidor treatment and in agreement with those obtained by (Ffrench-Constant et al., 1988), the relatively low percentage of reduction one week after Pirimor treatment demonstrated the rapid decay of available residues, which enabled M. persicae to survive on treated plants. According to Georghiou (1963), field strain of M. persicae reared in the laboratory for 9 months resulted in partial loss of resistance or tolerance. ...
Toxic effect of insecticides on the green peach aphid, Myzus persicae Sulzer (Homoptera: Aphididea) and its parasitoid species Aphidius matricariae (Hal.) (Hymenoptera: Aphidiidae) was studied on sweet pepper plants under greenhouse conditions in Jordan. Five insecticides: Confidor, Decis, Metasystox, Pirimor and Vertimec at their LC50 values were tested. The insecticides were applied directly to infested plants by spraying aphids or dipping their mummies. According to the obtained results compared to control treatment, all insecticides tested had toxic effect on M. persicae, while they had less effect on survival of mummified aphids and activity of A. matricariae adults emerged from treated mummies.
p>The insecticides deltamethrin, dimethoate and Studies investigated the intrinsic toxicity of pirimicarb to Rhopalosiphum padi (Walk) (Homoptera: Aphididae) in the laboratory on a simple glass substrate. The dose-response data generated was used to predict reductions of cereal aphid populations in the field using reduced dose insecticide rates. The predicted reductions were initially tested under semi-field conditions and the results showed that above a certain dose threshold the predictions fitted well for deltamethrin. When predictions were tested in the field, predicted and observed population reductions were found to correlate well for deltamethrin and aphid control using reduced rate insecticide doses was not significantly different to a full field rate application. Temperature was shown to influence the toxicity of topically applied X-cyhalothrin and dimethoate to the cereal aphids R. padi and Sitobion avenae (Homoptera: Aphididae). The toxicity of A-cyhalothrin was negatively and dimethoate positively correlated with temperature. S. avenae was more susceptible than R. padi to topical applications of both insecticides. Residual exposure to ?L-cyhalothrin and dimethoate affected their toxicity to the aphids R. padi and S. avenae at different temperatures. A negative temperature coefficient was shown for 1-cyhalothrin whilst that of dimethoate was more complicated. Altering the route of exposure affected the susceptibility of the aphids to the insecticides. Laboratory exposure of aphids to deposits of l-cyhalothrin applied in the field showed the same trends as X-cyhalothrin applied in the laboratory. sub-lethal The application of padi individuals affected measurements of their growth and development. Development time, adult weight, number of nymphs produced, mrgr and rm values of the aphids were significantly different from untreated aphids when reared at an ambient temperature of 12°C. There were no differences between measurements of aphid growth and development at ambient temperatures of 18 and 25°C. 1-cyhalothrin to R. doses of Substrate type affected the residual toxicity of laboratory applied doses of deltamethrin and dimethoate to carabid beetles (Goleoptera: Carabidae). Application of insecticide dose-rates similar to those used for aphid control were toxic on glass but relatively harmless on soil. The exposure to an insecticide by topical or residual application affected aphid consumption of carabid beetles in the laboratory. Presenting carabid beetles with insecticide contaminated aphids reduced the beetles consumption of the aphids compared to controls. When the contaminated prey were removed aphid consumption returned to that of the controls. The potential and limitations of reduced dose insecticide rates for iPM in cereals are discussed.</p
The last decade has witnessed significant changes in both the philosophy and methods used for the monitoring of insecticide and acaricide resistance. The traditional emphasis has been on the development of precise but artificial techniques that measure change only in the physiological resistance of a strain under laboratory conditions (Busvine 1957). These techniques commonly use topical application of technical-grade insecticide in a suitable solvent and the calculation of median lethal dose estimates (e.g., LD50 or LC50) on a per-body-weight basis.
Good pesticide resistance management is just good IPM. Managing pesticide resistance means using the chemistry with enough restraint, and enough understanding of its role in an agroecosystem, to sustain that use. One interpretation is to maximize the number of applications that result in close to 100% control. To achieve this goal means optimizing the trade-off between the selection pressure exerted by use of the chemistry and the control benefits in terms of rapid reduction of pest population density. Too much population reduction too quickly leads quickly to resistance, whereas too much restriction of use denies economically justified control. The hope is that the chosen pattern of use provides many more effective applications than any alternative pattern, ideally an infinite number of effective applications. Models of resistance development, however, typically predict a finite number of effective applications, followed by a rapid increase in resistance gene frequency and rather sudden control failure. Experience in agroecosystems has generally been consistent with model predictions, for example resistance within a few generations to a long list of insecticides in Colorado potato beetle (Leptinotarsa decemlineata) on Long Island (Forgash, 1985; Mota-Sanchez et al., 2006). Agroecosystems include both people and the land, and their functioning needs to be considered in light of this combination and at large spatial extents and long time-frames. Pesticide resistance management programs that have taken a comprehensive and cooperative approach to maximizing the number of effective applications have been in place for about 20 years.
This book contains 31 chapters covering aphids as crop pests, from recent advances in molecular science and chemical ecology to forecasting and insect pest management decision support systems. It is a comprehensive reference volume on all aspects of the biology of aphids that are relevant to their pest status (including aphid taxonomy, population genetics, life cycle, host plant selection and feeding, nutrition and symbiosis, growth and development, movement, predators, parasitoids, entomopathogens, insecticide resistance and population dynamics) and management strategies to control these pests. Intended for students, researchers and practitioners in the field of entomology and crop production, this book includes several case study chapters on integrated pest management in specific crops, such as cotton, sorghum and cucurbits.
A freqüência e a intensidade da resistência de Myzus persicae (Sulz.) a inseticidas foram avaliadas em duas áreas localizadas no município de Ibicoara, BA, onde as aplicações com inseticida falharam no controle do afídeo. Em uma das áreas com a cultura em sua fase final, foram feitas duas aplicações de pirimicarbe, com intervalo de quatro dias, enquanto a outra não recebeu pulverizações. Foram feitas seis coletas ao acaso, de 700 afídeos cada, antes e após as aplicações e também na área não tratada e em plantas voluntárias (plantas que nasceram espontaneamente em áreas cultivas com batata em safras anteriores) de batata. No laboratório, foi estimada a CL50 das populações de campo, que foram posteriormente submetidas à avaliação de esterases totais através de teste colorimétrico. Após as aplicações de pirimicarbe, a freqüência da população suscetível (S), moderadamente resistente (R1) e das populações mistas (S/R1) reduziu-se de 36,6 para 9,9; 12 para 7,5 e 11,4 para 5,9%, respectivamente. As populações altamente resistente (R2), extremamente resistente (R3) e a mista R1/R2, entretanto tiveram a sua freqüência elevada após as aplicações (17,7 para 36,7; 2,3 para 9,1 e 20 para 30,8%, respectivamente). A sobrevivência de indivíduos S foi devida, possivelmente, ao incremento da movimentação para evitar o contato com o inseticida. Todas as mudanças na freqüência de indivíduos resistentes e suscetíveis de M. persicae refletiram-se na CL50 e na razão de resistência (RR), demonstrando a sensibilidade do bioensaio. Na área não tratada com pirimicarbe observou-se alta freqüência de R2 + R3 (86,9) e R1/R2. A alta freqüência de populações de M. persicae resistentes a inseticidas e a elevada intensidade da resistência observadas nesta pesquisa podem estar ligadas à seleção de indivíduos resistentes e à entrada de migrantes alados resistentes provenientes das plantas voluntárias , que apresentaram freqüência de R2 + R3 (81,4%).
Modification of an immunoassay for detection of esterase-4 (E4), the enzyme conferring insecticide resistance in Myzus persicae, enabled further discrimination of extremely high levels of insecticide resistance (R3) from the very high levels (R2) previously characterised by this technique. The modified immunoassay was used to study the rate and pattern of loss of resistance in 10 R3 clones (all possessing an A 1,3 chromosomal translocation) isolated from the field and maintained in population cages. Clones lost resistance at varying rates and one remained stable at a level intermediate between R2 and R3. Loss was catastrophic; high frequencies of susceptible individuals were produced within a clone in the space of one generation without the formation of stable intermediates. However, this was not associated with loss of the chromosomal translocation. Of a number of other R3 clones isolated from the field only one stabilized at an intermediate level of E4 production equivalent to R1. Reselection of resistance in reverted susceptible subclones, by increasing concentrations of insecticide, was due to gradual selection for existing variation in E4 levels which was not apparent in clones of normal karyotype.
Insecticide resistant Myzus persicae (Sulzer) employ increased esterase activity to detoxify insecticides by hydrolysis and sequestration. The amount of esterase, and hence resistance, in individual aphids can be determined by measuring either overall naphthyl acetate hydrolysis in crude homogenates, or the specific enzyme responsible (E4 or FE4) after electrophoresis or immunological isolation. The ability of a total esterase assay, done in microplates, to discriminate between susceptible (S) aphids and resistant variants (R1, R2) with different amounts of E4/FE4, was compared with the resolving power of the more elaborate immunoassay technique. The immunoassay gave the better discrimination between variants, resolving them all with greater than 95% confidence, with particularly good separation of R1, from S. The microplate assay using crude homogenates, although a poorer discriminator, identified most of the very resistant (R2) aphids, and provided a robust and widely accessible method for broadly representing the resistance of field populations.
This review of our work on resistance in Myzus persicae over the past 20 years is divided into three sections. After a brief introduction, the biochemistry of the resistance mechanism is discussed, followed by a description of how the understanding of this has been used to develop sensitive and reliable methods for monitoring resistance in field populations. Finally, recent work on the molecular genetic basis of the resistance mechanism is described, and its practical implications for understanding the build-up of resistance in populations are discussed.
A resurgence of Myzus persicae occurred in potato plots treated regularly from June to August with a cypermethrin/oil mixture. Early in the season, insecticide-resistant forms were selected and these increased in numbers during August on favourable senescent foliage. Although numbers of predacious carabid beetles on the cypermethrin/oil plots decreased at about the time numbers of aphids in these plots began to exceed those in other plots, signs of the resurgence were beginning earlier and evidence for the role of reduced carabids is not conclusive. There was no evidence of stimulation of growth or reproduction of the aphids by the cypermethrin and oil, either acting directly, or indirectly via changes in the plants. Cypermethrin with oil greatly decreased spread of potato leaf roll virus in spite of the increase in numbers of aphids at the end of the season, probably because of better early season control. Although cypermethrin with oil decreases spread of viruses, it increases the level of resistant aphids in the population, which may have serious consequences for their control in the future.
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.
This review addresses some of the biological complexities presented by aphid-transmitted viruses of potato,Solanum tuberosum L., and their vectors and discusses the application of this knowledge to the management of potato viruses with particular
emphasis on seed potato production.
Behavioral responses of insect herbivores to toxins are examined in managed and natural systems with reference to two important but largely ignored factors: heterogeneity in toxin distributions and the nature of the relationship between behavioral responses and physiological adaptation to the same toxins. Heterogeneous toxin distributions, which provide the opportunity for behavioral responses, are ubiquitous in managed and natural systems. Insect herbivores have evolved a wide variety of behavioral responses to such toxins. The nature of behavioral responses reflects toxin apparency, mode of action, and the extent to which sublethal effects influence behavior. The interaction between these behavioral responses to heterogeneously distributed toxins and physiological mechanisms of tolerance has influenced the evolution of insecticide resistance in managed systems and the evolution of plant defensive strategies in natural systems. An understanding of this interaction could lead to more evolutionarily stable methods of crop protection.
We have been exploring the behavioral response ot insect pests to heterogeneous distribution of toxins (low dose with refugia), and its genetic correlation with physiological tolerance to these toxins. A field-collected population of diamondback moth, Plutella xylostellu (L.) (Lepidoptera Plutellidae), from Celeryville, OH, was selected with permethrin to determine whether low heterogeneous doses could lead to increased susceptibility to permethrin by selecting indirectly on behavior. Two replicates of each of three selection regimes: uniform high concentration hypothesized to result in increased physiological tolerance, heterogeneous low concentration hypothesized to result in increased susceptibility through indirect selection on behavior, and a control with no exposure to permethrin, were maintained in 1-in3 cages in a greenhouse, for 33 generations. All life stages of the diamondback moth were exposed to the selection regimes, and new generations were started with a random selection of pupae from the previous generation. Lines selected with uniform high concentrations developed 76-fold levels of resistance to permethrin by the 17th generation, with little changes thereafter. For generations 1-20, lines selected with heterogeneous low concentrations remained slightly lower in LC50 but not significantly different from the unselected control lines. Based on confidence intervals from probit analyses, the LC50 of the lines selected with heterogeneous low concentration, however, were significantly lower than those of the control lines in generations 21-33. Our results demonstrate that selection on behavioral responses can result in greater susceptibility than no selection at all, despite exposure to the toxin and ample genetic variation and potential for increased physiological tolerance. The implications of our findings, which are based on selection scenarios that could take place in field situations, are that behavioral responses can prevent and even decrease the levels of resistance in insect populations, an important result with respect to resistance and resistance management.
In laboratory experiments, the responses to short photoperiod (10 h) of clones of Myzus persicae (Sulz.) established from random samples of summer populations in southern England were generally stable and characteristic for each clone, and were of four distinct categories: (i) holocyclic, with clones terminated under short photoperiod by production of male and female sexual forms, (ii) intermediate, with a mixed response involving alatae intermediate between gynoparae and virginoparae, (iii) androcyclic, with production of some males along with continued parthenogenesis, and (iv) truly anholocyclic, with no significant response to short photoperiod. All four types can occur within one population, but holocyclic and androcyclic forms are most common. There were clear differences in the proportions of these forms occurring simultaneously on adjacent crops of different host-plants, and in different years on the same crop in the same field. Males of androcyclic clones were able to transmit their partially anholocyclic character through the sexual phase.
Mutants of Drosophila melanogaster (Meigen) with altered resistance to the insecticide malathion were isolated and tested for their avoidance response to the insecticide. A correlation between sensitivity to the insecticide and increased avoidance was detected. Approximate chromosome map locations were determined for the loci of the mutations.
Carboxylesterase E4, the enzyme previously shown to cause resistance to organophosphorus insecticides in peach-potato aphids, Myzus persicae, was purified and characterized by electrophoretic and enzyme kinetic techniques. Its insecticidal substrate specificity, determined by following the rate of recovery of esterase activity after inhibition by a range of acylating inhibitors, included a variety of carbamates and organophosphates, although the catalytic center activity for these substrates was low. Radiometric measurement of hydrolysis of the pyrethroid, permethrin, showed that E4, whether purified or in crude aphid homogenates, hydrolyzed the (1S)trans enantiomer rapidly but hydrolysis of the other three isomers could not be detected. Such absolute specificity for one enantiomer of a pyrethroid is rare. The rates of hydrolysis of the various insecticidal classes correlated well with the relative degrees of resistance to them, and no other resistance mechanisms have been detected. Although the enzyme is relatively inefficient in degrading insecticidal esters, it is produced in very large quantity, accounting for approximately 3% of the total protein in very resistant aphids. Its effect is thus mediated not only by hydrolysis but also by sequestering a substantial proportion of a toxic dose of insecticide. It is effective in this respect because the molar amount present is similar to that of a lethal dose of insecticide. These results support earlier indirect evidence for “overproduction” of E4, probably because of structural gene duplication or amplification and have direct implications for strategies to delay the buildup of resistance or for developing synergists to overcome resistance.
Numbers of Myzus persicae on potatoes (Solanum tuberosum) receiving three insecticide regimes were recorded in 1985 and 1986. Frequencies of insecticide-resistant variants were determined using an immunoassay for esterase-4 (E4), the enzyme responsible. M. persicae was more abundant at the end of the season on plots sprayed alternately throughout the experiment with a mixture of pyrethroid with oil and pirimicarb, than on those treated with pirimicarb alone. Frequency distributions of E4 activity showed that very resistant variants intermediate between R2 and R3 levels accounted for >50% of the populations. Further samples of aphids, collected on separate farms from defoliated patches in late-growing potato crops where repeated spraying had failed to control aphids, showed that these highly resistant variants had again been selected. Possible reasons for the observed increase in numbers of M. persicae following pyrethroid/oil treatment and consequences for virus control are discussed.
Many instances of pest populations increasing following the application of pesticides to crops have been reported, with natural enemy destruction by the pesticide often cited as the cause (Putman and Heme 1959). Other explanations include a greater food supply available due to the death of competing pest species (Root and Gowan 1978), and direct stimulation of the enhanced species by sublethal doses of a pesticide, evidenced as increased fecundity (Leigh and Wynholds 1980; Boykin and Campbell 1982; Coombes 1983). In Ontario the use of the insecticide azinphosmethyl has been followed by population increases of the green peach aphid ( Myzus persicae (Sulzer)) (Founk and McClanahan 1970; Ritcey et al. 1982). Our study was undertaken to determine the causes.
Apterous green peach aphids, Myzus persicae (Sulzer), collected from potato plots treated with azinphosmethyl, when caged on either treated or nontreated foliage, produced 20-30% more offspring than aphids that were not exposed to the insecticide. The increase in fecundity resulted directly from the action of the insecticide on the reproduction of the aphids rather than indirectly from changes induced by the insecticide in the host potato plants. Suitability of plants to support populations of aphids varied within and between seasons. Applications of azinphosmethyl did not alter ability of the plants to support aphid populations.
Apterous green peach aphids (GPA), Myzus persicae (Sulzer), collected from plots of potatoes treated with azinphosmethyl (AM) and reared in the laboratory on leaf disks of potato, produced ca. 28% more offspring than GPA from untreated plots. The rate at which offspring were produced for the subsequent two generations did not differ for either group of GPA, suggesting that the increase in reproduction noted in the parental generation resulted from direct exposure to AM. Stage-specific developmental times and reproduction of fourth-generation aphids did not differ for either group, indicating that a strain of GPA resistant to AM had not been selected that had a higher rate of reproduction. GPA reared in the laboratory on leaf disks of potato that were treated with a 550 ppm solution of AM produced ca. 10% more offspring than GPA on untreated disks, whereas GPA on leaf disks of potato treated with concentrations higher and lower than 550 ppm did not produce more offspring than GPA on untreated leaf disks. High survival and fecundity of GPA reared on leaf disks of potato in the laboratory demonstrated that this method was suitable for laboratory studies but results did not necessarily apply to field conditions.
Field cages in southern England enclosing single rows of potatoes and infested with differing initial proportions of S (susceptible), R1 (moderately insecticide resistant) and R2 (very resistant) clones of Myzus persicae (Sulzer) were sprayed three times, at 14-day intervals, with pirimicarb (carbamate), demeton-S-methyl (organophosphorus) or a mixture of deltamethrin and heptenophos (pyrethroid and organophosphorus insecticides). The numbers of aphids on top, middle and basal leaves were counted, pre-treatment and one and eight days after each of the three sprays. The resistance genotype frequencies of the three variants were determined by an immunoplate assay which measures the amount of the carboxylesterase E4, the enzyme conferring resistance, in individual aphids. All three chemicals selected strongly for the very resistant variant. After three sprays, R2 aphid frequencies approached or equalled fixation (1·00) for both starting frequencies. However, the deltamethrin-heptenophos mixture selected for R2 aphids more rapidly than the other chemical treatments. Increasing the initial starting frequency of R2 aphids from 0·02 to 0·20 led to a more rapid increase of their frequencies towards 1·00 for all chemicals. The numbers of aphids on all treated plots were less than on the control. However, the more rapid increase in the proportion of R2's on plots treated with deltamethrin plus heptenophos, coupled with enhanced nymph production, resulted in a smaller reduction in numbers than was achieved by the other chemical treatments. The need for novel control methods is discussed in the light of the strong selection for R2 aphids exerted by all three insecticide classes.
An antiserum was prepared against carboxylesterase E4, the enzyme conferring resistance in Myzus persicae (Sulzer) to a wide range of insecticides, and the immunoglobulin G (IgG) fraction was purified from it by affinity chromotography. Interactions of the antiserum and IgG with aphid homogenates and the purified esterase proteins were studied by immune diffusion, immunoelectrophoresis and enzyme-linked immunosorbent assay (ELISA). In M. persicae, the interactions were specific for E4 and its closely-related mutant form, FE4, and except for Phorodon humuli (Schrank), there was no cross-reaction with homogenates of the nine other aphid species examined. These studies confirmed the quantitative changes in E4 protein previously reported and established that the increased esterase activity in P. humuli also arises from the production of more protein, or proteins, homologous to E4. Resistance of M. persicae could be characterized by immunoelectrophoresis even after preservation of the insects in 30% ethanol. Although ELISA could also be used to identify resistance, a simpler immunoplate assay was developed based on measuring the esterase activity of E4 retained when the enzyme bound to IgG. This assay discriminates well between the three resistant M. persicae variants common in the field in the UK, and its simplicity allows the study of large numbers of insects.
A series of experiments in the laboratory and greenhouse, were designed to test the possible causes of the field resurgence of the aphid Myzus persicae. Stimulation of reproduction occurred at topical dosages of around the LD5 value. Residual film tests indicated a significant depression in fecundity when aphids were held on sub-lethal deposits of fenvalerate, even at dosages below the LD5 value. Trends in the population build-up experiments in the greenhouse suggested there may be some stimulation when aphids are confined to aged deposits of fenvalerate 7 days after treatment, but the slight increase was not significant.
The response of susceptible (S), moderately resistant (R1) and strongly resistant (R2) peach-potato aphids, Myzus persicae (Sulz.) to organophosphorus, carbamate and pyrethroid insecticides was tested by a leaf-dip bioassay. The aphids were placed on potato leaves (dipped in insecticide solutions 1–2 or 24 h before infestation) and their mortality examined 48 h later. R1 aphids were virtually susceptible to most of the carbamates, demephion and acephate, but were slightly to moderately resistant (2.1–9.4 times) to permethrin, cypermethrin and (S)--cyano-3-phenoxybenzyl (1R)-cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropanecarboxylate (I), (NRDC 161), to 5,6,7,8-tetrahydro-2-methylquinolin-4-yl dimethylcarbamate (II), (Hoechst 25 682) and demeton-S-methyl. R2 aphids resisted more strongly or very strongly (between 65 and 1280 times) the pyrethroids, demeton-S-methyl (×94), II (×83) and demephion (×9), and were slightly to moderately (2–5 times) resistant to acephate, pirimicarb, ethiofencarb and 2-(dimethylcarbamoyloxyimino)-3-methoxyimino-N,N- dimethylbutyramide (III), (DPX 3853). Both resistant strains were susceptible to nitrilacarb [4,4-dimethyl-5-(methylcarbamoyloxyimino)pentanenitrile] complex (1:1) with zinc chloride (IV), (AC 85 258). The implications of these results in terms of practical aphid control are discussed.
Dispersal of a laboratory susceptible strain (VPI) of German cockroaches, Blattella germanica (L.), was compared with that of a field-collected, propoxur-resistant strain (BP) in laboratory experiments. VPI-strain adults dispersed significantly faster from 18.9-liter aquaria than BP strain adults after exposure to vapors of a formulation of 1% propoxur in oil. No differences occurred in control experiments or between dispersal of VPI and BP middle-instar or early instar nymphs. Early instars of both strains dispersed the least but found refuge in water-vial sponges. Reasonsfor decreased avoidance by the BP-resistant strain are discussed.
Egg implant studies on sheep demonstrate that the relative fitness of resistance genotypes of the sheep blowfly, Lucilia cuprina, changes over time for the 2 insecticides dieldrin and diazinon. The results suggest that selection may occur following exposure of larvae to sub-lethal concentrations and help to explain the relative rates of the development of resistance to dieldrin and diazinon by L.cuprina.
The significance of DDT-irritability tests on mosquitos
- Busvine