Insecticidal genes

Selection of Insecticidal Genes. Although in the presently generated transgenic plants, B.t. protein levels are sufficiently high to control M. sexta, other insect species,... 

Interestingly, it appears that earlier selective pressure by dichlorodiphenyl trichloroethene (DDT) raised the frequency of kdr genes in the population before pyrethroids came to be used. Thus, some pyrethroid resistance already existed before these insecticides were applied in the field. 

Devonshire, A.L. and Sawicki, R.M. (1979). Insecticide resistant Afyz 5 persicae as an example of evolution by gene duplication London. Nature 280,140-141. 

Wilson and Madsen [152] used the metabolic pathway for bacterial naphthalene oxidation as a guide for selecting l,2-dihydroxy-l,2-dihydronaphthalene as a unique transient intermediary metabolite whose presence in samples from a contaminated field site would indicate active in situ naphthalene biodegradation (Fig. 26). Naphthalene is a component of a variety of pollutant mixtures. It is the major constituent of coal tar [345], the pure compound was commonly used as a moth repellant and insecticide [345], and it is a predominant constituent of the fraction of crude oil used to produce diesel and jet fuels [346]. Prior studies at a coal tar-contaminated field site have focused upon contaminant transport [10,347], the presence of naphthalene catabolic genes [348, 349], and non-metabolite-based in situ contaminant biodegradation [343]. 

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],... 

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. 

Spiering MJ et al. Gene clusters for insecticidal loline alkaloids in the grass-endophytic fungus Neotyphodium uncinatum, Genetics 169 1403—1414, 2005. 

The phytoalexins are a special class of defensive agents that has attracted much attention in view of agricultural applications. Perhaps the most advanced study concerns insecticidal and antimicrobial benzoxazins of the Gramineae, which have been elucidated to the gene level (Frey 1997). A survey of phytoalexins is presented in Chart 12.2. 

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