Modification of acetylcholinesterase as a mechanism of resistance to insecticides.

Aphis gossypii Glover is a destructive pest of over two dozen crops world wide Damage to a few of these crops is due to direct feeding, but for most of these crops its impact is through its role as a virus vector As expected, this has resulted in many articles dealing with methods of controlling this insect The aphid has the ability to become resistant to many pesticides and there is growing concern over environmental impacts of pesticide use As a result, manipulation of the agroecosystem will play an ever increasing role in the management of this insect Most aspects of the biology of this aphid are covered in this review The recurrent theme centers around the importance of host plant influences on the biology of the aphid In addition to examining the literature on the biology of the aphid, a large section is devoted to organisms which influence mortality in the aphid, and to aphid borne viruses transmitted by this aphid This review covers the literature from 1912 to 1995, but articles on aphid management (eg pesticide efficacy, planting date) were omitted except where they deal with the aphid's biology or ecology Research on the biology of this aphid has been heavily skewed into several disparate categories First, research has focused on the influence of host plant and temperature on the reproductive rate of this aphid Second, research has focused on the cause for alate production such as nutritional stress, other nutritional factors, crowding, and temperature Third, research has focused on the viral borne pathogens transmitted by this aphid Three specific cases are highlighted: citrus tristeza, cucumber mosaic virus, and the potyviruses Last, research has focused on the role of organisms which feed on this aphid Due to the complexity of research possible in this area, very little research has explored the effect of these "beneficial organisms" on life history traits of this aphid

Biology and ecology of Aphis gossypii glover (Homoptera: Aphididae)

Overexpression of carboxylesterase gene associated with organophosphorous insecticide resistance in cotton aphids, Aphis gossypii (Glover)

Association between Biochemical Markers and Insecticide Resistance in the Cotton Aphid,Aphis gossypiiGlover☆

BACKGROUND: The polyphagous cotton-melon aphid Aphis gossypii Glover is structured into geographically widespread host races comprising a few clones specialised on Cucurbitaceae, cotton, eggplant or pepper. To assess insecticide resistance among andwithin host races, leaf disc bioassays were conducted on aphid clones collected from Cucurbitaceae (genotypes C4 and C9), cotton (genotypes Burk and Ivo), eggplant (genotype Auber) and pepper (genotype PsP4). Molecular diagnostic (PCR-RFLP) and enzyme assays were also performed to detect the basicmechanisms underlying insecticide resistance. RESULTS: All six clones were susceptible to acetamiprid (neonicotinoid) or carbosulfan (carbamate). Conversely, all clones were resistant to dimethoate (organophosphate) (RF = 4.1-38.1) and carried mutation S431F in the acetylcholinesterase gene. Auber, PsP4 and Burk also carried mutation A302S in this gene,which possibly conferredmoderate resistance (RF= 3.7-6.8) to profenofos andmonocrotophos (organophosphates). Auber and Burk were highly resistant (RF= 41.2 and 473 respectively) to cypermethrin (pyrethroid). This resistance was likely associated with point mutation super-kdr (M918L) in the voltage-gated sodium channel gene (para gene) ormetabolic detoxificationmediated by esterase and oxidase enzymes. CONCLUSION:Multiple resistance to a broad range of insecticides andmultiplemechanisms of resistance in some clones could explain to some extent the low genetic diversity observed within A. gossypii host races. (Resume d'auteur)

Insecticide resistance traits differ among and within host races in Aphis gossypii

The cotton aphid Aphis gossypii Glover is oue of the most important pests infesting cotton in the cotton areas of North China. Since 1953 organophosphorus insecticides have been used to-control the aphid for keeping up good yield of cotton. At present, resistance of the aphid to insecticides has become a vital probl閙 in cotton production. This has prompted us to investi-gata the mechanism of resistance to organophosphorus insecticides and to search for the strategy to control the resistant aphids.All experiments were performed on apterous viviparous female aphids and topical applica-tion was adopted for testing the effct of insecticides on the aphids. Three populations of cot-ton aphids (B-Beijing, Q = Qing Dao, and G = Gao Mi) were compared. The LD50 values of parthion and paraoxon on aphids of population B, Q and G were 38 and 4, 59 and 9, and 93,5 and 21 ng/aphid respectively. Besides the slower penetration of organophosphorus insecticides into the aphids of resistant populations, the use of synergists including methyl iodide, SV1 (O, O-diethyl O-phenyl phosphorothionate) and piperonyl bul oxide has given evidence indica-ting whether mixed function oxidases (MFO), carboxylcsterase and glutathion S-transferase are involved in the formation of resistance. MFO seems to be one of the factors causing resistance, but the cotton aphid homogenates in v韙ro are found to contain endogenous inhibitors of MFO. The results also showed that the sensitivity of AChE to paraoxon in resistant population G was 1.9 and 14.2 times lowcr than that in populations Q and B. The activities of L-Na este-rases and L-NA carboxylesterases in population G were respectively 2.3-15.4 and 18.0-70.0 times higher than that in populations Q and B. The activities of esterases showed rnore conspi-cuous difference in the three populations.

G. L. Feng

Papers

Biochemical mechanism of resistance of cotton aphids to organophosphorus insecticides.