The emergence of insecticide resistance in mosquito vectors was an important issue to be considered as one of factors influencing the success of vector control. The early detection of resistance could help the health personnel to plan and select appropriate alternative control measures or insecticide for effective control. Therefore biochemical assay of enzymes in mosquito was conducted to detect the emergence of insecticide resistance and to define the machanisms involved in pyrethroid resistance. Adults of Aedes aegypti from two localtities in Ratchaburi province were subjected to permethrin and deltamethrin selection in laboratory. After three generations of selection, permethrin-selected and deltamethrin-selected strains were established. Their LT 50 increased to 7.46 and 1.18 folds in the F3 strains that were selected with permethrin and deltamethrin respectively. The enzymes of these mosquitoes were assayed biochemically to study the mechanisms of resistance. The results revealed significant increase of esterase activity and monooxygenase levels in both strains when compared with labolatory susceptible strain. Glutathione-S-transferase activity was found to increase in permethrin-selected strain but not in deltamethrin-selected strain. This suggested that not only esterase and monooxygenase but also glutathione-S-transferase were associated with permethrin resistance in Ae. aegypti. The exposing of permethrin-selected and deltamethrin-selected mosquitoes to diagnostic concentration of permethrin (0.75%) and deltamethrin (0.05%) indicated no cross resistance for permethrin to deltamethrin while slight cross resistance from deltamethrin to permethrin was evident. It seemed that glutathione S-tranferase was not associated with cross resistance since its activity in deltamethrin-selected strain remained unchanged as compared with that of laboratory susceptible strain.
Cancer resistance to treatment ; Permethrin ; decamethrin ; Culicidae ; Pyrethroid insecticide

OBJECTIVETo investigate the genotypes , allele frequencies and dynamic distribution on resistance associated esterase genes of Culex pipiens complex in Hangzhou.

METHODSThe PCR-restriction fragment length polymorphism (PCR-RFLP) assay was applied to type the resistance associated esterase genes, and dynamic surveillance on frequencies of the resistance associated esterase gene of natural population of Culex pipiens complex in Hangzhou during 2003-2005, and phenotype of the resistance associated esterase genes were detected by esterase starch gel electrophoresis technique.

RESULTSThe PCR-RFLP assay of esterase allele genes for three consecutive years disclosed four esterase genotypes, namely, the world-wide highly active homozygous Est beta 1(1) (50%-54%), homozygous Est beta 2 (29%-34%), heterozygous Est beta 1(1)/beta 2 (5%-10%) and Est beta N (3.13%) of a new homozygous genotype. The research of the resistance associated esterase genes phenotype in natural population of Culex pipiens complex in Hangzhou in 2005 with esterase starch gel electrophoresis technique revealed four major types, namely, Est beta 1(1) (61%), Est alpha 2/beta 2 (12%), Est alpha 8/beta 8 (7%) and sensitive phenotype (29%).

CONCLUSIONThere should be various resistance associated esterase genotypes in natural population of Culex pipiens complex in Hangzhou. During the period of 2003-2005, Est beta 1(1) was the major type; Est alpha 2/beta 2 was the second. Est beta N was a new esterase genotype detected in 2005 only with a mere percentage of 3.13%. As for its resistance to the new insecticide, a follow-up study should be needed. The molecular typing of the amplified esterase gene should be consistent with the resistance associated esterase genes phenotype.

Alleles ; Animals ; China ; Culex ; genetics ; physiology ; Esterases ; analysis ; genetics ; Gene Frequency ; Genotype ; Insecticide Resistance ; genetics ; Phenotype

OBJECTIVETo investigate the diversity of acetylcholinesterase (AChE) activity in variety classes and strains of Culex pipiens pallens and provide a basis for the insecticide-resistance detection of mosquito by biochemical method.

METHODSAChE insensitivity of single mosquito was determined, using acetythiocholine iodide (ATch) as the substrate, 5,5'-dithio-bis (2-nitrobenzoic acid) (DTNB) as the developer, and propoxur as the inhibitor.

RESULTThere were significant differences in AChE activity among the four types of IV instar larvae and 3-day-old adult female of sensitive strain mosquito (P<0.01). The AChE activity of the 3-day-old adult female was higher than that of IV instar larvae of the four types of sensitive strain mosquito (P<0.01). The AChE activity of anti-DDVP (Rd) and anti-propoxur (Rp) strains of Culex pipiens pallens was significantly higher than that of sensitive (S) strain (P<0.01), while the AChE activity of anti-cypermethrin (Rc) strain of Culex pipiens pallens was similar to that of S strain (P>0.05). The individual frequency of insensitive AChE of Rd and Rp strains of Culex pipiens pallens was significantly higher than that of sensitive (S) strain (P<0.01), while the individual frequency of insensitive AChE of Rc strain of Culex pipiens pallens was similar to that of S strain(P>0.05).

CONCLUSIONThe AChE activity determination can be used to examine the insecticide-resistance of mosquito.

Acetylcholinesterase ; metabolism ; Animals ; Culex ; classification ; enzymology ; Dichlorvos ; pharmacology ; Female ; Insecticide Resistance ; Propoxur ; pharmacology ; Pyrethrins ; pharmacology ; Species Specificity

OBJECTIVETo investigate the heterozygous genotype and molecular characteristics of Organophosphorus resistance associated with heterozygous Estbeta2 of esterase B2 gene from natural population of Culex pipiens complex.

METHODSGenomic DNA was extracted from natural populations of Culex pipiens complex in Hangzhou. The PCR-restriction fragment length polymorphism (PCR-RFLP) assay was applied to type the resistance associated esterase gene. Estbeta2 of esterase B2 gene was identified by PCR-RFLP, and the genotyping for heterozygous Estbeta2 was carried out after restriction enzyme digesting by Bfm I endonuclease.

RESULTSThe DNA was isolated from 207 Culex pipiens respectively, while 156 PCR samples showed positive and the positive rate was 75.36% (156/207). The PCR-RFLP assay of esterase B2 gene revealed that the Estbeta2 was accounted about 28.20% (44/156) in 156 positive samples. There were two genotypes identified, namely homozygous Estbeta2 (90.90%, 30/33) and heterozygous Estbeta2 (9%, 3/33), heterozygous Estbeta2 was in existence of a hybrid form as which combined with Estbeta2 and a subtype (Estbeta2/Estbeta2(1)).

CONCLUSIONHeterozygous Estbeta2 of Organophosphorus resistance associated with esterase genotype was determined in natural population of Culex pipiens, and a genotyping method was established.

Animals ; Culex ; enzymology ; genetics ; Genes, Insect ; Genotype ; Heterozygote ; Insecticide Resistance ; genetics ; Insecticides ; pharmacology ; Organophosphorus Compounds ; pharmacology ; Phenotype ; Serine Endopeptidases ; genetics

The beet armyworm Spodoptera exigua (Lepidoptera: Noctuidae) is difficult to control using chemical insecticides because of the development of insecticide resistance. Several pest control agents are used to control the beet armyworm. Entomopathogenic fungi are one of the candidates for eco-friendly pest control instead of chemical control agents. In this study, among various entomopathogenic fungal strains isolated from soil two isolates were selected as high virulence pathogens against larva of beet armyworm. Control efficacy of fungal conidia was influenced by conidia concentration, temperature, and relative humidity (RH). The isolates Metarhizium anisopliae FT83 showed 100% cumulative mortality against second instar larvae of S. exigua 3 days after treatment at 1 x 10(7) conidia/mL and Paecilomyces fumosoroseus FG340 caused 100% mortality 6 days after treatment at 1 x 10(4) conidia/mL. Both M. anisopliae FT83 and P. fumosoroseus FG340 effectively controlled the moth at 20~30degrees C. M. anisopliae FT83 was significantly affected mortality by RH: mortality was 86.7% at 85% RH and 13.4% at 45% RH. P. fumosoroseus FG340 showed high mortality as 90% at 45% RH and 100% at 75% RH 6 days after conidia treatments. These results suggest that P. fumosoroseus FG340 and M. anisopliae FT83 have high potential to develop as a biocontrol agent against the beet armyworm.
Beta vulgaris ; Fungi* ; Humidity ; Insecticide Resistance ; Insecticides ; Larva ; Metarhizium* ; Mortality ; Moths ; Paecilomyces* ; Pest Control ; Soil ; Spodoptera* ; Spores, Fungal ; Virulence*

OBJECTIVE AND METHODSInsecticide use, grower preferences regarding genetically engineered (GE) corn resistant to corn rootworm (CRW), and the health effects of using various CRW insecticides (organophosphates, pyrethroids, fipronil and carbamates) are reviewed for current and future farm practices.

RESULTSPest damage to corn has been reduced only one-third by insecticide applications. Health costs from insecticide use appear significant, but costs attributable to CRW control are not quantifiable from available data. Methods reducing health-related costs of insecticide-based CRW control should be evaluated. As a first step, organophosphate insecticide use has been reduced as they have high acute toxicity and risk of long-term neurological consequences. A second step is to use agents which more specifically target the CRW.

CONCLUSIONWhereas current insecticides may be poisonous to many species of insects, birds, mammals and humans, a protein derived from Bacillus thurigiensis and produced in plants via genetic modification can target the specific insect of CRW (Coleoptra), sparing other insect and non-insect species from injury.

Animals ; Consumer Product Safety ; Food, Genetically Modified ; Insecta ; Insecticide Resistance ; Insecticides ; adverse effects ; Pest Control, Biological ; economics ; methods ; Plant Roots ; Plants, Genetically Modified ; Zea mays ; genetics ; growth & development

Bacillus thuringiensis is widely used as an insecticide which is safe and environmentally friendly to humans and animals. One of the important insecticidal mechanisms is the binding of Bt toxins to specific toxin receptors in insect midgut and forming a toxin perforation which eventually leads to insect death. The resistance of target pests to Bt toxins is an important factor hampering the long-term effective cultivation of Bt crops and the continuous use of Bt toxins. This review summarizes the mechanism of insect resistance to Bt toxins from the perspective of important Bt toxin receptors in midgut cells of Lepidopteran insects, which may facilitate the in-depth study of Bt resistance mechanism and pest control.
Animals ; Bacillus thuringiensis/genetics* ; Bacillus thuringiensis Toxins ; Bacterial Proteins/metabolism* ; Endotoxins/metabolism* ; Hemolysin Proteins/metabolism* ; Insecta/metabolism* ; Insecticide Resistance/genetics* ; Insecticides/pharmacology* ; Pest Control, Biological