GENETIC BASIS FOR INSECTICIDE RESISTANCE Current research: To understand the TPB's biochemistry and gene regulation, as well as developing techniques for managing pesticide resistance. General description of research: Dr. Zhu is currently researching cDNA cloning, mRNA expression levels, gene mutation, enzyme activity, etc. using Cytochrome P450 oxidases: CYP6 and CYP4, Sodium channel, and Esterase. He is also researching the development of DNA marker and monitoring for resistance gene frequency. Results: More than eleven-fold resistance level to malathion was detected in a natural population of TPB collected in Mississippi. It is very likely that TPB has developed metabolic resistance to malathion, because synergists, TPP and DEF, could dramatically enhance toxicity of the malathion. Our research was designed to compare enzyme activities between susceptible and resistant strains. First, we cloned several esterase cDNAs from both susceptible and resistant strains. The cDNAs from both strains coded identical protein sequence. Secondly, we developed quantitative RT-PCR technique to examine esterase gene expression levels. Results showed that the resistant strain had 5.1-fold higher esterase gene expression levels than the susceptible strain. Finally, we compared esterase and glutathione s-transferase activities between susceptible and resistant strains. Results exhibited: (1) resistant strain had 6.-fold higher alpha-naphthyl acetate activity and up to 95% enzyme activity was suppressed by DEF and TPP; (2) resistant strain showed 3-fold higher beta-alpha-naphthyl acetate activity, and up to 84% enzyme activity was suppressed by DEF or TPP; (3) resistant strain had 10.4-fold higher 4-nitrophenyl acetate activity than S starin, and up 89% enzyme activity was suppressed by DRF; (4) resistant strain showed 1.5-fold higher glutathione s-transferase activity, and up to 99% enzyme activity was inhibited by ethacrynic acid. Future Research: Further investigation of the TPB's biochemistry and gene regulation, as well as developing new techniques for managing pesticide resistance. For more information contact: Yu Cheng Zhu PO Box 346 141 Experiment Station Rd Stoneville, MS  38776 662-686-5231 yc.zhu@ars.usda.gov Relevant Publications: Zhu, Y. C. and G. L. Snodgrass. 2003. Cytochrome P450 CYP6X1 cDNAs and mRNA expression levels in three strains of the tarnished plant bug Lygus lineolaris (Heteroptera: Miridae) having different susceptibilities to pyrethroid insecticide Insect Molecular Biology (Hemiptera: Miridae). Zhu, Y. C., F. Zeng, and B. Oppert. 2003. Molecular cloning of trypsin-like cDNAs and comparison of proteinase activities between salivary glands and gut of the tarnished plant bug, Lygus lineolaris (Hemiptera: Miridae). Insect Biochem. Molec. Biology. 33: 889-899.