Aphids, insecticidal resistance

The current insecticidal seed dressing are very effective at controlling peach potato aphids. Insecticide resistance is now a problem with some post emergence insecticides. 

L. M. Field, A. L. Devonshire, B. G. Forde, Molecular Evidence that Insecticide Resistance in Peach-Potato Aphids (Myzus persicae Sulz.) Results from Amplification of an Esterase Gene , Biochem. J. 1988, 257, 309-312. 

Devonshire, A.L., The properties of a carboxylesterase from the peach-potato aphid, Myzuz persicae (Sulz.), and its role in conferring insecticide resistance, Biochem. J., 161, 675,1977. 

Field, L.M. and Devonshire, A.L., Evidence that the E4 and FE4 esterase genes responsible for insecticide resistance in the aphid Myzus persicae (Sulzer) are part of a gene family, Biochem. j., 330, 169,1998. 

Villatte, F., Auge, D., Touton, P, Delorme, R., and Fournier, D., Negative cross-resistance in insecticide-resistant cotton aphid Aphis gossypii Glover, Pestic. Biochem. Physiol., 65,55,1999. 

Both Aphis gossypii and Myras persicae are major agricultural pests, and insecticide resistance in these species is a significant problem. Organophosphate and carbamate tolerance in these aphids has been related to detoxification via increased carboxylesterase activity Suzuki el al., 1993 Devonshire and Moores, 1977). 

Moores, G.D., Gao, X.. Denholm. I. and Devonshire, A.L. (1996). Characterisation of insensilive acetylcholinesterase in insecticide-resistant cotton aphids. Aphis gussypti Glover (liomopiera Aphididac). Pestic. Bioehem. Physiol. 5fi, 102-110-... 

In the aphid M. perslcae, molecular evidence that insecticide resistance results from amplification of an esterase (E4) gene was provided following successful isolation and use of cDNA clones for the esterase. The degree of amplification of the structural gene was correlated with the activity of the esterase and the level of resistance. Quantitative differences between restriction patterns in different clones of resistant aphids were found to be correlated with the presence or absence of a specific chromosome translocation and with production of the esterase (22). 

Neonicotinoids are insecticides acting on insect nAChRs (1). For a long time they are very effective on commercially important Hemipteran pest species such as aphids, whiteflies and planthoppers, but also control Coleopteran and some Lepidopteran pests (/). The biochemical mode of action (MoA) of neonicotinoids has been studied and characterized extensively in the past 10 years. Ail neonicotinoids act selectively as agonists at the insect nAChRs and they are part of a single MoA group as defmed by the Insecticide Resistance Action Committee (IRAC an Expert Conunittee of Crop Life) for resistance management purposes (2). Today the neonicotinoids are ... 

The knockdown and residual aphicidal activity of an insecticide depends on one or more of these biological properties (a) contact advity, (b) translaminar systemicity, (c) downward or phloem systemicity, (d) upward or xylem systemicity, and (e) inherent efficacy against insecticide-resistant aphids. We have compared RH7988 with several important commerdal aphicidal compounds for these properties through laboratory tests. 

Recently, a change from a green to a red morph has occurred in the tobacco aphid, Myzus nicotianae Blackman. Although, the red morph of the tobacco aphid is often associated with an increase in insecticide resistance, this color change has not been directly linked to use of insecticides. However, since the red aphid develops faster, has a higher reproduction rate and tolerates higher temperatures, it is more difficult to control than the green form (5). 

In the middle of the 1980s in the USSR, approximately 150 species acquired resistance to one of the various OCPs and OPPs used [3], and now require more complicated means of suppression. For example, until the 1950s, weevils and boll weevils were the main pests damaging cotton. After the widespread use of OCP insecticides - DDT, toxafene, and others - cottonworms, tobacco tortricids, tobacco aphids, spider mites and loopers must now be fought as well. Their number jumped after suppression of the first two target species. 

Carboxylesterases are well-represented in insects and are sometimes important in the development of resistance to insecticides. Thus, a well-characterized carboxylesterase E4 is responsible for resistance to organophosphorus insecticides in the aphid (Myzuspersicae) [107]. In the California Culex mosquito, the esterase B1 is 500-fold more abundant in organophosphate-resistant than in susceptible insects. The increase of esterase levels is the result of gene amplification, i.e., the resistant animals have an increased number of copies of the structural esterase gene [108],... 

The mechanisms of resistance fall into two main categories. Many insects produce an increased level of detoxifying enzymes, such as esterases, that modify the insecticides to inactive metabolites very rapidly. Such a system is seen in aphids that are resistant to OP insecticides. In other cases it is the target site that is modified such that the insecticide (the enzyme inhibitor) no longer binds to the target and is, therefore, ineffective. This has recently been shown to occur in some aphids that are resistant to OP insecticides but the classical example is knockdown resistance (kdr) and super-kdr to pyrethroid insecticides shown by many insects but particularly house flies Musca domes tied). This resistance is thought to result from a modification of... 

Aphids are a little more resistant to a simple castiie soap spray, so I recommend using insecticidal soap on them. These soaps contain salts of fatty acids and are quite safe to use, even within days of harvest. The directions say the soap can be left on, but I wash the leaves off the following day after application just to be safe. 

Aphids are a little more resistant to a simple castile soap spray, so I recommend using insecticidal soap on them. 

In Culex, for example, the overproduced esterase amounts to 6%-12% of the total protein of the insect (24.) and in the aphid 3% (12) This is a large diversion of resources into production of an enzyme that is apparently of little or no use in the absence of insecticide, but its consequences to the insect in terms of "fitness" are not yet adequately known. In Culex, resistance in newly colonized field strains is moderately unstable, but becomes relatively stable after prolonged rearing of the strain under insecticidal selection in the laboratory. 

This enzyme, purified from aphids (24). was very slow in hydrolyzing paraoxon compared to mammalian arylester hydrolases (Table III) however, it was twice as fast in recovery from paraoxon inhibition compared to a porcine carboxylester hydrolase (35) and >300 times faster than monomeric carboxylester hydrolase of rabbit liver (26). No qualitative differences were found in the enzyme, E4, isolated from resistant and susceptible aphids E4 was one of seven electrophoretic forms of hydrolases observed (34). Recovery indicates that resistance is due to both reaction with the insecticide and a very slow turnover, or catalysis. A similar mechanism of was observed with paraoxon in resistant green rice leafhoppers (37). 

The major agricultural pests susceptible to oxadimeter are aphids, planthoppers and leafhoppers. It is of particular interest for the control of ricehoppers which became resistant to carbamate and organophosphorus insecticides. 

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