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Submitted to: Meeting Abstract
Publication Type: Other Publication Acceptance Date: 5/11/2004 Publication Date: 5/11/2004 Citation: Zhu, Y. 2004. Insecticide resistance mechanisms in the tarnished plant bug, lygus lineiolaris. Meeting Abstract. International Plant Protection Congress. May 11, 2004 Interpretive Summary: Technical Abstract: hree cDNAs, cloned from both pyrethroid-susceptible and -resistant strains of Lygus lineolaris, contained a 1548-nucleotide open reading frame encoding a 516 amino acid residue protein. A total of 26 nucleotide substitutions were revealed between cDNAs of susceptible and resistant strains. Two nucleotide substitutions resulted in amino acid changes, Asp373 to Ala373 and Ser487 to Ala487, between susceptible and resistant strains. The resistant laboratory strain contained 2.1-fold higher cytochrome P450 mRNA per microgram total RNA than the susceptible laboratory strain. Topical treatment with 10 ng permethrin elevated cytochrome P450 mRNA levels by ~2-fold. The results of this study indicated that cytochrome P450 gene mutation, coupled with up-regulation, was present only in the pyrethroid resistant strains, and was possibly related to resistance development in the tarnished plant bug. We also examined malathion resistance mechanisms in the tarnished plant bug. Esterase activities were compared in vitro between malathion susceptible and resistant strains. More than 6-, 3- and 10-fold higher activities were obtained with the resistant strain using three esterase substrates. Up to 95% of the esterase activity was inhibited by 1 mM DEF or 0.03 mM TPP. Esterase activities in field populations increased by up to 5.4-fold during the fall season. Examination of esterase gene expression levels using quantitative RT-PCR revealed that the resistant strain had a 5.1-fold higher level of esterase mRNA than the susceptible strain. The results of this study indicated that up-regulation of the esterase gene appeared to be related to the development of malathion resistance in the tarnished plant bug. TECHNICAL ABSTRACT (15th IPPC Poster)Ribosomal ITS2 DNA fragments were sequenced from four Peristenus species, two Leiophron species, and two Lygus species. Specific primers for PCR amplification were designed from ITS2 DNA sequences to separate each species from the others. Using this molecular approach, we were able to determine if Lygus hesperus Knight and Lygus lineolaris were parasitized by Peristenus and Leiophron parasitoids. The PCR technique was very sensitive and could detect Peristenus stygicus Loan DNA at a concentration of 0.01 pg/ul or 7.5X10-7 wasp DNA equivalents. Detection of P. stygicus eggs confirmed that early detection of parasitoids was possible. Parasitoid DNA was readily recovered from all L. hesperus nymphs which were parasitized by a single P. stygicus after one hr of contact between the parasitoid and putative hosts. Nymphs of L. lineolaris were collected from an uncultivated field in Mississippi; approximately 10% of the nymphs were parasitized (i. e., contained wasp DNA). ITS2 sequence comparison and phylogenetic analysis indicated that L. lineolaris nymphs had been parasitized by a wasp closely related to Peristenus pallipes. This study demonstrates the effectiveness of a molecular technique for detecting parasitoids developing inside their hosts. |
