Insect detoxifying enzymes: Their importance in pesticide synergism and resistance

Abstract

Pyrethroid esterases of Trichoplusia ni, Spodoptera littoralis and Bemisia tabaci hydrolyze the trans-isomers of various pyrethroids more extensively than the cis-isomers. Profenofos fed to T. ni larvae at a level inhibiting the gut pyrethroid esterases by 65% with trans-permethrin and of 95% with cis-cypermethrin increased the toxicity of topically applied trans-permethrin by fourfold and cis-cypermethrin by 20-fold. Similar assays with S. littoralis resulted in an increase of about threefold in the toxicity of both compounds. Monocrotophos, profenofos, acephate, and methidathion inhibited pyrethroid esterase activity in B. tabaci and synergized considerably the toxicity of cypermethrin. The remarkable tolerance of the predator Chrysopa carnea to pyrethroids is attributed to the presence of a high level of pyrethroid esterase activity with a unique specificity for hydrolyzing the cis-isomer. Phenyl saligenin cyclic phosphonate, a potent inhibitor for larval pyrethroid esterases synergized the toxicity of trans-permethrin by 68-fold from an LD50 of 17,000 micrograms/g to 250 micrograms/g. In contrast, oxidase inhibitors such as piperonyl butoxide, SV-1, and MPP synergized considerably the toxicity of pyrethroids in Tribolium castaneum and Musca domestica. Hence the predominant pathway for pyrethroid detoxification in insects, whether hydrolytic or oxidative, depends largely on the insect species. The high toxicity of the recent developed acylureas results from their high retention in the insects. Assays using radiolabeled diflubenzuron and chlorfluazuron applied to fourth instar T. castaneum larvae revealed a rapid elimination of diflubenzuron (T1/2 approximately equal to 7 h) as compared with chlorfluazuron (T1/2 > 100 h). Addition of 100 ppm DEF to the diet increased both the retention time and the toxicity of diflubenzuron in both T. castaneum and S. littoralis, which was due probably to the inhibition of diflubenzuron hydrolase activity. Esterases, hydrolyzing pyrethroids, and acylureas may serve as tools for evaluating potential synergists and for monitoring resistance in various agricultural pests due to increased metabolism.

Novaluron (Rimon), a novel IGR: Potency and cross‐resistance

“…The relatively mild resistance of the field strain of S. littoralis to teflubenzuron results probably from combination of effects due to its exposure to benzoylphenyl ureas and other groups of insecticides such as organophosphate and pyrethroids. Enhanced detoxification plays, probably, a major role in this observed resistance (Ishaaya, 1993). Novaluron and chlorfluazuron seem to be more resistant to such detoxification as compared to teflubenzuron.…”

Mechanisms for Bt Toxin Resistance and Increased Chemical Pesticide Susceptibility in Cry1Ac10-resistant Cultured Insect Cells

“…Many articles have reported the role of esterase in resistance of insects to chemical insecticides (Devonshire 1991;Ishaaya 1993). The susceptibility of insects to some chemical pesticides changes with the esterase activity because the esterase can bind to, sequester and detoxify them.…”

Pesticide Mixtures

“…For example, pesticide mixtures may, in fact, promote the expression of multiple resistance, which could extend across other chemical classes resulting in specific arthropod pest populations being very difficult to manage (Forgash 1984;Brattsten et al 1986;Ahmad 2004;Attique et al 2006). Furthermore, multiple evolutionary pathways may exist that eventually result in a pesticide-resistant arthropod pest population (Metcalf 1980;Georghiou 1983;Brattsten et al 1986;Ishaaya 1993). Although pesticide mixtures may delay resistance due to target site insensitivity, which is usually specific to a certain class of pesticides, the use of pesticide mixtures enhances the selection for increased expression of metabolic enzymes that can simultaneously detoxify both pesticides (Roush and McKenzie 1987;Roush and Daly 1990;Roush and Tabashnik 1990;Stenersen 2004).…”

“…The effect of pesticide mixtures is, however, unpredictable because differences in the mode of action do not necessarily insure a lack of common resistance mechanisms and may only reflect the specificity associated with enzymes responsible for detoxification (Sawicki 1981;Yu 2008). Moreover, the effects of pesticide mixtures may differ depending on the arthropod pest population as a result of peculiarities associated with species, strain, and even biotype (Sawicki 1981;Georghiou and Taylor 1986;Ishaaya 1993). These differences could be related to physiology and the resistance mechanisms present in the population (Georghiou and Taylor 1977a;Brattsen et al 1986).…”