用浸叶法测定了采自我国不同地区（泰安、莱阳、南京、北京和安阳）的棉蚜品系Ⅰ、Ⅱ、Ⅲ、Ⅳ、Ⅴ对久效磷、甲胺磷、抗蚜威和灭多威等杀虫剂的抗性水平，各棉蚜品系对杀虫剂的抗性依次为Ⅴ>Ⅳ>Ⅲ，Ⅱ>Ⅰ。进一步研究表明，Ⅴ和Ⅳ品系棉蚜乙酰胆碱酯酶对杀虫剂的敏感性显著下降，Ⅱ品系次之，Ⅲ和Ⅰ品系接近于敏感品系。Ⅴ和Ⅳ品系乙酰胆碱酯酶的Km值显著下降，表明酶发生了质的变化。不同棉蚜抗性品系的酯酶（全酯酶和羧酸酯酶）活性均显著升高，其中Ⅲ品系的酯酶活力为Ⅱ品系的2倍。Ⅴ品系羧酸酯酶Km值达2460.4μmol/L，而Ⅳ品系仅为84.4μmol/L，该两个品系羧酸酯酶发生了质的变化。研究结果表明，不同抗性程度的棉蚜品系均存在代谢抗性和靶标抗性。低抗水平的棉蚜品系，以代谢抗性为主，靶标抗性为辅；中抗水平的棉蚜品系，抑或由于解毒代谢酶的活性显著增强，也可能由于靶标的敏感性显著下降；而高抗水平的棉蚜品系，依赖于代谢抗性和靶标抗性的联合作用。

ated by the PHYLIP program package inferred that AChE2 of A. gossypii is a more ancestral form of AChE. Homology modeling of structures using Torpedo californica (2ACE_) and Drosophila melanogaster (1Q09:A) native acetylcholinesterase structure as main template indicated that the two AChEs of Aphis gossypii might have different three-dimensional structures. Alternative splicing of Ace1 near the 5’-end resulting in two proteins differing by the presence or absence of a fragment of four amino acids is also reported.

A field population of the rice stem borer (Chilo suppressalis Walker) with 203.3-fold resistance to triazophos was collected. After 8-generation of continuous selection with triazophos in laboratory, resistance increased to 787.2-fold, and at the same time, the resistance to isocarbophos and methamidophos was also enhanced by 9- and 4-fold, respectively, implying some cross-resistance between triazophos and these two organophosphate insecticides. Resistance to abamectin was slightly enhanced by triazophos selection, and fipronil and methomyl decreased. Synergism experiments in vivo with TPP, PBO, and DEM were performed to gain a potential indication of roles of detoxicating enzymes in triazophos resistance. The synergism results revealed that TPP (SR, 92) and PBO (SR 63) had significant synergistic effects on triazophos in resistant rice borers. While DEM (SR 0.83) showed no effects. Assays of enzyme activity in vitro demonstrated that the resistant strain had higher activity of esterase and microsomal O-demethylase than the susceptible strain (20- and 30-fold, respectively). For glutathione S-transferase activity, no difference was found between the resistant and the susceptible strain when DCNB was used as substrate. However, 28-fold higher activity was observed in the resistant strain when CDNB was used. These results showed that esterase and microsomal-O-demethylase play some roles in the resistance. Some iso-enzyme of glutathione S-transferase may involve in the resistance to other insecticides, for this resistant strain was selected from a field population with multiple resistance background. Acetylcholinesterase as the triazophos target was also compared. The results revealed significant differences between the resistant and susceptible strain. The Vmax and Km of the enzyme in resistant strain was only 32 and 65% that in the susceptible strain, respectively. Inhibition tests in vitro showed that I50 of triazophos on AChE of the resistant strain was 2.52-fold higher. Therefore, insensitive AChE may also involved in triazophos resistance mechanism of rice stem borer.

The activity and electrophoretic mobility of nonspecific esterases, and the sensitivity of acetylcholinesterase (AChE) to organophosphate and carbamate insecticides, was determined for 21 strains or clones of Aphis gossypii of worldwide origin and related to patterns of insecticide resistance disclosed by diagnostic dose bioassays with demeton-S-methyl, pirimicarb, and permethrin. Results confirmed previous work showing the occurrence of two forms of mutant AChE, both conferring insensitivity to pirimicarb and representing the primary mechanism of resistance to this insecticide. One of these mutant AChE enzymes also caused resistance to demeton-S-methyl in its own right, whereas the other only conferred resistance in combination with moderate or high levels of nonspecific esterase activity. Lack of any correlation between permethrin resistance and quantitative or qualitative changes in esterases implied a distinct, as yet uncharacterised, mechanism of resistance to pyrethroids, possibly based on insensitivity in the target protein for these pesticides.

A field population of brown planthoppers (Nilaparvata lugens St

Dynamics of pyrethroid resistance in a field population of cotton bollworm (Helicoverpa armigera) was demonstrated by continuous monitoring with twin discriminating dosages, and the influencing factors were also experimentally analysed. Resistance in a field population in China increased rapidly in the 3rd and 4th generations when population density became higher and insecticides were applied repeatedly, then decreased suddenly during over-wlntering and slowly in the 1st and 2nd generations when insecticide spraying was suspended. Resistance increase could be countered by dilution as a result of immigration of susceptible moths from corn fields, which were found to be a natural refuge for this pest in China, The reduction of resistance during over-wintering and the 1st and 2nd generations was affected by the lower fitness of resistant cotton bollworms to low temperature and disadvantages in reproduction. The possibilities of managing the resistance in field populations on the basis of these observations are discussed.

Observation of the oviposition behavior of cotton bollworm demonstrated the existence of substances that can act as oviposition deterrents. The scales, abdomens and tarsi of the moths, the most likely carrier, were extracted for the substances. An acetone extract exhibiting an oviposition deterrent effect was analyzed using gas chromatography and combined gas chromatography-massspectroscopy. Three components, 4-methyl-4-hydroxyl-pentanone-2, hexadecanoic acid and (Z)-9-octadecenoic acid, were identified, being present in the ratio 1:2:2. Experiments with synthetic mixtures indicated that a mixture of equal amounts of the two organic acids exhibited similar repellent and deterrent activity to a synthetic mixture of all three components. It is concluded that the natural oviposition-deterring pheromone is a mixture of hexadecanoic acid and (Z)-9-octadecenoic acid.

Two acetylcholinesterase genes, Acel and Ace2, have been fully cloned and sequenced from both oranophoshate-resistant and susceptible clones of cotton aphid. Comparison of both nucleic acid and deduced amino acid sequences revealed considerable nucleotide polymorphisms. Further study found that two mutations occurred consistently in all resistant aphids. The mutation F139L in Ace2 corresponding to F115S in Drosophila acetylcholinesterase might reduce the enzyme sensitivity and result in insecticide resistance. The other mutation A320S in Acel abutting the conserved catalytic triad might affect the activity and insecticide sensitivity of the enzyme. Phylogenetic analysis showed that insect acetylcholinesterases fall into two subgroups, of which Acel is the paralogous gene whereas Ace2 is the orthologous gene of Drosophila AChE. Both subgroups contain resistance-associated AChE genes. To avoid confusion in the future work, a nomenclature of insect AChE is also suggested in the paper.

Insensitive acetylcholinesterase was identified as a esistance mechanism by comparing biochemical analysis with a laboratory selected monocrotophos resistant cotton bloodworm (RR: 200) and the susceptible strain The cDNA enCODING AChE was cloned by the method of RACE (rapid amplification of cDNA ends). The complete AChE gene deduced from the cDNA consisted of a putative signal peptide of 32 amino acid residues, a mature protein of 615 residues, 5' untranslated regions (UTR) of 315bp and 3' UTR of 324bp. The Coding sequence had a high degree of Homology to the AChE from other insect species reported in the GenBank. After comparing analysis of the entire AChE gene sequence from 5 resistant and 6 susceptible cotton bollworm individuals, nine mutations were identified. One of them, the Ala/Thr mutation, is likely to be responsible for the AChE insensitivity to monocrotophos.

gossypii Glover. The procedure involved filtration on a sephadex G-25 column, separation with sephadex G-200 and procainamide offinity column. AChE from both susceptible and resistant strains were purified to a single band as resolved on denaturing polyacrylamide gel electrophoresis (SDS-PAGE). The specific activity increased by 35, 100- and 33, 680-fold with a yield of 30.3 and 29.8%, respectively. The molecular mass of the purified AChE was about 63, 500 Dalton as etermined by SDS-PAGE. However, three bands resolved on PAGE gel electrophoresis, leading to the inference that native AChE exists in three forms. The optimum conditions for measuring the activity of purified AChE with kinetic method were 0.02M phosphate buffer, pH7.2, 0.02mM 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), AND 25℃. Investigation also revealed that crude extract and purified AChE had different kinetic characteristics and inhibiroty properties. They responded differently to varied DTNB, ATChI, and phosphate buffer ion concentrations, as well as pH, temperature, and inhibitors. The purified AChE was more sensitive to eserine, methamidophos, and pirimicarb. Especially for resistant aphids, the sensitivity of purified AChE to methamidophos and pirimicarb was enhanced 6.43 and 11.73 times, respectively. We infer that one or more factors in the crude extract from the resistance stain have more influence on AChE sensitivity. Further study is needed to investigate the basis of these observations.