Response of susceptible and resistant peach-potato aphids Myzus persicae (Sulz.) to insecticides in leaf-dip bioassays

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)-α-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.     

Field-simulator study of insecticide resistance conferred by esterase-, MACE- and kdr-based mechanisms in the peach-potato aphid,Myzus persicae (Sulzer)

Insecticide sprays were applied to Myzus persicae (Sulzer) populations carrying various combinations of three insecticide resistance mechanisms (esterase-based metabolic resistance and two target site mechanisms, known as MACE and kdr), supported on host plants growing in field simulator cages. The study showed that MACE confers extreme resistance to pirimicarb and triazamate (carbamate insecticides) but not to deltamethrin + heptenophos (16 + 1) (Decisquick) or dimethoate (an organophosphorus insecticide). Resistance to dimethoate depends solely on levels of esterase-based resistance, while resistance to Decisquick depends on kdr and esterase. None of the four insecticides is effective against aphids carrying MACE combined with extreme esterase-based resistance. This knowledge, in association with current monitoring of the mechanisms, will play an important role in making decisions on insecticide use against M persicae in the UK. © 1999 Society of Chemical Industry     

辛氰和乐氰混剂对甘蓝桃蚜抗性演化的影响

用辛硫磷与氰戊菊酯,乐果与氰戊菊酯的最佳配比及其相应单剂对甘蓝桃蚜进行抗性选育,汰洗２０代时桃蚜对两种混剂的抗性,分别为４．２０和２．６８倍,比相应单剂的抗性发展速度慢,尤其比氰戊菊酯单剂（２８９倍）更慢,表明上述两种混剂都可延缓桃蚜的抗性发展。用酶抑制剂进行增效应用测定结果表明：Ｋ１和ＴＰＰ对辛硫磷和乐果都有增效作用,尤以Ｋ１的增效作用更显著,其增效比分中辊为１０５３和３８,说明桃蚜对辛硫磷和乐     

The symbiotes of Myzus persicae (Sulz.) in strains resistant and susceptible to demeton-S-methyl

The lengths of individual symbiotes and the numbers of these per unit area in ultrathin sections of the mycetomes did not differ significantly between strains of Myzus persicae (Sulz.) that were resistant or susceptible to demeton-S-methyl in Britain. This is contrary to observations made in Germany on the symbiotes of similar aphids resistant or susceptible to parathion.     

Use of biochemical and DNA diagnostics for characterising multiple mechanisms of insecticide resistance in the peach-potato aphid,Myzus persicae (Sulzer)

The peach-potato aphid Myzus persicae (Sulzer) can resist a range of insecticides by over-producing detoxifying esterase and having mutant-insensitive forms of the target proteins, acetylcholinesterase (AChE), and the sodium channel. Using a combination of bioassays, biochemical and DNA diagnostics, it is now possible to diagnose all three mechanisms in individual aphids, and thereby establish their spatial distributions and temporal dynamics. A survey of 58 samples of wide geographic origin showed that all 46 resistant clones had amplified esterase genes (E4 or FE4) conferring broad-spectrum resistance to pyrethroids, organophosphates and carbamates. These occurred in combination with insensitive AChE (11 clones), conferring resistance to pirimicarb and triazamate, and/or mutant sodium channel genes (25 clones), conferring knockdown (kdr) resistance to pyrethroids and DDT. Amplified esterase genes were in linkage disequilibrium with both insensitive AChE and the kdr mutation, reflecting tight physical linkage, heavy selection favouring aphids with multiple mechanisms, and/or the prominence of parthenogenesis in many M. persicae populations. An ability to monitor individual mechanisms with contrasting cross-resistance profiles has important implications for the development of resistance management recommendations. ©1997 SCI     

A biochemical mechanism of resistance to pirimicarb in two glasshouse clones of Aphis gossypii

The susceptibility of three clones of Aphis gossypii Glover to 15 insecticides was established by bioassay. A high level of resistance towards pirimicarb was confirmed for a clone from Holland (Dutch R) and a clone from Japan (Jap R), while the susceptible clone (S) was killed by very low doses of the insecticide. However, only limited cross-resistance was shown towards other carbamates and organophosphates, and no marked resistance to the pyrethroids tested. The acetylcholinesterase (AChE) of both resistant clones hydrolysed acetyl-choline faster than that of susceptible aphids, with greatest enzyme activity shown by the Dutch R clone. Inter-clone differences in these rates were consistent with differences in catalytic centre activities. Inhibition (I₅₀) of AChE by pirimicarb was approximately 900-fold higher for the resistant clones than for the S clone. First-order kinetics revealed that resistance to pirimicarb in Dutch R and Jap R involved a modified AChE which had a reduced (approximately 350-fold) affinity (K_d) for pirimicarb. The marked change in AChE affinity for pirimicarb was not repeated with the other carbamates tested, ethiofencarb and aldicarb. It was considered that the resistant aphids would not require mechanisms in addition to insensitive AChE in order to show the high level of resistance to pirimicarb shown in the bioassay.     

Proinsecticides effective against insecticide-resistant peach-potato aphid (Myzus persicae (Sulzer))

A range of potential proinsecticides was synthesised and tested against insecticide-susceptible and -resistant clones of Myzus persicae (Sulzer). They were all esters of compounds known to be toxic or pharmacologically active, and were designed to have increased lipophilicity and to be subject to more rapid activation by hydrolysis in resistant than in susceptible aphids due to the increased amount of esterase present in the resistant clones. The most potent toxins were esters of monofluoroacetic acid. When applied topically, the toxicity of these esters to M. persicae was directly proportional to the esterase content of the aphids. Such compounds would not be suitable as commercial insecticides, but the results serve to illustrate the potential benefits of exploiting a resistance mechanism against one class of compounds to render another class more toxic, i.e. to design compounds that show negative cross-resistance. © 1998 SCI     

上海地区菜缢管蚜对有机磷的抗药性及其生化检测

呼伦贝尔盟农田杂草计49科、198属、348种,其中包括6个亚种、29个变种和1个变型。杂草发生特点:种类多、多年生杂草多、恶性杂草多、群落结构特殊、危害严重。主要优势群落:茅香和光稃茅香群落、匍匐冰草群落、野燕麦群落与裂边鼬瓣花群落。防治措施与策略:适当压缩小麦,扩大油菜种植面积,在休闲地应用草甘膦防治多年生杂草,用2甲4氯取代2,4-D丁酯防治小麦田杂草,发展应用磺酰脲类除草剂与禾草灵混用,以兼治野燕麦与宽叶杂草。     

Resistance to some organophosphorus insecticides in field populations of Myzus persicae from sugar beet in 1974

Following the failure of insecticides to control Myzus persicae on sugar beet, populations from the field were examined for susceptibility to dimethoate. Topical application of discriminating doses of dimethoate showed a 30-fold variation in susceptibility between different populations. After this preliminary screening, clones were established from some populations and their resistance determined by both topical application and a systemic bioassay. This confirmed resistance to dimethoate and demonstrated resistance to demeton-S-methyl. There was no resistance to some other compounds tested. In all populations tested, resistance was associated with increased carboxylesterase activity.     

Resistance mechanisms and associated mutations in acetylcholinesterase genes in Sitobion avenae (Fabricius)

Wheat aphid, Sitobion avenae (fabricius), is one of the most important wheat pests and has been reported to be resistant to commonly used insecticides in China. To determine the resistance mechanism, the resistant and susceptible strains were developed in laboratory and comparably studied. A bioassay revealed that the resistant strain showed high resistance to pirimicarb (RR: 161.8), moderate reistance to omethoate (32.5) and monocrotophos (33.5), and low resistance to deltamethrin (6.3) and thiodicarb (5.5). A biochemistry analysis showed that both strains had similar glutathione-S-transferase (GST) activity, but the resistant strain had 3.8-fold higher esterase activity, and its AChE was insensitive to this treatment. The I₅₀ increased by 25.8-, 10.7-, and 10.4-folds for pirimicarb, omethoate, and monocrotophos, respectively, demonstrating that GST had not been involved in the resistance of S. avenae. The enhanced esterase contributed to low level resistance to all the insecticides tested, whereas higher resistance to pirimicarb, omethoate, and monocrotophos mainly depended on AChE insensitivity. However, the AChE of the resistant strain was still sensitive to thiodicarb (1.7-fold). Thus, thiodicarb could be used as substitute for control of the resistant S. avenae in this case. Furthermore, the two different AChE genes cloned from different resistant and susceptible individuals were also compared. Two mutations, L436(336)S in Sa.Ace1 and W516(435)R in Sa.Ace2, were found consistently associated with the insensitivity of AChE. They were thought to be the possible resistance mutations, but further work is needed to confirm this hypothesis.     

The fate of some organophosphorus compounds applied topically to peach-potato aphids (Myzus persicae (Sulz.)) resistant and susceptible to insecticides

The fate of [¹⁴C]-dimethoate and [¹⁴C]-parathion after topical application to strains of Myzus persicae resistant and susceptible to organophosphorus compounds was investigated. In 4 h approximately 65% of the dimethoate or para-thion applied was lost from the aphids by evaporation, and this limited the amount available for penetration into the insect. Only approximately 25% of the dose applied penetrated, of which a very small proportion was excreted as metabolites. There was no difference in the amounts penetrating into the resistant and susceptible strains, indicating that penetration was not a factor contributing to the observed resistance. These findings emphasise that evaporation from the cuticle can greatly influence results when insecticides are applied topically.     

Evaluation of insecticides against aphids (Myzus persicae Sulzer) and caterpillars (spodoptera litura [f.]) on tobacco in Karnataka State (India)

0.02% a.i. dicrotophos and dimethoate, 0.025% a.i. demeton-S-methyl, thiometon, chlorfenvinphos and methomyl, and 0.03% a.i. phosphamidon were evaluated in the field for control of aphids (Myzus persicae Sulzer) infesting tobacco. All the insecticides were effective but chlorfenvinphos and methomyl were inferior to the rest. 0.03% and 0.06% a.i. endosulfan and trichlorfon, 0.05% and 0.1% a.i. carbaryl, and 0.025% and 0.05% a.i. methomyl were evaluated in the field for control of caterpillars ofSpodoptera litura (F.) defoliating tobacco. Nearly all the insecticides were effective and carbaryl and trichlorfon gave satisfactory control even at the lower concentrations tested.     

Toxicity of selected insecticides to the two-spot ladybird <Emphasis Type="Italic">Adalia bipunctata</Emphasis>

The toxicity of pirimicarb, imidacloprid, dimethoate, lambda-cyhalothrin, flonicamid and spinosad to the two-spot ladybird, Adalia bipunctata, was evaluated in a laboratory study. Susceptibility of fourth instars and female adults was assessed by measuring toxicity via residual contact and ingestion through feeding on contaminated green peach aphids (Myzus persicae). Flonicamid and spinosad had no lethal effects on larvae and female adults. Pirimicarb was harmless to the predator by ingestion exposure but showed some residual toxicity at high concentrations to both larval and adult stages. Imidacloprid was highly toxic to the larval stage by residual and ingestion exposure but caused very low adult mortality when ingested through contaminated prey. Dimethoate and lambda-cyhalothrin were highly toxic to both the larval and adult stages of the ladybird. Our findings indicate that pest management programs in agricultural crops using dimethoate, lambda-cyhalothrin and, to a lesser degree, imidacloprid, are detrimental to A. bipunctata, whereas pirimicarb, flonicamid and spinosad are more compatible with the use of this predator.     

Communication to the Editor Insecticide Resistance in a Strain of Aphis gossypii from Southern France

A strain (R) of Aphis gossypii from Southern France was found to be resistant to several insecticides, particularly to pirimicarb, as compared to a susceptible strain (S). Resistance levels were determined by biological tests, and the highest resistance factor (1350) was for pirimicarb. Resistance was mainly restricted to anticholinesterase inhibitors. Use of synergists, DEF and PB, suggested that resistance mechanisms based on detoxification were involved to a minor extent, since a good correlation was observed between I₅₀ values and k_i values of AChE and in-vivo bioassay data. The two strains differed in esterase activity, with a 27·7-fold increase in the R strain. Resolution of esterases by polyacrylamide gel electrophoresis showed different patterns in the S and R strains, and two isozymes were less sensitive to pirimicarb in the S strain; however, no in-vitro degradation of [¹⁴C]pirimicarb was observed. These data suggest that the main mechanism of resistance was through a decrease in the sensitivity of the target, AChE, to the insecticides. © 1997 SCI.     

Insecticide resistance in cotton aphid Aphis gossypii (Glov.) in the Sudan Gezira

The resistance to insecticides of three Sudanese strains of A. gossypii (Glov.) collected from cotton fields in the Sudan Gezira Scheme over three seasons (1988, 1989, 1990) and that of two French strains was studied in the laboratory. When compared with a known susceptible strain, the aphids were found to be resistant-to the eight insecticides tested. Evolution of resistance in Sudanese strains during the three crop seasons was observed. Assay of aphid homogcnate for carboxytesterase activity towards the substrates α-naphthyl acetate and β-naphthyl acetate showed that there was no enhancement of this class of enzyme and thus it was not a cause of resistance in this species. A study of interaction between the acetylcholinesterase (AchE) and pirimicarb established the kinetics of the inhibition process. I₅₀ values were found to be much higher for the Sudanese strains than for the susceptible strain. First-order inhibition kinetics revealed that resistance towards pirimicarb in Sudanese-strains was caused by a modified AchE which had a reduced affinity (higher K_a value) and poor carbamylation ability (lower K₂ value) for pirimicarb. The resistance mechanisms for the other insecticides remain to be studied.     

Further studies on the genetics of the carboxylesterase regulatory system involved in resistance to organophosphorus insecticides in Myzus persicae (Sulzer)

Levels of carboxylesterase activity in F₁ clones of Myzus persicae, obtained by crossing sexuales from a resistant, high esterase clone with those from a susceptible, low esterase clone, fell into two distinct groups intermediate between the levels of carboxylesterase in the parent clones. When sexuales of F₁ clones of the lower of these two intermediate levels of carboxylesterase activity were crossed, segregation ratios in the F₂ generation indicated that this lower intermediate activity level (about 0.4 μmol mg^?1 h^?1). which is about twice the level in susceptible clones, is due to mutation at a single regulatory locus. The results obtained with backcrosses, between sexuales of an F₁ clone having the higher intermediate level of carboxylesterase activity and a parent susceptible, low esterase clone, suggest that a second locus may be involved in the expression of higher levels of esterase activity.     

Present status and countermeasures of insecticide resistance in agricultural pests in China

Of the 23 species of agricultural pest known to resist insecticides in China, 4 are cotton pests, 4 rice pests and 5 are pests of brassicae. In the green rice leafhopper, malathion resistance is caused by increased carboxylesterase (CarE) activity, which plays a more important role in the resistance to dimethoate than the mixed-function oxidases (mfos). The in-vitro and in-vivo results are in agreement with studies of synergism of malathion and dimethoate by TPP and EBP. These synergists delay the development of resistance, and EBP when added to malathion has limited the development of resistance to malathion in the green rice leafhopper. In the cotton aphid, resistance to organophosphates involves several factors: acetylcholinesterase (AChE) insensitivity, high CarE activity, slight (× 2) increase in glutathione S-transferases (GSH-ases), mfo activity as well as reduced penetration. In vitro, the I₅₀ of the insensitive AChE is × 14 that of S aphids, and anaphthyl-acetate CarE hydrolysing activity is 70 times greater in R than in S aphids. Insecticide mixtures, alternation or rotation can delay build-up of resistance; resistance to malathion and trichlorfon was delayed in Culex pipiens pallens when the two insecticides were used together. Used singly each insecticide selected for high resistance within 25 generations. Mosaic rotation of dimethoate and fenvalerate delayed the onset of insecticide resistance in Lipaphis erysimi pseudobrassicae.     

Behaviour modifying effects of low systemic concentrations of imidacloprid on Myzus persicae with special reference to an antifeeding response

With a combination of biological, analytical, electrophysiological, and video-optical methods, it was possible to show that low concentrations of the new chloronicotinyl insecticide, imidacloprid, strongly affect the behaviour of Myzus persicae (Sulz.), leading eventually to the death of the aphids. Tests to elucidate the biological properties were performed under laboratory conditions with cabbage leaf petioles placed in insecticidal solutions over different periods of time. LC_15(24h) values were considered as low concentrations and calculated for imidacloprid and pirimicarb, respectively. Imidacloprid at low concentrations depressed the honeydew excretion of apterous adults of M. persicae by almost 95% within 24 h without affecting the vitality of the majority of aphids, whereas, at equitoxic concentrations, pirimicarb showed much weaker effects on honeydew excretion, which strongly coincided with mortality. In choice experiments with alate morphs of M. persicae over 48 h, their larvae almost always occurred on the untreated control leaf, and were not found on the leaf which was treated systemically with low concentrations of imidacloprid. Apterous aphids placed on cabbage leaves systemically treated with low concentrations of imidacloprid showed nearly the same decrease in weight as untreated starving aphids, suggesting that their death was caused by starvation. Aphids that were moved from imidacloprid-treated to untreated leaves after 24 h began feeding on the latter and showed a steady increase in weight and honeydew production. This suggests that the behavioural response is reversible. Aphids on pirimicarb-treated (equitoxic dose) leaves showed no decrease in weight. Electrical penetration graphs revealed that M. persicae on artificial membranes containing imidacloprid probed more often before feeding than aphids on control sachets. Time-lapse videofilming of apterous adults placed on cabbage leaves revealed a migration from the leaf treated with low concentrations of imidacloprid to an untreated leaf. From the results of these experiments and the observed symptomatology it is possible to postulate two different and dose-dependent modes of action of imidacloprid on M. persicae: (1) the well-known mode of action with visually obvious irreversible symptoms (paralysis, tremor, uncoordinated leg-movement) at field rates, and (2) the reversible starvation response as an antifeedant effect, which is not coupled with typical symptoms of neuronal disorder, at lower concentrations.     

Partial purification and characterization of a methyl-parathion resistance-associated general esterase in Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae)

Increased hydrolytic metabolism of organophosphate insecticides has been associated with resistance among Nebraska western corn rootworm populations. In this study, resistance-associated esterases were partially purified by differential centrifugation, ion exchange, and hydroxyapatite column chromatography, with a final purification factor of 100-fold and recovery of approximately 10%. Kinetic analysis of the partially purified enzyme indicated that the K_m of the group II esterases was identical for the two populations, although V_max was consistently threefold higher in the resistant population. A putative esterase, DvvII, was further purified to homogeneity by preparative polyacrylamide gel electrophoresis. DvvII is a monomer with a molecular weight of approximately 66 kDa, although three distinct isoforms with similar pIs were evident based on isoelectric focusing gel electrophoresis. Immunoassays with the Myzus persicae E4 antiserum indicated that group II esterases from D. v. virgifera were cross-reactive and expressed at much higher titers in the resistant population relative to the susceptible counterpart. These results suggest that the resistance is likely associated with overproduction of an esterase isozyme in resistant D. v. virgifera populations.