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Doctoral Thesis
DOI
https://doi.org/10.11606/T.11.2019.tde-20191220-133320
Document
Author
Full name
Mário Eidi Sato
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
Piracicaba, 1999
Supervisor
Title in Portuguese
Mecanismos de resistência ao inseticida metidation em amblyseius womersleyi Schicha, 1975 (Acari: Phytoseiidae)
Keywords in Portuguese
ÁCAROS PREDADORES
RESISTÊNCIA AO INSETICIDA
Abstract in Portuguese
O ácaro predador Amblyseius womersleyi Schicha é um importante inimigo natural do ácaro Tetranychus kanzawai Kishida, considerado praga-chave da cultura do chá no Japão. Com o objetivo de estudar os mecanismos de resistência a metidation neste fitoseídeo, selecionou-se para o aumento da resistência ao inseticida, urna população resistente de A. womersleyi . Concomitantemente, realizou-se a seleção para o aumento da suscetibilidade, utilizando-se uma outra população, mais suscetível a metidation. Após quatro seleções para resistência e três seleções para suscetibilidade, houve um aumento na razão de resistência (R/S), ao nível de CL50 , de 16 para 342 vezes. Estudou-se o efeito de alguns sinergistas (PBO, DEM e DEF) na toxicidade de metidation, sobre A. womersleyi . A razão de sinergismo (RS: CL50 sem sinergista/ CL50 com sinergista) mais alta foi obtida para PBO (inibidor de ofm, oxidases com funções múltiplas), com aumento de 12,3 vezes na toxicidade do inseticida, na população R deste predador. Realizou-se um segundo teste com sinergistas, desta vez utilizando PBO e PTPE (inibidor de ofm). A mais alta RS foi verificada para PTPE, com 59,3 vezes, para a população R de A. womersleyi . Os resultados indicam que um aumento no metabolismo oxidativo estaria envolvido nesta resistência. Em um outro experimento, observou-se que urna acetilcolinesterase menos sensível a metidation estaria envolvida nesta resistência. sendo considerada porém, de importância secundária. Analisou-se também a penetração cuticular de metidation em A. womersleyi , verificando-se que a penetração não seria um fator envolvido nesta resistência. Estudou-se em seguida, o metabolismo "in vitro" do metidation, utilizando-se diferentes frações subcelulares destes ácaros. A degradação de [14C]-metidation, pela fração microssomal dos ácaros resistentes, na presença de NADPH, foi 48% maior que a obtida para os ácaros suscetíveis, confirmando que as ofm estariam envolvidas nesta resistência. Em um último experimento, comparou-se a toxicidade de oito pesticidas nas populações R e S do ácaro predador. A população R mostrou-se mais resistente que a população S a todos os inseticidas testados, com a exceção de bifenthrin. As maiores razões de resistência foram observadas para os inseticidas metidation, acefuto e malation, para os quais a população R mostrou-se, respectivamente, 311; 20,4 e 13,1 vezes mais resistente que a população S. No caso do piretróide bifenthrin, nenhuma resistência cruzada foi observada para o produto.
Title in English
Mechanisms of resistance to the insecticide methidathion in amblyseius womersleyi schicha, 1975 (acari: phytoseiidae)
Abstract in English
The predaceous mite Amblyseius womersleyi Schicha is an important natural enemy of Kanzawa spider mite Tetranychus kanzawai Kishida, which is considered a key pest of tea in Japan. In order to study the mechanisrns of methidathion in this phytoseiid mite, a resistant strain of A. womersleyi was selected for resistance; and along with this selection, a susceptible strain was selected for susceptibility to methidathion. After four selections for resistance and three selections for susceptibility, the resistance ratio (R/S) at the LC50 increased from 16 to 342 times. The effect of some synergists (PBO, DEM, and DEF) was investigated on the toxicity of methidathion in A. womersleyi . The highest synergistic ratio (SR: LC50 without synergist/ LC50 with synergist) was observed for piperonyl butoxide (inhibitor of mfo, mixed function oxidases), which increased 12.3 times the toxicity of the insecticide in the resistant population. A second test was carried out using PBO and PTPE (inhibitor of mfo) as synergists. The highest SR was observed for PTPE, with 59.3 times in the R strain. The results suggest that an increase in oxidative metabolism is involved in this resistance. ln another experiment, an insensitive acetylcholinesterase was observed to have some effect on this resistance, however this acetylcholinesterase was thought to be a minor factor for resistance. Cuticular penetration of methidathion was also analyzed, and the results obtained indicate that the penetration is not a factor involved in this resistance. Another study was about "in vitro" metabolism of methidathion. using different subcellular fractions of the predaceous mite. The degradation of [14C]-methidathion by the microsomal fraction of resistant mite, in the presence of NADPH, was 48% higher than that obtained for the susceptible strain, corroborating observations that mfo are involved in this resistance. ln a final experiment, the toxicity of eight pesticides was evaluated in the R and S strains of this phytoseiid mite. The R strain showed to be more resistant to all compounds with the exception of bifenthrin. The highest resistance ratios were observed for the insecticides methidathion, acephate, and malathion, for which the R strain was respectively 311, 20.4, and 13.1 times more resistant than the S strain. ln the case ofthe pyrethroid bifenthrin, no crossresistance was observed for this chemical.
 
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Publishing Date
2019-12-20
 
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