Diamondback Moth Resistance Research Articles

Insecticide Resistance Study in Plutella xylostella L. IX. The Selective Metabolism of Insecticides

The genetic dilution of resistance and the selective metabolism of insecticides were investigated in the diamondback moth (DBM), Plutella xylostella L. The resistance to mevinphos, diethquinalphion, carbofuran and fenvalerate reduced differently which indicated that the resistance mechanisms for these insecticides were independent from each other. The crossbreeding progenies of a resistant and a susceptible DBMs showed higher tolerance to cartap which may attribute to the stronger total esterase activity as the broad-spectrum esterases may attack the thio-ester bond of cartap. So far, no resistance of DBM to the two registered benzoylarylureas i.e., teflubenzuron and chlorfluazuron has been recorded in Taiwan. The susceptible DBM possesses natural MFO activity which can degrade diflubenzuron, triflumuron and ethofenprox, while with only minimum effect on teflubenzuron, chlorfluazuron and fenvalerate. With the synergist piperonyl butoxide (pb), teflubenzuron and chlorfluazuron still exert better effect on the DBM than diflubenzuron and triflumuron. This may attribute to the fitness of insecticidal structure to the receptor of their toxic action. With the action of pb, ethofenprox performed better than fenvalerate in killing the DBM, which leads to the conclusion that the ether-bond structure in ethofenprox does not make it undesirable to the action receptor of the ester-bond synthetic pyrethroid.

Model for Managing Resistance to Fenvalerate in the Diamondback Moth (Lepidoptera: Plutellidae)

Evolution of resistance to the pyrethroid insecticide fenvalerate in the diamondback moth, Plutella xylostella (L.), was simulated by a computer model. Predictions from the model agree with data documenting development of diamondback moth resistance to fenvalerate in Ban-chau, Taiwan, in <4 years. Sensitivity analyses varying fecundity (4-fold), initial R gene frequency (10,000-fold), initial population density (100-fold), and percentage of larvae escaping insecticide exposure (0–20%) resulted in predicted times for resistance development under Ban-chau conditions ranging from <1–4 years. Simulations of 15 management strategies suggest that under tropical conditions, spray frequency must be less than two per cabbage cycle or spray concentration less than the LC75 of susceptible larvae to substantially delay resistance development. Adoption of alternative tactics for management of the diamondback moth is strongly urged.

Resistance of Diamondback Moth (Lepidoptera: Plutellidae) to a Combination of Fenvalerate and Piperonyl Butoxide

pyrethroid and carbamate resistance persisted longer than organophosphorus resistance when selection pressure on diamondback moth, Plutella xylostella (L.), larvae was relaxed. Selection with fenvalerate and a mixture of fenvalerate and piperonyl butoxide (PB) resulted in the development of high levels of resistance to selection agents within a few generations. Thus selected, the diamondback moth had strong cross-resistance to three other pyrethroids (i.e., permethrin, cypermethrin, and deltamethrin) while cross-resistance (if any) to several organophosphorus insecticides was slight. PB, a microsomal oxidase inhibitor, lost its synergistic action with fenvalerate and permethrin in diamondback moth resistant to the mixture of fenvalerate and PB. The synergist MGK 264, another microsomal oxidase inhibitor, still retained its synergistic action. Selection with fenvalerate plus PB apparently caused development of resistance to the synergistic as well as toxic action of PB. Possible causes of this resistance are described, and implications of these phenomena in the chemical control of the diamondback moth are discussed.

Effect of Pyrethroids on Knockdown and Lack of Coordination Responses of Susceptible and Resistant Diamondback Moth (Lepidoptera: Plutellidae)

Among DDT and the 10 pyrethroids tested, permethrin, cypermethrin, deltamethrin, and fenvalerate were most toxic against a field strain of Plutella xylostella (L.) that had high levels of resistance to all insecticides tested. Knockdown effect of these compounds against larvae and adults of susceptible and resistant strains was evaluated by a residual-film method. Symptoms of poisoning are described. When larvae or adults could no longer stand and had to lie on their sides, they were considered knocked down. Pyrethroids with primary alcohol esters produced more acute symptoms than those with secondary alcohol esters. Responses of resistant larvae and adults were less pronounced than those of susceptible ones. In the resistant strain, addition of synergist piperonyl butoxide (PB) to the pyrethroids produced symptoms displayed by the susceptible strain. Tetramethrin, which was not highly toxic, was the most potent knockdown agent against susceptible larvae. Knockdown action of all pyrethroids appeared much more slowly in resistant larvae; fluvalin ate and flucythrinate were least effective as knockdown as well as killing agents. Addition of synergists PB, S,S,S-tributyl phosphorotrithioate, and chlordimeform generally enhanced knockdown action of most pyrethroids in resistant larvae, but had only limited effect in susceptible larvae. Maximal knockdown of adults by fenvalerate was reached 60–90 min after exposure; PB synergized this action of fenvalerate and reduced recovery of the moths within 24 h.

Absence of Synergism of DDT by Piperonyl Butoxide and DMC in Larvae of the Diamondback Moth (Lepidoptera: Yponomeutidae)

Susceptible and multiple-resistant (resistance ratio for DDT = 200) strains of diamondback moth, Plutella xylostella (L.), were used to determine the effect of a microsomaloxidase inhibitor, piperonyl butoxide (pb) and a DDT-dehydrochlorinase inhibitor, DMC, on DDT toxicity. For both strains, DMC did not increase, but as a mailer of fact, decreased DDT toxicity somewhat. Although pb synergized DDT by twofold against the susceptible strain, it produced very little effect in the resistant strain. The absence of synergisym by pb and DMC raised the possibility of existence of a nonmetabolic mechanism of DDT resistance in the diamondback moth. This mechanism might also play an important role in diamondback moth resistance to synthetic pyrethroids and may be similar to previously described nonmetabolic mechanism for DDT-pyrethroid resistance in houseflies and mosquitoes.

Diamondback Moth Resistance to Several Synthetic Pyrethroids12

Most field strains of Plutella xylostella (L.) in Taiwan developed resistance to the four major synthetic pyrethroids—permethrin, cypermethrin, decamethrin, and fenvalerate—and the resistance levels to the three α-cyano 3-phenoxybenzyl esters were generally higher than that to permethrin. A diazinon-resistant strain showed significant cross resistance to all four compounds, whereas a methomyl-resistant strain had slight, yet consistent negative cross resistance to these compounds, except fenvalerate. Synergism of pyrethroid toxicity by piperonyl butoxide, but not DEF, was observed against a highly resistant strain. Fenvalerate resistance in the diamondback moth lacked sex linkage and was partially recessive and due to more than one gene.

Diamondback Moth Resistance to Diazinon and Methomyl in Taiwan12

Diazinon- and methomyl-resistant strains of Plutella xylostella (L.) with resistance ratios of 14.4 and 175, respectively, were developed in the laboratory by continuous selection for 14 and 19 generations. The susceptibility to these 2 chemicals of this insect pest at several locations in Taiwan from 1975–77 was determined. This survey confirms the development of resistance to these insecticides in some field populations of the diamondback moth. Electrophoretic studies revealed qualitative differences in esterase and phosphatase zymograms in susceptible and resistant strains.